Hydrocarbon Generation and Expulsion from Early Cretaceous ... · the presence of generated bitumen in pores of all sizes near the base of the formation, but not within the underlying

G E O S C I E N C E A U S T R A L I A

Hydrocarbon Generation and Expulsion from Early Cretaceous Source Rocks in the Browse Basin, North West Shelf, Australia: a Small Angle Neutron Scattering and Pyrolysis StudyAnalysis and report by

Andrzej P. Radlinski, Dianne S. Edwards, Alan L. Hinde, Rachel Davenport and John M. Kennard

Record

2007/04

S P A T I A L I N F O R M A T I O N F O R T H E N A T I O N

GEOSCIENCE AUSTRALIA

Hydrocarbon Generation and Expulsion from Early Cretaceous Source Rocks in the Browse Basin,

North West Shelf, Australia: a Small Angle Neutron Scattering and Pyrolysis Study

Analysis and report by

Andrzej P. Radlinski, Dianne S. Edwards, Alan L. Hinde, Rachel Davenport and John M. Kennard 2003 Rachel Davenport and John M. Kennard 2003 Rachel Davenport and John M. Kennard

Petroleum Promotion and Specialist Studies Research Group, Marine and Petroleum Division

Geoscience Australia,PO Box 378, Canberra, ACT, 2601.

Ph. 61 6 249 9111 Fax. 61 6 249 9980

Geoscience Australia Record No 2007/04

ISBN 9781921236273

3 February 2006

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Summary

Small Angle Neutron Scattering (SANS), Rock-Eval pyrolysis and total organic carbon (TOC) analyses were carried out on 165 organic-rich Upper Jurassic-Lower Cretaceous sedimentary rock samples from nine wells in the Browse Basin (Adele-1, Argus-1, Brecknock South-1, Brewster-1A, Carbine-1, Crux-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1). Cutting samples and some sidewall cores have been used. Out of the total 165 samples, 47 samples (22 for Brewster-1A and 25 for Dinichthys-1) were also analysed using the Ultra-small Angle Neutron Scattering (USANS) technique. The focus of the study was to identify potential Lower Cretaceous source rocks and the depth at which the onset of hydrocarbon generation occurred in each well, and to determine the onset of hydrocarbon expulsion in the wells for which USANS data were available.

This Record contains a complete description of geochemical and SANS methods and data acquired in 2003 and later selectively used to produce an APPEA publication (Radlinski et al. 2004). This is the first time that such a study has combined the approaches offered by the two disciplines.

The neutron scattering and geochemical techniques provide complementary information about petroleum source rocks. Together, the TOC content and Rock-Eval pyrolysis data evaluate source richness, source quality, kerogen type and thermal maturity, whereas SANS/USANS detect the presence of generated bitumen in pores and are pore-size specific. As the pore-size range in mudstones extends from about 0.001 µm to about 40 µm, the presence of bitumen in the small pores (up to 0.1 µm) detected by SANS indicates the onset of hydrocarbon generation, whereas the presence of bitumen in the largest pores detected by USANS (about 10 µm) indicates a significant saturation and the onset of hydrocarbon expulsion.

Brewster-1A and Carbine-1 were drilled with water-based muds which had no detrimental effects on the Rock-Eval pyrolysis and TOC data. Adele-1, Argus-1, Brecknock South-1, Crux-1 and Dinichthys-1 have been drilled using water-based muds containing 'glycol' additives. The shallow sections of the Titanichthys-1 and Gorgonichthys-1 wells were drilled with water-based muds containing glycol additives, and the deeper sections were drilled using synthetic-based muds (SBMs). To determine the hydrocarbon potential of these contaminated samples, extraction procedures with organic solvents were devised, and on analysis, these procedures were observed to have variable success in removing the organic contaminants. The solvent extraction process removes the naturally occurring free hydrocarbons, as well as the organic contaminants, from the whole rock, resulting in the absence of, or a reduction in, the Rock-Eval pyrolysis S1 peak depending on the rigorousness of the extraction process. Other pyrolysis parameters are also affected if contamination remains; namely S2 values increase and Tmax values decrease. The affected S1 and S2 peaks also result in erratic potential yields (S1+S2), an apparent increase in Hydrogen Index (HI = S2*100/TOC), and a decrease in, or null value for, the Production Index (PI = S1/S1+S2). In contrast to the pyrolysis data, the SANS/USANS data obtained on the untreated whole-rock samples do not appear to be influenced by the type of drilling mud used.

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The Lower Cretaceous Echuca Shoals Formation contains some source rocks with the potential to generate and expel liquid hydrocarbons, with the present day values of the hydrogen index, reduced from the original values by the maturity and mineral matrix effects, in the range 150-264mg/gTOC. The formation is also sufficiently thermally mature for hydrocarbon generation to occur. SANS/USANS data for Dinichthys-1 show the presence of generated bitumen in pores of all sizes near the base of the formation, but not within the underlying 57 m thick mudstone of the Upper Vulcan Formation juxtaposed between the Echuca Shoals Formation and the Berriasian ‘Brewster’ Sandstone, which is an important reservoir rock within the Upper Vulcan Formation. It appears that the top mudstone of the Upper Vulcan Formation acts as a barrier for hydrocarbon migration from the Echuca Shoals Formation towards the Berriasian ‘Brewster’ Sandstone, and, therefore, hydrocarbons generated in the Echuca Shoals Formation have not been expelled into the Berriasian Sandstone reservoir. This is consistent with previous findings based on oil-source correlation that the Upper Vulcan reservoirs have not been charged from Early Cretaceous source rocks. In Brewster-1A there is SANS/USANS evidence of pore-size-specific oil-to-gas cracking within the Echuca Shoals Formation. SANS evidence for bitumen generation in small pores of the Echuca Shoals Formation has also been found in Adele-1, Crux-1, Gorgonichthys-1 and Titanichthys-1. There is no conclusive SANS evidence for bitumen generation in small pores of Argus-1 (overmature organic matter in this deep well), Brecknock South-1 (potential generation signature possibly overprinted by variable source rock lithology) and Carbine-1 (possible generation signature overprinted by strong sediment compaction in this shallow well).

The Lower Cretaceous Jamieson Formation has similar source potential to the underlying Echuca Shoals Formation, but slightly lower organic carbon content and lower thermal maturity. For Brewster-1A and Dinichthys-1, SANS/USANS indicate the presence of bitumen in small pores but not in the largest pores, which indicates that the volume of generated hydrocarbons was insufficient to saturate the pore space and create an effective source charge. There is also SANS evidence of the presence of bitumen in the small pores of this formation in Adele-1, Crux-1, Gorgonichthys-1 and Titanichthys-1.

In summary, the Rock-Eval pyrolysis and TOC data imply the existence of a potential source rock in the Lower Cretaceous sediments of the Browse Basin, whereas the SANS/USANS data indicate significant generation but little or no expulsion. This source limitation may explain poor exploration success for liquid hydrocarbons in the area. SANS/USANS data preclude the possibility of an oil charge to the Berriasian ‘Brewster’ Sandstone from the Echuca Shoals Formation, although some gas charge in Brewster-1A well is possible.

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Contents

Summary ..................................................................................................................... iii

1. Introduction .............................................................................................................1

2. Analytical Procedures .............................................................................................3

2.1 Samples ..........................................................................................................3

2.2 Analytical Techniques ....................................................................................52.2.1 Small Angle Neutron Scattering and Ultra-small Angle Neutron

Scattering ..............................................................................................52.2.2 Rock-Eval Pyrolysis .............................................................................5

2.3 Rock-Eval Pyrolysis Size Fraction Experiments ...........................................5

2.4 Washing Method Experiments .......................................................................62.4.1 Pyrograms of Water-based Drilling Mud Samples ...............................62.4.2 Pyrograms of Glycol Contaminated Samples ......................................72.4.3 Pyrograms of SBM Contaminated Samples .......................................10

3 Results ...................................................................................................................13

TOC and Rock-Eval Pyrolysis ..............................................................................13

SANS and USANS Analysis .................................................................................14

3.1 Brewster-1A .................................................................................................153.1.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons ..............153.1.2 Source Richness .................................................................................163.1.3 Source Quality, Kerogen Type and Maturity ......................................173.1.4 Analysis of SANS and USANS data .................................................18

3.2 Carbine-1 .....................................................................................................333.2.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons ..............333.2.2 Source Richness .................................................................................333.2.3 Source Quality, Kerogen Type and Maturity ......................................333.2.4 Analysis of SANS data .......................................................................37

3.3 Adele-1 ........................................................................................................443.3.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons ..............443.3.2 Laboratory Comparisons ....................................................................473.3.3 Source Richness .................................................................................473.3.4 Source Quality, Kerogen Type and Maturity ......................................473.3.5 Analysis of SANS data .......................................................................49

3.4 Argus-1 ........................................................................................................603.4.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons ..............603.4.2 Maturity ..............................................................................................61

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3.4.3 Analysis of SANS data .......................................................................63

3.5 Brecknock South-1 ......................................................................................723.5.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons ..............723.5.2 Source Richness .................................................................................733.5.3 Source Quality, Kerogen Type and Maturity ......................................753.5.4 Analysis of SANS data .......................................................................76

3.6 Crux-1 ..........................................................................................................843.6.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons ..............843.6.2 Source Richness .................................................................................853.6.3 Source Quality, Kerogen Type and Maturity ......................................883.6.4 Analysis of SANS data .......................................................................88

3.7 Dinichthys-1 ..............................................................................................1023.7.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons ............1023.7.2 Source Richness ...............................................................................1033.7.3 Source Quality, Kerogen Type and Maturity ....................................1033.7.4 Analysis of SANS and USANS data ...............................................105

3.8 Gorgonichthys-1 ........................................................................................1183.8.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons ............1183.8.2 Source Richness ...............................................................................1193.8.3 Source Quality, Kerogen Type and Maturity ....................................1193.8.4 Analysis of SANS data .....................................................................121

3.9 Titanichthys-1 ............................................................................................1313.9.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons ............1313.9.2 Source Richness ...............................................................................1333.9.3 Source Quality, Kerogen Type and Maturity ....................................1343.9.4 Analysis of SANS data .....................................................................135

4 Discussion: Well Comparisons ............................................................................145

4.1 Pyrolysis results: Adele-1 compared to Brewster-1A ...............................145

4.2 Pyrolysis results: new Ichthys Field wells compared to Brewster-1A .......145

4.3 SANS results: new Ichthys Field wells compared to Brewster-1A ...........148

4.4 SANS Results: Adele-1 and Crux-1 compared to Brewster-1A ................152

4.5 Source Rock Summary ..............................................................................154

5 Conclusions .........................................................................................................157

6 Recommendations and Further Work ..................................................................159

7 References ...........................................................................................................161

Well Completion Reports ....................................................................................162

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APPENDICES ..........................................................................................................163

Appendix 1: List of Wells, Samples and Depository Sequences ..............................165

Appendix 2:Analytical Procedures ...........................................................................173

A2.1 Comparison of the Small Angle Scattering and Geochemical Methods ....173

A2.2 SANS/USANS Sample Preparation (extracted from Geoscience Australia Sedimentology Laboratory Operating Procedure) .....................................1741.0 Introduction ......................................................................................1742.0 Purpose .............................................................................................1743.0 Scope ................................................................................................1744.0 Responsibilities ................................................................................1745.0 Hazards .............................................................................................1746.0 Hazard Control Measures and Limitations .......................................1757.0 Procedural Steps ..............................................................................1758.0 Flow Chart ........................................................................................178

A2.3 Introduction to SANS/USANS and its Applications to Source Rock Generation 179Introduction ................................................................................................179Background ................................................................................................179Application to Petroleum Geology ............................................................181Summary ....................................................................................................187References ..................................................................................................187

A2.4 TOC and Rock-Eval Pyrolysis Sample Preparation ..................................190

A2.5 TOC and Rock-Eval Pyrolysis Method .....................................................190

Appendix 3: Results of Size Fraction Experiments ..................................................193

Appendix 4: Rock-Eval Pyrolysis Definitions ..........................................................195

Appendix 5: TOC and Rock-Eval Pyrolysis Results ................................................199

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Figures

Figure 1.1 Location of the Browse Basin. .................................................................2

Figure 1.2. Location of Browse Basin wells sampled in the study. ............................3

Figure 1.3 Browse Basin Mesozoic and Cainozoic stratigraphy (after Blevin et al., 1998a). ............................................................................................4

Figure 2.1a Pyrogram (FID) from Brewster-1A 3050-3055 m (#20010664) for raw cuttings sample showing resolved S1 and S2 peaks. ..........................6

Figure 2.1b Pyrogram (IR) from Brewster-1A 3050-3055 m (#20010664) for raw cuttings sample showing CO2 (top trace) and CO (bottom trace) released during pyrolysis. ........................................................................7

Figure 2.1c Pyrogram (IR) from Brewster-1A 3050-3055 m (#20010664) for raw cuttings sample showing resolved CO2 (top trace) and CO (bottom trace) released during oxidation. ..............................................................7

Figure 2.2 Pyrogram (FID) from Crux-1 3055-3060 m (#20020131) for raw cuttings sample. ........................................................................................8

Figure 2.3 Pyrogram (FID) from Crux-1 3460-3465 m (#20020131) for extracted cuttings sample. ........................................................................9

Figure 2.4 Pyrogram (FID) from Crux-1 2450-2460 m (#20020110) for extracted cuttings sample containing contaminant peaks. .......................9

Figure 2.5 Pyrogram (FID) from Crux-1 3055-3060 m (#20020123) for extracted cuttings sample containing contaminant peak. .......................10

Figure 2.6 Pyrogram (FID) from Crux-1 3155.2 m (#20020136) for extracted SWC sample. ..........................................................................................10

Figure 2.7 Pyrogram (FID) from Gorganichthys-1, 3420-3425 m (#20010692) for extracted cuttings sample drilled using a water-based mud. ............11

Figure 2.8 Pyrogram (FID) from Gorganichthys-1 4320-4325 m (#20010700) for extracted cuttings sample drilled using a SBM. ...............................11

Figure 3.1 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Brewster 1A sediments (HC indicates samples which contain hydrocarbons). ...........................................................................16

Figure 3.2 TOC and Rock-Eval pyrolysis cross plots for Brewster 1A sediments (HC indicates samples which contain hydrocarbons). ..........17

Figure 3.3 TOC and Rock-Eval pyrolysis cross plots for selected sediments in Brewster-1A. ..........................................................................................19

Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (a): 11 samples (claystones, 5 m interval each), depth range 2450 m to 2950 m. ..............................................................22

Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (b): 9 samples (claystones, 5 m interval each), depth range 3000 m to 3600 m. .............................................................23

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Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (c): 4 samples (claystones, 5 m interval each), depth range 3695 m to 4230 m. ..............................................................24

Figure 3.5. SANS intensity versus depth at four Q-values of (a) 0.025 Å-1, (b) 0.0025 Å-1, (c) 0.00025 Å-1, and (d) 0.000025 Å-1, which corresponds to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, for cuttings samples from Brewster-1A ...................................................................................25

Figure 3.6. Variation of the Scattering Length Density (SLD) with depth for Brewster-1A. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. .........................................................................................28

Figure 3.7. Pore size distribution at various depths for samples of cuttings from Brewster-1A. (a): 11 samples (claystones, 5 m interval each), depth range is 2450 m to 3055 m. (b): 11 samples (claystones, 5m interval each), depth range 3100 m to 4235 m ...................................................29

Figure 3.8. Variation of the pore number density for four selected pore sizes versus depth for Brewster-1A. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text. .................................................................................31

Figure 3.9. Variation of apparent porosity with depth for Brewster-1A. For discussion see text. ..........................................................................32

Figure 3.10 Depth plots of TOC and Rock-Eval pyrolysis data for Carbine-1. ........34

Figure 3.11 TOC and Rock-Eval pyrolysis cross plots for Carbine-1 sediments ......35

Figure 3.12 TOC and Rock-Eval pyrolysis cross plots for selected sediments in Carbine-1. ...............................................................................................36

Figure 3.13. SANS absolute intensity curves for samples of cuttings from Carbine-1. Data are shown for seven samples (nominally claystones and silty slaystones, 3 m interval each). Depth range is 1349 m to 1559 m. ..................................................................................................39

Figure 3.14. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Carbine-1. .....................................................................................40

Figure 3.15. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Carbine-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. ........................................................41

Figure 3.16. Pore size distribution at various depths for samples of cuttings from Carbine-1. Seven samples (nominally claystones and silty claystones, 3 m interval each), depth range is 1349 m to 1559 m. ........42

Figure 3.17. Variation of the pore number density for selected pore sizes versus depth for Carbine-1. Note the significant decrease of the pore number density with depth, indicative of compaction. For full discussion see text. .................................................................................43

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Figure 3.18. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Carbine-1. For discussion see text. ..................44

Figure 3.19 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Adele-1. .....................................................................................46

Figure 3.20 TOC and Rock-Eval pyrolysis cross plots for Adele-1 samples. ...........48

Figure 3.21 TOC and Rock-Eval pyrolysis cross plots for selected samples from Adele-1. ..................................................................................................49

Figure 3.22. SANS absolute intensity curves for samples of cuttings from Adele-1. .................................................................................................53

Figure 3.23. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Adele-1. ........................................................................................55

Figure 3.24. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Adele-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. .........................................................................................56

Figure 3.25. Pore size distribution at various depths for samples of cuttings from Adele-1. A: ten samples (claystones, 5 m interval each), depth range is 2530 m to 2980 m. B: nine samples (claystones, 5 m interval each), depth range 3030 m to 3405 m. ..............................................................57

Figure 3.26. Variation of the pore number density for selected pore sizes versus depth for Adele-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text. .......59

Figure 3.27. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Adele-1. For discussion see text. ......................60

Figure 3.28. Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Argus-1 samples. .......................................................................62

Figure 3.29. SANS absolute intensity curves for samples of cuttings from Argus-1. Eight samples (seven claystones and one calcareous claystone, 5 m interval each), depth range 4270 m to 4535 m. ..............................66

Figure 3.30. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Argus-1. .................................................................................................67

Figure 3.31. Vitrinite reflectance and thermal maturity data for extracts and condensates for Argus-1 . ......................................................................68

Figure 3.32. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Argus-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement. ........................................................69

Figure 3.33. Pore size distribution at various depths for samples of cuttings from Argus-1. Eight samples (seven claystones and one calcareous claystone, 5 m interval each), depth range is 4270 m to 4535 m. ..........70

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Figure 3.34. Variation of the pore number density for selected pore sizes versus depth for Argus-1. ................................................................................71

Figure 3.35. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Argus-1. ...........................................................72

Figure 3.36 Depth plots of TOC and Rock-Eval pyrolysis data for Brecknock South-1. ................................................................................74

Figure 3.37 Tmax versus Hydrogen Index for selected samples from Brecknock South-1. ...............................................................................76

Figure 3.38. SANS absolute intensity curves for samples of cuttings from Brecknock South-1. Ten samples (nominally claystones, 5 m interval each), depth range is 3530 m to 3995 m. .................................79

Figure 3.39. SANS intensity versus depth at Q=0.01A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Brecknock South-1. ......................................................................80

Figure 3.40. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Brecknock South-1. .......................................81

Figure 3.41. Pore size distribution at various depths for samples of cuttings from Brecknock South-1. Ten samples (nominally claystones, 5 m interval each), depth range is 3530 m to 3995 m. ...............................................82

Figure 3.42. Variation of the pore number density for selected pore sizes versus depth for Brecknock South-1. ..............................................................83

Figure 3.43 Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Brecknock South-1. For discussion see text. ...84

Figure 3.44 Depth plots of TOC and Rock-Eval pyrolysis data for Crux-1 (GA data only). ...............................................................................................86

Figure 3.45 Depth plots of TOC and Rock-Eval pyrolysis data for Crux-1. .............87

Figure 3.46 Tmax versus Hydrogen Index for selected samples from Crux-1. .........89

Figure 3.47 SANS absolute intensity curves for samples from Crux-1. .................92

Figure 3.48. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for samples from Crux-1. ..................................................................................................95

Figure 3.49. Vitrinite reflectance versus depth for Crux-1 (after Well Completion Report). ...............................................................................96

Figure 3.50. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Crux-1. ..................................................................................97

Figure 3.51. Pore size distribution at various depths for samples from Crux-1. ......98

Figure 3.52. Variation of the pore number density for selected pore sizes versus depth for Crux-1. ..........................................................................................100

Figure 3.53. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Crux-1. ..........................................................101

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Figure 3.54. Interpretation of SANS data for Crux-1. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for samples from Crux-1. ...................102

Figure 3.55 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Dinichthys-1. ..........................................................................104

Figure 3.56 Tmax versus Hydrogen Index for selected samples from Dinichthys-1. 105

Figure 3.57 SANS absolute intensity curves for samples of cuttings from Dinichthys-1. ......................................................................................109

Figure 3.58 SANS intensity versus depth at four Q-values of (a) 0.025 Å -1, (b) 0.0025 Å -1, (c) 0.00025 Å -1, and (d) 0.000025 Å -1, which corresponds to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, for cuttings samp ...........................112

Figure 3.59 Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Dinichthys-1. ................................................114

Figure 3.60 Pore size distribution at various depths for samples of cuttings from Dinichthys-1. ...............................................................................115

Figure 3.61 Variation of the pore number density for four selected pore sizes versus depth for Dinichthys-1. . ...........................................................117

Figure 3.62 Variation of apparent porosity (within the pore size range 2 nm to 20 µm) with depth for Dinichthys-1. For discussion see text. .........118

Figure 3.63 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Gorgonichthys-1. ....................................................................119

Figure 3.64 Tmax versus Hydrogen Index for selected samples from Gorgonichthys-1. ..................................................................................121

Figure 3.65 SANS absolute intensity curves for samples of cuttings from Gorgonichthys-1. ................................................................................124

Figure 3.66 SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Gorgonichthys-1. ........................................................................126

Figure 3.67 Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Gorgonichthys-1. ...........................................127

Figure 3.68 Pore size distribution at various depths for samples of cuttings from Gorgonichthys-1. ..................................................................................128

Figure 3.69 Variation of the pore number density for selected pore sizes versus depth for Gorgonichthys-1. ................................................................130

Figure 3.70 Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Gorgonichthys-1. ............................................131

Figure 3.71 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Titanichthys-1. ........................................................................133

Figure 3.72 Tmax versus Hydrogen Index for selected samples from Titanichthys-1. ......................................................................................134

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Figure 3.73. SANS absolute intensity curves for samples of cuttings from Titanichthys-1. ......................................................................................137

Figure 3.74 SANS intensity versus depth at Q = 0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Titanichthys-1. ............................................................................139

Figure 3.75 Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Titanichthys-1. .............................................140

Figure 3.76 Pore size distribution at various depths for samples of cuttings from Titanichthys-1. .....................................................................................141

Figure 3.77 Variation of the pore number density for selected pore sizes versus depth for Titanichthys-1. ....................................................................143

Figure 3.78 Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Titanichthys-1. ..............................................144

Figure 4.1 Comparison of pyrolysis data from nearby wells drilled using water-based mud and without glycol additives. ..................................146

Figure 4.2 Comparison of pyrolysis data from near-by wells drilled using different mud systems. Depth is expressed in mSS. ............................147

Figure 4.3 Scattering intensity versus depth (below sea level) for stratigraphic formations in Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1. ......................................................................................151

Figure 4.4 Interpretation of SANS data for Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1. ...................................................152

Figure 4.5 Scattering intensity versus depth (below sea level) for stratigraphic formations in Brewster-1A, Crux-1 and Adele-1. ................................154

Figure 4.6 Comparison of source rock data from Browse Basin study wells. ......156

In Appendices

Diagram 1.0 Set up of sieving apparatus ..................................................................176

Image 1.0 Sample pot at right, holding jig at left. ...............................................177

Image 2.0 Sample mount in holding jig ready for sectioning. ..............................178

Figure 1 Range of linear sizes that can be observed with various types of neutron optics. ......................................................................................180

Figure 2 Neutron scattering length density for major minerals and organic matter types present in sedimentary rocks. ..........................................181

Figure 3 The comparison of SANS/USANS scattering data for a typical sandstone [24, 25], shale [20, 24] and coal [19]. ...............................182

Figure 4 The comparison of SANS/USANS-derived pore size distribution for a sandstone [23, 24], shale [23, 24], and coal [19]. .......................183

Figure 5. The comparison of SANS/USANS-derived specific surface area for a sandstone [23, 24], shale [23, 24] and coal [19]. .......................184

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Figure 6. The variation of SANS intensity at a single Q-value versus the annealing temperature for an immature hydrocarbon source rock. .....185

Figure 7. A schematic representation of the SANS intensity (for a selected Q-value) versus depth within the hydrocarbon generation window. ....186

Figure 8. The comparison of specific surface area for coals of different rank obtained using SANS and the nitrogen adsorption method. The probe size is 4Å (after Reference 19). ..................................................187

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Tables

Table 3.1. XRF raw data for Adele-1. .....................................................................52

Table 3.2. XRF data for Argus 1. ............................................................................65

Table 4.1 Drilling information and depths of lithological units for Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1. ............................150

Table A1.1 List of wells studied in this project. ....................................................165

Table A1.2 Samples analysed in this study from Adele-1 ......................................166

Table A1.3 Samples analysed in this study from Argus-1 ......................................166

Table A1.4 Samples analysed in this study from Brecknock South-1 ....................167

Table A1.5 Samples analysed in this study from Brewster-1A ..............................167

Table A1.6 Samples analysed in this study from Carbine-1 ...................................168

Table A1.7 Samples analysed in this study from Crux-1 .......................................168

Table A1.8 Samples analysed in this study from Dinichthys-1 ..............................169

Table A1.9 Samples analysed in this study from Gorgonichthys-1 ........................170

Table A1.10 Samples analysed in this study from Titanichthys-1 ............................171

Table A1.11. Depository sequences for nine wells in the Browse Basin. Part 1 - Geoscience Australia classification of depository sequences. Part 2 - depository sequences as in Well Completion Reports. All depths are in mRT. .........................................................................172

Table A2.1 Comparison of the SAS and geochemical methods. ............................173

Table A3.1 Reproducibility of data for different size fractions for cuttings sample from Brewster 1A, 2750-2755m (#20010658). .......................193

Table A3.2 Reproducibility of data for different size fractions for cuttings sample from Brewster 1A, 3695-3700 m (#20010672). ......................193

Table A3.3 Comparison of data for different size fractions for cuttings samples from Brewster 1A. ..................................................................194

Table A4.1 Definitions of Rock-Eval pyrolysis parameters (modified after Espitalié et al., 1985; Peters, 1986). ....................................................196

Table A4.2. Guidelines for interpreting (a) source rock generative potential and (b) type of petroleum generated from immature sediments (VR <0.6 %), and, c) degree of thermal maturation (modified after Peters, 1986; Espitalié and Bordenave,1993). ..............................198

Table A4.2a Source rock generative potential (richness) for VR < 0.6 %. ..............198

Table A4.2b Source rock quality for VR < 0.6 %. ....................................................198

xvi

Table A4.2c Source rock thermal maturity. ..............................................................198

Table A5.1 TOC and Rock-Eval pyrolysis results for cuttings samples from Brewster-1A. ........................................................................................199

Table A5.2 TOC and Rock-Eval pyrolysis results for cuttings samples from Carbine-1. .............................................................................................200

Table A5.3 TOC and Rock-Eval pyrolysis results for cuttings samples from Adele-1 extracted with methanol and dichloromethane (90:10). S1 values are invalid. ............................................................................200

Table A5.4 TOC and Rock-Eval pyrolysis results for cuttings samples from Argus-1 extracted with methanol and dichloromethane (90:10). S1 values are invalid. ............................................................................201

Table A5.5 TOC and Rock-Eval pyrolysis results for cuttings samples from Brecknock South-1 extracted with methanol and dichloromethane (90:10). .................................................................................................201

Table A5.6 TOC and Rock-Eval pyrolysis results for cuttings and side-wall-core samples from Crux-1. S1 values are invalid. ................202

Table A5.7 TOC and Rock-Eval pyrolysis results for cuttings samples from Dinichthys-1. S1 values are invalid. .....................................................203

Table A5.8 TOC and Rock-Eval pyrolysis results for cuttings samples from Gorgonichthys-1. S1 values are invalid. ...............................................204

Table A5.9 TOC and Rock-Eval pyrolysis results for cuttings samples from Titanichthys-1. S1 values are invalid. ...................................................205

1

1. Introduction

The aim of this study was to determine the timing of hydrocarbon generation and expulsion in the Early Cretaceous Echuca Shoals Formation and Jamieson Formation in the Browse Basin (Figs. 1.1, 1.2 and 1.3) using synergies between classical organic geochemistry and the technique of Small Angle Neutron Scattering.

The tectonic and stratigraphic evolution of the Browse Basin and its potential for petroleum generation and entrapment have been studied previously (Struckmeyer et al. 1998, Blevin et al. 1998a). Based on the intra-basin oil-oil and oil-source rock correlation, an effective Lower Cretaceous Petroleum System (Westralian W3 Petroleum System) in the Browse Basin has been postulated (Blevin et al. 1998b).

The study has been performed on rock cuttings and sidewall cores originating from eight recently drilled wells and one older well (Table A1 in Appendix 1). Small Angle Neutron Scattering (Thiyagarajan et al. 1998), Rock-Eval pyrolysis and total organic carbon (TOC) analyses were carried out on 165 organic-rich Jurassic-Cretaceous sedimentary rock samples from nine wells in the Browse Basin (Table A2 in Appendix 1). Out of the total of 165 samples, 47 (22 for Brewster-1A and 25 for Dinichthys-1) were additionally analysed using the Ultra Small Angle Neutron Scattering (USANS) technique (Hainbuchner et al. 2000). Major findings of this work have been published by Radlinski et al. (2004). Geological applications of SANS and USANS are reviewed by Radlinski (2006).

Stratigraphic classification for the Browse Basin wells is at the development stage. Table A1-11 in Appendix 1 lists depositional sequences for the nine wells studied in this work. Uniform classification according to the Geoscience Australia scheme is available for wells Adele 1, Brecknock South 1, Brewster 1A, Crux 1 and Gorgonichthys 1 (part 1 of Table A1-11 in Appendix 1). For wells Argus 1, Carbine 1, Dinichthys 1 and Titanichthys 1 the sequences shown follow the company classification scheme used in Well Completion Reports (part 2 of Table A1-11 in Appendix 1).

The focus of the study was to identify potential source rocks and the depth at which the onset of hydrocarbon generation and saturation of pore spaces occurred within each well. However, in the course of the pyrolysis component of the study two other objectives became apparent: firstly, it was necessary to determine whether or not the organic matter in the (>355 µm, <475 µm) size fraction provided was representative of the whole rock sample; and secondly, because the wells were drilled using a variety of drilling fluids, the effect of the these fluids on the quality of the data had to be ascertained.

2

Figure 1.1 Location of the Browse Basin.

15

14

13

122 123 124 125

Ashmore Platform

Yampi Shelf

Leveque Shelf

KIMBERLEY BASIN

VulcanSub-basin

Londonderry

High

B R O W S E

B A S I N

Caswell Sub-basin

Prudoe

Tce

ied)

Leveque 1

Trochus 1

Buffon 1

Caswell 2

North Scott Reef 1

Circinus 1

Psepotus 1

Scott Reef 2, 2A

Brewster 1A

WA

NT

SA

QLD

NSW

ACTVIC

TAS

03-227-13

Major Palaeozoic fault

Minor Palaeozoic fault

Jurassic fault

Platform of Precambrian / Palaeozoicwith thin (<2 km) Mesozoic cover

Shallow/exposed Precambrian rocksor Proterozoic basin

Late Palaeozoic to Mesozoic basin

Brecknock 1

Barcoo

Sub-basin

EchucaShoals 1Se

ring

apat

am

Sub-

basin

Yampi 2 Gwydion 1

Argus 1

Dinichthys 1

Gorgonichthys 1

Carbine 1

Adele 1

Titanichthys 1

Cornea 1

BrecknockSouth 1

Crux 1

Discorbis 1

Columbia 1A

Asterias 1

Bassett 1A

Heywood 1

3

2. Analytical Procedures

2.1 Samples

A complete list of the samples analysed in this study from the nine Browse Basin wells (Adele-1, Argus-1, Brecknock South-1, Brewster-1A, Carbine-1, Crux-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1) are given in Appendix 1. Unless otherwise stated, all depth measurements are given with respect to the rotary table (RT).

The selected sedimentary rock samples comprise side-wall-cores (SWCs) and cuttings (CUTT). Given sufficient quantity of the rock material, each rock sample was divided into three portions (in the priority sequence): one for SANS/USANS, one for geochemistry, and one (archived) for possible future palaeontology work. The geochemistry portion was preserved for future biomarker work.

Figure 1.2. Location of Browse Basin wells sampled in the study.

15

13

122 124

Ashmore Platform

Yampi Shelf

VulcanSub-basin

B R O W S E

B A S I N

Caswell Sub-basin

PrudoeTce

Buffon 1

Caswell 2

North Scott Reef 1

Scott Reef 2, 2A

Brewster 1A

WA

NT

SA

QLD

NSWACT

VIC

TAS

Barcoo

Sub-basin

EchucaShoals 1Se

ring

apat

am

Sub-

basin

Yampi 2 Gwydion 1

Argus 1

Gorgonichthys 1

Adele 1

Titanichthys 1

Crux 1

Dinichthys 1

South 1Brecknock

Brecknock 1

Carbine 1

Londonderry High

KIMBERLEY BASIN

Proterozoic basin

Late Palaeozoic toMesozoic basin

Precambrian /Palaeozoic Platform

04-054-4

Cornea

4

Figure 1.3 Browse Basin Mesozoic and Cainozoic stratigraphy (after Blevin et al., 1998a).

MAASTRICHTIAN

CAMPANIAN

SANTONIANCONIACIAN

CENOMANIAN

ALBIAN

APTIAN

BARREMIAN

HAUTERIVIAN

VALANGINIAN

BERRIASIAN

TITHONIAN

KIMMERIDGIAN

OXFORDIAN

CALLOVIAN

BATHONIAN

BAJOCIAN

AALENIAN

TOARCIAN

PLIENSBACHIAN

SINEMURIAN

HETTANGIAN

NORIAN

CARNIAN

ANISIAN

NAMMALIANSPATHIAN

PLEISTOCENE

PLIOCENE

MIOCENE

OLIGOCENE

Era

Syst

em

AgeMa

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250

Seq

BB9

BB7

BB6

BB4

BB5

BB8

BB10

BB11

BB12ABB12B

BB12C

BB13

BB14

BB15BB16

BB17

BB18

BB19

BB20

BB21

BB22Barracouta Fm

Oliver Fm

Cartier Fm

PrionFm

GrebeFm

Bassett Fm

Puffin FmFenelon andGibson Fms

Woolaston Fm

Jamieson Fm

Echuca Shoals

Fm

UpperVulcan Fm

LowerVulcan

Fm MontaraFm

Plover Fm

Nome Fm

Osprey Fm

Series/Epoch/Stage

TR

IASSIC

JUR

ASSIC

CR

ETA

CEO

US

Q

MESO

ZO

ICC

AIN

OZO

ICLitho-

stratigraphy

E

L

M

E

L

M

E

LADINIAN

GRIESBACHIAN

Challis Fm

Pollard Fm

Mt Goodwin Fm

RHAETIAN

TURONIAN

SCYT

HIA

N

EOCENE

PALEOCENE

TER

TIA

RY

L

NEO

GEN

EPA

LA

EO

GEN

E

03-227-16

5

2.2 Analytical Techniques

2.2.1 Small Angle Neutron Scattering and Ultra-small Angle Neutron Scattering

Details of the sample preparation for SANS/USANS can be found in Appendix 2.1. An introduction to the SANS/USANS techniques and its application to source rock generation are presented in Appendix 2.2 and 2.3.

Briefly, samples for SANS/USANS were prepared by gently crushing the rock material and dry-sieving into three fractions <355 µm; 355-475 µm; and >475 µm. The dry sieved 355-475 µm grain size fraction, to be used for the SANS/USANS measurements, was planted in resin and, after curing, two to three 25 mm diameter slices (about 1mm thick and about 0.4mm thick) were cut off with a precision diamond saw. The thick (1 mm) slices were directly used for the SANS measurements and the thin (0.4 mm) slices were used for the USANS measurements. The Standard Operating Procedure for SANS sample preparation is reproduced in Appendix 2.2.

Many of the samples submitted for this project were too small to perform a three-way split. Hence, the left over portion of the size-fractionated sample (355-475 µm) from the SANS preparation was submitted for Rock-Eval pyrolysis and TOC analysis. In a series of independent Rock Eval pyrolysis and TOC measurements it was confirmed that this SANS size fraction yielded the same results as the recombined whole rock sample, as detailed in Appendix 3.

For the small angle neutron scattering a time-of -flight SANS instrument SAND at the Intense Pulsed Neutron Source, Argonne National Laboratory, USA (Thiyagarayan et al, 1998) and the USANS instrument S18 at the High Flux Reactor in Grenoble, France (Hainbuchner et al., 2000) were used.

2.2.2 Rock-Eval Pyrolysis

The Rock-Eval pyrolysis sample preparation and analytical procedures used in this study are detailed in Appendix 2.4 and 2.5, respectively. Briefly, the dry-sieved sample fractions from wells using water-based drilling muds were powdered and pyrolysed in a Turbo Rock-Eval 6. Samples from wells which were drilled using either ‘Glycol’ or the synthetic-based mud (SBM), Syntech were extracted with the organic solvent mixture methanol:dichloromethane (90:10 and 50:50, respectively) by sonication after crushing to a fine powder using a mortar and pestle. The sediment was recovered by centrifuging and dried at 40 oC. It was then placed into an oxidized crucible ready for analysis.

2.3 Rock-Eval Pyrolysis Size Fraction Experiments

Experiments to determine whether the SANS 355-475 µm sized fraction was representative of the whole rock sample were carried out on Brewster-1A cuttings samples because this well was drilled using a water-based mud, hence erroneous values arising from drilling fluid contaminants were minimised.

6

Rock-Eval pyrolysis was carried out on all three dry-sieved fractions (viz <355 µm; 355-475 µm; and >475 µm) and a recombined whole rock sample over three depth ranges 2750-2755 m (#20010658), 3600-3605 m (#20010671), and 3695-3700 m (#2001072) in Brewster-1A. These samples were chosen to reflect any differences that may occur between the Jamieson and Echuca Shoals formations, as well as increasing maturity.

The results show that the variation seen between the three different size fractions and the recombined sample is generally within experimental error between repeat samples (see Appendix 3; Tables A3.1 and A3.2). The biggest variation in the results is seen between the Tmax, S3 and TOC values between repeat analyses. Therefore, the 355-475 µm size fraction was deemed representative of the whole-rock sample and used in the pyrolysis experiments.

2.4 Washing Method Experiments

For the samples recovered from wells drilled using glycol additives and synthetic-based muds (SBMs), a method for washing the samples had to be determined to maximise the removal of the contaminants while being practical in terms of laboratory time and use of resources. Initially, the samples were washed in water and then methanol and dichloromethane, prior to crushing and analysis. However, this methodology did not remove the drilling contaminants. Therefore, the extraction method detailed in Appendix 2.4 was employed on the powdered sample.

2.4.1 Pyrograms of Water-based Drilling Mud Samples

On pyrolysis, the cuttings samples from Brewster-1A and Carbine-1, drilled using water-based muds, gave well resolved, individual S1, S2 and S3 peaks, as shown in Figure 2.1.

Figure 2.1a Pyrogram (FID) from Brewster-1A 3050-3055 m (#20010664) for raw cuttings sample showing resolved S1 and S2 peaks.

7

Figure 2.1b Pyrogram (IR) from Brewster-1A 3050-3055 m (#20010664) for raw cuttings sample showing CO2 (top trace) and CO (bottom trace) released during pyrolysis.

Figure 2.1c Pyrogram (IR) from Brewster-1A 3050-3055 m (#20010664) for raw cuttings sample showing resolved CO2 (top trace) and CO (bottom trace) released during oxidation.

2.4.2 Pyrograms of Glycol Contaminated Samples

On pyrolysis, samples from the five wells; Adele-1, Argus-1, Brecknock South-1, Crux-1 and Dinichthys-1 showed contamination by glycol additives in the drilling mud. There are large, multiple S1 and S2 peaks, as shown in Figure 2.2, due to the contaminant compounds adding to, and obscuring, the indigenous free hydrocarbons (S1 peak) and the hydrocarbons cracked from the kerogen (S2 peak) upon pyrolysis.

8

Figure 2.2 Pyrogram (FID) from Crux-1 3055-3060 m (#20020131) for raw cuttings sample.

After the solvent extraction, most of the glycol contaminants appear to have been removed from the sample (Fig. 2.3), as well as the free hydrocarbons within the rock. Hence, the S1 peak in the pyrogram is either small or undetected, resulting in the S1 peak being unreliable and consequently all values calculated [viz. Bitumen Index (BI), Production Index (PI)] are also unreliable. The kerogen in the rock is unaffected by the solvent extraction process therefore the S2 peak in the program, and the interpreted Tmax values, should be an accurate measure of the quantity, quality and maturity of the kerogen in the rock, as long as the S2 peak is fully resolved from any remaining contamination.

Although all of the samples were extracted in the same way, the pyrograms of some samples still showed the effects of contaminants (Figs 2.4 and 2.5). The bimodal, and in some cases multimodal, S2 peak results in an anomalously low Tmax value since Tmax is typically assigned to the peak with the greatest height after 300 oC; in this case the first (lower temperature) peak.

The S1 and S2 values are also anomalously high. Despite further extraction, the contaminants remained in some samples. It is undetermined whether the level of contamination in these samples was much greater than the other samples, whether the permeability and/or porosity differed in these samples or that the chemical composition of the contaminant has changed.

Furthermore, comparison of the extracted cuttings samples with those of the extracted sidewall core samples in the Adele-1 and Crux-1 wells (Figs 2.5 and 2.6) show that the glycol additive has had a considerable effect on the pyrolysis values of the cuttings samples with respect to the sidewall core samples of similar depth. Despite the fully resolved appearance of the S2 peak in both the pyrograms, the S2 peak in the sidewall core (Fig. 2.6) has a symmetrical and narrow peak shape, whereas a shoulder remains on the broader S2 peak from the cuttings sample (Fig. 2.5). Effects of this additive appear to be inconsistent but generally result in lower than expected Tmax values, enhanced TOC contents and enhanced S2 values. Depending on the relative increases in the TOC and S2 values, the resultant Hydrogen Index values typically increase.

9

Figure 2.3 Pyrogram (FID) from Crux-1 3460-3465 m (#20020131) for extracted cuttings sample.

Figure 2.4 Pyrogram (FID) from Crux-1 2450-2460 m (#20020110) for extracted cuttings sample containing contaminant peaks.

10

Figure 2.5 Pyrogram (FID) from Crux-1 3055-3060 m (#20020123) for extracted cuttings sample containing contaminant peak.

Thus, independent of the extraction process, there is an inability to remove all the ‘glycol’ contaminants, which are still contributing to the S2 peak. Therefore, the Rock-Eval pyrolysis results produced for samples obtained from mud systems with glycol additives should either be used with caution, or not at all, when carrying out source rock appraisal.

Figure 2.6 Pyrogram (FID) from Crux-1 3155.2 m (#20020136) for extracted SWC sample.

2.4.3 Pyrograms of SBM Contaminated Samples

On pyrolysis, the samples from the two wells Gorgonichthys-1 and Titanichthys-1 showed contamination by mud additives. In Gorgonichthys-1 the well was drilled using water-based drilling mud to a depth of 3930 m, below this depth the mud system was

11

changed and SBMs were used to the bottom of the well. Titanichthys-1 was also drilled using two mud systems, an initial water-based mud followed by a SBM being used from a depth of 3905 m to the bottom of the well. All of the cuttings samples were powdered and extracted using methanol and dichloromethane (50:50). Figures 2.7 and 2.8 compare the pyrograms for the extracted cuttings drilled using the water-based drilling fluid and the SBM drilling fluid. The S2 peak in the SBM pyrogram is much broader than the sample drilled using the water-based mud, resulting in a low Tmax value.

Figure 2.7 Pyrogram (FID) from Gorganichthys-1, 3420-3425 m (#20010692) for extracted cuttings sample drilled using a water-based mud.

Figure 2.8 Pyrogram (FID) from Gorganichthys-1 4320-4325 m (#20010700) for extracted cuttings sample drilled using a SBM.

12

13

3 Results

TOC and Rock-Eval Pyrolysis

The results for the project are ordered by the type of drilling fluid used in each well (water-based, water-based with glycol additive and SBM-based) and then in alphabetical order of the wells. Pyrolysis data from well completion reports (WCRs) are also included to make the source rock interpretations as complete as possible for each well, to compare the Geoscience Australia’s laboratory data with that of service company data, and compare the data from sidewall cores with that of cuttings, which are inherently more prone to contamination issues.

Definitions of the Rock-Eval pyrolysis parameters used are given in Appendix 4 Table A4.1 after Espitalié et al (1985) and Peters (1986), with a summary of the criteria used to define a source rock (after Peters, 1986) being listed in Table A4.2.

For a sediment to have hydrocarbon potential, the minimum total organic carbon (TOC) content for a carbonate is taken to be 0.2 % and 0.5 % for a clastic sediment (Table A4.2a), although TOC’s in excess of 2.0 % are typically required for NW Shelf sediments to have the capacity to generate and expel hydrocarbons.

Immature samples often have poorly resolved S1 and S2 peaks, therefore Tmax values less than 380 °C were excluded from the evaluation of hydrocarbon source potential. Low S2 values can arise from adsorption of the produced hydrocarbons on the mineral matrix (Espitalié et al., 1980; Orr, 1983), resulting in an underestimation of the Hydrogen Index. The mineral matrix effect was found to be significant in a previous source rock appraisal of the Browse Basin (Blevin et al., 1998b). Therefore, samples with small S

2 peaks (< 0.2 mg hydrocarbons/g rock) were considered to be unreliable

and hence such samples have been omitted from the assessment of source rocks.

In order to prevent migrated oil and contaminants interfering with the identification of source rocks, samples with anomalously high production indices (PI), and low Tmax values, were excluded from the source rock evaluation sections and included in the discussion of drilling fluids, contaminants and migrated hydrocarbons. The cut-off values applied to the data to allow evaluation of source rocks sensu stricto are as follows; PI ≤ 0.1 for immature (VR ≤ 0.5 %) sediments, 0.1 > PI ≤ 0.25 for early mature (0.5 > VR ≤ 0.8 %), sediments and 0.25 > PI ≤ 0.4 for mature (0.8 > VR ≤ 1.2 %) sediments. Hence, only a proportion of the total number of analyses carried out on sediments from the Browse Basin are shown in some figures.

A brief summary of source richness (TOC, potential yield), source quality (oil- or gas-prone) and kerogen type is given in this report for the formations in each well. The majority of samples chosen in this study come from the Lower Cretaceous Jamieson, Echuca Shoals and Upper Vulcan formations and the Upper Jurassic Lower Vulcan Formation (Fig. 3.1). A few samples from the Lower-Middle Jurassic Plover Formation and the Triassic Mount Goodwin Formation are also included. In this study, a source rock has been assumed to be gas-prone if the Hydrogen Index is below a minimum of 150 mg hydrocarbons/g TOC, condensate-prone when the HI is between 150 and 200

14

mg hydrocarbons/g TOC and oil-prone with some gas at higher values. Oil-prone source rocks with HI > 300 mg hydrocarbons/g TOC were not recorded in the Browse Basin samples.

An assessment of thermal maturity was made using a combination of Tmax, PI and vitrinite reflectance (VR). The degree of thermal maturity required for the generation of hydrocarbons depends on the type of organic matter present in the source rock. The Mesozoic succession of the Browse Basin comprises thick Lower Jurassic deltaic to coastal plain sediments, thin Upper Jurassic fluvio-deltaic sediments and a thick sequence of Lower Cretaceous prograding fluvio-deltaic and shallow marine sediments (Blevin et al. 1998a, b). These sediments contain varying proportions of indigenous sapropellic material (disseminated remains of bacteria, algae, acritarchs, dinoflagellates etc) and allochthonous land-plant-derived material. Hence, the predominant type of hydrocarbon-prone organic matter within these sediments ranges from Type II to Type III kerogen. Higher maturities are usually required for the generation and expulsion of hydrocarbons from hydrogen-poor Type III kerogens than for Type II kerogens (see Appendix 4, Table A4.2c), thus:

Kerogen Type VR oil window Tmax oil window

Type II 0.5-1.2 % 435-460 °C

Type III 0.65-1.4 % 440-470 °C

The peak oil window was taken to correspond to vitrinite reflectances between 0.8 and 0.9 %, peak wet gas at VR = 1.2 % and dry gas at VR > 1.6 %. A minimum temperature of 170 °C (VR > 1.2 %) was assumed to be required for the cracking of oil to gas. Sediments in which oxidised organic material (inertinite) or Type IV kerogen is prevalent are considered to be a source of methane and carbon dioxide at high thermal maturities, i.e. within the dry gas window (VR = 1.4-4 %).

SANS and USANS Analysis

The outline of SANS/USANS methodology is given in Appendix 2 (Section A 2.2). The scattering intensity has been measured versus the scattering vector Q for each sample and converted to absolute units. From these data, plots illustrating the variation of the scattering intensity versus depth for several selected pore sizes have been constructed and examined for the existence of characteristic <-shaped patterns, which are indicative of the presence of mobile bitumen within the pores of a particular size. The pore sizes selected for analysis were 100 Å and 860 Å for wells with SANS data only, and 100 Å, 1000 Å, 10,000 Å and 100,000 Å (100 Å = 0.01 µm; 1 µm = 10,000 Å) for wells in which both SANS and USANS data were collected (Brewster-1A and Dinichthys-1). As the pore size range in mudstones extends from about 10 Å to about 40 µm, the presence of bitumen in the pores of the smallest size selected in this work (100 Å) indicates the onset of hydrocarbon generation, whereas the presence of bitumen in the largest pores (10 µm) indicates a significant pore space saturation and an interpreted onset of hydrocarbon expulsion. For wells in which only SANS data are available, only the onset of hydrocarbon generation (if any) could be determined.

15

In a separate measurement using X-ray fluorescence (XRF), the atomic composition of the inorganic rock matrix has been determined for a representative number of samples from every depositional sequence in every well. The organic component of the rock is burnt off during sample preparation for XRF measurements. From the atomic composition, values of scattering length density have been calculated and used in conjunction with the absolutely calibrated SANS/USANS data to determine the pore size distribution for every sample. Then, the variation of pore number density versus depth for several selected pore sizes has been calculated. These data have been used to determine the stability of the pore microstructure versus increased lithostatic load at depth, as well as to detect the possible re-arrangement of the pore space caused by changing rock lithology.

Finally, the variation of apparent SANS porosity versus depth has been deduced. The apparent SANS porosity is a proxy for the real geometric porosity. The two porosities are approximately equal if the pore space is filled with gas or formation water. If bitumen is present in the pore space, the apparent SANS porosity is generally smaller than the geometric porosity.

In the following numerical analysis, it is assumed that the value of SLD for the substance filling the pore space is small compared with the value of SLD for the inorganic rock matrix. In practical terms this assumption works well for brine, saturated hydrocarbons and gas. In the region of liquid hydrocarbon generation, however, the pore space gets filled (at least partially) with bitumen and the SANS characteristics become anomalous, the measured scattering intensity decreases, calculated pore number density decreases, and the calculated porosity decreases. Such anomalies are closely examined to identify regions of hydrocarbon generation and expulsion. This needs to be done with caution, and in conjunction with other geological and geochemical evidence, as there may be other reasons (e.g. overpressure, lithological and organic matter variations) for locally changed microstructural characteristics of the rock matrix.

3.1 Brewster-1A

The pyrolysis data for Brewster-1A is given in Appendix 5 Table A5.1. Figure 3.1 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S1, S2, HI and BI) plotted against depth (mKB). Figures 3.2 and 3.3 comprise cross plots of the pyrolysis data by laboratory and by formation, respectively.

In addition to the cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses were also available from previous work by the Australian Geological Survey Organisation (see ORGCHEM, Geoscience Australia’s Oracle-based geochemical database www.ga.gov.au/oracle/apcrc) and Robertson Research (1986). The three data sets appear comparable despite different instruments being used, as shown by Figures 3.1 and 3.2.

3.1.1 Drilling Fluids, Contaminants and Migrated Hydrocarbons

Brewster-1A was drilled with a water-based drilling mud comprising a brine polymer. The well completion report (Woodside, 1980) documents that diesel was added to the side tracked well at 4464 m. This is at a depth below where the SANS cuttings samples

16

were taken in this study. Therefore, contamination of the cuttings samples by diesel should not be an issue.

Elevated levels in the S1 abundance, low Tmax values, and high Production Index (PI) and Bitumen Index (BI) values within these sediments indicate the presence of free hydrocarbons (annotated by the open symbols in Figures 3.1 and 3.2) throughout the Echuca Shoals Formation over the depth range 3320-3865 m. Two samples within the Jamieson Formation (at 2800 m and 3225 m) may also contain free hydrocarbons. No hydrocarbon staining is evident in the samples analysed by Robertson Research from the Lower Vulcan and Plover formations, even though diesel was added to the drilling mud when the side tracked well penetrated the Plover Formation.

Since these free hydrocarbons occur predominantly within the Echuca Shoals Formation, which is currently within the upper oil window, it is believed that they represent in situ generated hydrocarbons from organic-rich units elsewhere within this formation.

Figure 3.1 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Brewster 1A sediments (HC indicates samples which contain hydrocarbons).

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

VR (%)

HI (mg/g TOC)S2 (mg/g Rock)S1 (mg/g Rock)

0.4 0.8 1.2 1.6 2.0 400 440 480 1 2 3 4 5

200 400300100 5001 2 3 4 5 60.5 1.0 1.5 2.0

(a) (b) (c)

(d) (e) (f)

100

(g)

BI20 40 60 80

14/OA/1766

Tmax ( C) TOC (%)

Geotrack

Geotrack population 2

Geotrack population 1

AGSO CUTT

Robertson Research CUTT

Robertson Research CUTT HC

AGSO CUTT HC

GA CUTT SANS

GA CUTT SANS HC

Brewster -1A

0 0

000 0

Diesel added

GA sequence

Tertiary

MaastrichtianCampanian

Lower Vulcan Fm

JamiesonFormation

Echuca ShoalsFormation

Upper VulcanFormation

Santonian-Turonian

GA sequence

Tertiary

MaastrichtianCampanian

Lower Vulcan Fm

JamiesonFormation



Santonian-Turonian

Diesel added

Diesel added Diesel added Diesel added Diesel added

Plover Fm

Plover Fm

3.1.2 Source Richness

The total organic carbon (TOC) contents of the organic-rich sediments of the Lower Cretaceous Jamieson Formation are fair to good, ranging from 0.5-1.4 % (average

17

TOC = 0.9 %). The Lower Cretaceous Echuca Shoals Formation source rocks have higher organic richness (range = 1.5-2.7 %; average TOC = 2.1 %; Fig. 3.3).

The potential yields of the Jamieson Formation sediments are poor (average S1+S2 = 1.3 mg hydrocarbons/g rock; Fig. 3.3). The Echuca Shoals source rocks (excluding those samples with apparent free hydrocarbons in them) have slightly higher potential yields (average S1+S2 = 2.7 mg hydrocarbons/g rock; Fig. 3.3).

3.1.3 Source Quality, Kerogen Type and Maturity

Source rock quality is measured by the Hydrogen Index (HI). The Jamieson and Echuca Shoals formation sediments have HI values ranging from 26 to 160 mg hydrocarbons/g TOC (average = 112 mg hydrocarbons/g TOC and 105 mg hydrocarbons/g TOC, respectively) which indicates that they are presently predominantly gas-prone (Fig. 3.3). The cross plot of HI versus Tmax is routinely used to depict both the type of kerogen present in a source rock and its maturity. Figure 3.3 shows that the Jamieson and Echuca Shoals formation sediments contain Type III to Type IV kerogen. Petrographic analyses (Woodside, 1980) show that the kerogen is predominantly inertinite in the samples analysed.

Figure 3.2 TOC and Rock-Eval pyrolysis cross plots for Brewster 1A sediments (HC indicates samples which contain hydrocarbons).

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

0

2

4

6

8

10

12

14

16

18

20

420

430

440

450

460

470

480(a) (b)

14/OA/1767

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

Immature

Condensatewindow

Oil window

S -enrichment byH/C migration

or contamination

1

1S -depletion byh/c expulsion

Production Index

Brewster -1A

Tm

ax (

C)

AGSO CUTT

Robertson Research CUTT

Robertson Research CUTT HC

AGSO CUTT HC

GA CUTT SANS

GA CUTT SANS HC

18

There is a significant discrepancy in the vitrinite reflectance values obtained by the two laboratories Robertson Research and Geotrack (Fig. 3.1). Maturity estimates from the Tmax values places the samples closer to the vitrinite reflectance curve of Geotrack than that of Robertson Research. Therefore, the Jamieson Formation sediments are presently believed to be within the early to peak oil window and the Echuca Shoals Formation sediments are within the upper oil window.

The Upper and Lower Vulcan formations are currently within the wet gas window and the Plover Formation sediments are within the dry gas window. These sediments may have generated liquid hydrocarbons in the past, hence, their present source potential is not discussed. Of note is that the highest gas readings in the well were encountered within the Lower Vulcan Formation (4285 m - 4345 m).

3.1.4 Analysis of SANS and USANS data

Small Angle Neutron Scattering (SANS) and Ultra Small Angle Scattering (USANS) analyses were performed on 22 claystone cuttings from the well Brewster-1A (Table A1.5 in Appendix 2). These cuttings were collected at 50 m to 100 m intervals between depths 2450 mRT to 4235 mRT.

Figure 3.4 shows the original SANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q.

Figure 3.5(a-d) illustrates that there is a significant and systematic variation of the scattering intensity with depth. This variation is clearly pore-size-dependent, as shown in Figure 3.5(a-d) for four Q-values of 0.025 Å -1, 0.0025 Å -1, 0.00025 Å -1 and 0.000025 Å -1, which correspond to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10µm +/-50%, respectively. (1 Å = 10-10 m; 1 µm = 1000 nm = 10,000 Å).

In Brewster-1A there are two depth intervals which contain bitumen in the small pores, interpreted as evidence for the onset of hydrocarbon generation: the upper Jamieson Formation and the Echuca Shoals Formation. The characteristic <-shaped intensity curve for the upper Jamieson Formation becomes less accentuated (shallower) for the largest pores (Figure 3.5(a-d)). This indicates that there is not enough hydrocarbon volume generated within the source rock to saturate the largest pores as the bitumen is successively replacing the brine from smaller pores toward the larger ones. This microscopic finding is consistent with the relatively marginal global values of TOC and the early to peak oil window maturity estimate in the Jamieson Formation source rocks (sections 3.1.2 and 3.1.3).

Within the Echuca Shoals Formation, there is a clear-cut pore-size-dependence of the depth at which the hydrocarbon generation peak is observed, followed, at greater depths, by the oil-to-gas cracking process. For the smallest pore sizes (Figure 3.5(a)), the bitumen saturation signature is strongest at depths near the base of the Jamieson Formation at about 3860 m. As the pore size increases, the position of the bitumen saturation peak shifts upwards through the mid-Formation to the top of the Echuca Shoals Formation near the depth of 3500 m (Figure 3.5 (b-d)). Given the vitrinite reflectance values of the order of 1.2% to 1.4% in the mid-Formation and at the base,

19

respectively, it is most likely that the upward shift of the intensity <-curve is caused by the process of oil-to-gas cracking preferentially taking place in larger pores.

Figure 3.3 TOC and Rock-Eval pyrolysis cross plots for selected sediments in Brewster-1A.

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

380 400 420 440 460 480 500

0

2

4

6

8

10

12

14

16

18

20

420

430

440

450

460

470

480

0

100

200

300

400

500

600

700

800

(a) (b)

(c)

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

VR = 1.35%

III

I

II

VR = 0.5%

Oil

Oil + Gas

Gas + Oil

Gas

VR = 0.8%

imm

atu

re

earl

y m

atu

re

matu

re

ove

r m

ature

Immature

Condensatewindow

Oil window


or contamination

1


Production Index

Hydro

gen I

ndex (

mg H

C/g

TO

C)

pre

sent

day

Brewster -1A

Tm

ax (

C)

Tmax ( C)

Jamieson Formation

Echuca Shoals Formation

Lower Vulcan Formation

Plover Formation

14/OA/1815

Figure 3.1(a) illustrates the variation of vitrinite reflectance with depth, based on data provided in the Well Completion Report. These values were used in Figure 3.5 to provide a conventional indication of source rock maturity at various depths. There

20

are two sets of data provided by two different laboratories (Robertson Research and Geotrack) which are grossly incompatible within the depth interval 3000 m to 4500 m. As discussed in section 3.1.3, the Geotrack data appear to be closer to maturity estimates based on Tmax values than the Robertson Research data.

Figure 3.6 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Brewster-1A. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.11x1010cm-2 was used in subsequent calculations for Brewster-1A.

The pore size distributions calculated for various depths from the full SANS/USANS curves (Figure 3.7) indicate that there is little variation of the geometry of the pore space with depth.

A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for four pore sizes 0.01µm, 0.1 µm, 1µm and 10µm, indicates a systematic slight compaction with depth throughout the Jamieson Formation and the Echuca Shoals Formation for the smallest pore size, and compaction within the Jamieson Formation followed by expansion in the Echuca Shoals Formation for the larger pore size (Figure 3.8). It appears that the onset of the expansion interval for the larger pores coincides with the "K Aptian sandstone member" (3250 to 3311 mRT) of distinct log characteristics and changed lithology (Figure 3.9), intersected near the base of Jamieson Formation. The smooth and only slight variation of the pore number density with depth indicates both a uniform lithology and mechanical stability of the inorganic rock matrix with depth.

Figure 3.9 illustrates calculated porosity (for the very large fraction of total porosity within the pore size range 20 Å to 20 µm) versus depth. Apparent SANS porosity has been computed by adding pore volumes obtained by fitting the combined SANS/USANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. The apparent SANS porosity values for Brewster-1A lie between 7% and 16%, with a maximum within the Jamieson Formation and at the base of the Echuca Shoals Formation (Figure 3.9). In this particular case, the log porosity of 12% reported in WCR within the 3250 m – 3311 m depth interval at the base of the Jamieson Formation remains in good agreement with the SANS/USANS apparent porosity of 13%.

Depth intervals characterised by changed conditions are indicated on the left hand side of the figure. The "K Aptian sandstone member" (3250 m to 3311 m) is characterised by a weak gamma ray signal and low penetration rate. Increased mud density was used throughout the Echuca Shoals Formation, which is indicative of overpressure. The depth interval 4335 m to TD at 4703 m (not sampled by SANS) recorded particularly high levels of gas.

Significance for hydrocarbon generation

The size of the pores found in claystones typically ranges from 1 nm to about 40 µm across. Combined SANS and USANS methods can access pore sizes from about 2 nm

21

to 20 µm, which covers nearly total porosity. These data can be used to determine all stages of hydrocarbon generation, saturation and expulsion within source rocks.

The microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Brewster-1A (Figure 3.7). Therefore, the marked variation of the scattering intensity for all sizes (Figure 3.5) is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast.

As discussed, in Brewster-1A there are two depth intervals which clearly indicate the presence of bitumen in small pores, interpreted as the evidence of the onset of hydrocarbon generation: the upper Jamieson Formation and the Echuca Shoals Formation.

The characteristic <-shape SANS intensity pattern within the upper Jamieson Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. The largest pores, however, do not appear to be fully saturated which indicates that the upper Jamieson Formation claystones are too organically lean to expel hydrocarbons and become an effective source rock.

The average scattering intensity near the top of the Echuca Shoals Formation appears to exhibit a discontinuity when compared to the adjacent region in the Jamieson Formation, which indicates that there is no communication between the pore spaces of these two sedimentary units. Mud weights indicate overpressuring of the Echuca Shoals Formation (Figure 3.9), which suggests that bitumen and other generated hydrocarbons remain trapped within the formation.

For the smallest pore size, the trend of decreasing intensity throughout the Echuca Shoals Formation terminates at a sandstone unit deposited within the depth range 3940-4173m (Figure 3.5(a). This might indicate that the sandstone reservoirs mobile hydrocarbons generated within the basal Echuca Shoals Formation. However, the upward shift of the intensity <-shape observed for larger pores (Figure3.5(b-d)) suggests another scenario. Given the vitrinite reflectance values of the order of 1.2% to 1.4% in the mid-formation and at the base, respectively, it is most likely that the upward shift of the intensity <-curve is caused by the process of oil-to-gas cracking preferentially taking place within the larger pores. As the oil-to-gas cracking process occurring in restricted volume regions results in a markedly increased pressure of the reaction products, it would indeed be accelerated in such microstructural environments that can facilitate the release of the extra pressure. Therefore, cracking within the larger pores, which are connected to the outside of the relatively tight claystone matrix of the source rock, can occur at lower temperatures than in the smaller, less easily accessible pores. The set of SANS/USANS results presented in Figure 3.5(a-d) is the first direct evidence for the pore size specificity of the oil-to-gas cracking process in the natural environment and has global implications for the modelling of the hydrocarbon generation kinetics.

The USANS results presented in Figure 3.5 (d) show the progressive generation of mobile hydrocarbons within the larger pore network of the upper and lower Jamieson and Echuca Shoals formations (increasing scattering intensity trends). The very rapid increase in scattering intensity in the lower Echuca Shoals Formation is interpreted

22

to mark the onset of gas expulsion. As illustrated in Figure 3.5 (e), this interpretation agrees well with the onset of gas expulsion from the geohistory model. Both data sets indicate that all of the source rocks sampled at Brewster-1A are too lean to expel liquid hydrocarbons.

It has been pointed out by one of the referees (Dr Chris Boreham) that an alternative interpretation is possible. It is based on an observation that organic matter with vitrinite reflectance values of 1.2-1.4% may not be mature enough for oil-to-gas cracking to occur and the gas detected by SANS in the pore space might have migrated from deeper, more mature sediments and displaced the liquid hydrocarbons generated in situ. Dr Boreham is also of the opinion that the process of gas-to-oil cracking would be more effective in the small rather than large pores due to greater exposure to heterogeneous catalysis.

Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (a): 11 samples (claystones, 5 m interval each), depth range 2450 m to 2950 m.

0.1

10

1000

105

107

109

1011

10-5 0.0001 0.001 0.01 0.1

Figure 3.4(a)Brewster-1A (SANS & USANS)

Scattering intensity versus Q for various depthspart 1: 2450 m to 2950 m

2450m2500m2600m2700m2750m2800m2850m2900m2950m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)

SCATTERING VECTOR Q (Å-1)

23

The relatively low scattering intensity at a depth of 4230 m within the Upper Vulcan Formation indicates that the pores contain significant amount of organic matter with a very low hydrogen-to-carbon ratio.

Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (b): 9 samples (claystones, 5 m interval each), depth range 3000 m to 3600 m.

0.1

10

1000

105

107

109

1011

10-5 0.0001 0.001 0.01 0.1

Figure 3.4(b)Brewster-1A (SANS & USANS)


3000m3050m3100m3150m3200m3325m3390m3500m3600m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


24

Figure 3.4. SANS absolute intensity curves for samples of cuttings from Brewster-1A. (c): 4 samples (claystones, 5 m interval each), depth range 3695 m to 4230 m.

0.1

10

1000

105

107

109

1011

10-5 0.0001 0.001 0.01 0.1

Figure 3.4(c)Brewster-1A (SANS & USANS)


3695m3800m3850m4230m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


25

Figure 3.5. SANS intensity versus depth at four Q-values of (a) 0.025 Å-1, (b) 0.0025 Å-1, (c) 0.00025 Å-1, and (d) 0.000025 Å-1, which corresponds to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, for cuttings samples from Brewster-1A.

2000

2500

3000

3500

4000

4500

50000 5 10 15 20

DEPT

H (m

RT)

SCATTERING INTENSITY AT Q=0.025Å -1 (cm-1)

0.59%

0.61%0.68%

0.73%0.80%0.82%0.92%0.89%0.89%

1.17%

1.19%

1.37%

1.65%

1.74%

vitrinitereflectance:RR KV

0.46%

0.54%

0.54%

0.52%

1.05%

1.03%

1.34%

permeability orkinetics barrier

(a)µ0.01 m

(100Å)

Gas Sst

ONSET

ONSET

ONSET

JAMIESO N

ECHUCASHOALS

VULCAN

UPPER

LOWER

PLOVER

26

JAMIESON

ECHUCASHOALS

VULCAN

UPPER

LOWER

PLOVER

0 5 104 110 5 5 2 105


3940m

4173m

(b)�0.1 m

(1000Å)

Gas Sst

1.5 10

2000

2500

3000

3500

4000

4500

5000

DEPT

H (m

RT)

2000

2500

3000

3500

4000

4500

50000 5 107 1 108 8 2 108

DEPT

H (m

RT)


3940m

4173m


(c)�1 m

Gas Sst

1.5 10

JAMIESON

ECHUCASHOALS

VULCAN

UPPER

LOWER

PLOVER

27

JAMIESON

ECHUCASHOALS

VULCAN

UPPER

LOWER

PLOVER

0 5 105 105 10 1 1011 11 2 1011

SCATTERING INTENSITY AT Q=0.000025Å -1 (cm (cm (c -1)

3940m

4173m


(d)

�10 �10 �m�m�

Gas Sst

1.5 10

2000

2500

3000

3500

4000

4500

5000

DEPT

H (m

RT)

Figure 3.5(e) Comparison of USANS scattering intensity trends with modelled kerogen transformation (TR – Transformation Ratio) and in-situ gas/oil generation and expulsion derived from geohistory and thermal history analysis for Brewster-1A. The good match between the measured Tmax values with the modelled Tmax trend indicates that the thermal and kerogen kinetics models are consistent with the observed pyrolysis data for this well.

0 5 100 5 100 510

1 1011

SCATTERING INTENSITY AT Q=0.000025Å-1

(cm-1

)

3940m

4173m

µ10 µ10 µmµmµ

Gas Sst

2000

25002500250

30003000300

35003500350

40004000400

4500

DE

PTH

(mR

T)

U Jamieson

M Jamieson

L Jamieson

U Echuca

L Echuca

U VulcanU Vulcan

L Vulcan 8C

L Vulcan 8A

0.0 0.5 400 450 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0ModelledModelledModelleSourceRocks

Volume (bbl equiv/m )2Volume (bbl equiv/m 2Volume (bbl equiv/m

03-227-15

TR Tmax

Robertson ResearchGeoscience AustraliaModelled Tmax

Gas (in situ)Gas (expelled)Oil light (in situ)Oil light (expelled)

28

Figure 3.6. Variation of the Scattering Length Density (SLD) with depth for Brewster-1A. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement.

2000

2500

3000

3500

4000

4500

3.5 4 4.5 5

Brewster-1A, Browse BasinScattering length density versus depth

DE

PT

H (

m)

SCATTERING LENGTH DENSITY (x1010cm-2)

29

Figure 3.7. Pore size distribution at various depths for samples of cuttings from Brewster-1A. (a): 11 samples (claystones, 5 m interval each), depth range is 2450 m to 3055 m. (b): 11 samples (claystones, 5m interval each), depth range 3100 m to 4235 m.

10-17

10-15

10-13

10-11

10-9

10-7

10-5

0.001

0.1

100 1000 104 105 106

PORE

SIZ

E DI

TRIB

UTIO

N DE

NSIT

Y f(r

)

PORE SIZE (Å)

(a)2450m2500m2600m2700m2750m2800m2850m2900m2950m3000m3050m

30

100 1000 104 105 106

PORE SIZE (Å)

(b)3100m3150m3200m3325m3390m3500m3600m3695m3800m3850m4230m

10-17

10-15

10-13

10-11

10-9

10-7

10-5

0.001

0.1PO

RE S

IZE

DITR

IBUT

ION

DENS

ITY

f(r)

31

Figure 3.8. Variation of the pore number density for four selected pore sizes versus depth for Brewster-1A. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text.

10-17 10-15 10-13 10-11 10-9 10-7 10-5 10-3 10-1

2000

2500

3000

3500

4000

4500

5000

PORE NUMBER DENSITY

DEPT

H (m

RT)

�� 1 m

(c)r= 10 m �0.1 m �0.01 m

JAMIESON

ECHUCASHOALS

VULCAN

PLOVER

UPPER

LOWER

32

Figure 3.9. Variation of apparent porosity with depth for Brewster-1A. For discussion see text.

JAMIESON

ECHUCASHOALS

VULCAN

PLOVER

UPPER

LOWER

0 5 10 15 20 25CALCULATED SANS POROSITY (%)

3250m3311m

4280m

changed lithology:gamma ray &

penetration ratelog porosity 12%

increasedmud density

4335m

TD 4703m

high gasreadings

Gas Sst

K apt Sst

2000

2500

3000

3500

4000

4500

5000

DEPT

H (m

RT)

33

3.2 Carbine-1

The pyrolysis data for Carbine-1 is given in Appendix 5 Table A5.2. Figure 3.10 is a compilation of total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S1, S2 and HI) plotted against depth (mRT). Figures 3.11 and 3.12 comprise cross plots of the pyrolysis data by laboratory and by formation, respectively. No other data was available for this well.


Carbine-1 was drilled with a water-based drilling mud comprising a brine polymer, therefore contamination of the cuttings samples should not be an issue.

Out of the seven Lower Cretaceous samples analysed from this well, four samples have anomalously low Tmax values, and slightly elevated S1, Production Index (PI) and Bitumen Index (BI) values, indicating the presence of naturally occurring free hydrocarbons within the Jamieson Formation, as annotated by the open symbols in Figures 3.10 and 3.11.

At this location, all of the Lower Cretaceous sediments analysed are immature for hydrocarbon generation, therefore it is believed that these free hydrocarbons are evidence of migration along more permeable zones from more mature sediments.


Only one sample from 1388 m depth in the Jamieson Formation is considered to be a potential source rock and does not contain any migrated hydrocarbons. The other four samples analysed from this formation appear to have higher S1 values than could have been generated from the amount and type of organic matter held within the rock. The sample from 1388 m has a good total organic carbon content (1.6 %) but its potential yield is poor (S1+S2 = 1.9 mg hydrocarbons/g rock; Fig. 3.12).

The Echuca Shoals sediments have very similar total organic carbon contents (average TOC = 1.7 %) and potential yields (average S1+S2 = 1.7 mg hydrocarbons/g rock) to the Jamieson Formation.


The Jamieson and Echuca Shoals formation sediments have HI values ranging from between 83 and 118 mg hydrocarbons/g TOC (average = 118 mg hydrocarbons/g TOC and 95 mg hydrocarbons/g TOC, respectively) which indicates that they contain Type III kerogen, being at best gas-prone. However, they are presently immature for hydrocarbon generation to occur (Fig. 3.12).

34

Figure 3.10 Depth plots of TOC and Rock-Eval pyrolysis data for Carbine-1.

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

(g) (b) (c)

(d) (e) (f)

VR (%)0.4 0.8 1.2 1.6 2.0 400 440 480 1 2 3 4 5

HI (mg/g TOC)200 400300100 500

14/OA/1794

S2 (mg/g Rock)1 2 3 4 5 6

S1 (mg/g Rock)0.5 1.0 1.5 2.0

0 0

000

Tmax ( C) TOC (%)

Carbine -1WRC sequence


Jamieson FmFenelon Fm

Borde MarlPuffin Sandstone

WRC sequence

Jamieson FmFenelon Fm

Borde MarlPuffin Sandstone

GA CUTT GA CUTT HC


35

Figure 3.11 TOC and Rock-Eval pyrolysis cross plots for Carbine-1 sediments

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

0

2

4

6

8

10

12

14

16

18

20

420

430

440

450

460

470

480(a) (b)

14/OA/1795

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

Immature

Condensatewindow

Oil window


or contamination

1


Production Index

Tm

ax (

C)

Carbine -1

GA CUTT SANS

GA CUTT SANS HC

36

Figure 3.12 TOC and Rock-Eval pyrolysis cross plots for selected sediments in Carbine-1.

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

380 400 420 440 460 480 500

0

2

4

6

8

10

12

14

16

18

20

420

430

440

450

460

470

480

0

100

200

300

400

500

600

700

800

(a) (b)

(c)

14/OA/1816

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

VR = 1.35%

III

I

II

VR = 0.5%

Oil

Oil + Gas

Gas + Oil

Gas

VR = 0.8%

imm

atu

re

earl

y m

atu

re

matu

re

ove

r m

ature

Immature

Condensatewindow

Oil window


or contamination

1


Production Index

Hydro

gen I

ndex (

mg H

C/g

TO

C)

pre

sent

day

Tm

ax (

C)

Tmax ( C)

Carbine -1

Jamieson Formation


37

3.2.4 Analysis of SANS data

Small Angle Neutron Scattering (SANS) analysis was performed on 7 claystone and silty claystone cuttings from the well Carbine-1 (Table A1.6 in Appendix 2). These cuttings were collected at about 20-50 m intervals between depths 1349 m to 1559 m.


Except for the out-lying (shallowest) sample at a depth of 1349 m, there is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.14 for scattering intensity measured at Q=0.01 Å -1, which corresponds to a pore size of about 0.025 µm +/-50% (1 Å = 10-10 m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity slightly decreases by a factor of 1.2 within the depth range 1388 m to 1478 m in the Jamieson Formation, followed by an apparent sharp decrease by a factor of 1.5 to the Echuca Shoals Formation and thereafter remains relatively constant at a low value down to the TD depth of 1561 m.

According to the Interpreted Lithology section of the Formation Evaluation Log provided by Santos, the sample of cuttings collected within the depth range 1349-1352 m may contain a significant amount of sandstone (cavings?). Consistent lithology is a prerequisite for a successful identification of hydrocarbon generation zones from SANS data. Therefore, results for this sample are shown but treated as anomalous and not taken into account when discussing trends.

Figure 3.15 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Carbine-1. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.38x1010 cm-2 was used in subsequent calculations for Carbine-1.

The pore size distributions calculated for various depths from the full SANS curves (Figure 3.16) indicate that there is little variation of the geometry of the pore space with depth.

A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a systematic and significant compaction with depth, but otherwise a consistent pore size distribution in the claystones throughout the Jamieson Formation and Echuca Shoals Formation (Figure 3.17).

Figure 3.18 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. Most of the values are between 2.5% and 5%, with a maximum within upper Jamieson Formation. Although the general trend of decreasing porosity with depth is consistent both with general expectation and data presented in Figure 3.17, the calculated SANS porosity values need to be calibrated against the log porosities. Gas readings were fairly high throughout the depth interval 1360 m to 1561 m.

38


The size of the pores found in claystones typically ranges from 1nm to about 40 µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to determine the early stages of hydrocarbon generation and saturation within source rocks.

Owing to significant compaction, the microstructure of the inorganic rock fabric also changes significantly throughout the depth range studied by SANS in Carbine-1 (Figures 3.17, 3.18). For the pore size 316 Å, the pore number density decreases by a factor of about 2 within the depth range of 1388-1559 m (Figure 3.17). The SANS intensity for a similar pore size of 250 Å decreases by a similar factor of 1.8 within the same depth range (Figure 3.14). The cause of the apparent marked change in SANS intensity at the top of the Echuca Shoals Formation is not fully understood.

Therefore, it is likely that the observed variation of SANS intensity with depth is dominated by the compaction of the inorganic rock matrix. There is no strong indication of progressive bitumen generation and/or cracking.

The strong deformation of inorganic matrix with depth observed by SANS in Carbine-1 is unusual since these samples are considerably shallower than other samples previously examined by SANS. This deformation with depth is attributed to normal compaction.

39

Figure 3.13. SANS absolute intensity curves for samples of cuttings from Carbine-1. Data are shown for seven samples (nominally claystones and silty slaystones, 3 m interval each). Depth range is 1349 m to 1559 m.

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.13Carbine-1

Scattering intensity versus Q for various depths1349m to 1559m

084 1349m085 1388m086 1439m087 1478m088 1499m089 1517m090 1559m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


40

Figure 3.14. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Carbine-1.

1200

1250

1300

1350

1400

1450

1500

1550

16000 100 200 300 400 500

DEPT

H (m

RT)


JAMIESON

ECHUCASHOALS

FENELON

�0.025 m(250Å)

(cm -1)

PUFFINSANDSTONE

41

Figure 3.15. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Carbine-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement.

1300

1350

1400

1450

1500

1550

1600

4 4.2 4.4 4.6 4.8 5

Carbine 1, Browse BasinScattering length density versus depth

DE

PT

H (

m)


42

Figure 3.16. Pore size distribution at various depths for samples of cuttings from Carbine-1. Seven samples (nominally claystones and silty claystones, 3 m interval each), depth range is 1349 m to 1559 m.

10-7

10-6

10-5

0.0001

0.001

0.01

0.1

100 1000

089 1517m090 1559m

PORE

SIZ

E DI

TRIB

UTIO

N DE

NSIT

Y f(r

)

PORE SIZE (Å)

084 1349m085 1388m086 1439m087 1478m088 1499m

JAMIESON

ECHUCASHOALS

FENELON

PUFFINSANDSTONE

43

Figure 3.17. Variation of the pore number density for selected pore sizes versus depth for Carbine-1. Note the significant decrease of the pore number density with depth, indicative of compaction. For full discussion see text.

10-7 10-6 10-5 10-4 10-3

1200

1250

1300

1350

1400

1450

1500

1550

1600

PORE NUMBER DENSITY

DEP

TH (m

RT)

r = 630Å 316Å 100Å

JAMIESON

ECHUCASHOALS

PUFFI NSANDSTONE

44

Figure 3.18. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Carbine-1. For discussion see text.

JAMIESON

ECHUCASHOALS

PUFFI NSANDSTONE

0 2 4 6 8CALCULATED SANS POROSITY (%)

TD 1561m

1360m

increasedgas reading

1200

1250

1300

1350

1400

1450

1500

1550

1600

DEP

TH (m

RT)

3.3 Adele-1

The pyrolysis data for Adele-1 is given in Appendix 5 Table A5.3. Figure 3.19 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S1, S2 and HI) plotted against depth (mRT). Figures 3.20 and 3.21 comprise cross plots of the pyrolysis data by laboratory and by formation, respectively.

In addition to the cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses were also available in the well completion report (Shell Development Australia, 1999) carried out on SWCs by Geotechnical Services, and vitrinite reflectance measurements were made by Kieraville Konsultants. There is no mention in the WCR that the SWC samples were washed or extracted using water or organic solvents.


Adele-1 was drilled with a water-based drilling mud with gel and polymer additives to a depth of 2560 m. Below this depth potassium chloride, PHPA and glycol was used to the bottom of the well. All of the cuttings samples analysed are contaminated with glycol

45

additives, and hence they were extracted with methanol and dichloromethane (90:10) as part of the preparative procedure.

In the WCR there is no mention that the SWC samples were washed or extracted. From the reported values for S1, it is surmised that these samples have not been solvent washed. Nevertheless, these samples do not appear to be affected by glycol contamination since the Tmax values are not depressed with respect to the extracted cuttings samples. With the possible exception of the shallowest SWC and deepest two SWC samples, migrated or contaminant hydrocarbons are not evident in the SWC samples from the Jamieson and Echuca Shoals formations in Adele-1 (Fig. 3.19). The samples suspected of containing free hydrocarbons are shown by the open symbols in Fig. 3.19.

Of note, petrographic analyses of a SWC sample from 4130 m (within the Echuca Shoals Formation) reported that this sample contained “possible oil drops that appear to be in artificial composites and may represent contamination”.

46

Figure 3.19 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Adele-1.

Geotech SWC

Geotech SWC HC

GA CUTT SANS extracted

Kieraville SWC

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

(a) (b) (c)

(d) (e) (f)

VR (%)0.4 0.8 1.2 1.6 2.0 400 440 480 1 2 3 4 5

HI (mg/g TOC)200 400300100 500

14/OA/1763

S2 (mg/g Rock)1 2 3 4 5 6

S1 (mg/g Rock)0.5 1.0 1.5 2.0

Adele -1

0 0

000

Tmax ( C) TOC (%)

PloverFormation


JamiesonFormation

Santonian - Turonian

Campanian

Maastrichtian

Tertiary

GA sequence

VulcanFormation

PloverFormation


JamiesonFormation


Campanian

Maastrichtian

Tertiary

GA sequence

VulcanFormation

Invalid data

47

3.3.2 Laboratory Comparisons

In general, the TOC content for the extracted cuttings samples tends to be slightly higher than the SWCs over the depth range analysed (Fig. 3.19). This may be due to the cuttings samples being homogenised compared with the SWC samples, or it may be an artifact introduced from residual glycol contaminants. There are some significant differences in the pyrolysis data between the SWC and extracted cuttings samples. The S1 abundances of the extracted cuttings samples are invalid because any naturally occurring free hydrocarbons (as well as contaminants) are removed during the extraction process, therefore only the S1, BI and PI values from the SWCs can be interpreted. The S2 values of the extracted cuttings samples are less than those of the SWC samples (~1 mg hydrocarbons/g rock) which, combined with the apparent higher TOC values, results in their much lower HI values over the depth range analysed. Since the kerogen in the rock is unaffected by the solvent extraction process, the S2 abundance should be similar for both the cuttings and SWC samples at the same depth. It is difficult to explain this discrepancy but it may be due to the different instruments used or that some contamination is present in the SWCs causing an increase in S2 and HI, which is not apparent in the TOC results. Despite the abundance of the S2 peak being less for the cuttings samples than the SWC samples, the derived Tmax values are comparable between the datasets.


The total organic carbon (TOC) contents of the organic-rich sediments of the Lower Cretaceous Jamieson Formation are consistently fair, ranging from 0.9-1.9% (average TOC = 1.4%; Fig. 3.21). The Lower Cretaceous Echuca Shoals Formation source rocks have more varied but overall similar organic richness (range = 0.7-2.3%; average TOC = 1.3%).

The potential yields of the Jamieson Formation sediments are poor (average S1+S2 = 2.7 mg hydrocarbons/g rock), whereas some of the Echuca Shoals sediments have fair potential yields (S1+S2 = 3.1 mg hydrocarbons/g rock).


The Jamieson Formation and Echuca Shoals Formation SWC sediments have similar HI values ranging from between 125 and 270 mg hydrocarbons/g TOC (average = 186 mg hydrocarbons/g TOC and 188 mg hydrocarbons/g TOC, respectively) which indicates that they are presently predominantly gas and condensate-prone. Of note is that the HI values from the extracted cuttings samples are somewhat lower (Fig. 3.21). Conventional interpretation of pyrolysis data would imply that samples which have HI values greater 200 mg hydrocarbons/g TOC have the capacity to generate oil. However, in the case of the majority of samples from both the Jamieson and Echuca Shoals formations in Adele-1, their corresponding TOC contents are typically less than 2 %. At these low-to-moderate TOC levels, any generated oil will probably remain within the source rock and expulsion will not occur until it is substantially cracked to gas at higher maturities.

48

Figure 3.21 shows that the Jamieson Formation and Echuca Shoals Formation sediments both contain Type II/III kerogen. A petrographic analysis of a SWC sample from 2580 m in the Jamieson Formation reports that lamalginite, a hydrogen-rich maceral, is common. The maceral assemblage in the majority of the Jamieson Formation sediments is dominated by liptodetrinite (fragments of spores, cuticles etc) with lesser amounts of inertinite, and vitrinite is a rare occurrence.

Presently, the Jamieson Formation is immature for hydrocarbon generation, the Echuca Shoals Formation is within the oil window, and the Upper Vulcan Formation is at peak oil generation.

Figure 3.20 TOC and Rock-Eval pyrolysis cross plots for Adele-1 samples.

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

0

2

4

6

8

10

12

14

16

18

20

420

430

440

450

460

470

480

Geotech SWC


(a) (b)

14/OA/1764

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

Immature

Condensatewindow

Oil window


or contamination

1


Production Index

Adele -1

Tm

ax (

C)

Geotech SWC HC

Invaliddata

Invaliddata

49

Figure 3.21 TOC and Rock-Eval pyrolysis cross plots for selected samples from Adele-1.

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

380 400 420 440 460 480 500

0

2

4

6

8

10

12

14

16

18

20

420

430

440

450

460

470

480

0

100

200

300

400

500

600

700

800

(a) (b)

(c)

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

VR = 1.35%

III

I

II

VR = 0.5%

Oil

Oil + Gas

Gas + Oil

Gas

VR = 0.8%

imm

atu

re

earl

y m

atu

re

matu

re

ove

r m

ature

Immature

Condensatewindow

Oil window


or contamination

1


Production Index

Adele -1

Tm

ax (

C)

Tmax ( C)

Hydro

gen I

ndex (

mg H

C/g

TO

C)

pre

sent

day

Jamieson Formation (SWC)

Jamieson Formation (CUTT extracted)

Echuca Shoals Formation (SWC)

14/OA/1814


Small Angle Neutron Scattering (SANS) analysis was performed on 19 claystone cuttings from the well Adele-1 (Table A1.2 in Appendix 2). These cuttings were collected at 25 m to 60 m intervals between depths 2530 m to 3405 m throughout the Upper Heywood Formation.

50


There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.23 for scattering intensity measured at Q = 0.01Å -1, which corresponds to a pore size of about 0.025 µm +/-50% (1 Å = 10-10 m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity decreases and increases twice with depth by a factor 1.5-1.8 within the Upper Heywood Formation (equivalent to the Jamieson Formation) within the depth range 2530 m to 3405 m, forming a characteristic “double <” pattern. The experimental error of the scattering intensity is of the size of the symbol in Figure 3.23.

Although all the samples used for SANS analysis were described as claystones, the XRF analysis of the shallowest sample (2530 m) reveals the presence of 11.8 wt% of CaO compared to 1.4-2.0 wt% in the remaining four samples analysed by XRF (Table 3.1). Therefore, the data for this sample (and possibly nearby samples) may be anomalous due to a different lithology (calcareous claystone) than for the rest of SANS samples (claystone).

Figure 3.19(a) illustrates the variation of vitrinite reflectance with depth, based on data provided in the Well Completion Report. These values were used in Figure 3.23 to provide a conventional indication of source rock maturity at various depths.

Figure 3.24 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Adele-1. There is little variation (at most 3%) with depth and, consequently, the average value of SLD = 4.39x1010 cm-2 was used in subsequent calculations for Adele-1.

The pore size distributions calculated for various depths from the full SANS curves (Figure 3.25) indicate that there is little variation of the geometry of the pore space with depth.

A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a systematic slight compaction with depth throughout the Upper Heywood Formation, perhaps with a small anomaly in the depth range 2530-2630 m (Figure 3.26). For the largest pore size (630 Å) the compaction is least evident.

Figure 3.27 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. The porosity values lie between 2.0% and 4.2%, with maximum values at depths 2530 m, 2885 m and 3380 m. The actual porosity values may not be reliable and need to be calibrated against the log porosities. Depth intervals characterised by changed conditions are indicated on the left hand side of the figure. The “K Aptian sandstone member equivalent” (3414 m to 3595 m) is composed of interbedded glauconitic sandstone, greensand, calcareous sandstone, argillaceous sandstone, claystone and siltstone. Gas and condensate were

51

recovered from the depth of 3514.3 m within this unit. The depth interval 3595 m to TD at 4822 m (Lower Heywood Formation, Upper Swan Formation, Lower Swan Formation, Petrel Formation and Londonderry Formation, all not sampled by SANS) recorded high levels of gas, as indicated in Figure 3.27.


The size of the pores found in claystones typically ranges from 1nm to about 40µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to determine the early stages of hydrocarbon generation and saturation within source rocks.

Except for the small anomaly in the depth range 2530-2630 m, the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range of 2530-3405 m studied by SANS in Adele-1 (Figures 3.25 and 3.26). Therefore, the marked variation of the scattering intensity with depth (Figure 3.23) is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast.

As discussed above, the low values of the scattering intensity indicate pores filled with bitumen at the onset of mobile hydrocarbon generation, and the high values pores filled with gas, formation brine and/or saturated hydrocarbons. Based on this, two regions of hydrocarbon generation (at different maturity) can be identified (Figure 3.23): (1) near the top of the Upper Heywood Formation at a depth of about 2630m, possibly affected by the presence of the microstructural anomaly, and (2) within the lower Upper Heywood Formation at a depth of about 3180 m. The two generation regions are separated from each other by a permeability barrier at a depth of about 2780 m.

The increasing SANS intensity with depth for the two hydrocarbon generation regions within the Upper Heywood Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of the hydrocarbons to larger pores with increasing depth within the formation.

The deeper of the two trends of increasing intensity within the Upper Heywood Formation (2630-2880 m and 3220-3380 m) terminates close to a “K Aptian sandstone member equivalent” unit (3414 m to 3595 m), from which gas and condensate were recovered with a FMT tool at the depth of 3514 m. This provides a strong argument that this trend may represent progressive cracking of bitumen into mobile hydrocarbons and migration of hydrocarbons to larger pores within the K Aptian sandstone member equivalent. The permeability barrier apparent within the Upper Heywood Formation at the depth of 2880 m is likely to impede vertical movement of generated hydrocarbons.

52

Table 3.1. XRF raw data for Adele-1.

AGSO No Loss on SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 SO3

ignition Si Ti Al Fe Mn Mg Ca Na K P S

(%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%)

20020065 15.521 45.492 0.63 12 5.538 0.08 1.41 11.8 1.25 2.665 0.119 2.1

20020069 10.065 57.151 0.75 15.2 5.747 0.03 1.76 1.42 1.11 3.489 0.104 1.6

20020073 10.087 58.939 0.66 13.5 6.188 0.04 1.68 1.99 0.75 2.908 0.15 1.6

20020078 9.491 60.145 0.74 15.1 5.401 0.03 1.53 1.56 0.82 3.041 0.128 1

20020083 8.1835 59.598 0.72 14.5 5.8 0.05 1.52 1.57 1.37 3.095 0.146 1.6

AGSO No Sc V Cr Ni Cu Zn Rb Sr Zr Ba Cl

(ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)

20020065 21 147 88 26 34 110 56 298 167 1945 10572

20020069 10 174 88 23 25 144 84 306 165 9651 4834

20020073 12 142 78 29 30 138 83 298 150 10367 3898

20020078 11 137 81 26 24 124 85 201 195 5061 3726

20020083 13 162 92 31 24 126 98 410 173 13706 3589

53

Figure 3.22. SANS absolute intensity curves for samples of cuttings from Adele-1. A: ten samples (claystones, 5 m interval each), depth range 2530 m to 2980 m. B: nine samples (claystones, 5 m interval each), depth range 3030 m to 3405 m.

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.22(A)Adele-1

Scattering intensity versus Q for various depthspart 1: 2530m to 2980m

065 2530m066 2580m067 2630m068 2680m069 2730m070 2780m071 2830m072 2880m073 2930m074 2980m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


54

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.22(B)Adele-1


075 3030m076 3080m077 3130m078 3180m079 3220m080 3280m081 3320m082 3380m083 3405m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


55

Figure 3.23. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Adele-1.

2000

2500

3000

3500

4000

4500

50000 100 200 300 400 500

DEPT

H (m

)

SCATTERING INTENSITY AT Q=0.01Å-1 (cm-1)

UPPER HEYWOOD(JAMIESON)

LOWER HEYWOOD(ECHUCA SHOALS)

UPPER SWAN(UPPER VULCAN)

LONDONDERRY(SAHUL / NOME )

Ro=0.52%

Ro=0.56%Ro=0.53%

Ro=0.56%

Ro=0.63%

Ro=0.62%

Ro=0.67%

Ro=0.87%Ro=0.97%

PETREL (PLOVER)

calcareous?

LOWER SWAN(LOWER VULCAN)

�0.025 m(250 Å )

ONSET

ONSET

56

Figure 3.24. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Adele-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement.

2000

2500

3000

3500

4 4.2 4.4 4.6 4.8 5

Adele-1, Browse BasinScattering length density versus depth

DE

PT

H (

m)


57

Figure 3.25. Pore size distribution at various depths for samples of cuttings from Adele-1. A: ten samples (claystones, 5 m interval each), depth range is 2530 m to 2980 m. B: nine samples (claystones, 5 m interval each), depth range 3030 m to 3405 m.

10-7

10-6

10-5

0.0001

0.001

0.01

0.1

100 1000

PORE

SIZ

E DI

TRIB

UTIO

N DE

NSIT

Y f(r

)

PORE SIZE (Å)

2530m2580m2630m2680m2730m2780m2830m2880m2930m2980m

58

100 1000PORE SIZE (Å)

3030m3080m3130m3180m3220m3280m3320m3380m3405m

10-7

10-6

10-5

0.0001

0.001

0.01

0.1

PORE

SIZ

E DI

TRIB

UTIO

N DE

NSIT

Y f(r

)

59

Figure 3.26. Variation of the pore number density for selected pore sizes versus depth for Adele-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text.

10-7 10-6 10-5 10-4 10-3

2000

2500

3000

3500

4000

4500

5000

PORE NUMBER DENSITY

DEPT

H (m

)

r = 630Å 316Å 100Å

UPPERHEYWOOD

(JAMIESON)

LOWERHEYWOOD(ECHUCASHOALS)


PETREL (PLOVER)

LONDONDERRY(SAHUL / NOME)


60

Figure 3.27. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Adele-1. For discussion see text.

UPPERHEYWOOD

(JAMIESON)

LOWERHEYWOOD(ECHUCASHOALS)


PETREL (PLOVER)

LONDONDERRY (SAHUL / NOME)

0 1 2 3 4 5 6POROSITY (%)

calcareous?2527m

3226m

3414m

3595m

4057m

4448m

4822m

claystonedominated lithology

claystone & siltstone

3514.3m; correlated to

"Kapt sandstoneequivalent"

fairlygoodgasreadings

stronggasreadings

h/c recovered

goodgasreadings


2000

2500

3000

3500

4000

4500

5000

DEPT

H (m

)

3.4 Argus-1

The pyrolysis data for Argus-1 is given in Appendix 5 Table A5.4. Figure 3.28 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S1, S2 and HI) plotted against depth (mRT).

In addition to the cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses were also available in the well completion report (BHPP, 2001) carried out on SWCs by Geotechnical Services, and vitrinite reflectance measurements were made by Kieraville Konsultants. There is insufficient data to enable an inter-laboratory comparison.


Argus-1 was drilled with a water-based drilling mud with gel additives to a depth of 2483 m. Below this depth potassium chloride, PHPA and glycol was added to the bottom of the well. Therefore, all of the cuttings samples analysed are contaminated with glycol additives, and hence they were extracted with methanol and

61

dichloromethane (90:10) as part of the preparative procedure. In the WCR there is no mention that the SWC samples were washed or extracted.

With the exception of one SWC sample, all of the samples from the Jamieson Formation contain free hydrocarbons, as indicated by the exceptionally low Tmax values (< 370 oC – off the scale of the graphs in Fig. 3.28). These low values are unreasonable for burial depths of over 4000 m and these hydrocarbons could not have been generated by the organic matter within the sediments. Comparison of the Argus-1 dataset with data from samples with identified free hydrocarbons in the Jamieson Formation at Brewster-1A and Carbine-1 (both drilled with water-based muds), suggests that the anomalous pyrolysis results originate from the incomplete removal of drilling fluid additives in the samples, rather than the occurrence of bona fide thermogenic hydrocarbons within the sediments.

The SWC sample from 4598 m appears to have Tmax and PI values in the range expected for a thermally mature sample, however, it has an anomalously high HI value of 484 mg hydrocarbons/g TOC. This places it outside of the range expected for a mature Type II kerogen, hence glycol contamination is suspected in this sample. Therefore, the quality of the data appears compromised by the addition of additives in the drilling fluid and no source rock interpretation was undertaken.

3.4.2 Maturity

Vitrinite reflectance measurements between 4535 m and 4665.5 m indicate that the Jamieson Formation is within the peak oil to peak wet gas windows (0.85 & 1.13%).

62

Figure 3.28. Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Argus-1 samples.

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

(a) (b) (c)

(d) (e) (f)

VR (%)0.4 0.8 1.2 1.6 2.0 400 440 480 1 2 3 4 5

HI (mg/g TOC)200 400300100 500

14/OA/1798

S2 (mg/g Rock)20

S1 (mg/g Rock)0.5 1.0 1.5 2.0

Argus -1

0 0

000

Tmax ( C) TOC (%)


Kieraville SWC

4 8 12 16

WRC sequence

WRC sequence

Tertiary

Bathurst IslandGroup

JamiesonFormation


Tertiary

Bathurst IslandGroup

JamiesonFormation

Geotech SWC HC

Invalid data

Most values off scale <370 C

Geotech SWC (suspect data)


63


Small Angle Neutron Scattering (SANS) analysis was performed on eight nominally claystone cuttings from the well Argus-1 (Table A1.3 in Appendix 2). These cuttings were collected at 25 m to 40 m intervals between depths 4270 mRT to 4535 mRT. A cut of cuttings was used to perform X-ray Fluorescence (XRF) analysis for selected samples (Table 3.2).


There is a significant variation of the scattering intensity with depth, well beyond the SANS experimental accuracy of about +/-5% (less than symbol size in Figure 3.29). However, no systematic variation in SANS intensity with depth can be seen within the entire depth range 4270 m to 4535 m. This is illustrated in Figure 3.30 for scattering intensity measured at Q=0.01 Å -1, which corresponds to a pore size of about 0.025 µm +/-50% (1 Å = 10-10 m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity fluctuates within the range 200-330 cm-1 throughout the Jamieson Formation and the top of the Vulcan Formation.

Although all the samples obtained from BHP Billiton for SANS analysis have been nominally described as claystones throughout the depth range of 4270 m to 4540 m, the Well Completion Report (WCR) provides detailed information indicating that the actual lithology has a significant calcareous component, gradually decreasing with depth within the depth range 4242 m - 4260 m (cuttings description) or 4242 m - 4290 m (sidewall cores description) at the top of the Jamieson Formation. Therefore, the shallowest SANS sample (4270m) is likely to be a calcareous claystone of different lithology than the remaining SANS samples. Although the CaO content in this sample (7.23%) is not much larger than for the remaining two samples analysed by XRF (7.01% and 4.13% for samples at the depths of 4390 m and 4535 m, respectively, Table 3.2), based on geological evidence it is treated as anomalous in the following discussion.

Figures 3.28(a) and 3.31 illustrate the variation of thermal maturity of the organic matter with depth, based on the petrology and geochemistry data provided in the Well Completion Report. Standard vitrinite reflectance data are reported only for three samples within the depth range 4535-4665.5 m. Thermal maturity indicators, expressed as vitrinite reflectance equivalent (VRe), have been converted from biomarker data (methylphenantrene index, MPI) obtained from three types of samples: mud-filtrate extracts, condensates and mechanical sidewall core (MDCT) extracts. Given their origin, the VRe data are subject to contamination with the mineral oil base present in the drilling fluid (Liquid New Drill) and are reliable only in the relative sense.

Only the petrographic VR values were used in Figure 3.30 to provide a conventional indication of source rock maturity at various depths.

Figure 3.32 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Argus-1. There is little variation (at most 2%) with depth and, consequently, the average value of SLD = 3.99x1010 cm-2 was used in subsequent calculations for Argus-1.

64

The pore size distributions calculated for various depths from the full SANS curves (Figure 3.33) indicate that there is little variation of the geometry of the pore space with depth, perhaps with the exception of the 4270 m sample.

A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a systematic slight compaction with depth throughout the Jamieson Formation and the top Vulcan Formation for the two smaller pore sizes, and a steady but more scattered trend for the largest pore size (Figure 3.34). The shallowest sample near the top of Jamieson Formation (4270 m) appears to be anomalous, which is consistent with its different lithology.

Figure 3.35 illustrates calculated SANS porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. The porosity values are about 4.0-5.5% throughout the Jamieson Formation, except for the sample at the depth of 4310 m which has a porosity of 2.8%. The actual porosity values may not be reliable and need to be calibrated against the log porosities.


The size of the pores found in claystones typically ranges from 1 nm to about 40 µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to determine the early stages of hydrocarbon generation and saturation within source rocks.

Except for shallowest sample (4270 m), the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Argus-1 (Figures 3.33), perhaps with the exception of the pore size 650 Å, for which a significant scatter is observed (Figure 3.34). The variation of the scattering intensity within the Jamieson Formation for pore size 250 Å (Figure 3.30) does not follow any particular pattern. There is no evidence of progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. This is consistent with the relatively high thermal maturity of the organic matter within the Jamieson Formation (Figure 3.31).

The scattering intensity is generally low, which indicates that the small pores contain significant amount of organic matter with a very low hydrogen-to-carbon ratio, e.g. residual bitumen.

65

Table 3.2. XRF data for Argus 1.

AGSO No Loss on SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 SO3

ignition Si Ti Al Fe Mn Mg Ca Na K P S

(%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%)

20020101 14.698 39.5 0.56 10.37 5.368 0.29 1.45 7.23 1.306 5.229 0.151 5.316

20020104 14.485 41.3 0.53 8.952 4.772 0.12 1.34 7.01 0.929 5.569 0.121 4.794

20020108 12.364 50.3 0.5 8.483 4.231 0.15 1.06 4.13 0.919 6.016 0.102 3.489

AGSO No Sc V Cr Ni Cu Zn Rb Sr Zr Ba Cl

ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

20020101 14 214 78 52 137 181 61 1391 78 58102 24943

20020104 13 220 123 58 156 458 52 1408 77 68875 29177

20020108 14 168 46 36 105 183 54 994 90 48329 32522

66

Figure 3.29. SANS absolute intensity curves for samples of cuttings from Argus-1. Eight samples (seven claystones and one calcareous claystone, 5 m interval each), depth range 4270 m to 4535 m.

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.29Argus-1


101 4270m102 4310m103 4350m104 4390m105 4430m106 4475m107 4510m108 4535m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


67

Figure 3.30. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Argus-1.

4200

4400

4600

4800

50000 100 200 300 400

DEPT

H (m

RT)

SCATTERING INTENSITY AT Q=0.01Å-1 (cm -1)

JAMIESON

ECHUCA SHOALSABSENT

VULCAN

UNDIFFERENTIATEDVOLCANICS

PLOVERNOT CONFIRMED

top gas 4672m

gas

colu

mn

TD 4878m

weak gas effect3950.5-3952m

1.04%0.85%

1.13%

vitrinitereflectance:

calcareous?

(a) µ0.025 m(250Å)

68

Figure 3.31. Vitrinite reflectance and thermal maturity data for extracts and condensates for Argus-1 .

0.6 0.8 1 1.2 1.4 1.6 1.8

3900

4000

4100

4200

4300

4400

4500

4600

4700

Figure 3.31Argus-1

Maturity vs depthVR% - vitrinite reflectance, VRe% - VR equivalent calculated from

MPI (methyl phenantrene index)Based on geochemistry and petrography data from WCR

VR% cuttings

VRe% filtrate extractsVRe% MSCT extracts

VRe% condensates

VITRINITE REFLECTANCE (%)

SA

MP

LE D

EP

TH

(m

RT

)

69

Figure 3.32. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Argus-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement.

4200

4250

4300

4350

4400

4450

4500

4550

4600

3.6 3.8 4 4.2 4.4

Argus 1, Browse BasinScattering length density versus depth

DEP

TH (m

)


70

Figure 3.33. Pore size distribution at various depths for samples of cuttings from Argus-1. Eight samples (seven claystones and one calcareous claystone, 5 m interval each), depth range is 4270 m to 4535 m.

10-7

10-6

10-5

0.0001

0.001

0.01

0.1

100 1000

PORE

SIZ

E DI

TRIB

UTIO

N DE

NSIT

Y f(r

)

PORE SIZE (Å)

4270m

4310m

4350m

4390m

4430m

4475m

4510m

4535m

JAMIESON

ECHUCA SHOALSABSENT

VULCAN

UNDIFFERENTIATEDVOLCANICS

PLOVERNOT CONFIRMED

71

Figure 3.34. Variation of the pore number density for selected pore sizes versus depth for Argus-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text.

10-7 10-6 10-5 10-4 10-3

4200

4300

4400

4500

4600

4700

PORE NUMBER DENSITY

DEP

TH (m

RT

)

calcareous?r = 630Å 316Å 100Å

JAMIESON

VULCAN

ECHUCA SHOALSABSENT

72

Figure 3.35. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Argus-1. For discussion see text.

JAMIESON

VULCAN

0 5 10CALCULATED SANS POROSITY (%)

calcareous?

ECHUCA SHOALSABSENT

03-227-8

4200

4300

4400

4500

4600

4700

DEP

TH (m

RT)

3.5 Brecknock South-1

The pyrolysis data for Brecknock South-1 is given in Appendix 5 Table A5.5. Figure 3.36 is a compilation of the total organic carbon and Rock-Eval pyrolysis parameters (Tmax, S1, S2 and HI) plotted against depth (mRT). Figure 3.37 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples. The ten samples analysed span the Middle Jurassic-Lower Cretaceous. No additional source rock or maturity information was available for this well or for the near-by Brecknock-1 well. Hence, none of the Plover, Vulcan, Echuca Shoals and Jamieson formations are adequately represented.


Brecknock South-1 was drilled with a water-based drilling mud with gel, guar gum and Flowzan additives to a depth of 3151 m. Below this depth potassium chloride, PHPA and glycol was used to complete the drilling of this well. Therefore, all of the cuttings samples analysed are contaminated with glycol additives, and hence they were extracted with methanol and dichloromethane (90:10) as part of the preparative procedure. As such, the S1 values and values produced from calculations using the S1 peak are unreliable (viz. BI, PI).

Since the samples are extracted, the presence of naturally occurring free hydrocarbons cannot be determined. The deepest sample (3995 m), still contains free hydrocarbons/contaminants despite the extraction process.

73


Given that there is some doubt as to the quality of the pyrolysis data due to the glycol additive remaining in the samples, and the lack of comparative data in adjacent wells, the following interpretation should be viewed with caution, since such contaminants can lead to an over estimation of hydrocarbon potential and an under estimation of thermal maturity.

The total organic carbon (TOC) contents of the two sediments from the Jamieson Formation are fair (average TOC = 0.9%), and good for samples from the Echuca Shoals (average TOC = 1.4% for five samples) and Vulcan (average TOC = 1.3% for two samples) formations. The potential yields of the sediments from Brecknock South-1 cannot be discussed due to the removal of the S1 peak by the preparative processes used to eliminate the glycol contamination.

74

Figure 3.36 Depth plots of TOC and Rock-Eval pyrolysis data for Brecknock South-1.

1000

1500

2000

2500

3000

3500

4000

4500

5000

1000

1500

2000

2500

3000

3500

4000

4500

5000

(b) (c)

(d) (e) (f)

400 440 480 1 2 3 4 5

HI (mg/g TOC)200 400300100 500

14/OA/1796

S2 (mg/g Rock)1 2 3 4 5 6

S1 (mg/g Rock)0.5 1.0 1.5 2.0

0 0

000

Tmax ( C) TOC (%)

Brecknock South -1

GA CUTT SANS extracted HCGA CUTT SANS extracted

Top

Bottom

Maastrichtian

Campanian

GA sequence

GA sequence

Santonian -Turonian

JamiesonFormation


VulcanFormation

PloverFormation

Depth

(m

KB)

Maastrichtian

Campanian

Santonian -Turonian

JamiesonFormation


VulcanFormation

PloverFormation

Top

Bottom

Depth

(m

KB)

Invaliddata

75


The Jamieson Formation apparently has the best source quality with HI values ranging from between 163 and 234 mg hydrocarbons/g TOC (average HI = 199 mg hydrocarbons/g TOC; Fig 3.37). However, the TOC contents in these samples are poor, hence any generated liquid hydrocarbons will probably remain within the source rock and expulsion will not occur until it is substantially cracked to gas a higher maturities. The Echuca Shoals Formation has HI values ranging between 123 and 180 mg hydrocarbons/g TOC (average HI = 155 mg hydrocarbons/g TOC) which indicates that they are presently predominantly gas and condensate-prone. The Vulcan Formation samples are at best gas-prone (average HI = 121 mg hydrocarbons/g TOC).

Figure 3.37 shows that the Jamieson Formation sediments contain Type II/III kerogen, the Echuca Shoals Formation sediments contain Type III kerogen and the Vulcan Formation sediments contain Type III/IV kerogen.

Estimates of maturity from the Tmax values indicate that the Jamieson Formation sediments are presently immature for hydrocarbon generation, whereas the Echuca Shoals Formation and Vulcan Formation sediments are just within the oil window. Having said this, the Tmax values are lower than expected for the given depth range. This would suggest that glycol additives are still present in the samples despite the extraction process.

76

Figure 3.37 Tmax versus Hydrogen Index for selected samples from Brecknock South-1.

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

380 400 420 440 460 480 500

0

2

4

6

8

10

12

14

16

18

20

420

430

440

450

460

470

480

0

100

200

300

400

500

600

700

800

(a) (b)

(c)

14/OA/1797

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

VR = 1.35%

III

I

II

VR = 0.5%

Oil

Oil + Gas

Gas + Oil

Gas

VR = 0.8%

imm

atu

re

earl

y m

atu

re

matu

re

ove

r m

ature

Immature

Condensatewindow

Oil window


or contamination

1


Production Index

Hydro

gen I

ndex (

mg H

C/g

TO

C)

pre

sent

day

Tm

ax (

C)

Tmax ( C)

Brecknock South -1

GA CUTT extracted

Jamieson Formation (GA CUTT SANS extracted)

Echuca Shoals Formation (GA CUTT SANS extracted)

Vulcan Formation (GA CUTT SANS extracted)

Invaliddata

Invaliddata


Small Angle Neutron Scattering (SANS) analysis was performed on ten nominally claystone cuttings from the well Brecknock South-1 (Table A1.4 in Appendix 1). These cuttings were collected at about 15-45 m intervals between depths 3530 mRT to 3800 mRT, and the deepest sample (fluvial claystone) was recovered from the depth of 3995 mRT.


There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.39 for scattering intensity measured at Q = 0.01 Å -1, which corresponds to a pore size of about 0.025 µm +/-50% (1 Å = 10-10 m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity is practically constant (320-340 cm-1) within the depth range 3530 m to 3585 m in the Jamieson Formation and top Echuca Shoals Formation, followed by an apparent sharp decrease by a factor of 2.6 at the

77

depth of 3675 m in the mid Echuca Shoals Formation and thereafter slightly increases throughout the Echuca Shoals Formation and the Upper Vulcan Formation by a factor of 1.2. The intensity remains at a low value in the Lower Vulcan Formation and at the base of the Plover Formation down to the TD depth of 4008 mRT.

There is a significant log change at the boundary between the Jamieson Formation and the Echuca Shoals Formation at 3575 m, and yet there is no scattering intensity change across the boundary until well within the upper Echuca Shoals Formation. This raises the possibility that the cuttings retrieved from the depth interval 3585 m to 3590 m near the top of the Echuca Shoals Formation (used to prepare SANS sample) might have been contaminated by cavings from the overlying Jamieson Formation.

Although all the samples obtained from Woodside for SANS analysis have been nominally described as claystones throughout the depth range of 3530 m to 3995 m, the Well Completion Report (WCR) provides detailed information indicating that the actual lithology undergoes significant variation with depth. Within the Jamieson Formation (3525-3575 m) the gamma log remains constant, except for a sharp jump at the depth of 3570 m due to the presence of 20% glauconite, followed by a jump at the sequence boundary and formation boundary at the depth of 3575 m. In the depth range 3575 m – 3664 m within the upper Echuca Shoals Formation there is a slight gradual decrease of the gamma signal, followed by a sudden increase in gamma, density and velocity at the depth of 3664 m. The WCR reports a gradual change of lithology to siltstone throughout the depth range 3664 m – 3766 m within the lower Echuca Shoals Formation and throughout the depth range 3776 m - 3779.5 m within the Upper Vulcan Formation, but this is not corroborated by the descriptions of sidewall cores. The only swc successfully retrieved within the Jamieson Formation (3570 m) is described as glauconitic claystone (65% siliceous clay, 35% siliceous silt, 10% siliceous sand) and the lithology of sidewall cores within the depth interval 3576 m to 3773 m (within the Echuca Shoals Formation and the Upper Vulcan Formation) is described as predominantly siliceous clay.

Since the SANS signal from the organic component of the rock is always superimposed on the SANS signal from the inorganic matrix, a consistent lithology throughout the entire depth range is a prerequisite for a successful identification of hydrocarbon generation zones from SANS data [1]. This is particularly accentuated for organic-lean potential source rocks. Therefore, in the following we first analyse the microstructural properties versus depth.

Figure 3.40 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Brecknock South-1. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.36x1010 cm-2 was used in subsequent calculations for Brecknock South-1.

The pore size distributions calculated for various depths from the full SANS curves are presented in Figure 3.41. A detailed analysis of the variation of pore number density, proportional to the pore size distribution, with depth for three pore sizes 100 Å, 316 Å and 630 Å (Figure 3.42) indicates a systematic compaction with depth for the pore size 100 Å. For the pore sizes 316 Å and 630 Å, however, the pore number density varies irregularly with depth in a way mirroring the scattering intensity curve (Figure 3.39). Three apparent distinct lithologies can be identified (Figure 3.42). This indicates that

78

SANS intensity is most probably dominated by the lithology-dependent scattering on the inorganic matrix, and any organic input is masked by the inorganic matrix signal.

Figure 3.43 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. The values are between 2.0% and 4.7%, with a maximum near the boundary between the Jamieson Formation and the Echuca Shoals Formation. The general trend with depth follows the pattern observed for the scattering intensity (Figure 3.39) and is also most probably dominated by the microstructure of the inorganic matrix. The calculated SANS porosity values need to be calibrated against the log porosities. Brecknock South-1 is a gas/condensate discovery and the gas-water contact and maximum gas reading are indicated in Figure 3.43.


The size of the pores found in claystones typically ranges from 1 nm to about 40 µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to determine the early stages of hydrocarbon generation and saturation within source rocks.

Owing to significant lithology variation, the microstructure of the inorganic rock fabric also changes significantly throughout the depth range studied by SANS in Brecknock South-1 (Figures 3.42, 3.43). For the pore size 316 Å, the pore number density decreases by a factor of about 3 within the depth range of 3585-3675 m (Figure 3.42). The SANS intensity for a similar pore size of 250 Å decreases also by a similar factor of 2.6 within the same depth range (Figure 3.39).

Therefore, it is likely that the observed marked variation of SANS intensity within the depth interval 3585-3675 m is dominated by the lithology variation of the inorganic rock matrix. The slight increase in scattering intensity throughout the depth interval 3675-3770 m could indicate (1) a slight systematic change of the microstructure of inorganic matrix or (2) progressive expulsion of mobile hydrocarbons. There is no strong indication of progressive bitumen generation and/or cracking.

79

Figure 3.38. SANS absolute intensity curves for samples of cuttings from Brecknock South-1. Ten samples (nominally claystones, 5 m interval each), depth range is 3530 m to 3995 m.

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.38Brecknock South-1


091 3530m

092 3565m

093 3585m

094 3635m

095 3675m

096 3705m

097 3750m

098 3770m

099 3800m

100 3995m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


80

Figure 3.39. SANS intensity versus depth at Q=0.01A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Brecknock South-1.

3500

3600

3700

3800

3900

4000

41000 100 200 300 400 500

DEPT

H (m

RT)


JAMIESON

ECHUCASHOALS

VULCANUPPER

LOWER

PLOVER

3782m

3810.8m

Reservoirinterval

siliceousclaystone to siltstonetransition

interbedded Clst & Sst

3570m

glauconiticclaystone

3664m

cavings?

�0.025 m(250Å)

(cm -1)

81

Figure 3.40. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Brecknock South-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement.

3300

3400

3500

3600

3700

3800

3900

4000

4100

3.5 4 4.5 5

Brecknock South-1Scattering length density versus depth

Calculated from XRF data

DE

PT

H (

m)


average SLD = 4.36x1010(cm-2)

82

Figure 3.41. Pore size distribution at various depths for samples of cuttings from Brecknock South-1. Ten samples (nominally claystones, 5 m interval each), depth range is 3530 m to 3995 m.

10-7

10-6

10-5

0.0001

0.001

0.01

0.1

100 1000

PORE

SIZ

E DI

TRIB

UTIO

N DE

NSIT

Y f(r

)

PORE SIZE (Å)

3530m3565m3585m3635m3675m3705m3750m3770m3800m3995m

83

Figure 3.42. Variation of the pore number density for selected pore sizes versus depth for Brecknock South-1. For the smallest pore size note the significant decrease of the pore number density with depth, indicative of compaction. For full discussion see text.

10-7 10-6 10-5 10-4 10-3

3400

3500

3600

3700

3800

3900

4000

4100

PORE NUMBER DENSITY

DEPT

H (m

RT)

LITHOLOGY1

LITHOLOGY2

LITHOLOGY3

r = 630Å 316Å 100Å

JAMIESON

ECHUCASHOALS

VULCAN

PLOVER

UPPER

LOWER

84

Figure 3.43. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Brecknock South-1. For discussion see text.

JAMIESON

ECHUCASHOALS

VULCAN

PLOVER

UPPER

LOWER


maximumgas reading

cavings?

3847m

3944m gas-watercontact

3400

3500

3600

3700

3800

3900

4000

4100

DEPT

H (m

RT)

3.6 Crux-1

The pyrolysis data for Crux-1 are given in Appendix 5 Table A5.6. Figures 3.44 and 3.45 are compilations of total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S1, S2 and HI) plotted against depth (mRT). Figure 3.44 compares the results for raw and extracted samples, and Figure 3.45 compares extracted data from different laboratories. Figure 3.46 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples.

In addition to the extracted cuttings and SWC samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses for both extracted cuttings and SWC samples were available from the well completion report which were analysed by Geotechnical Services (Nippon, 2001).

Comparison of the TOC contents and pyrolysis data from extracted samples between the two laboratories reveals that the data sets are comparable despite different preparative and analytical methodologies being used (Fig 3.45).


Crux-1 was drilled with water-based drilling mud to a depth of 2120 m. Below this depth potassium chloride, PHPA, glycol and Alplex was used to the bottom of the well. All of the cuttings and SWC samples analysed are contaminated with glycol additives, and hence they were extracted with methanol and dichloromethane (90:10) as part of the

85

preparative procedure. There is insufficient information in the WCR to determine the method employed to remove the glycol contamination from the cuttings and SWCs that Geotechnical Services analysed but they did solvent extracted the samples, at least with water (see sections 4.5.2 and 4.5.3.2 and table 14; Nippon, 2001).

The effects of the glycol additives on the pyrolysis data for both SWC and cuttings samples are demonstrated in Figure 3.44 from comparison of the extracted and unextracted samples. It is apparent that the glycol additive has had a considerable effect on the pyrolysis values. For example, the glycol additive increases the TOC contents, S1 and S2 values and the calculated BI and HI values. It also decreases Tmax values which may be variable and show inconsistent trends with increasing depth. Hence, the overall source potential could be overestimated and the maturity of the section underestimated if the type of drilling fluid used is not taken into consideration.

After extraction of the sediments with organic solvents (and water in the case of the Geotech-analysed samples), the resultant pyrograms, in most instances, have little or no S1 peaks and well resolved S2 and S3 peaks. This means that the S1 values, and the calculations involving S1 values (BI, PI) are invalid and the presence of naturally occurring free hydrocarbons in the sediments cannot be evaluated. Equally, the other pyrolysis parameters must also be interpreted with caution due to the unreliable nature of the S2 and TOC values. Some samples still had obvious contamination despite multiple extractions and are pronounced in the cuttings samples from to 2390 m to 2650 m (Fig. 3.45), as shown by the open symbols. Below this depth, the Tmax trend shows a fairly uniform increase with depth and the TOC and HI trends increase, albeit in a more erratic manner.

Bearing in mind the limitations imposed because of the glycol contamination, the following interpretations are an approximate guide to the greatest hydrocarbon potential that the sediments in Crux-1 may have, and the minimum thermal maturity that they may have attained. The Lower Cretaceous Jamieson Formation is not discussed since these extracted samples are still significantly affected by contamination, as highlighted by the exceptionally low Tmax values and high S1 values.


The total organic carbon (TOC) contents of the organic-rich sediments of the Lower Cretaceous Echuca Shoals Formation and Upper Vulcan Formation source rocks range from fair to good and have an overall fair TOC content (average TOC = 1%). The source rocks of the combined Upper Jurassic Lower Vulcan and Montara formations range from good to very good and have an overall good TOC content (average TOC = 1.2%). The potential yields of the sediments from Crux-1 cannot be discussed due to the removal of the S1 peak by the preparative processes used to eliminate the glycol contamination.

86

Figure 3.44 Depth plots of TOC and Rock-Eval pyrolysis data for Crux-1 (GA data only).

Crux -1

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

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Depth

(m

KB)

(b) (c)

(d) (e) (f)

1 2 3 4 5

HI (mg/g TOC)

14/OA/1801

S2 (mg/g Rock)S1 (mg/g Rock)0.5 1.0 1.5 2.0

0

000

Tmax ( C) TOC (%)300 340 380 420 460

2 4 6 8 10 200 400 600 800

GA CUTT

GA CUTT extracted

GA SWC

GA SWC extracted

GA sequence

GA sequence

Tertiary

Maastrichtian

Campanian

Santonian -Turonian

JamiesonFormation

Echuca Shoals FmUpper Vulcan

Formation

Lower VulcanFormation

PloverFormation

Tertiary

Maastrichtian

Campanian

Santonian -Turonian

JamiesonFormation


Formation


Invaliddata

PloverFormation

87

Figure 3.45 Depth plots of TOC and Rock-Eval pyrolysis data for Crux-1.

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

1000

1500

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Depth

(m

KB)

(b) (c)

(d) (e) (f)

400 440 480 1 2 3 4 5

HI (mg/g TOC)200 400300100 500

14/OA/1800

S2 (mg/g Rock)1 2 3 4 5 6

S1 (mg/g Rock)0.5 1.0 1.5 2.0

0

000

Tmax ( C) TOC (%)

Geotech SWC washed

GA SWC extracted

GA CUTT extracted

GA sequence

GA sequence

Tertiary

Maastrichtian

Campanian

Santonian -Turonian

JamiesonFormation


Formation


Tertiary

Maastrichtian

Campanian

Santonian -Turonian

JamiesonFormation


Formation


Crux -1

Invalid data

PloverFormation

PloverFormation

GA CUTT extracted (HC)

88


The Lower Cretaceous Echuca Shoals Formation samples are poor in hydrogen and are at best gas-prone (average HI = 116 mg hydrocarbons/g TOC; Fig. 3.46). The Lower Cretaceous-Upper Vulcan sediments have an average HI value of 178 mg hydrocarbons/g TOC indicating that they have the potential to generate both condensate and gas. Likewise, the Upper Jurassic Lower Vulcan Formation and Montara Formation sediments have similar source quality with average HI values of 194 mg hydrocarbons/g TOC and 197 mg hydrocarbons/g TOC, respectively which indicates that they have the potential to generate both condensate and gas.

Figure 3.46 shows that the Echuca Shoals Formation sediments contain immature Type III/IV kerogen. The Upper and Lower Vulcan formations contain Type II/III kerogen that is presently within the early oil window.


Small Angle Neutron Scattering (SANS) analysis was performed on 25 claystone and silty claystone cuttings as well as five claystone and silty claystone sidewall cores from the well Crux-1 (Table A1.7 in Appendix 2). The cuttings were collected at 20 m to 80 m intervals between depths 2390 mRT to 3550 mRT.

Figure 3.47 shows the original SANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q. Data for sidewall cores are presented separately in Figure 1C.

There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.48 for scattering intensity measured at Q=0.01 Å -1, which corresponds to a pore size of about 0.025 µm +/-50% (1 Å = 10-10 m; 1 µm = 1000 nm = 10,000 Å). Except for one data point (a sidewall core at a depth of 3471.1 m), there is a good agreement between the intensity values measured from samples of sidewall cores and cuttings

Within the Jamieson Formation, the scattering intensity rapidly decreases by a factor of 1.8 within the depth range 2390 m to 2450 m and then sharply increases by a factor of 1.6 within the depth range 2450 m to 2570 m. This is followed by an abrupt decrease at the top of the Echuca Shoals Formation and than a slight decrease throughout the Echuca Shoals Formation and uppermost Upper Vulcan Formation within the depth range 2600 m to 2691.5 m.

A general decreasing trend, with somewhat scattered data points, is observed within the top Upper Vulcan Formation within the depth range 2775 m to 2990 m, followed by a roughly constant, relatively low value within the depth range 2990 m to 3110 m. At the base of the Upper Vulcan Formation the scattering intensity increases by a factor of 1.3 (3100-3155.5 m). At the top of the Lower Vulcan Formation the scattering intensity returns to a low value and, following the trend exhibited in the mid Upper Vulcan Formation, remains roughly constant throughout the Lower Vulcan Formation, except for one data point (swc) at a depth of 3471.1 m near the base.

89

Figure 3.46 Tmax versus Hydrogen Index for selected samples from Crux-1.

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

380 400 420 440 460 480 500

0

2

4

6

8

10

12

14

16

18

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430

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450

460

470

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0

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400

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600

700

800

(a) (b)

(c)

14/OA/1802

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

VR = 1.35%

III

I

II

VR = 0.5%

Oil

Oil + Gas

Gas + Oil

Gas

VR = 0.8%

imm

atu

re

matu

re

ove

r m

ature

Immature

Condensatewindow

Oil window


or contamination

1


Production Index

Hydro

gen I

ndex (

mg H

C/g

TO

C)

pre

sent

day

Tm

ax (

C)

Tmax ( C)

Geotech SWC

Geotech SWC HC


Upper Vulcan Formation


GA CUTT

GA CUTT extracted

GA SWC

GA SWC extracted

earl

y m

atu

re

Crux -1

invalid data

Invalid data

Figure 3.49 illustrates the variation of the organic matter maturity with depth, using two sets of data: the vitrinite reflectance and FAMM equivalent (CSIRO report in WCR). These values were used in Figure 3.48 to provide a conventional indication of source rock maturity at various depths.

90

Figure 3.50 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Crux-1. There is little variation (at most 3%) with depth and, consequently, the average value of SLD = 4.32x1010 cm-2 was used in subsequent calculations for Crux-1.

The pore size distributions calculated for various depths from the full SANS curves (Figure 3.51) indicate that there is little variation of the geometry of the pore space with depth and that there is little difference between data for sidewall cores and cuttings.

A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a systematic slight compaction with depth throughout the entire depth interval 2390 m to 3550 m (Figure 3.52) . Superimposed onto this general trend are two anomalies, one located within the Upper Vulcan Formation within the depth range 2690 m to 2850 m and another within the basal Upper Vulcan Formation within the depth range 3110 m to 3200 m.

Figure 3.53 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. Most of the values are between 1.6% and 3.2%, with a maximum of about 3.2% at the top of the Jamieson Formation.

Crux-1 is a gas discovery well, with a gas cap located within the Nome Formation within the depth range 3635 m to 3884 m (GWC).


The sizes of the pores found in claystones typically range from 1 nm to about 40 µm across. SANS experiments can access pore sizes at the lower end of this range, from about 2 nm to 100 nm, which typically comprise about 30% of total porosity. These data can be used to identify the early stages of hydrocarbon generation and saturation inside source rocks.

Except for two relatively weak anomalies within the Upper Vulcan Formation (at a depth of about 2800 m and 3150 m), the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Crux-1 (Figures 3.51 and 3.52). Therefore, the marked variation of the scattering intensity (Figure 3.48) throughout the Jamieson Formation and the Echuca Shoals Formation is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast.

As discussed above, the low values of the scattering intensity indicate pores filled with bitumen at the onset of hydrocarbon generation, and the high values pores filled with gas, formation brine and/or saturated hydrocarbons. Based on this, three regions of the onset of mobile hydrocarbon generation (at different maturity) can be identified (Figure 3.54): (1) within the upper Jamieson Formation at a depth of about 2450 m,

91

(2) at the base of the Echuca Shoals Formation at a depth of about 2690 m, and (3) possibly within the Upper Vulcan Formation at a depth of about 3000-3155 m. All three generation regions are separated from each other by barriers, most probably due to low permeability or markedly different thermal kinetics for transformation of organic matter. The increasing SANS intensity with depth for hydrocarbon generation region within the lower Jamieson Formation and at the base of the Upper Vulcan Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation.

The low scattering intensity at the base of the Echuca Shoals Formation, as compared to the adjacent region in the Upper Vulcan Formation, indicates that there is no communication between the pore spaces of these two sedimentary units. Claystones within these two units are separated by numerous sandstone layers (up to 10 m thick) intersected within the depth range 2676-2750 m. It is possible that these sandstones reservoir mobile hydrocarbons generated at the base of the Echuca Shoals Formation and at the top of the Upper Vulcan Formation.

92

Figure 3.47. SANS absolute intensity curves for samples from Crux-1. (a): 13 samples of cuttings (claystones and silty claystones, 5 m interval each), depth range 2390 m to 2945 m. (b): 12 samples of cuttings (claystones and silty claystones, 5 m interval each), depth range 2990 m to 3550 m. C: five sidewall core samples (claystones and silty claystones, 5 m interval each), depth range 2599.6 m to 3471.1 m.

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.47(A)Crux-1

Scattering intensity versus Q for various depthspart 1: cuttings 2390m to 2945m

109 2390m110 2450m111 2500m112 2550m113 2570m114 2600m115 2650m116 2690m117 2775m118 2805m119 2850m120 2900m121 2945m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


93

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.47(B)Crux-1

Scattering intensity versus Q for various depthspart 2: cuttings 2990m to 3550m

122 2990m

123 3055m

124 3110m

125 3150m

126 3200m

127 3270m

128 3325m

129 3359m

130 3400m

131 3460m

132 3500m

133 3550m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


94

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.47(C)Crux-1

Scattering intensity versus Q for various depthspart 3: sidewall cores 2599.6m to 3471.1m

134 swc 2599.6m

135 swc 2691.5m

136 swc 3155.5m

137 swc 3266.6m

138 swc 3471.1m

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)


95

Figure 3.48. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for samples from Crux-1.

2000

2500

3000

3500

40000 50 100 150 200 250 300 350

DEP

TH (m

RT)

SCATTERING INTENSITY AT Q=0.01Å -1

WOOLASTON

JAMIESON

ECHUCASHOALS

VULCAN

MALITA

0.51%

0.79%0.42%

0.44%

0.38%

0.90%0.45%

0.44%

0.57% 0.88%

0.57-0.8%

0.64%

UPPER

LOWER

Sst intervals2750m

2676m

NOME

MATURITY:

Ro% FAMM

0.80%

0.93%

0.98%

1.06%

kinetics orpermeability

barrier

ONSET 2

(cm -1)

µ0.025 m(250Å)

ONSET 3

ONSET 1

96

Figure 3.49. Vitrinite reflectance versus depth for Crux-1 (after Well Completion Report).

0.2 0.4 0.6 0.8 1 1.2 1.4

2000

2500

3000

3500

4000

Figure 3.49Crux-1

Vitrinite reflectance versus depthcircles - vitrinite reflectance results

squares - FAMM results

Average VRMinimum Maximum Average FAMMMinimumMaximum

VITRINITE REFLECTANCE (%)

SA

MP

LE D

EP

TH

(m

RT

)

97

Figure 3.50. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Crux-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement.

2000

2200

2400

2600

2800

3000

3200

3400

3600

4 4.2 4.4 4.6 4.8 5

Crux1, Browse BasinScattering length density versus depth

DEP

TH (m

)

SCATTERING LENGTH DENSITY (x1010 cm-2)

98

Figure 3.51. Pore size distribution at various depths for samples from Crux-1. (a): 13 samples of cuttings (claystones and silty claystones, 5 m interval each), depth range 2390 m to 2945 m. (b): 12 samples of cuttings (claystones and silty claystones, 5 m interval each), depth range 2990 m to 3550 m. (c): five sidewall core samples (claystones and silty claystones, 5 m interval each), depth range 2599.6 m to 3471.1 m.

10-7

10-6

10-5

0.0001

0.001

0.01

0.1

100 1000

PORE

SIZ

E DI

TRIB

UTIO

N DE

NSIT

Y f(r

)

PORE SIZE (Å)

(a)2390m2450m2500m2550m2570m2600m2650m2690m2775m2805m2850m2900m2945m

99

100 1000

PORE SIZE (Å)

(b)2990m3055m3110m3150m3200m3270m3325m3359m3400m3460m3500m3550m

10-7

10-6

10-5

0.0001

0.001

0.01

0.1PO

RE S

IZE

DITR

IBUT

ION

DENS

ITY

f(r)

100 1000

PORE SIZE (Å)

(c)

swc 2599.6m

swc 2691.5m

swc 3155.5m

swc 3266.6m

swc 3471.1m

10-7

10-6

10-5

0.0001

0.001

0.01

0.1

PORE

SIZ

E DI

TRIB

UTIO

N DE

NSIT

Y f(r

)

100

Figure 3.52. Variation of the pore number density for selected pore sizes versus depth for Crux-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text.

10-7 10-6 10-5 10-4 10-3

2000

2500

3000

3500

4000

PORE NUMBER DENSITY

DEPT

H (m

RT)

(e)

r = 630Å 316Å 100Å

WOOLASTON

JAMIESON

ECHUCASHOALS

UPPER

VULCAN

LOWER

MALITA

NOME

101

Figure 3.53. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Crux-1. For discussion see text.

WOOLASTON

JAMIESON

ECHUCASHOALS

UPPER

VULCAN

LOWER

MALITA

NOME


GWC 3884m

3635m

GAS

2000

2500

3000

3500

4000

DEPT

H (m

RT)

102

Figure 3.54. Interpretation of SANS data for Crux-1. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for samples from Crux-1.

2000

2500

3000

3500

40000 50 100 150 200 250 300 350

DEP

TH (m

RT)


WOOLASTON

JAMIESON

ECHUCASHOALS

VULCAN

MALITA

0.51%

0.79%0.42%

0.44%

0.38%

0.90%0.45%

0.44%

0.57% 0.88%

0.57-0.8%

0.64%

UPPER

LOWER

Sst intervals2750m

2676m

NOME

MATURITY:

Ro% FAMM

0.80%

0.93%

0.98%

1.06%

kinetics orpermeability

barrier

ONSET 2

(cm -1)

µ0.025 m(250Å)

ONSET 3

ONSET 1

3.7 Dinichthys-1

The pyrolysis data for Dinichthys-1 is given in Appendix 5 Table A5.7. Figure 3.55 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S1, S2 and HI) plotted against depth (mRT). Figure 3.56 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples.

In addition to the extracted cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses for cuttings samples (which were analysed by Geotechnical Services) were available from the well completion report (Inpex, 2001a). Vitrinite reflectance measurements were obtained by Kieraville Konsultants.


The well completion report states that Dinichthys-1 was drilled with water-based drilling muds with various additives (KCl, Aquadrill and Pyrodrill). However, both the GA cuttings samples and those analysed by Geotechnical Services appear contaminated by glycol additives, as confirmed by subsequent GC-MS work by Geotechnical Services. The samples analysed in this study were extracted with methanol and

103

dichloromethane (90:10) as part of the preparative procedure. The Geotech-analysed samples were unwashed cuttings.

Comparison of the two laboratory data sets shows that the glycol additive has had a considerable effect on the pyrolysis values (Fig. 3.55). For example, the glycol additive generally (but not always) increases the TOC content, it increases the S1 and S2 values and the calculated BI and HI values. It decreases the Tmax values which may be variable and show inconsistent trends with increasing depth. Hence, the overall source potential could be over estimated and the maturity of the section under estimated if the type of drilling fluid used is not taken into consideration.

After extraction of the sediments with organic solvent, the resultant pyrograms, in most instances, have little or no S1 peaks and well resolved S2 and S3 peaks. This means that the S1 values, and the calculations involving S1 values (BI, PI) are invalid and the presence of naturally occurring free hydrocarbons in the sediments cannot be evaluated. Equally, the other pyrolysis parameters must also be interpreted with caution due to the unreliable nature of the S2 and TOC values.

Bearing in mind the limitations imposed because of the glycol contamination, the following interpretations are an approximate guide to the greatest hydrocarbon potential that the sediments in Dinichthys-1 may have, and the minimum thermal maturity that they may have attained. It must be stated that many samples in Dinichthys-1 still appear to be strongly affected by contamination, as highlighted from the exceptionally low Tmax values and high S1 values, even after multiple solvent extractions. Therefore, the samples evaluated for their hydrocarbon potential are identified with a black dot in Figure 3.55, and only these data are plotted on the Tmax versus HI plot in Figure 3.56.


The total organic carbon (TOC) contents of both the Lower Cretaceous Jamieson Formation and Echuca Shoals Formation samples appear to be good (average TOC = 1.6% and 2.2%, respectively; Fig. 3.56). The potential yields of the sediments from Dinichthys-1 cannot be discussed due to the removal of the S1 peak by the preparative processes used to eliminate the glycol contamination.


The Jamieson and Echuca Shoals formations range from being gas-prone to having some liquids potential (average HI = 163 mg hydrocarbons/g TOC and 148 mg hydrocarbons/g TOC, respectively). Figure 3.56 shows that the Jamieson Formation sediments contain immature Type III kerogen, and the Echuca Shoals Formation sediments contains Type III kerogen that is presently within the peak oil window.

104

Figure 3.55 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Dinichthys-1.

1000

1500

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4000

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5000

Depth

(m

KB)

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Depth

(m

KB)

(a) (b) (c)

(d) (e) (f)

VR (%)0.4 0.8 1.2 1.6 2.0 320 360 400 1 2 3 4 5

HI (mg/g TOC)400 800600200 1000

14/OA/1803

S2 (mg/g Rock)10

S1 (mg/g Rock)

0 0

000

Tmax ( C) TOC (%)

Geotech CUTT

GA CUTT

GA CUTT extracted

GA acceptable SR dataKieraville SWC

51 2 3 4 2 4 6 8

440 480280

WCR sequence

Lower Vulcan Fm

Upper Vulcan Fm


JamiesonFormation

Woolaston Fm

Fenelon Fm

PuffinFormation

Tertiary

WCR sequence

Lower Vulcan Fm

Upper Vulcan Fm


JamiesonFormation

Woolaston Fm

Fenelon Fm

PuffinFormation

Tertiary

Dinichthys -1

Invaliddata

Plover Fm

Plover Fm

105

Figure 3.56 Tmax versus Hydrogen Index for selected samples from Dinichthys-1.

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

380 400 420 440 460 480 500

0

2

4

6

8

10

12

14

16

18

20

420

430

440

450

460

470

480

0

100

200

300

400

500

600

700

800

(a) (b)

(c)

14/OA/1804

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

VR = 1.35%

III

I

II

VR = 0.5%

Oil

Oil + Gas

Gas + Oil

Gas

VR = 0.8%

imm

atu

re

earl

y m

atu

re

matu

re

ove

r m

ature

Immature

Condensatewindow

Oil window


or contamination

1


Production Index

Hydro

gen I

ndex (

mg H

C/g

TO

C)

pre

sent

day

Tm

ax (

C)

Tmax ( C)

Geotech CUTT

GA CUTT

GA CUTT extracted

Jamieson Formation


Dinichthys -1

Invalid dataInvalid data

3.7.4 Analysis of SANS and USANS data

Small Angle Neutron Scattering (SANS) and Ultra-small Angle Neutron Scattering (USANS) analyses were performed on 25 claystone cuttings from the well Dinichthys-1 (Table A1.8 in Appendix 2). These cuttings were collected at 50 m to 100 m intervals between depths 2550 mRT to 4350 mRT

106

Figure 3.57 shows the original SANS/USANS data presented in the standard manner: scattering intensity, I(Q) in absolute units, versus the scattering vector Q.

There is a significant and systematic variation of the scattering intensity with depth. This variation is clearly pore-size-dependent, as shown in Figure 3.58(a-d) for four Q-values of 0.025 Å -1, 0.0025 Å -1, 0.00025 Å -1, and 0.000025 Å -1, which correspond to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, respectively (1 Å = 10-10 m; 1 µm = 1000 nm = 10,000 Å).

For the smallest pore size (Figure 3.58(a) the scattering intensity initially increases by a factor of 2 within the depth range 2550 m to 3355m in the Jamieson Formation. The scattering intensity is markedly lower at the top of the Echuca Shoals Formation and it decreases by a factor of 2 within the depth range 3450 m to 3950 m throughout the Echuca Shoals Formation and thereafter remains relatively constant at a low value within the Vulcan Formation.

The characteristic <-shaped intensity curve, visible for the smaller pores within the upper Jamieson Formation, effectively washes out for the largest pores (Figure 3.58(a-d)). This indicates that there is not enough hydrocarbon volume generated within the source rock to saturate the largest pores as the bitumen is successively replacing brine from smaller pores toward the larger ones. This microstructural evidence is consistent with the marginal global values of TOC and the early to peak oil window maturity estimate in the Jamieson Formation source rocks at nearby Brewster-1A well, for which the TOC values are reliable (sections 3.1.2 and 3.1.3).

Within the Echuca Shoals Formation, the hydrocarbon generation peak is consistently observed in the depth interval 3850 m – 3950 m, and its position moves slightly to shallower depths with increased pore size. The bitumen generation region is not immediately adjacent to the Berriasian Sandstone (regional reservoir rock in the depth interval 4065 m to 4184 m). The depth of the <-shaped intensity curve is smaller for 10 µm pores than for 1 µm pores (Figures 3.58(d) and 3.58(c), respectively). This indicates that the largest pores may not be fully saturated, which would prevent the expulsion of a significant volume of hydrocarbons from the Echuca Shoals Formation. Given the vitrinite reflectance values of the order of 0.63% to 1.16% in the mid-formation and at the base, respectively, it is most likely that the small upward shift of the intensity <-curve is caused by the process of oil generation preferentially taking place in larger pores.

Figure 3.59 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Dinichthys-1. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.40x1010 cm-2 was used in subsequent calculations for Dinichthys-1.

The pore size distributions calculated for various depths from the full SANS curves (Figure 3.60) indicate that there is little variation of the geometry of the pore space with depth, except at the depth of 3350 m near the base of the Jamieson Formation, where an increased number of larger pores is observed. This anomaly coincides with the “K Aptian sandstone equivalent” region of changed lithology within the depth interval 3340 m – 3424 m (Figure 3.62).

107

A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for four pore sizes 0.01 µm, 0.1 µm, 1 µm and 10 µm, indicates a systematic slight compaction with depth throughout the Jamieson Formation and slight decompaction throughout the Echuca Shoals Formation, regardless of the pore size (Figure 3.61). The onset of the expansion interval coincides with the different lithology region (Figure 3.62), intersected near the base of Jamieson Formation. The smooth and only slight variation of the pore number density with depth indicates both a uniform lithology and mechanical stability of the inorganic rock matrix with depth.

Figure 3.62 illustrates calculated porosity (for the very large fraction of total porosity within the pore size range 20 Å to 20 µm) versus depth. Apparent SANS porosity has been computed by adding pore volumes obtained by fitting the combined SANS/USANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. The apparent SANS porosity values for Dinichthys-1 lie between 6% and 14%, with a maximum at the base of Jamieson Formation (Figure 3.62).

Depth intervals characterised by changed conditions are indicated on the left hand side of the Figure 3.62. The "K Aptian sandstone equivalent" (3340 m to 3424 m) is characterised by low gamma ray signal and low penetration rate. Gas readings were fairly high throughout the well, and the depth interval 3700 m to 3750 m recorded a particularly elevated level of gas readings. Significant overpressure was recorded within the Echuca Shoals Formation.


The size of the pores found in claystones typically ranges from 1 nm to about 40 µm across. Combined SANS and USANS methods can access pore sizes from about 2 nm to 20 µm, which covers nearly the total porosity. These data can be used to determine all stages of hydrocarbon generation, saturation and expulsion within source rocks.

Except for the anomaly at the base of the Jamieson Formation (at 3350 m), the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Dinichthys-1 (Figures 3.60 and 3.61). Therefore, the marked variation of the scattering intensity (Figure 3.58) is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast. Typically, the low values of the scattering intensity indicate pores filled with bitumen at the onset of mobile hydrocarbon generation, and the high values pores filled with gas, formation brine and/or saturated hydrocarbons.

As discussed above, in Dinichthys-1 there are two depth intervals which clearly indicate the presence of bitumen in small pores, interpreted as the evidence of the onset of hydrocarbon generation: the upper Jamieson Formation and the lower Echuca Shoals Formation.

The characteristic <-shape SANS intensity pattern for small pores within the upper Jamieson Formation (Figure 3.58(a) and 3.58(b)) indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. The largest pores, however, do not appear to

108

be saturated at all which indicates that the upper Jamieson Formation claystones are too organically lean to become saturated, expel hydrocarbons and become an effective source rock for hydrocarbons.

The average scattering intensity for small pores near the top of the Echuca Shoals Formation appears to exhibit a discontinuity when compared to the adjacent region in the Jamieson Formation (Figure 3.58(a) and 3.58(b)), which indicates that there is no communication between the pore spaces of these two sedimentary units. There is evidence of the presence of bitumen in pores of all sizes in the depth interval 3850 m – 3950 m (slightly pore size dependent), but the largest pores are evidently less saturated than the smaller ones (Figures 3.58(d) and 3.58(c), respectively). This indicates insufficient charge volume to fully saturate the pore space of the claystone with hydrocarbons and, therefore, a very limited capacity to expel hydrocarbons.

The relatively low scattering intensity at a depth of 4230 m within the Upper Vulcan Formation indicates that the pores contain significant amounts of organic matter with a very low hydrogen-to-carbon ratio, e.g. residual bitumen.

109

Figure 3.57. SANS absolute intensity curves for samples of cuttings from Dinichthys-1. (a): nine samples (claystones, 5m interval each), depth range is 2550 m to 2950 m. (b): nine samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3000 m to 3760 m. (c) four samples (claystones and claystones plus silty claystones, 5 m interval each), 3850 m to 4190 m.

0.1

10

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105

107

109

1011

10-5 0.0001 0.001 0.01 0.1

Figure 3.57(a)Dinichthys1 (SANS & USANS)


2550m2610m2650m2700m2740m2790m2850m2895m2950m

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ITY

(cm

-1)


110

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Figure 3.57(b)Dinichthys1 (SANS & USANS)


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ITY

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-1)


111

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1011

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Figure 3.57(c)Dinichthys1 (SANS & USANS)


3850m3950m4040m4190m

SC

ATTE

RIN

G IN

TEN

SIT

Y (c

m-1

)


112

Figure 3.58. SANS intensity versus depth at four Q-values of (a) 0.025 Å -1, (b) 0.0025 Å -1, (c) 0.00025 Å -1, and (d) 0.000025 Å -1, which corresponds to four pore sizes of 0.01 µm +/-50%, 0.1 µm +/-50%, 1 µm +/-50% and 10 µm +/-50%, for cuttings samples from Dinichthys-1.

2000

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50000

DEPT

H (m

RT)


Ro=0.50%

Ro=0.53%

Ro=0.59%

Ro=0.61%

Ro=0.64%

Ro=0.63%

Ro=0.63%Ro=0.67%Ro=0.70%Ro=1.16%

Ro=1.23%

Ro=1.48%

Ro=1.78%

4065m4184m

ONSET

ONSET

Gas Sst


5 10 15 20

µ0.01 m(100Å)

(a)

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JAMIESO N

ECHUCASHOALS

VULCAN

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LOWER

PLOVER

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JAMIESO N

ECHUCASHOALS

VULCAN

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LOWE R

PLOVER

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113

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µ10 m

(d) 2000

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3500

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DEPT

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RT)

114

Figure 3.59. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Dinichthys-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement.

2000

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3000

3500

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4500

4 4.2 4.4 4.6 4.8 5

Dinichthys1, Browse BasinScattering length density versus depth

DEP

TH (m

)

SCATTERING LENGTH DENSITY (x1010

cm-2

)

115

Figure 3.60. Pore size distribution at various depths for samples of cuttings from Dinichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range is 2550 m to 3250 m. (b): nine samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3350 m to 4190 m.

10-17

10-15

10-13

10-11

10-9

10-7

10-5

0.001

0.1

10 100 1000 104 105 106

PORE

SIZ

E DI

TRIB

UTIO

N DE

NSIT

Y f(r

)

PORE SIZE (Å)

2550m2610m2650m2700m2740m2790m2850m2895m2950m3000m3045m3150m3250m

(a)

116

10 100 1000 104 105 106

PORE SIZE (Å)

3350m3450m3550m3640m3760m3850m3950m4040m4190m

(b)

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10-15

10-13

10-11

10-9

10-7

10-5

0.001

0.1PO

RE S

IZE

DITR

IBUT

ION

DENS

ITY

f(r)

117

Figure 3.61. Variation of the pore number density for four selected pore sizes versus depth for Dinichthys-1. Note the slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text.

10-15 10-13 10-11 10-9 10-7 10-5 10-3

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PORE NUMBER DENSITY

DEPT

H (m

RT)

µµ 1 mr= 10 m µ0.1 m µ0.01 m

JAMIESO N

ECHUCASHOALS

VULCAN

PLOVER

UPPER

LOWER

WOOLASTON

118

Figure 3.62. Variation of apparent porosity (within the pore size range 2 nm to 20 µm) with depth for Dinichthys-1. For discussion see text.

JAMIESON

ECHUCASHOALS

VULCAN

PLOVER

UPPER

LOWER

WOOLASTON

0 5 10 15 20 25 30

CALCULATED SANS POROSITY (%)

3350m

3340m3424m

4008m


penetration rate


3700m3750m

particularlyincreasedgas readings

(h) 2000

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DEP

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(m

RT)

3.8 Gorgonichthys-1

The pyrolysis data for Gorgonichthys-1 are given in Appendix 5 Table A5.8. Figure 3.63 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S1, S2 and HI) plotted against depth (mRT). Figure 3.64 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples.

In addition to the extracted cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses for cuttings samples (which were analysed by Geotechnical Services) were available from the well completion report (Inpex, 2001b). Vitrinite reflectance measurements were obtained by Kieraville Konsultants.


Gorgonichthys-1 was drilled with a water-based drilling mud with gel and polymer additives to a depth of 3940 m. Below this depth Syntech (a synthetic-based mud) was used to the bottom of the well. The cuttings samples analysed by Geotechnical Services were extracted but no details are given in the WCR. However, it is apparent from these data that the Tmax values were anomalously low (Fig. 3.63) and the S2, TOC and HI values were high for samples drilled using the water-based mud, as well as the SBMs. This indicates that other organic compounds (possibly glycol) are also present in the water-based mud. Therefore, all of the cuttings samples analysed in this study

119

were extracted with methanol and dichloromethane (50:50) as part of the preparative procedure.

After extraction of the sediments with organic solvents, the resultant pyrograms, in most instances, have little or no S1 peaks and well resolved S2 and S3 peaks. This means that the S1 values, and the calculations involving S1 values (BI and PI) are invalid and the presence of naturally occurring free hydrocarbons in the sediments cannot be evaluated. Equally, the other pyrolysis parameters must also be interpreted with caution due to the unreliable nature of the S2 and TOC values.

Bearing in mind the limitations imposed because of the contamination, the following interpretations are an approximate guide to the greatest hydrocarbon potential that the sediments in Gorgonichthys-1 may have, and the minimum thermal maturity that they may have attained. The samples evaluated for their hydrocarbon potential are identified with a black dot in Figure 3.63, and only these data are plotted on the Tmax versus HI plot in Figure 3.64. It must be stated that there is a reversal in the Tmax trend from the depth that the SBM was added (Fig. 3.63). This indicates that SBM contaminants remain within the cuttings samples in Gorgonichthys-1. Therefore, data from only the samples above 3940 m are interpreted and shown on the Tmax versus HI plot in Figure 3.64.

It must be noted that the WCR report states that coals are present in the Plover Formation at 4500 and 4530 m. This lithology was not represented in the current sampling suite.


The total organic carbon content of samples from the Lower Cretaceous Jamieson and Echuca Shoals formations appear to range from fair to good with an average TOC of 1.4% and 1.7%, respectively. The potential yields of the sediments from Gorgonichthys-1 cannot be discussed due to the removal of the S1 peak by the preparative processes used to eliminate any contamination.


The source quality of the Jamieson Formation ranges from being gas-prone to having the potential to generate oil (range HI = 50-259 mg hydrocarbons/g TOC; average HI = 153 mg hydrocarbons/g TOC; Fig. 3.3.64). The Echuca Shoals Formation has similar hydrocarbon potential to the aforementioned formation, with HI values ranging from 128 to 264 mg hydrocarbons/g TOC (average HI = 181 mg hydrocarbons/g TOC). However, in the samples with the highest HI values, the corresponding TOC contents are less than 2%. Hence, any generated oil will probably remain within the source rock and expulsion will not occur until it is substantially cracked to gas at higher maturities.

Figure 3.64 shows that the Jamieson Formation contains immature to marginally mature Type II/III to Type III kerogen, and the Echuca Shoals Formation contains Type II/III to Type III kerogen that is presently within the early oil window.

Figure 3.63 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data

120

for Gorgonichthys-1.

1000

1500

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3500

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4500

5000

Depth

(m

KB)

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Depth

(m

KB)

(a) (b) (c)

(d) (e) (f)

VR (%)0.4 0.8 1.2 1.6 2.0 1 2 3 4 5

HI (mg/g TOC)

14/OA/1805

S2 (mg/g Rock)8

S1 (mg/g Rock)0.5 1.0 1.5 2.0

0 0

2000

Tmax ( C) TOC (%)

Gorgonichthys -1

340 380 420 460 500

2 4 6

Kieraville

120 220 320 420 520 620 720

GA sequence

Tertiary

Maastrichtian

Campanian


JamiesonFormation




PloverFormation

GA sequence

Tertiary

Maastrichtian

Campanian


JamiesonFormation




GA acceptable SR data Geotech CUTT extracted (SBM) GA CUTT extracted (SBM)

Invalid data

SBM SBM

SBM SBM SBM

PloverFormation

Geotech CUTT extracted (glycol) GA CUTT extracted (glycol)

121

Figure 3.64 Tmax versus Hydrogen Index for selected samples from Gorgonichthys-1.

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

380 400 420 440 460 480 500

0

2

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8

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14

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S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

VR = 1.35%

III

I

II

VR = 0.5%

Oil

Oil + Gas

Gas + Oil

Gas

VR = 0.8%

imm

atu

re

earl

y m

atu

re

matu

re

ove

r m

ature

Condensatewindow

Oil window


or contamination

1


Production Index

Hydro

gen I

ndex (

mg H

C/g

TO

C)

pre

sent

day

Tm

ax (

C)

Tmax ( C)

Jamieson Formation


Gorgonichthys -1

Immature

Geotech CUTT extracted (SBM)

GA CUTT extracted (SMB)

Invalid dataInvalid data

Geotech CUTT extracted (glycol)

GA CUTT extracted (glycol)


Small Angle Neutron Scattering (SANS) analysis was performed on 27 claystone cuttings from the well Gorgonichthys-1 (Table A1.9). These cuttings were collected at 50 m to 100 m intervals between depths 2520 mRT to 4770 mRT.

122

Figure 3.65 shows the original SANS data presented in the standard manner; scattering intensity, I(Q) in absolute units, versus the scattering vector Q. On the log-log scale the shapes of scattering curves for all samples appear similar, except for the (small) scattering background in the large-Q region, which groups into two different values. This is an artifact due to slightly different SANS data processing protocols used in December 2001 and May 2002, and it does not affect the scattering intensity in the small-Q region used in the following analysis.

There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.66 for scattering intensity measured at Q=0.01 Å -1, which corresponds to a pore size of about 0.025 µm +/-50% (1 Å = 10-10 m; 1 µm = 1000 nm = 10,000 Å). On this and many subsequent figures, generalised trend lines have been added to aid interpretation. The scattering intensity initially decreases in the depth range 2620 m to 2870 m and then increases by a factor of 2.3 within the depth range 2870 m to 3360 m in the Jamieson Formation. The scattering intensity is markedly lower at the top of the Echuca Shoals Formation and it decreases by a factor of 1.3 within the depth range 3370 m to 3905 m. The scattering intensity remains at a relatively low value throughout the Vulcan Formation, Plover Formation and Mt Goodwyn Formation, down to a depth of 4720 m.

Figure 3.67 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Gorgonichthys-1. There is little variation (at most 2%) with depth and, consequently, the average value of SLD = 4.49x1010 cm-2 was used in subsequent calculations for Gorgonichthys-1.

The pore size distributions calculated for various depths from the full SANS curves (Figure 3.68) indicate that there is little variation of the geometry of the pore space with depth, except at around the depth of 3320 m, near the base of the Jamieson Formation.

A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100 Å, 316 Å and 630 Å indicates a more complex picture (Figure 3.69). For the two smaller pore sizes there is a systematic slight compaction with depth, but otherwise, there is a consistent pore size distribution in the claystones throughout the Jamieson Formation, Echuca Shoals Formation and Vulcan Formation. The exception is an anomalous region in the lower portion of the Jamieson Formation. For the pore size 630 Å, the initial compaction trend seems to be reversed in the Echuca Shoals Formation and Vulcan Formation, and the extent of the anomalous region within the lower Jamieson Formation is increased.

Figure 3.70 illustrates calculated SANS porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. Most of the calculated SANS porosity values are about 4%, with a peak of about 11% at the base of the Jamieson Formation. The calculated SANS porosity values appear high and need to be calibrated against the log porosities. Depth intervals characterised by changed conditions are indicated on the left hand side of the figure. The “K Aptian sandstone equivalent” (3288 m to 3365 m) contains siltstone and sandstone,

123

and shows a low gamma ray signal and a low penetration rate. The depth range 3288 m to 3952 m shows varying, elevated levels of gas. Significant overpressure was recorded within the Echuca Shoals Formation.


Except for the anomaly at the base of the Jamieson Formation within the range 3288 m – 3365 m, the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Gorgonichthys-1 (Figures 3.68 and 3.69). Therefore, the marked variation of the scattering intensity (Figure 3.66) is ascribed to the change of the density and chemical composition of the organic matter contained within the pores, which affects the neutron scattering contrast. As discussed above, the low values of the scattering intensity indicate pores filled with bitumen at the onset of mobile hydrocarbon generation, and the high values are indicative of pores filled with gas, formation brine and/or saturated hydrocarbons. Based on this, two regions of present-day onset of mobile hydrocarbon generation (at different maturity) can be identified (Figure 3.66): (1) at depth of about 2800 - 2900 m (within the upper Jamieson Formation) and (2) within the Echuca Shoals Formation at a depth of about 3900 m.

The increasing SANS intensity with depth within the lower Jamieson Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation. The low scattering intensity within the Echuca Shoals Formation, as compared to the adjacent region in the Jamieson Formation, indicates that there is no communication between the pore spaces of these two sedimentary units. Mud weights indicate overpressuring of this unit (Figure 3.70), which suggests that bitumen and other hydrocarbons generated remain trapped within the formation.

The decreasing intensity trend throughout the Echuca Shoals Formation appears to terminate at the top of sandstone intersected within the depth range 3952 – 4115 m, which may indicate that the sandstone reservoirs mobile hydrocarbons generated within the basal Echuca Shoals Formation. The relatively low scattering intensity throughout the Vulcan Formation indicates that the pores contain significant amount of organic matter with a very low hydrogen-to-carbon ratio, e.g. residual bitumen.

124

Figure 3.65. SANS absolute intensity curves for samples of cuttings from Gorgonichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range is 2520 m to 3220 m. (b): 14 samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3265 m to 4765 m.

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.65(a)Gorgonichthys-1


676 2520m677 2620m678 2720m679 2780m680 2820m681 2870m682 2920m683 2970m684 3020m685 3070m686 3120m687 3170m688 3220m

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Figure 3.65(b)Gorgonichthys-1


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126

Figure 3.66. SANS intensity versus depth at Q=0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Gorgonichthys-1.

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DEPT

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JAMIESON

ECHUCASHOALS

VULCAN

MT GOODWYN

Ro=0.54%

Ro=0.51%

Ro=0.51%

Ro=0.50%

Ro=0.59%

Ro=0.61%

Ro=0.75%Ro=0.81%

Ro=1.02%

Ro=1.03%

Ro=1.15%

Ro=1.12%

2481m2536m

3365m

3911.5m

UPPER

LOWER

4218m

TD 4772m

4467m

4718mPLOVER

3952m

4115m

(cm -1)

Gas Sst

µ0.025 m(250Å)

127

Figure 3.67. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Gorgonichthys-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement.

2000

2500

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3500

4000

4500

5000

4 4.2 4.4 4.6 4.8 5

Gorgonichthys1, Browse BasinScattering length density versus depth

DEP

TH (m

)


128

Figure 3.68. Pore size distribution at various depths for samples of cuttings from Gorgonichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range is 2520 m to 3220 m. (b): 14 samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3265 m to 4765 m.

10-7

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PORE

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)

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129

100 1000PORE SIZE (Å)

3265m3320m3370m3420m3520m3620m3720m3820m3905m4120m4220m4320m4720m4765m

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PORE

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)

130

Figure 3.69. Variation of the pore number density for selected pore sizes versus depth for Gorgonichthys-1. At shallow depths, note slight decrease of the pore number density with depth, indicative of compaction. For full discussion see text.

10-7 10-6 10-5 10-4 10-3 10-2

2000

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PORE NUMBER DENSITY

DEP

TH (m

RT)

r = 630Å 316Å 100Å

JAMIESON

ECHUCASHOALS

VULCAN

PLOVER

MT GOODWYN

WOOLASTON

131

Figure 3.70. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Gorgonichthys-1. For discussion see text.

JAMIESON

ECHUCASHOALS

VULCAN

PLOVER

MT GOODWYN

WOOLASTON

0 5 10 15CALCULATED SANS POROSITY (%)

3322.5m

3288m3365m

3952m


penetration rate



2000

2500

3000

3500

4000

4500

5000

DEP

TH (m

RT)

3.9 Titanichthys-1

The pyrolysis data for Titanichthys-1 is given in Appendix 5 Table A5.9. Figure 3.71 is a compilation of vitrinite reflectance, total organic carbon and the Rock-Eval pyrolysis parameters (Tmax, S1, S2 and HI) plotted against depth (mKB). Figure 3.72 comprises a graph of Tmax versus Hydrogen Index for potential source rock samples.

In addition to the extracted cuttings samples analysed in this study, results of Leco TOC and Rock-Eval pyrolysis analyses for cuttings samples (which were analysed by Geotechnical Services) were available from the well completion report (Inpex, 2001c). Vitrinite reflectance measurements were obtained by Kieraville Konsultants.


Titanichthys-1 was drilled with a water-based drilling mud with gel and polymer additives to a depth of 3905 m. Correspondence with Inpex suggested that glycol additives were also likely to be present in the water-based muds. Below 3905 m Syntech (a synthetic-based mud) was used to the bottom of the well. Irrespective of the drilling mud used, all of the cuttings samples analysed in this study were extracted with methanol and dichloromethane (50:50) as part of the preparative procedure. The cuttings samples analysed by Geotechnical Services were solvent extracted but no details are given in the WCR.

132

Comparison of the datasets from the two laboratories (Fig. 3.71) reveals that the values for TOC and Tmax are comparable, whereas Geotechnical Services recorded higher values for the S1, S2 and HI parameters, indicating that their extraction process has not removed all of the free organic compounds from within the sediments.

After extraction of the sediments with organic solvents, the resultant pyrograms, in most instances, have little or no S1 peaks and well resolved S2 and S3 peaks. This means that the S1 values, and the calculations involving S1 values (BI and PI) are invalid and the presence of naturally occurring free hydrocarbons in the sediments cannot be evaluated. Equally, the other pyrolysis parameters must also be interpreted with caution due to the unreliable nature of the S2 and TOC values.

Bearing in mind the limitations imposed because of the contamination, the following interpretations are an approximate guide to the greatest hydrocarbon potential that the sediments in Titanichthys-1 may have, and the minimum thermal maturity that they may have attained. The samples evaluated for their hydrocarbon potential are identified with a black dot in Figure 3.71, and only these data are plotted on the Tmax versus HI plot in Figure 3.72. It must be stated that there is an offset in the Tmax trend from the depth that the SBM was added (Fig. 3.71). This indicates that SBM contaminants remain within the cuttings samples in Titanichthys-1. Therefore, data from only the samples above 3905 m are interpreted and shown on Figure 3.72.

133

Figure 3.71 Depth plots of vitrinite reflectance, TOC and Rock-Eval pyrolysis data for Titanichthys-1.

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

KB)

(a) (b) (c)

(d) (e) (f)

VR (%)0.4 0.8 1.2 1.6 2.0 400 440 480 1 2 3 4 5

HI (mg/g TOC)800

14/OA/1807

S2 (mg/g Rock)10

S1 (mg/g Rock)

0 0

000

Tmax ( C) TOC (%)

2 4 6 2 4 6 8 200 400 600

WCR sequence

Tertiary

PuffinFormation

FenelonFormationWoolaston Fm

JamiesonFormation




WCR sequence

Tertiary

PuffinFormation

FenelonFormationWoolaston Fm

JamiesonFormation




Titanichthys -1

SBM SBM

SBMSBMSBM

Invalid data

Kieraville

Geotech CUTT extracted (SBM) GA CUTT extracted (SBM)Geotech & GAacceptable SR data

Plover Fm

Plover Fm

Geotech CUTT extracted (glycol) GA CUTT extracted (glycol)


The total organic carbon content gradually increases with depth in Titanichthys-1 until the SBM was used. The samples from both the Lower Cretaceous Jamieson and Echuca

134

Shoals formations appear to range from fair to very good with an average TOC of 1.4% and 2.0%, respectively. The potential yields of the sediments from Titanichthys-1 cannot be discussed due to the removal of the S1 peak by the preparative processes used to eliminate any contamination.


The source quality of the Jamieson Formation ranges from being gas-prone to having the potential to generate some oil (range HI = 34-412 mg hydrocarbons/g TOC; average HI = 232 mg hydrocarbons/g TOC; Fig. 3.72). The Echuca Shoals Formation has similar hydrocarbon potential to the aforementioned formation, with HI values ranging from 122 to 336 mg hydrocarbons/g TOC (average HI = 227 mg hydrocarbons/g TOC). The corresponding TOC contents are around 2 %, hence upon maturation some oil expulsion is predicted.

Figure 3.72 shows that both the Jamieson and the Echuca Shoals formations contain Type II/III, however it is unknown to the extent that the SBM has contributed to the relatively high HI values. From Tmax values the Jamieson Formation is immature to marginally mature, and the Echuca Shoals Formation is presently within the oil window.

Figure 3.72 Tmax versus Hydrogen Index for selected samples from Titanichthys-1.

0 1 2 43 5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

380 400 420 440 460 480 500

0

2

4

6

8

10

12

14

16

18

20

420

430

440

450

460

470

480

0

100

200

300

400

500

600

700

800

(a) (b)

(c)

14/OA/1808

S1 +

S2

(m

g/g

Rock

)

TOC (%)

Good

Very

good

Poor

Poor

Fair

Very good

Good

Fair

Oil

Gas

VR = 1.35%

III

I

II

VR = 0.5%

Oil

Oil + Gas

Gas + Oil

Gas

VR = 0.8%

imm

atu

re

earl

y m

atu

re

matu

re

ove

r m

ature

Immature

Condensatewindow

Oil window


or contamination

1


Production Index

Hydro

gen I

ndex (

mg H

C/g

TO

C)

pre

sent

day

Tm

ax (

C)

Tmax ( C)

Jamieson Formation


Titanichthys -1

Geotech CUTT extracted (SBM)

Geotech CUTT extracted (glycol)

GA CUTT extracted (glycol)

Invalid data

Invalid data

135


Small Angle Neutron Scattering (SANS) analysis was performed on 20 claystone cuttings from the well Titanichthys-1 (Table A1.10 in Appendix 1). These cuttings were collected at 50 m to 100 m intervals between depths 2450 mRT to 3955 mRT.


There is a significant and systematic variation of the scattering intensity with depth. This is illustrated in Figure 3.74 for scattering intensity measured at Q = 0.01 Å -1, which corresponds to a pore size of about 0.025 µm +/-50% (1 Å = 10-10 m; 1 µm = 1000 nm = 10,000 Å). The scattering intensity remains roughly constant within the upper Jamieson Formation and then sharply increases by a factor of 1.9 within the depth range 2750 m to 2855 m, followed by a sharp decrease by a factor of 1.3 at the depth of 2900 m. A second sharp increase by a factor of 1.6 occurs in the lower Jamieson Formation within the depth range 3100 m to 3255 m. At the top of the Echuca Shoals Formation the scattering intensity decreases by a factor of 2, down to its original value in the upper Jamieson Formation and remains roughly constant throughout the Echuca Shoals Formation. There is only one data point in the Upper Vulcan Formation with a value 1.2 times higher than the scattering level within the Echuca Shoals Formation.

Figure 3.75 illustrates the calculated values of SLD versus depth for the inorganic component of the rock matrix in Titanichthys-1. There is little variation (at most 5%) with depth and, consequently, the average value of SLD = 4.38x1010 cm-2 was used in subsequent calculations for Titanichthys-1.

The pore size distributions calculated for various depths from the full SANS curves (Figure 3.76) indicate that there is little variation of the geometry of the pore space with depth, except around the depth of 3250m, near the base of the Jamieson Formation, where an increased number of larger pores is observed.

A detailed analysis of the variation of pore number density (proportional to the pore size distribution) with depth for three pore sizes 100Å, 316Å and 630Å indicates a systematic slight compaction with depth throughout the Jamieson Formation and a systematic expansion throughout the Echuca Shoals Formation (Figure 3.77). There is an anomalous region near the base of the Jamieson Formation, coinciding with the “K Aptian sandstone member” (3234 to 3305 mRT) which has distinct log characteristics and a changed lithology.

Figure 3.78 illustrates calculated porosity (only for the fraction of total porosity within the pore size range 20 Å to 1000 Å) versus depth. SANS porosity has been computed by adding pore volumes obtained by fitting the corresponding SANS scattering intensity curve using an assumption that all pores are filled with a fluid of low scattering length density, like brine, gas or saturated hydrocarbons. Therefore, the calculated SANS porosity values for depths where pores are filled with bitumen are too low. Most of the values are between 4% and 6.5%, with a peak of about 11.5% at the base of Jamieson Formation. The calculated SANS porosity values need to be calibrated against the log porosities. Depth intervals characterised by changed conditions are indicated on the left hand side of the figure. The “Kapt sandstone member” (3234 m to 3305 m) shows a

136

low gamma ray signal and a low penetration rate. Gas readings were somewhat elevated throughout the Echuca Shoals Formation, and within the depth range 4361 m to 4444 m within the Lower Vulcan Formation (not sampled by SANS), particularly high levels of gas were recorded. Significant overpressure was recorded within the Echuca Shoals Formation.


Except for the anomaly at the base of the Jamieson Formation (sample at 3250 m), the microstructure of the inorganic rock fabric changes only slightly throughout the entire depth range studied by SANS in Titanichthys-1 (Figures 3.76 and 3.77). Therefore, the marked variation of the scattering intensity (Figure 3.74) is ascribed to the change of the chemical composition of the organic matter contained in the pores, which affects the neutron scattering contrast.

As discussed above, the low values of the scattering intensity indicate pores filled with bitumen at the onset of hydrocarbon generation, and the high values pores filled with gas, formation brine and/or saturated hydrocarbons. Based on this, three regions of the onset of mobile hydrocarbon generation (at different maturity) can be identified (Figure 3.74): (1) within the upper Jamieson Formation at a depth of about 2500 - 2750 m, (2) within the lower Jamieson Formation at a depth of about 2900 - 3050 m, and (3) possibly within the Echuca Shoals Formation at a depth of about 3650 m. All three generation regions are separated from each other by barriers due either to lack of permeability or markedly different thermal kinetics for transformation of organic matter. The increasing SANS intensity with depth for two hydrocarbon generation regions within the Jamieson Formation indicates progressive cracking of bitumen to mobile hydrocarbons and migration of hydrocarbons to larger pores with increasing depth within the formation.

The low scattering intensity within the Echuca Shoals Formation, as compared to the adjacent region in the Jamieson Formation, indicates that there is no communication between the pore spaces of these two sedimentary units. Mud weights indicate overpressuring at the base of the Jamieson Formation below a depth of 3170 m and of the entire Echuca Shoals Formation (Figure 3.78), which suggests that bitumen and other hydrocarbons generated remain trapped within these units. This may not apply to the base of the Echuca Shoals Formation and to the top of the Upper Vulcan Formation, which are in close proximity to the sandstone intersected within the depth range 3969 – 4197 m. It is possible that the sandstone reservoirs mobile hydrocarbons generated at the base of the Echuca Shoals Formation and at the top of the Upper Vulcan Formation.

In contrast, the permeability barrier apparent within the Jamieson Formation is likely to impede vertical movement of generated hydrocarbons.

137

Figure 3.73. SANS absolute intensity curves for samples of cuttings from Titanichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range 2450 m to 3255 m. (b): seven samples (claystones and one silty claystone, 5 m interval each), depth range 3350 m to 3955 m.

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.73(a)Titanichthys-1


703 2450m704 2550m705 2650m706 2750m707 2800m708 2850m709 2900m710 2950m711 3000m712 3050m713 3100m714 3145m715 3250m

SCAT

TER

ING

INTE

NSI

TY (c

m-1

)


138

0.1

1

10

100

1000

104

105

0.01 0.1 1

Figure 3.73(b)Titanichthys-1


716 3350m717 3450m718 3550m719 3650m720 3745m721 3850m722 3950m

SCAT

TER

ING

INTE

NSI

TY (c

m-1

)


139

Figure 3.74. SANS intensity versus depth at Q = 0.01 A-1 (corresponding to the pore size 25 nm +/-50%, or 0.025 µm +/-50%) for cuttings samples from Titanichthys-1.

2000

2500

3000

3500

4000

45000 200 400 600 800

DEPT

H (m

RT)


WOOLASTON

JAMIESON

ECHUCASHOALS

VULCAN

Ro=0.53%

Ro=0.46%

Ro=0.52%

Ro=0.56%

Ro=0.56%

Ro=0.55%

Ro=0.58%

Ro=0.56%

Ro=0.69%

Ro=0.60%

Ro=0.89%

Ro=1.06%


UPPER

LOWER

3967m

4197m

Sst

(cm-1)

µ0.025 m(250Å)

140

Figure 3.75. Variation of the Scattering Length Density (SLD) for thermal neutrons with depth for Titanichthys-1. SLD values were calculated from the elemental composition as determined by a separate X-ray Fluorescence (XRF) measurement.

2000

2500

3000

3500

4000

4 4.2 4.4 4.6 4.8 5

Titanichthys1, Browse BasinScattering length density versus depth

DEP

TH (m

)


141

Figure 3.76. Pore size distribution at various depths for samples of cuttings from Titanichthys-1. (a): 13 samples (claystones, 5 m interval each), depth range is 2450 m to 3250 m. (b): 12 samples (claystones and claystones plus silty claystones, 5 m interval each), depth range 3350 m to 3950 m.

10-7

10-6

10-5

0.0001

0.001

0.01

0.1

100 1000

Figure 3.76(a)Titanichthys-1

Pore size distributionpart 1: 2450 m to 3250 m

703 2450m704 2550m705 2650m706 2750m707 2800m708 2850m709 2900m710 2950m711 3000m712 3050m713 3100m714 3145m715 3250m

POR

E SI

ZE D

ITR

IBU

TIO

N D

ENSI

TY f(

r)

PORE SIZE (Å)

3250m

142

10-7

10-6

10-5

0.0001

0.001

0.01

0.1

100 1000

Figure 3.76(b)Titanichthys-1

Pore size distributionpart 2: 3350 m to 3950 m

716 3350m

717 3450m

718 3550m

719 3650m

720 3745m

721 3850m

722 3950m

POR

E SI

ZE D

ITR

IBU

TIO

N D

ENSI

TY f(

r)

PORE SIZE (Å)

143

Figure 3.77. Variation of the pore number density for selected pore sizes versus depth for Titanichthys-1. Note the slight decrease of the pore number density with depth, indicative of compaction.

10-7 10-6 10-5 10-4 10-3

2000

2500

3000

3500

4000

PORE NUMBER DENSITY

DEPT

H (m

RT) JAMIESON

ECHUCASHOALS

3250m

r = 630Å 316Å 100Å

UPPERVULCAN

144

Figure 3.78. Variation of apparent porosity (within the pore size range 2 nm to 100 nm) with depth for Titanichthys-1.

2000

2400

2800

3200

3600

4000

4400

4800

0 5 10 15

Figure 3.78Titanichthys-1

Calculated porosity versus depth in pore size range 2nm to 100nm

DE

PT

H (

mR

T)

CALCULATED SANS POROSITY (%)

JAMIESON

ECHUCASHOALS

VULCAN

2402m

3888m

3305m3234m3305m

3888m


penetration rate


4459m

TD 4602m

PLOVER

4274m

UPPER

LOWER4361m4444m

high gasreading

3170m


145

4 Discussion: Well Comparisons

The following four sections document the effect of mud additives on pyrolysis and SANS/USANS results and the effect of sample age on SANS/USANS results by comparing adjacent wells. The last section gives an overall summary of the source potential of the formations in the wells examined in this study.

4.1 Pyrolysis results: Adele-1 compared to Brewster-1A

The use of the glycol additive in the drilling fluid does not appear to have affected the TOC and Tmax results from the unwashed SWCs in Adele-1 when compared to the results obtained from Brewster-1A, drilled using a water-based mud without organic additives. This is shown in Figure 4.1, which plots vitrinite reflectance, TOC and pyrolysis parameters versus depth (mSS). However, a relative increase in the S2 and HI values in the SWCs from Adele-1 are apparent.

The integrity of the data from the extracted cuttings samples from Adele-1 which are not compromised by the extraction process (i.e. S2, Tmax and TOC) is comparable with that of the unwashed cuttings samples from Brewster-1A (Fig. 4.1).

4.2 Pyrolysis results: new Ichthys Field wells compared to Brewster-1A

The wells Dinichthys-1, Gorgonichthys-1, Titanichthys-1 and Brewster-1A are in close proximity and penetrate similar stratigraphy, therefore an indication of the effect that different drilling fluids have on pyrolysis data can be obtained. Dinichthys-1 was drilled with a glycol additive. The Gorgonichthys-1 and Titanichthys-1 wells were drilled with water-based drilling mud, however glycol additives are suspected, from the top of the well until around 3900 m, from which depth SBM was used.

Figure 4.2 compares TOC and pyrolysis data for extracted cuttings samples (with no apparent contamination) from the wells Dinichthys-1, Gorgonichthys-1 and Titanichthys-1 with cuttings samples from Brewster-1A. No data from samples below 3900 m in Gorgonichthys-1 and Titanichtys-1 are plotted, since these samples have obvious contamination from the SBM.

146

Figure 4.1 Comparison of pyrolysis data from nearby wells drilled using water-based mud and without glycol additives. Depth is expressed in mSS.

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

SS)

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

SS)

VR (%)

HI (mg/g TOC)S2 (mg/g Rock)S1 (mg/g Rock)

0.4 0.8 1.2 1.6 2.0 400 440 480 1 2 3 4 5

200 400300100 5001 2 3 4 5 60.5 1.0 1.5 2.0

(a) (b) (c)

(d) (e) (f)

100

(g)

BI20 40 60 80

14/OA/1809

Tmax ( C) TOC (%)0 0

000 0

Brewster-1A, Geotrack

Brewster-1A, Robertson Research

Brewster-1A, GA & RR CUTT

GA sequence

GA sequence

Lower Vulcan Fm

Campanian

JamiesonFormation



PloverFormation

Santonian-Turonian

Lower Vulcan Fm

Campanian

JamiesonFormation



PloverFormation

Santonian-Turonian

Adele-1 Geotech, SWC

Adele-1, Kieraville, SWC

Adele-1, GA CUTT extracted

Although the vitrinite reflectance trends show that the sediments in these wells have obtained comparable levels of thermal maturity, the Tmax values of Gorganichthys-1 and Titanichthys-1 are slightly lower, indicating that drilling additives are still present in the cuttings samples despite solvent extraction. The Tmax trend for Dinichthys-1 and Brewster-1A are comparable.

The TOC trends are fairly comparable, with slightly higher values being obtained in Dinichthys-1, Gorgonichthys-1 and Titanichthys-1 over the depth range 2600-3000 m. In general, the S2 and HI values of the extracted samples from Dinichthys-1, Gorgonichthys-1 and Titanichthys-1 are relatively higher than those from Brewster-1A, in particular over the depth range 3000 – 3400 m. Since these two trends do not coincide, residual contamination may remain within the cuttings samples, resulting in the apparent enrichment of their source quality and increased hydrocarbon potential.

147

Figure 4.2 Comparison of pyrolysis data from near-by wells drilled using different mud systems. Depth is expressed in mSS.

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

SS)

1000

1500

2000

2500

3000

3500

4000

4500

5000

Depth

(m

SS)

(a) (b) (c)

(e) (f)

VR (%)0.4 0.8 1.2 1.6 2.0 400 440 480 1 2 3 4 5

HI (mg/g TOC)200 400300100 500

14/OA/1810

S2 (mg/g Rock)1 2 3 4 5 6

0 0

00

Tmax ( C) TOC (%)

Titanichthys-1, Kieraville

Brewster-1A, Geotrack

Gorgonichthys-1, Kieraville

Dinichthys-1, Kieraville

Brewster-1A, GA & RR (water-based)

Dinichthys-1, GA CUTT extracted (glycol)

Gorgonichthys-1, GA CUTT extracted (glycol or SBM)

Titanichthys-1, GA CUTT extracted (glycol or SBM)

148

4.3 SANS results: new Ichthys Field wells compared to Brewster-1A

The geographical proximity and geological similarities between Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1 (Figure 1.2 and Table 4.1) enables a meaningful comparison between the corresponding sets of SANS data. Furthermore, owing to the various ages of recovered cuttings and different types of drilling mud used (Tables A1.1 and 4.1), the effect of these factors on the quality of SANS data can be examined. In particular, it is well known that certain types of drilling muds and/or contaminants render the results of some geochemical analyses unreliable and the question arises whether the same is true for SANS results.

Figure 4.3 illustrates the variation of scattering intensity with depth normalised to the sea level datum and measured for the four wells at Q=0.01 Å -1. The general character of the intensity versus depth curve is similar for all four wells: low intensity near the top of the Jamieson Formation, a rapid increase towards a maximum value near the base of the Jamieson Formation, a sharp decrease at the top of Echuca Shoals Formation and gradually decreasing values throughout the Echuca Shoals Formation, with local increase at the base of the Echuca Shoals Formation and top of Vulcan Formation (for Titanichthys-1 and Dinichthys-1 only). For Brewster-1A and Titanichthys-1 there is an additional rapid increase - sharp decrease intra-Jamieson cycle.

In Section 3 of this report it is demonstrated that for each individual well the pore number density for pore sizes of about 250 Å does not vary significantly with depth except for the narrow region at the base of the Jamieson Formation (61 m to 84 m thick “K Aptian sandstone member” or “K Aptian sandstone member equivalent”). Bitumen has a scattering length density much larger than brine or gas, and being rather similar to that of the rock matrix, which results in the loss of scattering contrast. Therefore, low values of scattering intensity are interpreted as being caused by the presence of generated bitumen in the pore space. Based on this interpretation, depths of the onset of mobile hydrocarbon generation and expulsion to larger pores (referred to as “onset” below) predicted by SANS are marked in Figure 4.4.

The first onset identified by SANS is located at the top of Jamieson Formation within the depth range 2500 m (Dinichthys-1) to 2900 m (Gorgonichthys-1), depending on the well. In this depth region the vitrinite reflectance values are in the range 0.5% (Dinichthys-1) to 0.54% (Brewster-1A, Keiraville data).

The second onset was identified only in Titanichthys-1 and Brewster-1A and is located in the mid Jamieson Formation within the depth range 2900 – 3100 m. In this depth region the vitrinite reflectance values are in the range 0.52%-0.56% for Titanichthys-1 and 0.54% for Brewster-1A (Keiraville data).

The third onset identified by SANS is located either in the lower Echuca Shoals Formation (Titanichthys-1), basal Echuca Shoals Formation (Dinichthys-1) or the uppermost Vulcan Formation (Gorgonichthys-1 and Brewster-1A) within the depth range 3650 – 3950 m. In this depth region the vitrinite reflectance values are widely spread in the range 0.56% (Titanichthys-1) to 1.03% (Brewster-1A, Gorgonichthys-1).

149

The existence of two (three for Titanichthys-1 and Brewster-1A) SANS-identified onsets of mobile hydrocarbon generation and expulsion to larger pores is interpreted to be due to markedly different kinetics for thermal maturation of organic matter deposited in each of the two (three) hydrocarbon generation units (source rocks).

The overall magnitude of the scattering intensity versus depth is similar for Gorgonichthys-1 and Titanichthys-1, and for Brewster-1A and Dinichthys-1. The absolute SANS intensity differs between these two groups of wells by a factor of two (Figure 4.3), whereas the experimental error for the absolute intensity does not exceed 10% absolute and is much less in relative terms.

The close similarity between SANS data for Brewster-1A (spudded in 1980) and Dinichthys-1 (spudded in 2000) indicates that ageing (weathering) of cuttings stored in sealed plastic bags over a period of many years is most likely not an issue for SANS. This is a very important finding, as it demonstrates that SANS data taken on old cuttings can be reliable. It is possible, however, that the significant scatter of SANS data for Brewster-1A within the Echuca Shoals Formation may be caused by the particle-size-specific ageing of the cuttings, and more specifically may be related to the size variation of the original cuttings particles used for SANS sample preparations. The original cuttings size was not monitored in this work.

The similarity of the SANS data for Gorgonichthys-1 and Titanichthys-1, as opposed to Dinichthys-1, all spudded in 2000, can by interpreted in several ways. Firstly, one reason could be purely geochemical and has to do with differences in the hydrocarbon generation process and/or the composition of bitumen expelled into the pore space. Secondly, the potential influence of the type of drilling mud on the SANS signal needs to be considered. Brewster-1A and Dinichthys-1 were drilled using sea-water based muds, whereas Gorgonichthys-1 and Titanichthys-1 were drilled using synthetic based muds. Although it is unlikely that mud particles could significantly penetrate 150 Å diameter pores in cuttings, such a possibility cannot be entirely discarded.

Out of the four wells, Brewster-1A and Titanichthys-1 are geographically closest to each other (about 5 km). Although they exhibit markedly different SANS intensities, in both wells an intra-Jamieson permeability/kinetics barrier is observed at a depth of about 2900 mRT. There is no indication of such a barrier in Dinichthys-1 and Gorgonichthys-1.

150

Table 4.1 Drilling information and depths of lithological units for Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1.

Formation Brewster-1A Dinichthys-1 Gorgonichthys-1

Titanichthys-1

Water Depth (m) 256 263.6 260 247

RT (m) 8 26.4 26.4 26.4

TD (mRT) 4703 4562 4772 4602

Drilling Mud Salt/Polymer Aquadrill/Pyrodrill

Syntec (SBM) Syntec (SBM)

below 2366 mRT

below 2471 mRT below 2405 mRT

below 2337 mRT

Mud contaminants

diesel fuel glycol, alkenes

Spud Date 23-May-80 3-Mar-00 23-May-00 26-Sep-00

Top Woolaston 2484 2481 2326

(mRT) Jamieson 2430 2516 2536 2402

Echuca Shoals 3311 3424 3365 3305

Upper Vulcan 3863 4008 3911.5 3888

Lower Vulcan 4280 4204.5 4218 4274

Plover 4453 4418.5 4467 4459

Top Woolaston 2457.6 2454.6 2299.6

(m below Jamieson 2422 2489.6 2509.6 2375.6

sea level) Echuca Shoals 3303 3424 3338.6 3278.6

Upper Vulcan 3855 3397.6 3885.1 3861.6

Lower Vulcan 4272 4178.1 4191.6 4247.6

Plover 4445 4392.1 4440.6 4432.6

Thickness (m) Woolaston 32 55 76

Jamieson 881 908 829 903

Echuca Shoals 552 584 546.5 583

Upper Vulcan 417 196.5 306.5 386

Lower Vulcan 173 214 249 185

Plover >250 >143.5 251 >143

151

Figure 4.3. Scattering intensity versus depth (below sea level) for stratigraphic formations in Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1.

0 200 400 600 800

2000

2500

3000

3500

4000

4500

5000


DEP

TH (m

bel

ow s

ea le

vel)

(cm-1)

Br JamiesonBr Echuca ShoalsBr Upper VulcanDi JamiesonDi Echuca ShoalsDi Upper VulcanDi Lower VulcanGo WoolastonGo JamiesonGo Echuca ShoalsGo Upper VulcanGo Lower VulcanGo Mt GoodwynTi JamiesonTi Echuca ShoalsTi Upper Vulcan

µ0.025 m(250Å)

152

Figure 4.4. Interpretation of SANS data for Brewster-1A, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1.

2000

2500

3000

3500

4000

4500

50000 200 400 600 800

DEPT

H (m

Bel

ow S

ea L

evel

) ONSET 1

ONSET 2

ONSET 3

BARRIER

BARRIER

SCATTERING INTENSITY AT Q=0.01Å-1 (cm -1)

Brewster-1 (depth BSL)Dinichthys-1 (depth BSL)Gorgonichthys-1 (depth BSL)Titanichthys -1 (depth BSL)

µ0.025 m(250Å)

4.4 SANS Results: Adele-1 and Crux-1 compared to Brewster-1A

Brewster-1A and Adele-1, both located in the Caswell Sub-basin, are geographically close and geologically similar. Crux-1, which has been drilled in the northern part of the Heywood Graben for a Triassic Nome Formation, is located over the Jurassic rift graben overlaid by a proximal portion of the Cretaceous prograde, and has the Jamieson and Echuca Shoals sections much thinner and the Jurassic section much thicker than the other two wells (Figures 1.2 (well location), 3.5 (Brewster-1A), 3.23 (Adele-1) and 3.38 (Crux-1)). Despite these significant differences, the depth of burial of the upper part of

153

the Jamieson Formation is similar for all three wells, which enables some meaningful comparison between the corresponding sets of SANS data.

Figure 4.5 illustrates the variation of scattering intensity with depth normalised to the sea level datum and measured for the three wells at Q=0.01Å -1. For the Brewster-1A and Adele-1 wells, the general character of the intensity versus depth curve is similar: low intensity near the top of the Jamieson Formation, a rapid increase towards a maximum value in mid-Jamieson Formation, followed by another rapid increase - sharp decrease cycle ending at the bottom of the Jamieson Formation. For the Crux-1 well there is a minimum scattering intensity in mid-Jamieson Formation, clearly visible despite the relatively low sampling density.

In Section 3 of this report it is demonstrated that for each individual well the pore number density for pore sizes of about 250 Å does not vary significantly with depth except for the narrow region at the base of the Jamieson Formation (61 m to 84 m thick “K Aptian sandstone member” or “K Aptian sandstone member equivalent”). Bitumen has the scattering length density much larger than brine or gas, and being rather similar to that of the rock matrix, which results in the loss of scattering contrast. Therefore, low values of scattering intensity are interpreted as being caused by the presence of generated bitumen in the pore space. Based on this interpretation, depths of the onset of mobile hydrocarbon generation and expulsion to larger pores (referred to as “onset” below) predicted by SANS coincide with the minimum values of the scattering intensity.

The first onset identified by SANS is located at the top of Jamieson Formation at the depth of 2700 m for Brewster-1 and 2650 m for Adele-1. In this depth region the vitrinite reflectance values are 0.54% for Brewster-1A (Keiraville data) and 0.52% for Adele-1. The first onset for Crux-1 is located in the mid-Jamieson Formation at the depth of 2400 m and the corresponding vitrinite reflectance value is 0.51%.

The second onset identified in Brewster-1A and Adele-1 is located in the mid-Jamieson Formation at depth of 3050 m and 3200 m, respectively. In this depth region the vitrinite reflectance values are 0.54% for Brewster-1A (Keiraville data) and 0.62% for Adele-1. The second onset for Crux-1 can be identified at the base of the Echuca Shoals Formation at the depth of about 2690 m, with the corresponding vitrinite reflectance value of 0.42% (directly measured, probably suppressed) or 0.80% (from FAMM).

A third onset of hydrocarbon generation has been identified for Crux-1 near the base of the Upper Vulcan Formation (Figure 3.54), with corresponding vitrinite reflectance value of 0.45% (measured directly) or 0.90% (from FAMM). This Formation was not sampled for SANS work neither within Brewster-1A nor Adele-1.

The existence of two Cretaceous SANS-identified onsets of mobile hydrocarbon generation and expulsion to larger pores is interpreted to be due to the markedly different kinetics for thermal maturation of organic matter deposited in each of the two hydrocarbon generation units (source rocks).

The overall magnitude of the scattering intensity versus depth is similar for Brewster-1A and Adele-1, and by a factor of two smaller for Crux-1 (Figure 4.5), whereas the experimental error for the absolute intensity does not exceed 10% absolute and is much less in relative terms.

154

Figure 4.5. Scattering intensity versus depth (below sea level) for stratigraphic formations in Brewster-1A, Crux-1 and Adele-1.

0 100 200 300 400 500 600 700 800

2000

2500

3000

3500

4000

4500

Figure 4.5Comparison of SANS data for three wells

SANS intensity vs depth at Q=0.01Å-1, pore size 250Å+/-50%Br - Brewster-1A, Crux - Crux-1, Adele - Adele-1

Br Jamieson

Br Echuca Shoals

Br Upper Vulcan

Crux Jamieson

Crux Echuca Shoals

Crux Upper Vulcan

Crux Lower Vulcan

Adele Jamieson

SCATTERING INTENSITY AT Q=0.01Å-1 (cm-1)

DE

PT

H (

m b

elow

sea

leve

l)

calcareous?

onset 1 Br

onset 2 Br

4.5 Source Rock Summary

Rock-Eval/TOC source rock data was obtained from the Jamieson Formation from the wells Brewster-1A, Carbine-1, Adele-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1, as is summarised in Figure 4.6. Overall the Jamieson Formation has poor source richness. Although the TOC contents range from 0.6%-2% with average values of 1.3% their potential yields are low (range S1+S2 = 0.4-2.7 mg hydrocarbons/g rock; average S1+S2 = 1.4 mg hydrocarbons/g rock), as summarised from Brewster-

155

1A and Carbine-1 (the other wells had the S1 peak removed). This formation contains Type II/III to Type III kerogen that is immature-marginally mature for hydrocarbon generation (average Tmax = 431oC). However, those samples with HI values between 150-259 mg hydrocarbons/g TOC typically have TOC contents less than 1.8%.

Therefore, based on the pyrolysis results, where sampled the Jamieson Formation is not expected to have generated liquid hydrocarbons. This conclusion is confirmed by SANS/USANS evidence. Although SANS has detected the presence of bitumen in small pores (about 0.01 µm diameter) within two or three different depth intervals within the Jamieson Formation in Adele-1, Crux-1, Gorgonichthys-1, Titanichthys-1, Dinichthys-1 and Brewster-1A, USANS data acquired for the two latter wells clearly indicate that the amount of generated bitumen has been insufficient to saturate the pore space and create an effective source rock. SANS data for Brecknock South-1 and Carbine-1 are inconclusive, as they are masked by the varying source rock lithology and strong compaction signal, respectively.

Rock-Eval/TOC source rock data were obtained for the Echuca Shoals Formation from the wells Brewster-1A, Carbine-1, Crux-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1. Overall the Echuca Shoals Formation has poor source richness. Although the TOC contents range from 0.6%-2.8% with average values of 1.8% their potential yields are low (range S1+S2 = 0.9-4.8 mg hydrocarbons/g rock; average S1+S2 = 2.4 mg hydrocarbons/g rock), as observed in Brewster-1A and Carbine-1 (the other wells had the S1 peak removed). This formation contains Type II/III to Type III kerogen that is early mature for hydrocarbon generation (average Tmax = 441oC). The samples with HI values between 150-264 mg hydrocarbons/g TOC typically have TOC contents between 1% and 2.8%.

Therefore, based on the pyrolysis results, some liquid hydrocarbons could have been generated within the Echuca Shoals Formation. SANS has detected the presence of bitumen in small pores (about 0.01 µm diameter) within the Echuca Shoals Formation in Adele-1, Crux-1, Gorgonichthys-1, Titanichthys-1, Dinichthys-1 and Brewster-1A. SANS data for Brecknock South-1 and Carbine-1 are inconclusive, as they are masked by the varying source rock lithology and strong compaction signal, respectively. USANS data, which are crucial for detecting the presence of bitumen in largest pores and, therefore, determine whether hydrocarbon expulsion could occur, have only been acquired for two wells: Dinichthys-1 and Brewster-1A.

Combined SANS/USANS data for Dinichthys-1 show the presence of generated bitumen in pores of all sizes near the base of the Echuca Shoals Formation, but not at the depths adjacent to the Berriasian 'Brewster' Sandstone, which is an important reservoir rock. That is, hydrocarbons generated in the Echuca Shoals Formation do not appear to have been expelled into the Berriasian Sandstone reservoir. This is consistent with previous findings based on oil-source correlation that the Berriasian Sandstone reservoirs have not been charged from Early Cretaceous source rocks. In Brewster-1A there is SANS/USANS evidence of pore-size-specific oil-to-gas cracking within the Echuca Shoals Formation.

Based on pyrolysis data, the most oil-prone source rocks are apparently found in Gorgonichthys-1 and Titanichthys-1, however there is the possibility that these samples may still contain residual contaminants from the drilling mud.

156

The only source rock data available for the Upper and Lower Vulcan formations and the Montara Formation are from Crux-1, therefore no comparisons could be made to other wells.

Figure 4.6 Comparison of source rock data from Browse Basin study wells.

380 400 420 440 460 480 5000

100

200

300

400

500

600

700

800

VR = 1.35%

III

I

II

VR = 0.5%

Oil

Oil + Gas

Gas + Oil

Gas

VR = 0.8%

imm

atu

re

earl

y m

atu

re

matu

re

ove

r m

ature

Hydro

gen I

ndex (

mg H

C/g

TO

C)

pre

sent

day

Tmax ( C)

Jamieson Formation

Browse Basin Source Rocks


Upper Vulcan Formation


14/OA/1811

157

5 Conclusions

Modern drilling practices typically involve the addition of organic compounds to water-based muds, such as glycol, or the use of SBMs. Not all WCRs list the total additives used while drilling the well, as highlighted by the wells Dinichthys-1, Gorgonichthys-1 and Titanichthys-1. Organic additives present in the sediment samples have a significant effect on TOC and Rock-Eval pyrolysis results; notably low and variable Tmax values, high S1, S2, TOC, HI and BI values. Such results can lead to an underestimation of thermal maturity and an overestimation of hydrocarbon source potential.

Extraction of samples obtained from mud systems using glycol additives or SMBs with organic solvents removes any organic compounds present to varying degrees. The amount of contamination remaining in the sample depends on the initial concentration of the contaminant, the porosity and permeability of the rock sample and the rigorousness of the extraction process. This means that the validity of the TOC and pyrolysis data is still questionable even after solvent extraction.

A full set of data is routinely reported in WCRs for samples that have been extracted with solvents. However, the S1 abundances of the extracted samples are invalid because any naturally occurring free hydrocarbons (as well as contaminants) are removed during the extraction process. Therefore, the S1 and the derivatives, BI and PI cannot be used for source rock evaluation. Since the kerogen in the rock is unaffected by the solvent extraction process, the S2 and derivatives Tmax and HI values should reflect the maturity and source quality of the sediment. In reality, Tmax trends seem to be fairly reliable regardless of the drilling fluid used. However, widely varying TOC, S2 and HI values were obtained from the extracted samples due to contaminants remaining in the sample. Generally, SWC samples were less affected by contaminants than cuttings samples, as shown by the results from Adele-1.

In summary, reliable TOC and pyrolysis data were obtained for Brewster-1A and Carbine-1 which were used in the evaluation of the source potential of the Lower Cretaceous Jamieson and Echuca Shoals formations. Data that were used with caution were obtained from Adele-1, Crux-1, Dinichthys-1, Gorgonichthys-1 and Titanichthys-1. No useable data were obtained from Argus-1 and the data from Brecknock South-1 were not used in the source rock evaluations due to the lower than expected Tmax values.

The Lower Cretaceous Jamieson Formation and Echuca Shoals Formation have similar TOC contents with averages of 1.3% and 1.8%, respectively. Evaluation of their source richness could only be made from the wells Brewster-1A and Carbine-1, since all other samples in the study were extracted, removing the S1 peak. The data from these wells showed that the sediments had poor generative potential with average S1+S2 values less than 3 mg hydrocarbons/g rock. They contain Type II/III to Type III kerogen. The samples from the Jamieson Formation with HI values between 150-259 mg hydrocarbons/g TOC typically have TOC contents less than 1.8%. This, coupled with their lack of thermal maturity implies that this formation has not generated and expelled hydrocarbons. The samples from the Echuca Shoals Formation with the highest source rock quality have sufficient maturity to have generated and expelled some liquid hydrocarbons.

158

In contrast to Rock-Eval/TOC, drilling mud contamination does not seem to affect SANS/USANS data. Similarly, natural weathering of cuttings stored in sealed plastic bags seems to have little effect (Brewster-1A was drilled in 1980). SANS/USANS results, however, can be strongly affected by microstructural variations caused either by varying sample lithology (Brecknock South-1) or strong compaction caused by shallow burial (Carbine-1). SANS interpretation is also inconclusive for overmature source rocks (Argus-1). For the remaining six wells there is SANS evidence of bitumen generation in the small pores both within the Jamieson Formation and the Echuca Shoals Formation. Depending on the well, there are two or three distinct generative depth intervals within the Jamieson Formation, separated by permeability barriers.

USANS data for Brewster-1A and Dinichthys-1 indicate that there is insufficient bitumen saturation of larger pores in the Jamieson Formation to create an effective source rock. Within the Echuca Shoals Formation, for Dinichthys-1 there is USANS evidence of bitumen presence in pores of all sizes, but not at depths adjacent to the Berriasian ‘Brewster’ Sandstone. There is also USANS evidence of oil-to-gas cracking for Brewster-1A within the Echuca Shoals Formation.

159

6 Recommendations and Further Work

1. Modify Extraction Method. Since the glycol contaminant contains a high proportion of alkenes, and the Rock-Eval pyrolysis results appear to be still effected by the contaminant, the washing process should be modified to include an additional wash with petroleum ether to remove the alkenes. However, this residual contamination may reside in smaller, water-wet pores. If this is the case, the petroleum ether will not be able to penetrate the sediments. An alternative extraction method would be to use the Accelerated Solvent Extractor (ASE), as this uses higher temperatures and generally facilitates a higher extraction yield. After extracting the samples by these two methods, use USANS to examine the efficiency of the extraction process in the larger pores.

2. Effect of glycol on S3 peak. Determine whether glycol decomposes at < 390oC to liberate CO2, and hence determine if the S3 peak is affected despite the Oxygen Index being low in both contaminated and uncontaminated samples.

3. Oil-source rock correlations. Prior to any oil-source rock correlations being run, the composition of the drilling fluid contaminants should be determined and an assessment made of the extent that these contaminants will interfere with biomarker and isotopic measurements which are used as the primary source characterisation parameters. The aromatic components of the drilling fluid need to be assessed to determine their influence on maturity parameters. Geotechnical Services have produced a commercial report “Drilling fluids and mud additives: their impact on the interpretation of geochemical data”, which documents the chemical compositions of typical fluids used to drill Australian wells. This report will assist in the identification of contaminant compounds. If oil-source rock correlations are carried out on the Jamieson and Echuca Shoals formations, the best samples would be from the wells around the Brewster Field. The Upper and Lower Vulcan Formation could be sampled from Crux-1. However, the effect of the drilling contaminants on the geochemical parameters must first be ascertained.

4. Kinetic Analysis. Carry out kinetic analysis to define the thermal maturity required to generate hydrocarbons from the Jamieson Formation compared with kerogen from the Echuca Shoals Formation.

5. Importance of combined SANS/USANS studies. The abundance, quality and maturity of the kerogen in the source rocks interpreted from conventional Rock-Eval pyrolysis data needs to be compared with the SANS/USANS results to verify which source rocks have generated and expelled liquid hydrocarbons. This study demonstrates that most conclusive results can be obtained when both SANS (generation) and USANS (saturation and expulsion) data are available.

160

161

7 References

Blevin, J.E., Struckmeyer, H.I.M., Cathro, D.L., Totterdell, J.M., Boreham, C.J., Romine, K.K., Loutit, T.S. and Sayers, J. (1998a). Tectonostratigraphic framework and petroleum systems of the Browse Basin, North West Shelf. In: Purcell, P.G. and R.R. (eds) The Sedimentary Basins of Western Australia 2. Proceedings of Petroleum Exploration Society of Australia Symposium, Perth, WA, 369-396.

Blevin, J.E., Boreham, C.J., Summons, R.E., Struckmeyer, H.I.M. and Loutit, T.S. (1998b). An effective Early Cretaceous petroleum system on the North West Shelf: evidence from the Browse Basin. In: Purcell, P.G. and R.R. (eds) The Sedimentary Basins of Western Australia 2. Proceedings of Petroleum Exploration Society of Australia Symposium, Perth, WA, 397-420.

Clementz, D.M. (1979). Effect of oil and bitumen saturation on source-rock pyrolysis. AAPG Bulletin 63, 2227-2232.

Espitalié, J. and Bordenave, M.L. (1993). Rock Eval pyrolysis. In: Bordenave, M.L. (ed) Applied PetroleumGeochemistry. Éditions Technip, Paris, 237-261.

Espitalié, J., Madec, M. and Tissot, B. (1980). Role of mineral matrix in kerogen pyrolysis: influence on petroleum generation and migration. AAPG Bulletin 64, 59-66.

Espitalié, J., Deroo, G. and Marquis, F. (1985). Rock-Eval pyrolysis and its applications. Rev. Inst. Franç, Pétr., Ref. 32961, vol. 2.

Hainbuchner M., Villa M., Kroupa G., Bruckner G., Baron M., Amenitsch H., Seidl E. and Rauch H. (2000) The new high resolution ultra small-angle neutron scattering instrument at the High Flux Reactor in Grenoble. J. Appl. Cryst. 33, 851-854.

Horsfield, B and Douglas, A.G. (1980). The influence of minerals on the pyrolysis of kerogens. Geochim. Cosmochim. Acta 44, 1119-1131.

Horsfield, B. (1984). Pyrolysis studies and petroleum exploration. In: Brooks, J. and Welte, D.H. (eds) Advances in Petroleum Geochemistry, Academic, London, vol. 1, pp. 247-298.

Orr, W. L. (1983). Comments on pyrolytic yield in source rock evaluation. In: Bjorøy, M. et al. (eds) Advances in Organic Geochemistry 1981, Wiley, Chichester, pp. 775-787.

Peters, K.E. (1986). Guidelines for evaluating petroleum source rock using programmed pyrolysis. AAPG Bulletin 70, 318-329.

Radlinski, A.P., Kennard J.M., Edwards D.S., Hinde A.L. and Davenport, R. (2004). Hydrocarbon generation and expulsion from Early Cretaceous source rocks in the Browse Basin, North West Shelf, Australia: a small angle neutron scattering study. APPEA Journal 2004, 151-180.

Radlinski, A.P. (2006). Small angle neutron scattering and the microstructure of rocks. Rev. Mineral. Geochem. (in press)

Robertson Research Australia Pty. Ltd. (1986). Northwest Shelf, Australia – Phase II. Petroleum Geology and Geochemistry. Volume 3: Well Summary Reports.

162

Thiyagarayan, P., Urban, V., Littrell, K., Ku, C., Wozniak, D.G., Belch, H., Vitt, R., Toeller, J., Leach, D., Haumann, J.R., Ostrowski, G.E., Donley, L.I., Hammonds, J., Carpenter, J.M., and Crawford, R.K. (1998). The performance of the small-angle diffractometer SAND at IPNS. ICANS-XIV, 14th Meeting of the International Collaboration on Advanced Neutron Sources, June 14-19 1998, Starved Rock Lodge, Utica, Illinois.

Well Completion Reports

Brewster-1A WA-35-P Well Completion Report (1980). Woodside Offshore Petroleum Pty. Ltd.

Well Completion Report Adele-1 WA-35-P (1February 1999). Shell Development (Australia) Pty. Ltd.

Argus-1, AC/P30 Well Completion Report (February 2001). Prepared by C. Ellis, BHP Petroleum Pty. Ltd.

Brecknock South-1 Well Completion Report (March 2001). Woodside Australian Energy.

Carbine-1, Well Completion Report WA-283-P, Browse Basin, Western Australia (April 2002). Santos Ltd.

Crux-1 Final Geological Report Volume 1, AC/P23 Territory of Ashmore and Cartier (March 2001). Nippon Oil Exploration (Vulcan) Pty. Ltd.

Well Completion Report Dinichthys-1 (WA-285-P, Browse Basin) (May 2001a). Inpex Browse Ltd.

Well Completion Report Gorgonichthys-1 (WA-85-P, Browse Basin) (May 2001b). Inpex Browse Ltd.

Well Completion Report Titanichthys-1 (WA-85-P, Browse Basin), (May 2001c). Inpex Browse Ltd.

163

APPENDICES

164

165

Appendix 1: List of Wells, Samples and Depository Sequences

Table A1.1 List of wells studied in this project.

Well name, water depth, company,

spud dateHydrocarbon type

Drilling mud type

SANS sample depth range (mRT), Formation names

Adele 1 (243m)

Shell, 7/98 gas + oil shows

water-based:KCl/PHPA/

glycol

2530m - 3405m (Jamieson Formation equivalent)

Argus 1 (572m)

BHP Petroleum, 8/2000

gas discovery (non-commercial)


glycol

4270m - 4535m (Jamieson & top Vulcan)

Brecknock South 1(423.7m)

Woodside, 8/2000gas/condensate

discovery

water-based:glycol

3530m - 3995m(Jamieson, Echuca Shoals,

Vulcan, Plover)

Brewster 1A (256m)

Woodside, 5/1980gas discovery

water-based:brine polymer


Upper Vulcan)

Carbine 1 (54.4m)

Santos, 11/2001dry?

water-based:KCl/PHPA

1349m -1559m(Jamieson, Echuca Shoals)

Crux 1 (168m)

Nippon Oil, 4/2000gas discovery


glycol/Alplex


Upper Vulcan, Lower Vulcan)

Dinichthys 1(263.6m)

Inpex Browse, 3/2000gas/condensate

discovery

seawater/gel/KCl to 4100m; Aquadrill below

4100m


Upper Vulcan, Lower Vulcan)

Gorgonichthys 1(260m)

Inpex Browse, 5/2000 gas/condensate discovery

seawater/gel/KCl to 3950m; Syntech (SBM) below 3950m


Upper Vulcan, Lower Vulcan, Mt.Goodwyn)

Titanichthys 1 (247m)Inpex Browse, 9/2000 gas/condensate

discovery

seawater/gel/KCl to 3900m; Syntech (SBM) below 3900m


Upper Vulcan)

166

Table A1.2 Samples analysed in this study from Adele-1

AGSO No Upper Depth

Lower Depth

Sample type

FormationWCR

SequenceGA

Lithology Drilling Fluid

(mDF) (mDF)

20020066 2580 2585 CUTT Upper Heywood 12C Cl KCl/PHPA/glycol












20020079 3220 3225 CUTT Upper Heywood 12B Cl KCl/PHPA/glycol

20020080 3280 3285 CUTT Upper Heywood 12B Cl KCl/PHPA/glycol

20020081 3320 3325 CUTT Upper Heywood 12A Cl KCl/PHPA/glycol



Table A1.3 Samples analysed in this study from Argus-1

AGSO No Upper Depth

Lower Depth

Sample Type

FormationWCR

SequenceGA


(mRT) (mRT)

20020101 4270 4275 CUTT Jamieson 12 Cl KCl/PHPA/glycol







20020108 4535 4540 CUTT Jamieson 8/9 Cl KCl/PHPA/glycol

167

Table A1.4 Samples analysed in this study from Brecknock South-1

AGSO No Upper Depth

Lower Depth

Sample Type

FormationWCR

SequenceGA


(mRT) (mRT)20020091 3530 3535 CUTT Jamieson 12 Cl M glycol

20020092 3565 3570 CUTT Jamieson 12 Cl glycol

20020093 3585 3590 CUTT Echuca Shoals 11 Cl glycol





20020098 3770 3775 CUTT Vulcan 10 Cl glycol

20020099 3800 3805 CUTT Vulcan 8A Cl glycol

20020100 3995 4000 CUTT Plover 5A Cl F glycol

Table A1.5 Samples analysed in this study from Brewster-1A

AGSO No Upper Depth

Lower Depth

Sample Type

Formation(Equiv GA)

SequenceGA


(mRT) (mRT)20010654 2450 2455 CUTT Jamieson 12C Cl Brine polymer

20010655 2500 2505 CUTT Jamieson 12C Cl Brine polymer







20010662 2950 2955 CUTT Jamieson 12B Cl Brine polymer

20010663 3000 3005 CUTT Jamieson 12B Cl Brine polymer

20010664 3050 3055 CUTT Jamieson 12A Cl Brine polymer




20010669 3390 3395 CUTT Echuca Shoals 11 Cl Brine polymer






20010675 4230 4235 CUTT Upper Vulcan 8C Cl Brine polymer

168

Table A1.6 Samples analysed in this study from Carbine-1

AGSO No Upper Depth

Lower Depth

Sample Type

FormationWCR

SequenceGA


(mRT) (mRT)20020084 1349 1352 CUTT Jamieson nd Cl KCl/PHPA

20020085 1388 1391 CUTT Jamieson nd SltCl KCl/PHPA

20020086 1439 1442 CUTT Jamieson nd Cl KCl/PHPA

20020087 1478 1481 CUTT Jamieson nd Cl KCl/PHPA

20020088 1499 1502 CUTT Jamieson/ Echuca Shoals

nd SltCl KCl/PHPA

20020089 1517 1520 CUTT Echuca Shoals nd Cl KCl/PHPA

20020090 1559 1561 CUTT Echuca Shoals nd Cl KCl/PHPA

Table A1.7 Samples analysed in this study from Crux-1

AGSO No Upper Depth

Lower Depth

Sample Type

FormationWCR

SequenceGA


(mRT) (mRT)

20020109 2390 2400 CUTT Jamieson 12C Cl KCl/PHPA/glycol/20020110 2450 2460 CUTT Jamieson 12C Cl Alplex20020111 2500 2510 CUTT Jamieson 12C Cl KCl/PHPA/glycol/20020112 2550 2560 CUTT Jamieson 12C Cl Alplex20020113 2570 2580 CUTT Jamieson 12C Cl KCl/PHPA/glycol/20020114 2600 2610 CUTT Echuca Shoals 11 Cl Alplex20020115 2650 2660 CUTT Echuca Shoals 10 Cl KCl/PHPA/glycol/20020116 2690 2700 CUTT Upper Vulcan 9 SltCl Alplex20020117 2775 2780 CUTT Upper Vulcan 8C SltCl KCl/PHPA/glycol/20020118 2805 2810 CUTT Upper Vulcan 8C SltCl Alplex20020119 2850 2855 CUTT Upper Vulcan 8C SltCl KCl/PHPA/glycol/20020120 2900 2905 CUTT Upper Vulcan 8B SltCl Alplex20020121 2945 2950 CUTT Upper Vulcan 8B SltCl KCl/PHPA/glycol/20020122 2990 2995 CUTT Upper Vulcan 8B SltCl Alplex20020123 3055 3060 CUTT Upper Vulcan 8B SltCl KCl/PHPA/glycol/20020124 3110 3115 CUTT Upper Vulcan 8B SltCl Alplex20020125 3150 3155 CUTT Upper Vulcan 8B SltCl KCl/PHPA/glycol/20020126 3200 3205 CUTT Lower Vulcan 8A SltCl Alplex20020127 3270 3275 CUTT Lower Vulcan 8A SltCl KCl/PHPA/glycol/20020128 3325 3330 CUTT Lower Vulcan 8A SltCl Alplex20020129 3359 3362 CUTT Lower Vulcan 8A SltCl KCl/PHPA/glycol/20020130 3400 3405 CUTT Lower Vulcan 8A Cl Alplex20020131 3460 3465 CUTT Lower Vulcan 8A Cl KCl/PHPA/glycol/20020132 3500 3505 CUTT Lower Vulcan 8A Cl Alplex20020133 3550 3555 CUTT Montara 8A Cl KCl/PHPA/glycol/

Alplexswc:20020134 2599.6 2599.6 SWC Echuca Shoals 11 Cl KCl/PHPA/glycol/20020135 2691.5 2691.5 SWC Upper Vulcan 9 SltCl Alplex20020136 3155.5 3155.5 SWC Lower Vulcan 8B SltCl KCl/PHPA/glycol/20020137 3266.6 3266.6 SWC Lower Vulcan 8A SltCl Alplex20020138 3471.1 3471.1 SWC Lower Vulcan 8A Cl KCl/PHPA/glycol/

Alplex

169

Appendix 1: Table A1.8 Samples analysed in this study from Dinichthys-1

AGSO No Upper Depth

Lower Depth

Sample Type

FormationWCR

Sequence Lithology Drilling Fluid

(mRT) (mRT) GA

20010723 2550 2555 CUTT Jamieson 12C Cl Seawater/gel/KCl










20010733 3045 3050 CUTT Jamieson 12A Cl Seawater/gel/KCl




20010737 3350 3355 CUTT Jamieson 11 Cl Seawater/gel/KCl

20010738 3450 3455 CUTT Echuca Shoals 11 Cl Seawater/gel/KCl


20010740 3640 3650 CUTT Echuca Shoals 11 Slt Seawater/gel/KCl

20010741 3760 3765 CUTT Echuca Shoals 11 SltCl Seawater/gel/KCl



20010744 4040 4045 CUTT Upper Vulcan 9 SltCl Seawater/gel/KCl

20010745 4190 4195 CUTT Upper Vulcan 9 Cl Aquadrill

20010746 4285 4290 CUTT Lower Vulcan 8C Cl+some Slt

Aquadrill

20010747 4345 4350 CUTT Lower Vulcan 8C Cl+some Slt

Aquadrill/Pyrodrill

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Appendix 1: Table A1.9 Samples analysed in this study from Gorgonichthys-1

AGSO No Upper Depth

Lower Depth

Sample Type

FormationWCR

Sequence GA


(mRT) (mRT)

20010676 2520 2525 CUTT Woolaston 12C Cl Seawater/gel/KCl




20010680 2820 2825 CUTT Jamieson 12B Cl Seawater/gel/KCl


















20010698 4120 4125 CUTT Upper Vulcan 9 Cl+Slt Syntech (SBM)

20010699 4220 4225 CUTT Lower Vulcan 8B Cl+SltCl Syntech (SBM)

20010700 4320 4325 CUTT Lower Vulcan 8A Cl+SltCl Syntech (SBM)

20010701 4720 4725 CUTT Mt Goodwin 4 Cl Syntech (SBM)

20010702 4765 4770 CUTT Mt Goodwin 4 Cl Syntech (SBM)

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Table A1.10 Samples analysed in this study from Titanichthys-1

AGSO No Upper Depth

Lower Depth

Sample Type

FormationWCR

SequenceGA


(mRT) (mRT)20010703 2450 2455 CUTT Jamieson Cl 13 Seawater/gel/KCl

20010704 2550 2555 CUTT Jamieson Cl 12C Seawater/gel/KCl






20010710 2950 2955 CUTT Jamieson Cl 12B Seawater/gel/KCl

20010711 3000 3005 CUTT Jamieson Cl 12B Seawater/gel/KCl

20010712 3050 3055 CUTT Jamieson Cl 12A Seawater/gel/KCl




20010716 3350 3355 CUTT Echuca Shoals Cl 11 Seawater/gel/KCl






20010722 3950 3955 CUTT Upper Vulcan SltCl 9 Syntech (SBM)

Sample type: Cutt - cuttingsswc - side-wall-core

Lithology key:Cl - claystone Cl F - fluvial claystone Cl M - marine claystoneSlt - siltstoneSltCl - silty claystone

Water-based drilling muds and additive: Alplex Aquadrill - complex polymerFlowzan - xanthan gum biopolymerKCl - potassium chlorideGuar gum - spud mud viscosifierPHPA - partially hydrolyzed polyacrylamidesGlycol Pyrodrill

Synthetic and oil-based muds:SyntechSynthetic-based mud

172

Table A1.11. Depository sequences for nine wells in the Browse Basin. Part 1 - Geoscience Australia classification of depository sequences. Part 2 - depository sequences as in Well Completion Reports. All depths are in mRT.

Sequence Top (Geoscience Australia classification)

Adele-1 Brecknock South-1

Brewster-1A

Crux -1

Gorgonichthys-1

Tertiary 287 450 264 194.5 286.8

Maastrichtian 1680 3350 1627 1509 1818

Campanian 1990 3376 1820 1824 1991

Santonian -Turonian

2372 3440 2020 1960 2267

Jamieson Fm (Turonian - Aptian)

2527 3525 2350 2388 2481

Echuca Shoals Fm (Aptian - Valanginian)

3445 3575 3345 2591 3365

Upper Vulcan Fm (Valanginian - Tithonian)

4055 3776 3868 2690 3880

Lower Vulcan Fm (Tithonian - Callovian)

4337 3782 4335 2900 4218

Plover Fm (below Callovian)

4362 3810 4465 3593 4467

Sequence Top (after WCR)

Argus Sequence Top (after WCR)

Carbine 1 Sequence Top (after WCR)

Din-ichthys

Titan-ichthys 1

Tertiary 594 Tertiary 107 Tertiary 290 273.4

Bathurst Island Group

4021 Prudhoe Deltaics Member (MidMaastrichtian)

922 Puffin Fm(Maastrichtian-Campanian)

1847 1662

Intra-Campanian

4218 Borde Marl(Late Campanian-Early Maastrichian)

1135 Fenelon Fm (Santonian-Turonian)

2262 2055

Jamieson Fm 4242 Puffin Sandstone(Early Campanian)

1263 Woolaston Fm(Cenomanian)

2484 2326

EchucaShoals Fm

absent Fenelon Fm (Santonian-Turonian)

1340 Jamieson Fm(Cenomanian- Albian)

2516 2402

Vulcan Fm 4535 Jamieson Fm(Cenomanian)

1343 Echuca Shoals Fm (Barremian-Valanginian)

3424 3305

Plover Fm not confrmd

Echuca Shoals Fm(Aptian - Cenomanian)

1500 Upper VulcanFm (Berrasian)

4008 3888

undifferentiatedvolcanics

4700 Lower VulcanFm (Tithonian-Oxfordian)

4204 4274

Plover Fm(Callovian -Bajocian)

4418.5 4528

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Appendix 2: Analytical Procedures

A2.1 Comparison of the Small Angle Scattering and Geochemical Methods

Table A2.1 Comparison of the SAS and geochemical methods.

Diagnostic function Small Angle Scattering Geochemistry

General

Microstructure of rock matrix (inorganic or organic):

pore size distribution (1 nm to 20 µm across)

specific internal surface area pore content non-invasive, cores and/or cuttings absolutely calibrated

Composition of organic matter: amount of OM kinetics of thermal

decomposition molecular composition

(including biomarkers): oil-source correlation

isotopic composition (C, H, O ,S): gas-oil correlation

invasive - crushed rocks, extracts

lab protocol dependent

Hydrocarbon source rock applications

Petroleum fill-spill history: direct evidence organic matter type independent timing of oil generation, oil

expulsion, oil-to-gas cracking presence of hydrocarbons in pores

(mudrocks) organic matrix reorganisation

(coals) pore size specific - follows h/c

migration within the pore network of a source rock

Petroleum fill-spill history: indirect evidence organic matter type dependent timing of oil generation, oil

expulsion, oil-to-gas cracking sum-of-pores information

Hydrocarbon reservoir rock and seal applications

hydrocarbon saturation in reservoir/seal rocks

porosity/permeability in reservoir rocks

seal capacity

hydrocarbon saturation in reservoir /seal rocks

Sensitivity to contamination by drilling muds

Not evident Strong (S1, S2, Tmax)

174

A2.2 SANS/USANS Sample Preparation (extracted from Geoscience Australia Sedimentology Laboratory Operating Procedure)

Authors: Neil Ramsay, Alex McLachlan and Tony Watson

1.0 Introduction

The SANS (Small Angle Neutron Scatter) sample procedures are used in the Sedimentology laboratory to prepare samples for SANS analysis.

2.0 Purpose

The purpose of this SOP is to:

- Communicate the hazards associated with this operation,

- document the control measures that will be used to control the hazards,

- document the protocols, methodology and procedures involved in performing the operation,

- document the precautions and limitations applicable to this operation, and

- define the required qualifications of personnel performing the operation.

3.0 Scope

The scope of this SOP covers all aspects of work undertaken in the Sedimentology Laboratory (Petroleum and Marine Division) at Geoscience Australia’s Canberra facilities relating to the SANS preparation procedures. Equipment used includes a mortar and pestle, compessed air, drying oven, ultrasonic bath, disposable sieving mesh, electronic balance (accurate to four decimal places), a set of aluminium sieve rings (100mm diameter), low viscosity epoxy resin, Buehler Isomet 1000 precision saw and a micometer.

4.0 Responsibilities

This document and procedures are the responsibility of Geoscience Australia.

5.0 Hazards

Hazards concerning this SOP include:

- Excessive noise when using compressed air to dry/clean equipment,

- samples can possibly contain coliforms and/or other harmful micro-organisms,

- fine dust particles when grinding or cleaning equipment,

- Occupational Overuse Syndrome (OOS),

- Epoxy fumes

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6.0 Hazard Control Measures and Limitations

6.1 Personal Protective Equipment (PPE) Control Measures

- Laboratory coat must be worn at all times in laboratory,

- ear protection is to be used at all times when noise is excessive,

- cotton gloves are to be worn at all times when in contact with sample for this proceedure,

- face shield or safety glasses are to be worn when using compressed air,

- lab coat, gloves and safety glasses must be worn when using potting epoxy,

- Store and use Epoxy in a well ventilated area.

6.2 Administrative Control Measures

- Operator must have read and be familiar with operating instructions for all equipment and this SOP,

- Geoscience Australia’s OH&S and OOS policies.

7.0 Procedural Steps

Grinding

IMPORTANT NOTE: When performing any procedures or analysis on SANS samples it is imperative that cotton gloves are worn. This is to avoid organic contamination of samples.

1. Enter all samples and attached information into pallab database and print off a running spread sheet to work off in the lab.

2. Weigh all of the samples as a bulk weight and record on running spread sheet.

3. Set out the samples on sufficient bench space according to their pallab numbers.

4. For every sample allocate three (3) 20ml vials. These will be labelled coarse fraction, SANS fraction, and fine fraction as well as their respective lab numbers etc. If sub samples are required for geochemistry and palynology then an addition two (2) labelled vials will be needed for these.

5. Use 100mm diameter aluminium sieve rings with base and lid to sieve material, no crushing of sample in the first instance. Place 475um disposable sieve mesh on top ring and 355um disposable mesh on bottom ring (see diagram 1.0) place sample on top mesh attach lid and shake gently.

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Diagram 1.0 – set up of sieving apparatus

6. Remove the top dividing ring and pour the coarse fraction of the sample into the mortar.

7. Carefully grind the coarse fraction so that more of it will pass through the sieve cloth. This needs to be done very gently and slowly if there is a limited amount of sample available. Return the coarse sample back to the sieve mesh and repeat the shaking of the sieve.

8. Repeat this process until there is between 1.5 & 2gms of the SANS fraction, do not process whole sample once target SANS yield (<475um >355um) is met.

9. Dismantle the sieving apparatus and transfer the SANS fraction to a piece of weighing paper. Ensure that this is done over clean white paper to catch any falling pieces of sample.

Note: dismantle sieves slowly and carefully, keeping hold of the sieve cloth as the ring and cloth may pop out unexpectedly.

10. Weigh SANS fraction then transfer to a glass vial. Record this final weight in the running spreadsheet.

11. Repeat this weighing process for the remaining coarse and fine fractions making sure that the weighing paper is clean between each. In some instances to reach target yield the coarse fraction may be entirely processed. Discard the used sieve cloths and weighing paper.

12. Clean the bench space to prevent contamination. Clean the mortar and pestle, and the sieve sets thoroughly. They can be scrubbed under hot water and placed in an ultrasonic bath to remove any contamination left from the previous sample.

13. After the equipment has been cleaned dry it with compressed air to remove most of the water.

177

14. The equipment can then be placed in a warm oven, about 50°C, until it is totally dry and ready to reuse.

15. Repeat this process for any remaining samples.

Encapsulation and sectioning of sample

1. Using the SANS fraction place the material into tailor made acrylic mounting pots (20mm internal diameter, 8mm internal height) 3.5mm-4.0mm depth of sample is required this equates to 1.5-2.0gms of sample (note: differing materials may require assessment for optimum encapsulation and sectioning results). Do not fill pots with sample as this may prevent epoxy from completely immersing the sample.

2. Prepare the Epoxy Resin for sample encapsulation ( Current product is Buehler EPO-THIN 2 pack low viscosity epoxy resin). When mixed, pour gently into potting mount, check base of mount to ensure sample is saturated, leave 24 hours to cure

3. Once cured place sample into sample holding Jig ( see image 1.0) with base outwards.

Image 1.0 Sample pot at right, holding jig at left.

4. Mount holding jig into Isomet 1000 precision saw unit (see image 2.0), cut off the mounts plastic base then reset the saw to slice a 1.0 - 1.2 mm wafer of sample and if possible (consult with project scientist) a 0.4 – 0.5mm wafer. Use a micrometer to measure thickness of wafer at it’s middle, record this on the clear plastic rim of the wafer along with sample number. Store sample for transport.

178

Image 2.0 Sample mount in holding jig ready for sectioning.

8.0 Flow Chart

Enter samples into database

Weigh each bulk sample and record

Label vials for each sample

Set up sieving apparatus with balance and mortar and pestle

Pour sample into sieve and shake through sieve cloth

Pour coarse fraction into mortar

Grind coarse fraction

Return sample to sieve

Repeat until 1.5- 2g of SANS fraction has been obtained or all sample used

Transfer fractions to respective vials and weigh and record

Discard used sieve cloth and weighing paper

Clean all equipment and bench space

sample encapsulation and sectioning

179

A2.3 Introduction to SANS/USANS and its Applications to Source Rock Generation

(Based on an article by A.P. Radlinski and A.L. Hinde, published in Neutron News vol.13 No.2, 2002, 10-14)

Introduction

The microstructure of the pore space in sedimentary rocks is the most important factor controlling fluid flow properties in geological formations, including the migration and retention of water, oil and gas. It is difficult to give a satisfactory description of the pore space microgeometry based on any direct imaging method because of the very wide distribution of pore sizes and complex, intrinsic 3-D character of the pore space geometry.

The minimum pore size in sedimentary rocks is of the order of 1 nm, whereas the maximum pore size depends on the rock coarseness and varies from several µm for siltstones to several hundred µm for sandstones.

Small Angle Neutron Scattering (SANS) is an ideal, non-destructive technique, well suited to study the microstructure of complex porous systems. The scattering occurs at the interface between the rock matrix and the pore space and information pertinent to the size distribution of the pores can be retrieved from the scattering intensity, I(Q). I(Q) is measured versus the scattering vector, Q: Q= (4π/λ) sin (Θ/2), where Θ is the (small) scattering angle and λ is the wavelength of neutrons [1-3]. For scattering objects of roughly spherical geometry (like pores), the dominant contribution to the scattering intensity, measured at a particular value of Q, comes from scattering objects within the linear size range 2.5/Q +/- 50% [4].

Figure 1 illustrates the range of sizes that can be observed with neutron scattering instruments using various types of optics: pinhole [5], time-of-flight [6], double crystal diffraction [7,8] and multiple Laue diffraction [9]. The latter configuration is listed for completeness, as it has not been put into a practical use in a small angle scattering instrument yet. Therefore, currently the range of sizes of scattering objects that can be detected with SANS is from 1 nm to about 30 µm. This range can be extended up to several hundred µm using statistical analysis of microscopic images (SEM, TEM, and optical [10,11]).

Background

A typical sedimentary rock is a complex and somewhat ill-defined “dirty” system. This is epitomised in the word “mudrock” (or mudstone) which may be described as a water-saturated, highly compacted fine mixture of many different oxides of light elements, numerous trace elements, and hundreds of species of fossil organic molecules. The question remains whether any meaningful microstructural information can be extracted from the neutron scattering curve of such a complex system.

The subject of small angle scattering is reviewed in several publications, both general [1-3] and specific to geological applications [12-16]. Since scattering takes place on the interface between two adjacent phases its effectiveness is determined by numerical values of the appropriate scattering length densities (SLD). In petroleum geology the

180

interest is focussed on the generation, migration and storage of formation fluids (brine and hydrocarbons). These processes occur in the pore space and, consequently, the scattering contrast between the pore space (filled with formation fluids or not) and the rock matrix is of central importance.

Figure 2 shows the neutron scattering length densities (SLD) for major organic and inorganic constituents of sedimentary rocks. The SLD of a material depends on its chemical composition and specific density. For various types of organic matter the value of SLD depends mostly on the carbon-to-hydrogen atomic ratio. The solid curve shown in Figure 2 has been calculated for saturated hydrocarbons (CnHn+2). The scatter reflects the departure from this formula for saturates, polars, aromatics, asphaltenes and macerals in whole coals and kerogens. These are the main organic components in sedimentary rocks. The major inorganic components or sedimentary rocks are quartz and corundum with the remaining oxides of light elements typically taking less than 10 wt%.

1

102

104

106

108

1010

10-7 10-5 10-3 10-1 101

Figure 1 Neutron NewsLinear scale range accessible

with SANS techniques

LIN

EA

R R

AN

GE

(Å

)

2 THETA (degrees)

Braggdiffraction

SANS(pinhole, TOF)

USANS(DCD)

LDSANS(multiple Laue

diffraction)

20 Å

3000 Å

30 mµ

= 5 Åλ

arcdegarcminarcsec

1 cm

Figure 1. Range of linear sizes that can be observed with various types of neutron optics.

When one component dominates the rock (eg quartz in sandstone) or various components are intimately mixed (eg siltstones) the inorganic matrix can be characterised by a single value of SLD, averaged over the rock composition. SLDs calculated for the crystalline rock (ash, crystalline) and the actual shale (ash, shale) are different owing to different specific densities of the ideal (crystalline) and the

181

actual (porous and amorphous) rock. Furthermore, it is important to note that SLDs for the organic macerals (ie whole coals) and the inorganic component of the rock (ash) are similar to each other. Consequently, it is possible to interpret SANS data for sedimentary rocks in the two-phase approximation, one phase being the pore space and the other the rock matrix.

SANS can be used to observe migration of fluid phases through the pore space. Migration of liquid hydrocarbons with significant polar, aromatic or asphaltene fractions leads to the loss of contrast and, consequently, decrease of the scattering intensity. The relatively large value of SLD for heavy water enables contrast matching experiments in water-saturated sedimentary rocks [17].

Application to Petroleum Geology

The microstructure of the rock matrix

For sedimentary rocks, a power law scattering curve (I(Q) = const x Qn) is frequently observed. This can be attributed to a polydisperse distribution, f(r), of pore sizes [18]. The pore size distribution, f(r), gives the proportion of pores whose radii lie between r and r + dr. It has been demonstrated that for sedimentary rocks the pores can be reasonably assumed to be roughly spherical. Consequently f(r) can be obtained from I(Q) through a straightforward numerical procedure [19]. Furthermore, the specific surface area, for probe size r, can be calculated from f(r) as the sum of surface areas of all pores of radius larger than r divided by the sample volume.

-1

0

1

2

3

4

5

6

7

0 0.5 1 1.5 2 2.5

SC

ATT

ER

ING

LE

NG

TH D

EN

SIT

Y (

x1010 c

m-2

)

C/H ATOMIC RATIO

ash, crystallinecalculated for

pure hydrocarbons

saturates

asphaltenes

polars and aromatics

wholecoals

quartz, SiO2

corundum, Al 2 O 3

ash, shale

anatase, TiO2

lime, CaO

K2O

periclase, MgO

H2O

void

heavy water, D2O

Figure 2. Neutron scattering length density for major minerals and organic matter types present in sedimentary rocks.

182

Figure 3. The comparison of SANS/USANS scattering data for a typical sandstone [24, 25], shale [20, 24] and coal [19]. Data for sandstone have been truncated at Q = 3x10-4 Å-1 in order to eliminate the data points affected by multiple scattering.

Typical examples of power law scattering are illustrated in Figure 3 for a sandstone, shale and coal. The exponent n usually falls between -3 and -4, indicating the surface fractal character of the pore/rock interface [20]. The fractal properties extend over the range of length scales of over 3 decades (11 decades in intensity), which makes sedimentary rocks one of the most extensive fractal systems found in nature. The ubiquitous fractal microstructure of sedimentary rocks has been explained as a consequence of the antisintering thermodynamic conditions at the grain/grain and grain/formation fluid interface prevalent during the rock formation process [21].

Figure 4 shows the pore size distribution f(r) calculated for a sandstone, shale and coal from SANS data. All three pore size distributions indeed follow a power law and the calculated fractal dimensions are very similar to those obtained directly from the slope of SANS curves plotted on a log-log scale. The range of pore sizes determined by SANS extends over 4 orders of magnitude, from 10 Å to 10 µm. This is similar to the

183

range accessible using the mercury injection porisimetry (MIP), however SANS is non-invasive and can potentially access pore sizes smaller than MIP.

Figure 5 shows the calculated internal specific surface area (SSA) for the three types of rock. For fractal systems the specific surface area depends on the size (diameter) of the measuring probe. SANS enables one to determine SSA down to a probe size of 10 - 25 Å, and the data can be readily extrapolated to probe sizes of several Å. It is interesting to note that in this limit SSAs for the three types of rock are all of the same order of magnitude, the one for the coal being the smallest. This illustrates the point that the high sorption capacity of coals for gases, like methane and carbon dioxide, is driven as much by the physiochemical affinity as the large internal surface area.

Figure 4. The comparison of SANS/USANS-derived pore size distribution for a sandstone [23, 24], shale [23, 24], and coal [19]. All three distributions follow a power law, from which the fractal dimension can be determined.

184

Figure 5. The comparison of SANS/USANS-derived specific surface area for a sandstone [23, 24], shale [23, 24] and coal [19]. Data are extrapolated to the probe size of 4Å, corresponding to the size of methane molecule.

Detection of hydrocarbon generation and migration

Hydrocarbons are generated in mudrocks by thermal maturation - a process of temperature-driven decomposition of organic macromolecules deposited in the pore space of the inorganic rock matrix. The consequent increase in molecular volume leads to the overpressure, formation of micro-cracks and transport of generated hydrocarbons through the network of conduits (interconnected pores) out of source rocks and, if geological conditions are suitable, ultimately into the more porous reservoir rocks, where commercial hydrocarbon accumulations are formed.

Hydrocarbon generation in typical natural conditions occurs over the period of millions of years at subsurface temperatures in the range 90 to 150°C. This process is governed by the Arrhenius-like time/temperature relationship and can be accelerated in laboratory conditions by pyrolising the rock samples at eleveated termperatures. For the duration of pyrolysis of 48 hours the temperature range that spans the oil generation window is 310 to 370°C. Both the geochemical and SANS data indicate the presence of the oil generation threshold at about 320°C [4]. Figure 6 shows the variation of SANS intensity versus the annealing temperature at a Q-value corresponding to the average pore size 300Å +/- 50%. The marked decrease of the scattering intensity between the annealing temperatures 320 and 330°C constitutes the SANS fingerprint of the process of primary migration of generated hydrocarbons through the pore space of the source rock.

185

200

300

400

500

600

700

800

280 300 320 340 360 380

SANS_D11_INT@750ÅScattering cross section vs temp of pyrolysis

immature Urapunga 4, 48h, p=14 bar, N2 atm, closed system, artificial maturity sequence, SANS data

SC

AT

TE

RIN

G IN

TE

NS

ITY

(cm

-1)

ANNEALING TEMPERATURE (°C)

2.5/Q = 300 Å

onset ofprimary

migration

Figure 6 Neutron News

Figure 6. The variation of SANS intensity at a single Q-value versus the annealing temperature for an immature hydrocarbon source rock. Data correspond to the average pore size of 300Å +/- 50%. The marked decrease of the scattering intensity constitutes the SANS fingerprint of the hydrocarbon generation and primary migration (after Reference 4). The rising trend is caused by increased hydrogen depletion as the annealing temperature increases.

Figure 7 schematically illustrates the variation of SANS intensity with depth in field conditions in the region of hydrocarbon generation as monitored for a fixed pore size. As the temperature increases with depth, bitumen generated from kerogen progressively saturates the small pores and then the increasingly larger pores, and expels formation brine. Bitumen has the scattering length density similar to kerogen and similar to the inorganic rock matrix (Figure 2) and, therefore, the scattering contrast is progressively lost with depth and the scattering intensity decreases. The scattering intensity reaches a minimum at the maximum bitumen saturation. At yet greater depth the bitumen is progressively cracked to mobile hydrocarbons which in turn migrate to larger pores as the result of volume expansion. Owing to the corresponding progressive decrease in hydrocarbon density and increase in mobile hydrocarbons with high H/C ratio and low SLD, the scattering contrast increases and the scattering intensity increases.

186

& expulsion of pore waters

2200

2400

2600

2800

3000

3200

3400

0 200 400 600 800 1000

DEP

TH (m

)

SCATTERING INTENSITY

Progressive bitumengeneration & saturation

Maximum bitumen saturation& onset of mobile hydrocarbon

generation & expulsion to larger pores

Progressive crackingof bitumen to mobile

hydrocarbons& migration of hydrocarbons

to larger pores

Figure 7. A schematic representation of the SANS intensity (for a selected Q-value) versus depth within the hydrocarbon generation window.

Gas sorption capacity of coal seams

The pore size distribution, f(r), and specific surface area, SSA, are important characteristics of coal as a reservoir rock for gas. In particular, f(r) and SSA for the molecular size probe are major parameters to be determined in order to understand coalbed methane desorption and extraction as well as CO2 sorption for carbon sequestration purposes. Mercury injection and nitrogen adsorption are commonly used to quantify SSA and f(r).

SANS is an excellent tool for non-invasive determination of SSA and f(r) in coals in a single experimental run [18,19]. Figure 8 illustrates the comparison of specific surface area for a probe of diameter 4 Å obtained using the nitrogen adsorption method and SANS. There is an excellent agreement across the entire range of coal ranks, with the

187

SANS values being consistently slightly larger than the N2 adsorption values. This is to be expected as the SANS technique measures all the pores while the nitrogen adsorption method probes only the open pores.

103

104

105

106

0.5 1

Figure 7 Neutron NewsSpecific surface area obtained for coals by SANS

for various probe sizes.Comparison with nitrogen adsorption data.

SP

EC

IFIC

SU

RF

AC

E A

RE

A (

cm2 /c

m3 )

VITRINITE REFLECTANCE Ro (%)

SANS data

N2 adsorption data

Figure 8. The comparison of specific surface area for coals of different rank obtained using SANS and the nitrogen adsorption method. The probe size is 4Å (after Reference 19).

Summary

SANS is a valuable technique to obtain quantitative information about the microstructure of pore space in sedimentary rocks in the scale range 1 nm to 30 µm. SANS can be applied to rocks with any organic matter content, from lean shales to pure coals. Examples of applications include the study of the fractal architecture of the pore space, detection of oil generation in hydrocarbon source rocks, and the assessment of methane and carbon dioxide sorption capacity in coal beds.

References

[1] Guinier, A., G. Fournet, C.B. Walker and K.L. Yudowitch, Small-angle scattering of X-rays, John Wiley and Sons, New York, 259 pp (1955).

[2] Espinat, D., Revue de l’Institut Francais du Petrole, vol. 45 No 6, 1-131 (1990).

[3] Lindner, P. and T. Zemb (Eds), Neutron, X-ray and Light Scattering, Elsevier Science B.V., Amsterdam (1991).

188

[4] Radlinski, A.P., Boreham, C.J., Lindner, P., Randl, O.G., Wignall, G.D. and Hope, J.M., “Small angle neutron scattering signature of oil generation in artificially and naturally matured source rocks”, Org. Geochem. 31, 1-14 (2000).

[5] Russell, T.P., Lin J.S., Spooner, S. and Wignall, G.D., “Intercalibration of small-angle X-ray and neutron scattering data”, J. Appl. Cryst. 21, 629-638 (1988).

[6] Thiyagarayan, P., Epperson, J.E., Crawford, R.K., Carpenter, J.M., Klippert, T.E., and Wozniak D.G., “The time-of-flight small angle neutron diffractometer (SAD) at IPNS, Argonne National Laboratory”, J. Appl. Cryst. 30, 280-283 (1997).

[7] Agamalian, M., Wignall, G.D. and Triolo, R., “Optimization of a Bonse-Hart ultra-small-angle neutron scattering facility by elimination of the rocking curve wings”, J. Appl. Cryst. 30, 345-352 (1997).

[8] Hainbuchner, M., Villa, M., Kroupa, G., bruckner, G., Baron, M., Amenitsch, H., Seidl, E. and Rauch, H., “The new high resolution ultra-small-angle neutron scattering instrument at the High Flux Reactor in Grenoble”, J. Appl. Cryst. 33, 851-854 (2000).

[9] Petrascheck, D. and Rauch, H., Acta Crystallographica, A40, 445-450 (1984).

[10] Thompson, A.H., “Fractals in rock physics”, Annual Review of Earth and Planetary Science, 19, 237-262 (1991).

[11] Bekri, S., et al., Journal of Petroleum Science and Engineering, 25, 107-134 (2000).

[12] Bale, H.D. and P.W. Schmidt, “Small-angle X-ray scattering investigation of submicroscopic porosity with fractal properties”, Phys.Rev. Lett. 53, 596-599 (1984).

[13] Wong, P.-z., Howard, J. and Lin, J.-s., “Surface roughening and the fractal nature of rocks”, Phys. Rev. Lett. 57, 637-640 (1986).

[14] Mildner, D.F.R. and P.L. Hall, “Small-angle scattering from porous solids with fractal geometry”, J. Phys. D: Appl. Phys. 19, 1535-1545 (1986).

[15] Radlinski, A.P., Boreham C.J., Wignall, G.D. and Lin, J.S., “Microstructural evolution of source rocks during hydrocarbon generation: A small-angle scattering study”, Phys. Rev. B, 53, 14152-14160 (1996).

[16] Radlinski A.P. and E.Z. Radlinska, in: Coalbed Methane: Scientific, Environmental and Economic Evaluation, M. Mastalerz, M. Glikson, and S. D. Golding (eds), Kluvier Scientific Publishers, Dodrecht, 329-365 (1999).

[17] Broseta, D., Barre, L. and Vizika, O., “Capillary condensation in fractal porous medium”, Phys. Rev. Lett., 86, 5313-5316 (2001).

[18] Schmidt, P.W., “Interpretation of small-angle scattering curves proportional to a negative power of the scattering vector”, J. Appl. Cryst. 15, 567-569 (1982).

189

[19] Radlinski, A.P., Mastalerz, M., Hinde, A.L., Hainbuchner, M., Rauch, H., Baron, M., Lin, J.S., Fan, L. and Thiyagarajan, P., “Application of SAXS and SANS in evaluation of porosity, pore size distribution and surface area of coal”, Int. J. Coal Geology 59, 245-271.

[20] Radlinski, A.P., Radlinska, E.Z., Agamalian, M., Wignall, G.D., Lindner, P. and Randl, OG, “Fractal geometry of rocks”, Phys. Rev. Lett. 82, 3078-3081 (1999).

[21] Cohen, M.H., “The morphology of porous sedimentary rocks”. In: Physics and Chemistry of Porous Media - II, J.R. Banavar, J. Koplik and K.W. Winkler (eds), AIP Conference Proceedings No. 154, American Institute of Physics, New York , 3-16 (1987).

[22] Pfeifer, P. and D. Avnir, “Chemistry of noninteger dimensions between two and three. I. Fractal theory of heterogeneous surface”, Journal of Chemical Physics 79, 3558-3565 (1983).

[23] Radlinski, A.P. and A.L. Hinde, “Applications of SANS and SAXS to Petroleum Geology”, Proceedings of the ESRF/ILL Workshop on Environmental Studies Using Neutron and Synchrotron Facilities, Feb. 20-21, 2001, Grenoble, France.

[24] Hinde, A.L., “PRINSAS – a Windows based computer program for the processing and interpretation of small angle scattering data tailored to the analysis of sedimentary rocks”, J. Appl. Cryst. 37, 1020-1024 (2004).

190

A2.4 TOC and Rock-Eval Pyrolysis Sample Preparation

The dry-sieved samples were ground to a fine powder. Several experiments were undertaken to determine the most time effective and thorough way to wash the samples that had been drilled with ‘glycol’ or ‘SBM’. The method used to prepare the samples is as follows:

1. Approximately 200 mg of sample was crushed with a mortar and pestle to a fine powder.

2. The powdered sample was then placed in a centrifuge tube.

3. 15-20 mL of wash solution was added to the centrifuge tube. The wash solution used depended on the drilling fluid used. 90:10 Methanol to dichloromethane was used for glycol contaminated samples, and 50:50 methanol to dichloromethane was used for SBM contaminated samples.

4. The centrifuge tube was placed in the ultrasonic bath for 15 minutes and then centrifuged for 10 minutes at 4200 rpm. The supernatant solution was then decanted and, in some cases, retained for further analysis.

5. The sample was repeatedly washed, nine times for glycol contamination and four times for SBM drilling fluid.

6. The sample was oven dried at 40 oC oven and then ground to a lose powder using a mortar and pestle. The homogenized, powdered sample was weighed into an oxidised crucible prior to analysis.

A2.5 TOC and Rock-Eval Pyrolysis Method

Instrument: Rock-Eval 6 Turbo supplied by Vinci Technologies – France

Aquistion parameters:

Pyrolysis: Held isothermal at 300 oC for 5 minutes Ramped at 25 oC per minute from 300 oC to 650 oC.

Oxidation: Held isothermal at 400 oC for 3 minutes Ramped at 20 oC per minute from 400 oC to 850 oC. Held isothermal at 850 oC for 5 minutes

Sample weights 80 mg. Roasted fine sand was added to make weights up to 80 mg where required.

Data Processing: Optkin 3.0.0 software supplied by Beicip Franlab - France

Machine Operator Rachel Davenport

Analysis Date 31/5/02

The crucible was oxidized before use by heating to 600 oC in the oxidation oven of the Rock-Eval 6 Turbo. An analysis blank was run with the sample batch. The blank data is automatically subtracted from all analyses.

191

NOTE: The Rock-Eval 6 Turbo instrument measures the temperature of the sample directly beneath the crucible. The temperature recorded at the maximum of the S2 peak is denoted Tpeak on the pyrogram. The thermocouple in the conventional Rock-Eval II (and older) instruments is located on the outside of the pyrolysis oven, and therefore measures the maximum S2 peak (Tmax) at a lower temperature than if the thermocouple was beside the crucible. Since Tmax is the most widely reported value for the maximum S2 peak, a conversion factor is applied to convert Tpeak to Tmax values.

The Rock-Eval 6 Turbo can determine TOC using the oxidation module. The TOC is the sum of the calculated carbon in the S1, S2 and S3 peaks together with the carbon in residual material remaining after pyrolysis. The oxidation module works under a flow of air and oxidation occurs up to 850 oC. For the Rock-Eval 6 instrument carbon monoxide is also detected. Summation of the carbon in all of these components results in TOC and is calculated using the following formula for decarbonated rocks:

TOC = PC (pyrolysable Carbon) + RC (Residual Carbon)

PC (wt %) = [(S1+S2) x 0.83] + [S3 x 12/44] + [(S3 CO+S3’ CO) x 12/28]/10

RC (wt %) = RC CO + RC CO2

RC CO = (S4 CO x 12/28) / 10

RC CO2 = (S4 CO2 x 12/44) / 10

For whole rocks with carbonate replace S3’CO with S3’ CO/2.

192

193

Appendix 3: Results of Size Fraction Experiments

Table A3.1 Reproducibility of data for different size fractions for cuttings sample from Brewster 1A, 2750-2755m (#20010658).

PREP TMAX S1 S2 S3 TOC PI HI OI

<355 429 0.07 1.41 2.78 0.94 0.05 150 296

<355 rpt 428 0.11 1.47 2.81 1.10 0.07 134 255

Average <355 428.5 0.09 1.44 2.80 1.02 0.06 142 276

SD <355 0.50 0.02 0.03 0.01 0.08 0.01 8 20

>355<475um 431 0.09 1.36 2.96 1.02 0.06 133 290

>355<475um rpt 429 0.11 1.48 2.42 0.98 0.07 151 247

Average >355<475 430 0.10 1.42 2.69 1.00 0.07 142 269

SD >355<475 1.00 0.01 0.06 0.27 0.02 0.00 9 22

>475 431 0.04 1.21 2.33 1.09 0.03 111 214

>475 rpt 433 0.07 1.26 1.52 1.10 0.05 115 138

Average >475 432 0.06 1.24 1.93 1.10 0.04 113 176

SD >475 1.00 0.02 0.03 0.41 0.00 0.01 2 38

RECOMBINED 429 0.09 1.49 2.56 1.01 0.06 148 253

Table A3.2 Reproducibility of data for different size fractions for cuttings sample from Brewster 1A, 3695-3700 m (#20010672).


<355 444 0.53 2.03 1.36 1.68 0.21 121 81

<355 rpt 446 0.49 2.02 0.52 1.86 0.20 109 28

Average <355 445 0.51 2.03 0.94 1.77 0.20 115 54

SD <355 1.00 0.02 0.00 0.42 0.09 0.01 6 26

>355<475um 443 0.49 1.71 2.34 1.85 0.22 92 126

>355<475um rpt 444 0.51 1.82 1.04 1.76 0.22 103 59

Average >355<475 443.5 0.50 1.77 1.69 1.81 0.22 98 93

SD >355<475 0.50 0.01 0.05 0.65 0.04 0.00 5 34

>475 447 0.45 1.30 1.41 1.73 0.26 75 82

>475 rpt 446 0.45 1.38 0.86 1.82 0.25 76 47

Average >475 446.5 0.45 1.34 1.14 1.78 0.25 75 64

SD >475 0.50 0.00 0.04 0.28 0.05 0.01 0 17

RECOMBINED 444 0.50 2.01 1.09 1.87 0.20 107 58

194

Table A3.3 Comparison of data for different size fractions for cuttings samples from Brewster 1A.


Sample Brewster 1A, 2750-2755m (#20010658).

<355 av 428.5 0.09 1.44 2.80 1.02 0.06 142 276

>355<475um av 430 0.10 1.42 2.69 1.00 0.07 142 269

>475 av 432 0.06 1.24 1.93 1.10 0.04 113 176

RECOMBINED 429 0.09 1.49 2.56 1.01 0.06 148 253

Average 430 0.08 1.40 2.49 1.03 0.06 136 243

SD between SANS fraction and recombined

0.50 0.01 0.03 0.06 0.01 0.00 2.67 7.55

SD between Sans and average

0.06 0.01 0.01 0.10 0.02 0.00 3.05 12.58

Sample Brewster 1A, 3600-3605m (#20010671).

<355 445 0.92 4.12 1.86 2.50 0.18 165 74

>355<475 446 0.95 4.25 1.50 2.69 0.18 158 56

>475 447 0.93 4.32 1.52 2.79 0.18 155 54

RECOMBINED 447 1.00 4.29 1.63 2.63 0.19 163 62

Average 446 0.95 4.25 1.63 2.65 0.18 160 62


0.50 0.02 0.02 0.07 0.03 0.00 2.56 3.11


0.13 0.00 0.00 0.06 0.02 0.00 1.10 2.95

Brewster 1A, 3695-3700 m (#20010672).

<355 av 445 0.51 2.03 0.94 1.77 0.20 115 54

>355<475um av 443.5 0.50 1.77 1.69 1.81 0.22 98 93

>475 av 446.5 0.45 1.34 1.14 1.78 0.25 75 64

RECOMBINED 444 0.50 2.01 1.09 1.87 0.20 107 58

Average 445 0.49 1.79 1.21 1.81 0.22 99 67


0.25 0.00 0.12 0.30 0.03 0.01 5 17


0.63 0.00 0.01 0.24 0.00 0.00 0.49 12.66

195

Appendix 4: Rock-Eval Pyrolysis Definitions

196

Tabl

e A

4.1

Defi

nitio

ns o

f Roc

k-Ev

al p

yrol

ysis

par

amet

ers

(mod

ified

afte

r Esp

italié

et

al.,

198

5; P

eter

s, 1

986)

.

Para

met

erN

ame

(uni

ts)

Defi

nitio

nSp

ecifi

city

Prob

lem

s/In

form

atio

nTO

CTo

tal O

rgan

ic C

arbo

n(w

t. pe

rcen

t)M

easu

re o

f the

rock

’s o

rgan

ic ri

chne

ss.

Org

anic

rich

ness

.E

rror

s of

up

to 1

0% c

an o

ccur

bet

wee

n ‘L

EC

O’

and

‘Roc

k-E

val’

met

hods

(coa

ls a

re th

e m

ost

diffi

cult

to m

easu

re a

ccur

ate

valu

es u

sing

the

Roc

k-E

val m

etho

d).

S1

mg

hydr

ocar

bons

(e

xtra

ctab

le) /

g ro

ckM

easu

re o

f the

am

ount

of f

ree

hydr

ocar

bons

pr

esen

t in

the

rock

. The

free

hyd

roca

rbon

s ar

e th

ose

ther

mal

ly d

esor

bed

at 3

00o C

for 3

m

inut

es

Ker

ogen

type

(sou

rce

qual

ity).

Mat

urity

.M

igra

ted

oil.

Can

be

seve

rely

affe

cted

(hig

h va

lues

) by

oil-

base

d dr

illin

g flu

id (s

ee T

raps

and

Tip

s)

S2

mg

hydr

ocar

bons

(ker

ogen

py

roly

sate

) / g

roc

kM

easu

re o

f hyd

roca

rbon

s fo

rmed

by

crac

king

of

ker

ogen

, res

ins

and

asph

alte

nes.

The

py

roly

sate

is m

easu

red

from

300

oC to

650

oC

at 2

5oC

/min

.

Ker

ogen

type

. Mat

urity

.H

igh

valu

es m

ay b

e ob

tain

ed if

oil

or b

itum

en

is p

rese

nt (C

lem

entz

, 198

0) a

nd m

iner

al

deco

mpo

sitio

n. D

rillin

g ad

ditiv

es a

lso

caus

e pr

oble

ms;

see

Tra

ps a

nd T

ips.

Low

er v

alue

s ca

n ar

ise

from

ads

orpt

ion

on th

e m

iner

al m

atrix

(E

spita

lié e

t al.,

198

0; O

rr, 1

983)

. The

late

r ‘s

uppr

essi

on’ c

an b

e el

imin

ated

usi

ng is

olat

ed

kero

gen

(see

HI)

S3

mg

CO

2 (o

rgan

ic) /

g ro

ckM

easu

re o

f CO

2 gen

erat

ed fr

om o

xyge

nate

d fu

nctio

nal g

roup

s in

ker

ogen

. The

CO

2 is

colle

cted

from

300

o C to

390

o C a

t 25o C

/min

.

Ker

ogen

type

. Mat

urity

.S

ubje

ct to

inte

rfere

nce

by C

O2 fro

m d

ecom

posi

tion

of c

arbo

nate

min

eral

s (H

orsfi

eld

& D

ougl

as, 1

980;

H

orsfi

eld,

198

4).

S1+

S2

Pot

entia

l Yie

ld (m

g hy

droc

arbo

ns /g

ro

ck)

The

tota

l hyd

roca

rbon

gen

etic

pot

entia

l i.e

. th

e fre

e an

d ke

roge

n-bo

und

hydr

ocar

bons

.S

ourc

e ric

hnes

s.K

erog

en ty

pe.

Sub

ject

to th

e co

mbi

ned

prob

lem

s w

ith S

1 an

d S

2 ab

ove

T max

Max

imum

hei

ght o

f the

S

2 pe

ak in

tem

pera

ture

pr

ogra

m (°

C)

Tem

pera

ture

cor

resp

ondi

ng to

the

max

imum

ra

te o

f hyd

roca

rbon

s ge

nera

ted

from

the

crac

king

of k

erog

en (S

2).

Mat

urity

: Ker

ogen

type

.D

epre

ssed

val

ues

indi

cate

mig

rate

d hy

droc

arbo

ns.

For m

ultip

le p

eaks

in S

2, th

e on

e w

ith th

e hi

ghes

t si

gnal

will

be

assi

gned

Tm

ax. A

nom

olus

ly lo

w

and

high

Tm

ax v

alue

s ca

n re

sult

for t

hese

mix

ed

sour

ces

or d

rillin

g ad

ditiv

es (s

ee T

raps

and

Tip

s),

whi

le h

igh

Tmax

(>50

0o C) c

an a

lso

resu

llt fr

om

min

eral

dec

ompo

sitio

n.Tp

eak

Max

imun

hei

ght

of S

2 pe

ak in

tem

pera

ture

pr

ogra

m (°

C);

RE

6

True

tem

pera

ture

cor

resp

ondi

ng to

the

max

imum

rate

of h

ydro

carb

ons

gene

rate

d fro

m th

e cr

acki

ng o

f ker

ogen

.

Use

d in

the

deriv

atio

n of

ki

netic

par

amet

ers

whe

re

abso

lute

tem

pera

ture

is

need

ed

Tem

pera

ture

mea

sure

d in

side

of t

he o

ven.

Tpe

ak

is a

ppro

xim

atel

y 30

o C g

reat

er th

an T

max

.

197

Para

met

erN

ame

(uni

ts)

Defi

nitio

nSp

ecifi

city

Prob

lem

s/In

form

atio

nP

IP

rodu

ctio

n In

dex

(S1/

S1+

S2)

Ext

ent t

o w

hich

ker

ogen

has

bee

n tra

nsfo

rmed

into

oil

and

gas.

Mat

urity

,. M

igra

ted

oil.

Ano

mal

ous

valu

es c

orre

spon

d to

acc

umul

atio

n or

dr

aina

ge o

f hyd

roca

rbon

s.or

con

tam

inat

ion

PC

Pyr

olys

able

Car

bon

(wt.

perc

ent)

The

amou

nt o

f TO

C re

pres

ente

d by

S1

and

S2.

; PC

= 0

.83*

(S1+

S2)

Sou

rce

richn

ess:

Ker

ogen

type

. Mat

urity

.O

xida

tion

of o

rgan

ic m

atte

r low

ers

the

valu

es.

CC

onve

rsio

n Fa

ctor

(PC

/TO

C) *

100

The

perc

enta

ge o

f TO

C a

vaila

ble

for

conv

ertio

n to

hyd

roca

rbon

s.O

rgan

ic ri

chne

ss, k

erog

en

type

.H

ighe

r val

ues

repr

esen

t inc

reas

ed o

il-pr

ones

e. C

ould

be

used

in th

e sa

me

way

as

HI b

ut ra

rely

is.

BI

Bitu

men

Inde

x(m

g hy

droc

arbo

ns (S

1) /

g TO

C

Am

ount

of f

ree

hydr

ocar

bons

(S1)

nor

mai

lsed

to

TO

C.

BI =

100

* S

2 / T

OC

Sou

rce

rich

ness

, Mat

urity

Am

ount

and

rate

of c

hang

e ca

n be

use

d to

iden

tify

the

onse

t of e

xpul

sion

and

the

begi

nnin

g of

the

gas

win

dow

.H

IH

ydro

gen

Inde

x[m

g hy

droc

arbo

ns (S

2) /

g TO

C]

Am

ount

of h

ydro

carb

ons

rele

ased

on

pyro

lysi

s (S

2) n

orm

alis

ed to

TO

C.

HI =

100

* S

2 / T

OC

Sou

rce

richn

ess,

K

erog

en ty

pe,.

Mat

urity

.H

I > 3

00 in

dica

tes

oil-p

rone

ness

. A th

eroe

tical

ly

max

imum

HI o

f 120

6 is

obt

aine

d fo

r 100

%

conv

ersi

on o

f the

org

anic

mat

ter t

o hy

droc

arbo

ns

assu

min

g th

e pr

opor

tion

of C

in th

e or

gani

c m

atte

r is

0.83

. For

rock

s w

ith T

OC

< 3

% th

e H

I ca

n be

sup

pres

sed

by u

p to

100

%, r

esul

ting

in

the

true

hydr

ocar

bon

pote

ntia

l bei

ng s

ever

ely

unde

rest

imat

ed. I

t is

reco

mm

ende

d th

at H

I de

term

ined

on

isol

ated

ker

ogen

be

used

for

orga

nic-

lean

rock

s.O

IO

xyge

n In

dex

[mg

CO

2 (S

3) /

g TO

C]

Am

ount

of c

arbo

n di

oxid

e re

leas

ed o

n py

roly

sis

norm

alis

ed to

TO

C.

OI =

100

* S

3 / T

OC

Ker

ogen

type

,. M

atur

ity.

Not

relia

ble

in c

arbo

nate

s an

d or

gani

cally

lean

se

dim

ents

. Hig

h va

lues

indi

cate

low

hyd

roca

rbon

yi

elds

. Hig

her O

Is o

ccur

in te

rres

trial

org

anic

or

gani

c m

atte

r wrt

mar

ine

orga

nic

mat

ter

hc h

ydro

carb

ons

Tabl

e A

4.1

Defi

nitio

ns o

f Roc

k-Ev

al p

yrol

ysis

par

amet

ers

(mod

ified

afte

r Esp

italié

et a

l., 1

985;

Pet

ers,

198

6) (c

ont’d

)

198

Table A4.2. Guidelines for interpreting (a) source rock generative potential and (b) type of petroleum generated from immature sediments (VR <0.6 %), and, c) degree of thermal maturation (modified after Peters, 1986; Espitalié and Bordenave,1993).

Table A4.2a. Source rock generative potential (richness) for VR < 0.6 %.

Quantity TOC S2 S1 + S2 EOM HC

Wt % mg hc / g rock mg hc / g rock Wt % ppm

Poor 0 - 0.5 0 - 2.5 0 - 3 <0.05 <200

Fair 0.5 - 1 2.5 - 5 3 - 6 0.05 – 0.1 200 – 500

Good 1 - 2 5 - 10 6 - 12 0.1 – 0.2 500 – 800

Very Good > 2 > 10 > 12 >0.2 >800

* for carbonate lithologies the TOC ‘cutoffs’ are approximately ½ those listed here for clastics

TOC = total organic carbon; S1 = yield of hydrocarbons(hc) released during thermal desorption; S2 = yield of hydrocarbons(hc) released during pyrolysis; EOM = extractable organic matter; HC = free saturated and aromatic hydrocarbon content of rock isolated during solvent extraction.

Table A4.2b Source rock quality for VR < 0.6 %.

Type

Gas*Gas and OilOil

Hydrogen Index(mg hc/g TOC)

50-200200-300>300

Rock Eval S2/S3

1-55-10>10

Extract Yield(mg hc/g TOC)*

<2020-5050-200* mature samples

Atomic H/C

0.6-0.9

0.9-1.1>1.1

* Wet gas content increases with increasing HI, with condensate potential for 150<HI<200

Table A4.2c Source rock thermal maturity.

MaturationLevel

Production Index (PI)

Tmax (oC) (VR %) for Type I

Tmax (oC) (VR %) for Type II

Tmax (oC) (VR %) for Type III

Immature <0.15 <445 (0.8) <435 (0.5) <440 (0.65)

Mature 0.15-0.4 445-455 (0.8-1.0) 435-460 (0.5-1.2) 440-470 (0.65-1.4)

Overmature <0.15 >455 (>1.0) >460 (>1.2) >470 (>1.4)

199

Appendix 5: TOC and Rock-Eval Pyrolysis Results

Table A5.1 TOC and Rock-Eval pyrolysis results for cuttings samples from Brewster-1A.

AGSO No. TMAX S 1 S 2 S 3 TOC H I O I

(oC) (mg/g) (mg/g) (mg/g) (wt%)

20010654 428 0.05 0.4 2.61 0.58 68 447

20010655 430 0.05 0.33 2.18 0.56 60 390

20010656 428 0.05 0.57 2.16 0.23 248 937

20010657 431 0.06 0.85 2.47 0.81 105 305

20010658 431 0.09 1.36 2.96 1.02 133 290

20010659 424 0.15 1.83 2.83 1.11 165 254

20010660 429 0.14 1.85 2.99 1.2 153 249

20010661 432 0.17 1.69 2.83 1.16 146 243

20010662 428 0.12 0.94 2.75 0.88 107 313

20010663 433 0.13 1.15 2.76 1.38 83 200

20010664 433 0.19 1.47 3.07 1.21 122 254

20010665 433 0.2 1.59 2.44 0.99 160 246

20010666 440 0.13 0.93 2.92 1.16 80 251

20010667 434 0.19 1.39 3.5 1.13 123 309

20010668 nd nd nd nd nd nd nd

20010669 444 0.24 1.91 1.9 1.51 127 126

20010670 428 0.54 1.94 3.65 0.75 259 488

20010671 446 0.82 3.95 1.89 2.77 143 68

20010672 443 0.49 1.71 2.34 1.85 92 126

20010673 445 0.59 2.06 2.47 2.36 87 105

20010674 408 0.36 2.4 2.38 2.44 98 98


200

Table A5.2 TOC and Rock-Eval pyrolysis results for cuttings samples from Carbine-1.

GA No. TMAX S 1 S 2 S 3 TOC H I O I


20020084 424 0.11 0.45 2.25 1.02 44 220

20020085 434 0.03 1.87 1.37 1.58 118 86

20020086 423 0.12 0.89 1.15 1.46 61 79

20020087 425 0.07 0.67 1.25 1.42 47 88

20020088 430 0.08 0.57 2.49 1.03 56 243

20020089 439 0.06 1.28 3.14 1.55 83 203

20020090 438 0.08 2.04 1.51 1.91 107 79

Table A5.3 TOC and Rock-Eval pyrolysis results for cuttings samples from Adele-1 extracted with methanol and dichloromethane (90:10). S1 values are invalid.



20020066 434 0.03 1.27 1.06 1.36 93 78

20020068 432 0.03 0.94 0.62 1.38 68 45

20020069 429 0.04 1.41 0.40 1.70 83 24

20020070 430 0.06 2.20 0.61 1.54 143 39

20020071 429 0.06 1.92 0.35 1.41 136 25

20020072 434 0.04 2.65 0.56 1.77 150 31

20020073 430 0.08 2.23 0.09 1.8 124 5

20020074 432 0.05 1.67 0.17 1.27 131 13

20020075 431 0.04 1.35 0.58 1.58 85 36

20020076 429 0.06 2.39 0.77 1.84 130 42

20020077 434 0.06 1.55 0.6 1.91 81 31

20020078 433 0.05 1.20 0.64 1.58 76 41

20020079 431 0.06 1.29 0.73 1.54 84 48

20020080 431 0.05 0.83 0.7 1.02 82 69

20020081 436 0.05 1.08 0.67 1.02 105 66

20020082* 416 0.05 2.48 0.34 1.32 188 26

20020083 436 0.04 1.00 0.86 0.90 111 95

* Data shows significant levels of glycol contamination after extraction.

201

Table A5.4 TOC and Rock-Eval pyrolysis results for cuttings samples from Argus-1 extracted with methanol and dichloromethane (90:10). S1 values are invalid.



20020101* 437 0.12 1.2 3.09 1.19 100 259

20020102* 328 0.93 9.34 8.38 3.57 262 235

20020103* 352 1.01 8.24 7.93 2.91 283 273

20020104* 350 1.09 18.01 7.20 4.92 366 146

20020105* 339 0.49 2.84 5.12 1.70 167 301

20020106* 333 0.41 1.89 4.04 1.48 127 273

20020107* 332 0.47 1.90 3.33 1.14 167 292

20020108* 344 0.40 2.20 3.38 1.24 178 273


Table A5.5 TOC and Rock-Eval pyrolysis results for cuttings samples from Brecknock South-1 extracted with methanol and dichloromethane (90:10).



20020091 429 0.23 1.52 1.06 0.93 163 114

20020092 428 0.27 2.04 0.83 0.87 235 95

20020093 427 0.28 1.33 0.91 1.08 124 84

20020094 432 0.53 1.58 0.89 1.12 141 80

20020095 436 0.45 2.96 1.19 1.77 167 67

20020096 435 0.46 3.16 0.99 1.72 184 57

20020097 441 0.38 2.10 0.97 1.31 160 74

20020098 436 0.42 2.01 1.04 1.33 150 78

20020099 435 0.14 1.12 1.50 1.22 91 122

20020100* 333 0.31 1.14 1.93 1.24 92 156


202

Table A5.6 TOC and Rock-Eval pyrolysis results for cuttings and side-wall-core samples from Crux-1. S1 values are invalid.



Cuttings

20020109* 318 1.1 3 3.13 1.19 252 263

20020110* 319 1.65 4.27 4.95 2.67 160 186

20020111* 317 0.9 1.41 1.14 1.07 132 106

20020112* 318 1.38 2 2.1 1.18 170 178

20020113* nd nd nd nd nd nd nd

20020114 317 0.79 1.68 2.11 1.15 146 183

20020115* 427 0.47 1.01 1.78 0.99 102 181

20020116 403 0.31 1.45 2.09 1.4 104 149


20020118 442 0.38 2.67 3.68 1.79 149 205

20020119 433 0.16 1.07 2.06 0.72 148 286

20020120 431 0.35 1.81 2.63 0.94 192 279

20020121 434 0.21 1.33 2.24 0.84 158 267

20020122 432 0.22 1.29 2.3 0.78 166 297

20020123 439 0.26 2.34 2.05 1.08 217 191

20020124 436 0.22 2.91 2 1.41 207 142

20020125 438 0.34 2.57 2.46 1.52 169 162

20020126 439 0.32 2.52 2.25 1.41 179 160

20020127 436 0.28 2.76 2.02 1.32 209 153

20020128 431 0.28 3.55 1.66 1.54 230 108

20020129 442 0.37 2.94 1.47 1.66 177 88

20020130* 435 0.33 3.32 2.06 1.68 197 123

20020131* 438 0.28 2.87 1.53 1.79 160 85

SWCs



20020134 432 0.17 0.95 0.45 1.37 69 33

20020135 431 0.15 0.6 0.45 0.65 92 68

20020136 437 0.04 1.47 0.94 0.59 247 158

20020137 442 0.11 4.32 0.99 1.38 313 72

20020138 440 0.11 3.12 1.65 2.28 137 73


203

Table A5.7 TOC and Rock-Eval pyrolysis results for cuttings samples from Dinichthys-1. S1 values are invalid.

GA No. Tmax S1 S2 S3 TOC HI OI

20010723* 341 0.89 1.42 1.34 0.98 144 137

20010724* 334 1.56 1.88 1.33 1.09 173 122

20010725* 320 2.51 2.5 2.57 1.08 232 238

20010726* 429 1.58 2.62 1.45 1.63 160 89

20010727* 434 1.78 2.75 1.76 nd nd nd

20010728* 433 0.84 2.27 0.99 1.61 141 61

20010729* 423 0.96 2.72 1.04 1.56 174 67

20010730* 435 1.29 2.66 1.40 1.58 169 89

20010731* 436 0.67 2.52 0.34 1.57 160 21

20010732* 436 1.21 3.2 1.17 1.79 178 66

20010733* 421 0.87 3.61 1.03 1.69 213 61

20010734* 318 0.95 1.91 1.22 1.44 133 85

20010735* 320 0.83 1.61 0.67 1.33 121 50

20010736 437 0.55 1.67 0.80 nd nd nd

20010737 439 0.36 1.63 1.30 nd nd nd

20010738 447 0.61 3.82 0.53 2.11 181 25

20010739 447 0.61 2.86 0.53 1.72 167 31

20010740 447 0.57 3.52 1.53 2.34 151 65

20010741 454 0.49 2.57 0.59 nd nd nd

20010742 455 0.54 2.41 0.69 2.65 91 26

20010743* 432 0.61 2.85 1.01 2.50 114 40

20010744 450 0.20 0.83 0.97 0.99 84 98

20010745* 397 0.19 1.57 1.59 1.01 155 157

20010746* 324 0.63 1.39 1.20 1.35 103 89

20010747* 367 0.18 1.74 2.80 2.40 72 117


204

Table A5.8 TOC and Rock-Eval pyrolysis results for cuttings samples from Gorgonichthys-1. S1 values are invalid.



20010676* 337 0.56 2.30 1.42 1.03 224 139

20010677* 417 0.10 0.87 0.74 0.85 102 87

20010678 420 0.04 0.70 0.57 1.40 50 41

20010679 428 0.06 1.62 0.50 1.28 127 39

20010680 431 0.04 1.25 0.38 1.18 106 32

20010681 433 0.04 1.58 0.42 1.26 125 33

20010682 432 0.03 1.33 0.31 1.33 100 23

20010683 431 0.08 3.11 0.55 1.65 188 33

20010684 432 0.15 3.87 0.59 1.60 243 37

20010685 426 0.23 3.28 0.57 1.46 224 39

20010686 427 0.10 1.79 0.45 1.53 117 29

20010687 431 0.11 2.97 0.51 1.44 206 36

20010688 431 0.07 1.71 0.62 1.17 146 53

20010689 430 0.17 3.29 0.76 1.27 259 60

20010691 435 0.10 2.88 0.48 1.32 218 36

20010692 436 0.10 3.11 0.50 1.77 176 28

20010695 441 0.09 2.55 0.74 2.00 128 37

20010696 432 0.15 3.71 0.43 2.67 139 16

20010697 436 0.06 1.33 0.44 0.83 160 53

20010698* 431 0.11 3.87 0.54 1.09 354 49

20010699* 425 0.08 2.92 0.72 1.03 283 70

20010700* 431 0.10 3.00 0.58 1.62 185 36

20010701* 423 0.09 2.43 0.60 0.76 317 79

20010702* 426 0.07 1.47 0.55 0.42 352 131


205

Table A5.9 TOC and Rock-Eval pyrolysis results for cuttings samples from Titanichthys-1. S1 values are invalid.



20010703 426 0.02 0.26 0.24 0.77 34 31

20010704* 421 0.03 0.61 0.19 1.18 52 16

20010705 431 0.02 1.52 0.16 1.44 106 11

20010706 428 0.02 1.48 0.1 1.38 107 7

20010707 428 0.04 2.21 0.09 1.61 137 5

20010708 431 0.04 2.93 0.04 1.68 175 2

20010709 429 0.03 1.19 0.03 1.06 111 3

20010710 430 0.03 1.34 0.03 1.64 82 2

20010711 430 0.07 1.98 0.61 1.81 109 33

20010712 429 0.06 1.47 0.42 0.93 158 45

20010713* 422 0.08 2.77 0.39 1.39 199 28

20010714 429 0.11 3.03 0.65 1.37 222 47

20010715 437 0.07 2.85 0.4 1.14 249 35

20010716 433 0.11 3.72 0.69 1.42 263 49

20010717 442 0.07 3.99 0.44 1.99 200 22

20010718 441 0.06 4.04 0.46 2.76 146 17

20010719 442 0.08 2.73 0.72 1.68 162 43

20010720 444 0.11 2.8 0.55 2.23 126 25

20010721 441 0.07 1.74 0.6 1.43 122 42

20010722* 417 0.16 2.35 0.87 0.83 284 105


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Hydrocarbon Generation and Expulsion from Early Cretaceous ... · the presence of generated bitumen in pores of all sizes near the base of the formation, but not within the underlying