Integration of Seismic Inversion, Pore Pressure Prediction, and TOC Prediction in Preliminary Study of Shale Gas Exploration

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Integration of Seismic Inversion, Pore Pressure Prediction, and TOC Prediction in Preliminary Study of Shale Gas Exploration

Andika Perbawa (1), Bayu Kusuma (1), Sonny Winardhi (2)

PIT HAGI 2012 - 216

(1) Medco E&P Indonesia (2) Institute of Technology Bandung

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• Introduction

• Basic theory

• Data Availability and Method

• Result

• Conclusions and Recommendations

Outline

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Unconventional Gas ?

Introduction

“Natural gas that cannot be produced at economic flow rates or in

economic volumes of natural gas unless the well is stimulated by a

large hydraulic fracture treatment, a horizontal wellbore, or by using

multilateral wellbores or some other technique to expose more of the

reservoir to the wellbore”

Holditch, 2007

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What is Shale Gas ?

Source: US Energy Information Administration

American Century Investment, 2011

1,275 TCF862 TCF

774 TCF681 TCF

485 TCF

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Organic rich shale : TOC > 1.0%, HI > 100

Gas type : Free gas and absorb gas

Permeability : Low need fracture job

Maturation : Mature to over-mature zone window (> 1.3 %Ro)

Thickness : > 75 ft

Kerogen type : Type I and II generates more gas than type III.

Mineralogy : More quartz / less clay, brittle shale / more fracture.

Storage : Fractures and pores

Low recovery efficiency : 8-15%

Performance of production : Depend on natural fractures and artificial fracture

Characteristics

Introduction

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• Rock type, lithology, mineralogy and V-clay estimation• Kerogen estimation and distribution • Fracture orientation• Maturation distribution• Shale distribution• TOC distribution• Reservoir pressure distribution• Brittleness and ductile distribution• Porosity distribution• Permeability distribution• Depositional setting, direction and isopach of shale distribution• Gas saturation and composition estimation• Fluid sensitivity• Volume calculation

Key Parameter in Shale Gas Exploration

Introduction

Materials covered

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Delineate potential shale gas play using available

data, then recommend a drilling location to acquire a

complete set of new data and to be able to evaluate

shale gas resources more intensively

Objectives

Introduction

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1. Geochemistry• Total Organic Carbon: TOC• Maturation : %Ro , Tmax, LOM• Kerogen type : HI, S2/S3

Data needed to evaluate the potential of shale gas in exploration:

Data Availability

2. Petrophysics and Petrography• Mineralogy: XRD, SEM• Permeability• Fracture evaluation• Gas content and capacity (absorbed and free)• Pressure

3. Well Data• GR, spectral GR, Vp, Vs, Density, Neutron, Resistivity,

Image log, dip meter, PE, ect.• Core Data• VSP/checkshot

4. Seismic Data• 3D pre-stack seismic data

*Red indicates data available for this study

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Workflow

Well Data(GR, ILD, Sonic, RHOB,

NPHI)

Seismic Data(PSTM Pre-Stack)

Geochemist Data(Ro, TOC)

Sweetspot identification and TOC prediction

Rock Physics(S-Wave prediction)

Seismic Simultaneous Inversion

Shale Distribution

Probable Shale Gas Potential Zone

Overpressure Identification

Overpressure ZoneTOC Distribution


Regional Tectonic Setting

Location

(After Argakoesoemah, 2005)

(Bishop, 2001)

Tectonostratigraphy

Objective area


Depositional Environment

Ginger and Fielding, 2005

Upper Talang Akar Fm.Lower Talang Akar Fm.

Objective area Objective area

TOC PREDICTION

TOCPrediction

Method

SimultaneousSeismic Inversion

Pore PressurePrediction


Passey (1990) Method:

TOC Prediction

Method – Theory (1)

TOCPrediction

Method



Ro transformation to LOM:


TOC Prediction

Method – Application (1)

Crossover between DT (green) and resistivity (purple) indicates potential zone

-------- DT ---------------- ILD --------Gamma ray ΔLogR

PseudoTOC

Cutoff TOC line (1%)

Target Zone

Pseudo TOC indicate Upper Talang Akar Fm. as potential zone (TOC ≥ 1%)

TOC original

TOC prediction

Ro ≈ 1.82 %TD: 7680

Ro ≈ 1.42 %Top TAF

TOCPrediction

Method



SIMULTANEOUS SEISMIC INVERSION

TOCPrediction

Method




Shear Wave Prediction


TOCPrediction

Method



Input: Vp, ρ, Vsh, Sw, Ф

𝜶Initial value α=0.01

𝜸=𝟏+𝟐𝜶𝟏+𝜶

𝝁𝒅𝒓𝒚=𝝁𝒎(𝟏−𝜽)(𝟏+𝜸𝜶𝜽)

𝑲 𝒅𝒓𝒚=𝑲𝒎(𝟏−𝜽)(𝟏+𝜶𝜽)

Vsh, Hashin-Strikman

𝑽 𝒑❑(𝜶)=√𝑲 𝒅𝒓𝒚+

𝟒𝟑 𝝁𝒅𝒓𝒚

𝝆

𝑽 𝒑❑ (𝜶 )−𝑽 𝒑𝒂𝒄𝒕𝒖𝒂𝒍 ≈𝒎𝒊𝒏𝒊𝒎𝒖𝒎yes no𝑽 𝒔

❑=√𝝁𝒅𝒓𝒚

𝝆

Update

Gassman’s equation

(Modified Lee, 2005)


Validation


TOCPrediction

Method



Good match

Good match

Velocity actual (ms)

Velo

city

pre

dict

ed (m

s)

Apply to Objective well data

Method test in the other well that has Vs

Check relationship between prediction and actual data


Cross plot analysis – Pseudo TOC vs Vp


TOCPrediction

Method



TOC

(%)

Vp (ft/s)

Gamma ray (API)

organic shale trend in the upper TAF

shale sand trend

sand trend


Cross plot analysis – Gamma Ray vs Vp/Vs


TOCPrediction

Method



2.1 Vp/Vs

Gammaray

86

Vp/Vs < 2.1 = SandyVp/Vs > 2.1 = Shaly

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Method – Application (2)Seismic section

Well X

TELISA MARKER 3

BASEMENT

26 m.a. LOWER TAF

23 m.a. -base inversion window-

NESW

21 m.a. UPPER TAF-top inversion window-

NE

SW

1000 ms

2000 ms

3000 ms

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Simultaneous Seismic Inversion Result: VpMethod – Application (2)

TOCPrediction

Method



Well-X

1000 ms

2000 ms

3000 ms

PORE PRESSURE PREDICTION

TOCPrediction

Method




Pore Pressure Prediction


(Chilingar et. al., 2002)

(Reynolds., 2002)

Gradient (psi/ft)

Equivalent mud-weight (ppg)

Geo-pressure characteristic

0.465-0.65 8.95 – 12.51 Soft to mild

0.65-0.85 12.51 – 16.36 Mild

> 0.85 > 16.36 Hard

(Dutta, 1987)TOC

Prediction

Method




Pore Pressure Prediction


TOCPrediction

Method



Pore Pressure Prediction using velocity data from:1. DT log/Sonic (purple).2. Pseudo DT derived from

resistivity (red) using Faust (1953) equation. VR=a(Rdeep)c

3. Calibrated velocity stacking (black).

After all of velocity data are aligned, apply Eaton’s equation to calibrated velocity stack cube

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Potential Shale Gas Area

Result

Potential Area

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• Passey’s method shows a sweet spot interval in Upper Talang Akar Fm.

• The potential shale gas is about 100 feet thick and has more than 1% of TOC in Upper Talang Akar Fm.

• The Lower Talang Akar Fm. has less potential shale gas.

• The shale distribution covers a whole objective area (Upper Talang Akar Fm.)

• There are several spotty areas that have a medium pressure regime in the north, west and south-east relative to well- X. Drilling needs to be aware.

• The two interesting potential shale gas areas (TOC ≥ 1%) are located in the west, trending north-south, and in the east relative to well-X.

• Both locations can be recommended for the next pilot holes in order to acquire a complete set of new data and to be able to evaluate more intensively

Conclusions

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• Use actual shear wave data to reduce uncertainty.

• Use TOC data from Core or SWC for accurate depth location.

• Drill a pilot hole in order to acquire a complete set of new data and to be able to evaluate more intensively.

• Core Data• SEM• XRD• Geochemist analysis (TOC, Ro, HI, Rock eval, etc.)• Complete well log data (include shear wave data)• VSP

• Conduct a 3D data with small bin and narrow inline/xline interval. Perform anisotropic processing and analysis to determine young modulus and bulk modulus cube for brittleness identification.

• Conduct coherence, variance, dip-azimuth attribute to determine fracture orientation.

Recommendations

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• Argakoesoemah R.M.I., Raharja M., Winardhi S., Tarigan R., Maksum T.F., Aimar A., 2005, Telisa Shallow Marine sandstone As An Emerging Exploration Target In Palembang High, South Sumatra Basin, Proceedings Indonesian Petroleum Association, 30th Annual Convention, Jakarta.

• Bishop, Michele. G., 2001, South Sumatra Basin Province, Indonesia: The Lahat/Talang Akar-Cenozoic Total Petroleum System. USGS 99-50-S. USA.

• Dutta, N.C., ed, 1987, Geopressure: Society of Exploration Geophysicists Reprint Series 7, 365 p.

• Eaton, Ben A., 1975. The Equation For Geopressure Prediction From Well Logs. SPE 50th Annual Fall Meeting, Dallas, TX, September 28 – October 1, 1975. SPE paper # 5544, 11 pp.

• Fatti, J. L., P. J. Vail, G. C. Smith, P. J. Strauss, and P. R. Levitt, 1994. Detection of gas in sandstone reservoirs using AVO analysis: A 3D seismik case history using the Geostack technique . Geophysics, 59, 1362–1376.

• Faust, L. Y., 1953, A velocity function including lithologic variation, Geophysics, 18, 271-288.

• Finnegan, J., 2011, Is Shale Gas a Game Changer in the Global Energy Supply Outlook?, American Century Investment, In-Fly-72552 1107.

• Ginger, D., K. Fielding, 2005, The Petroleum Systems and Future Potential of the South Sumatra Basin. IPA05-G-039.

• Holditch, S.A., 2007, Unconventional Gas. NPC Global Oil and Gas Study, Texas.

• Lee. M.W., 2005, A simple method of predicting S-wave velocity. Geophysics 71, 161-164.

• Passey. Q. R., 1990, A Practical Model For Organic Richness from Porosity and Resistivity Logs , AAPG Bulletin V.74, No.12.

References

THANK YOU

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Integration of Seismic Inversion, Pore Pressure Prediction, and TOC Prediction in Preliminary Study of Shale Gas Exploration