Australia Pacific LNG Upstream Phase 1 Groundwater ...€¦ · Australia Pacific LNG Upstream Phase 1 Groundwater Mitigation Plan commercial-in-confidence Q-LNG01-10-MP-0019 Australia

Australia Pacific LNG Upstream Phase 1 Groundwater Mitigation Plan

commercial-in-confidence Q-LNG01-10-MP-0019 Australia Pacific LNG Pty Limited ABN 68 001 646 331 Level 3, 135 Coronation Drive, Milton, Qld, 4064 GPO Box 148, Brisbane, Qld, 4001 • Telephone (07) 3858 0280• Facsimile 1300 863 446 • www.aplng.com.au 2

Table of Contents

1. Introduction ................................................................................................................. 3

2. Qualification of Authors .............................................................................................. 3

3. Springs ....................................................................................................................... 3

3.1 Risk Assessment .......................................................................................... 3 3.2 APLNG Springs Mitigation Responsibility ..................................................... 5 3.3 Springs Mitigation Strategy ........................................................................... 5 3.4 Mitigation options for springs for which APLNG is responsible .................... 6

3.4.1 Scott’s Creek Springs Complex ...................................................... 7 3.4.2 Barton Springs ................................................................................ 7

4. Groundwater Bores .................................................................................................... 8

4.1 Compromised Bores ................................................................................... 10

5. Aquifer Drawdown Mitigation - Aquifer Injection ....................................................... 11

6. References ............................................................................................................... 17

Appendix A - Wellbore Pathway Risk Assessment ............................................................... 18

Appendix B - Precipice Sandstone Modelling Report (SKM, 2013) ...................................... 24



1. Introduction

The following Groundwater Mitigation Plan documents local and regional mitigation options which are planned or have been assessed as available to Australia Pacific LNG to manage potential impacts from CSG production. The assessment is intended to be able to be updated as new information becomes available, but has been prepared at this time primarily to meet the requirements of the Stage 2 CSG Water Monitoring and Management Plan required by the Federal environmental approvals for the Australia Pacific LNG gasfields (EPBC 2009/4974).

2. Qualification of Authors

This plan has been prepared and reviewed by the following team:

Role Name Position Qualifications Relevant

Experience

Author Ryan Morris Senior

Hydrogeologist BScHons (Geology)

RPGeo (Hydrogeology) 13 years

Author Peter Evans Staff

Hydrogeologist

B App Sci (App Geol) B Econ M EnvMgmt Grad Dip (Applied Finance & Investment)

29 years

Author Andrew Moser Groundwater

Manager

BSc (Applied Geology)

RPGeo (Hydrogeology) 24 years

3. Springs

The progress of spring assessments and future work is documented in the Australia Pacific LNG’s 2013 Groundwater Assessment (APLNG, 2013a), while springs monitoring and vent monitoring is addressed in the Groundwater Monitoring Plan (APLNG, 2013b).

3.1 Risk Assessment

A risk assessment was undertaken for the Surat Cumulative Management Area (Surat CMA) Underground Water Impact Report (UWIR) (QWC, 2012). The UWIR numerical flow model was used to identify potentially affected springs, which were identified as: “a spring overlying a GAB aquifer where the long-term predicted impact on water pressures at the location of the spring resulting from the extraction of water petroleum tenure holders exceeds 0.2m As well as the springs identified using the regional groundwater flow model, the Commission has included high value springs that are located up to 10km beyond the 0.2m limit to allow for the limitations associated with modelling very small changes in water pressure.”

A standard risk assessment methodology was used, in which likelihood and consequence was identified for each potentially affected spring vent.



Likelihood was assessed through three criteria: Predicted water pressure declines from the UWIR model;

The proximity of the spring to the petroleum development areas; and

The stratigraphic separation between the spring source aquifer and the target

reservoirs. Spring sources aquifers were identified during a survey undertaken as part

of UWIR activities in 2010 (QWC, 2010).

Consequence was assessed through two criteria: The updated conservation ranking for the spring informed by the spring survey; and

The proximity of the spring to the recharge area of the spring’s source aquifer. This is

an indicator of the spring’s ecological resilience to changes in water availability

(QWC, 2012)

Each criterion was equally weighted in the risk assessment, allowing a maximum risk rating of 5.

Water pressure declines of greater than 0.2m were predicted to occur in the source aquifers of five spring complexes containing 38 spring vents, with these springs scoring greater than 3 on the risk assessment scale. Timing and an indication of the predicted drawdown for each of the springs considered to be at highest risk are summarised in Table 1.

The UWIR identified the tenure holder responsible (responsible tenure holder – RTH) for spring impact mitigation for each of these springs.

Table 1 Highest risk potentially affected spring complexes (after QWC, 2012)

Complex Source Aquifer

Summary of model predictions

Risk ranking

Estimated

years before

drawdown exceeds

0.2m (from 2012)

Maximum drawdown

Magnitude (m)

Timeframe (years)

MNES RTH

Lucky Last Evergreen

Formation/Precipice Sandstone

5-40 1-1.5 40-60 5 Yes Santos

Scotts Creek

Hutton Sandstone 20-40 0.2-0.5 30-35 5 Yes APLNG

Barton Gubberamunda

Sandstone 280-380 0.2-0.5 280-380 4 No APLNG

311/Yebna Evergreen

Formation/Precipice Sandstone

40-50 0.2-0.5 50-60 4 Yes Santos

Spring Rock Creek

Evergreen Formation/Precipice

Sandstone 5-60 1-1.5 30-50 4 No Santos



3.2 APLNG Springs Mitigation Responsibility The State’s delegation of responsibility for spring impact mitigation is assigned through the UWIR (QWC, 2012) in accordance with the Responsible Tenure Holder rules. Australia Pacific LNG has responsibility for the Scott’s Creek springs and Barton springs, of which only Scott’s Creek is of relevance to Federal project conditions.

Federal responsibility for mitigation of spring impacts is not explicit in project conditioning. The Joint Industry Plan for an Early Warning System for the Monitoring and Protection of EPBC Springs (JIP) (appended to APLNG, 2013c) allocates responsibility for spring impact mitigation in accordance with the allocations under the Responsible Tenure Holder rules.

3.3 Springs Mitigation Strategy

There are 6 impact mitigation options in accordance with the UWIR (QWC, July 2012):

Offset impacts by relocating existing water bores;

Offset impacts through surrender of entitlements that are not needed;

Offset impacts through improved water use efficiency;

Offset impacts through supply substitution;

Injection of treated water into spring source aquifers; and

Managing water extraction.

The JIP defines a response plan should monitoring data indicate a potential risk to MNES. This plan provides timing requirements for selection, design and implementation of final mitigation strategies, should they be required. The JIP identifies additional potential options, as reproduced in Table 2.

Table 2 Potential options for spring impact mitigation

Potential Concepts of Spring Mitigation

Possible Mitigation Methods

Block impact with recharge (injection) Early recharge at the spring (head increase ahead of impact)

Hydraulic barrier between propagation and spring (in source aquifer

or source of impact)

Provide flow at springs Use water from a different source or from the same source taped at

a distance from the spring to supply spring flow at surface

Remove invasive weeds

Use deeper artesian water for recharge

Recharge at spring with artesian water from another aquifer (this

may necessitate water treatment)

Increase flow from aquifer source to surface

Spring supply borehole

Spring impact offset through removal of impact from private usage

Relocation

Surrender

Substitute



3.4 Mitigation options for springs for which APLNG is responsible

The options outlined above were considered and evaluated for the Scott’s Creek and Barton springs in APLNG’s Desktop Assessment of Relocation, Surrender, Substitution Options to Prevent or Mitigate Spring Impacts (APLNG, 2013a) prepared in accordance with the conditions of approval of the UWIR. The assessment process as documented in the aforementioned report took into account discussions with the landholders at the springs to confirm if they were in agreement in principle with the implementation of mitigation options should they become necessary. A similar approach would be taken for any new springs that require mitigation options assessment for which APLNG is responsible.

Based on the preliminary assessments, the preferred impact mitigation option in both cases was the retirement of existing bores tapping the source aquifer for the springs and replacement of the retired bores into different aquifers. The analyses undertaken by APLNG (2013a) demonstrated the feasibility of mitigating the modelled drawdown by this method in the case of both the Scott’s Creek springs and the Barton springs.

The program of works provided for the preparation of the EPMOR is summarised in the following table.

Table 3 Works program for the preparation of the APLNG EPMOR

Action Status

Finalise Conduct & Compensation Agreement (CCA) negotiations with landholder of land parcel that hosts spring/s

Commenced

Develop program to assess local hydrogeology at site to provide increased certainty regarding spring source aquifer & improvement of understanding of the relationship between reductions in water pressure in source aquifer and flow of water to spring

Hydrogeological conceptualisation updated for Scott’s Creek springs & documented in joint industry report

Santos, Nov. 2013

Undertake initial baseline assessment of relevant spring/s Initial baseline monitoring round

completed October 2013

Identification of ongoing monitoring requirements for spring/s SKM report providing recommendations

for ongoing monitoring submitted to APLNG December 2013

Installation of any monitoring works/equipment required for spring monitoring

Equipment purchased. Awaiting finalisation of CCAs with landowners

prior to installation

EPMOR submitted to OGIA / DEHP EPMOR report submitted to OGIA 30

August 2013 (APLNG 2013b)

The additional investigations that were undertaken subsequent to the UWIR spring surveys in 2010 to refine the hydrogeological conceptualisations of the Scott’s Creek and Barton Group springs reconfirmed that the Hutton Sandstone is the source aquifer at Scott’s Creek



and the Gubberamunda Sandstone the source aquifer for Barton springs. This work was documented within a joint industry report to the Commonwealth (Santos, 2013b).

The final APLNG Evaluation of Prevention or Mitigation Options Report (EPMOR) was provided to OGIA on 30 August 2013 and included:

Discussion of the advantages and disadvantages of each mitigation option and

consideration of any additional options;

Identification and justification for a preferred option; and

A program of local hydrogeological assessment to improve source aquifer

designation.

3.4.1 Scott’s Creek Springs Complex

With respect to the mitigation of potential impact to the Scott’s Creek springs the EMPOR concluded that:

The surrender of existing water entitlements on Moorabinda without the provision of a

high reliability offsetting water supply is unlikely to be approved by the landholder.

Preliminary discussions with the landholder indicate that they would not support such

mitigation measures;

The preferred option is to replace one or both of the closest Hutton bores with

Precipice Sandstone bores as this appears likely to achieve recovery in groundwater

levels above the predicted maximum drawdown. Preliminary discussions with the

landholder indicate that this is their preferred option.

Relocation of existing supplies tapping the Hutton Sandstone source to locations

outside the 5 km exclusion radius is also possible, but less effective. Preliminary

discussions with the landholder indicate that they would support such mitigation

measures, but that it is not their preferred option.

As part of the landholder agreements, they are agreeing to negotiate in good faith on

the preferred mitigation option should that become necessary.

3.4.2 Barton Springs

With respect to the mitigation of potential impact to the Barton Group vent 702 spring, the final EPMOR(APLNG, 2013b) clarified the position regarding pumping from the hand dug well, which is located relatively close to the Barton Group vent 702 in Barton Creek. The landowner of Pine Hills station had indicated that the Hand Dug Well is used infrequently, but has been retained by the landowner so that it could be put back into service should this become necessary. A reduced pumping frequency at this location has the potential to affect drawdown calculations, however, it does not negate the fact that the bore exists in an operational condition and has the potential for greatest impact and also the potential to provide the best mitigation option, by decommissioning and replacement into a deeper aquifer.



On 25 October 2013 SKM the landholder has excavated out the bed of Barton Creek immediately downstream of spring vent 702 to provide a stock water supply in response to low rainfall conditions. While the excavation has not directly physically impacted on the immediate surrounds of the spring, stock water use and evaporation from the open excavation could be expected to further lower the groundwater levels in the vicinity of vent 702 and thus exert some hydrological impact at vent 702.

For the mitigation of potential impact to vent 702 at Barton Creek the final EMPOR (APLNG, 2013b) concluded that:

The preferred option to achieve impact mitigation at Barton Group springs is to

decommission well RN14360 and replace it with a bore tapping a deeper formation

(e.g. Hutton Sandstone). Preliminary discussions with the landholder indicate that

this is their preferred option, and that they would support such mitigation measures.

The surrender of the entitlement for RN14360 without provision of a replacement

water source appears to be unlikely to be acceptable. Preliminary discussions with

the landholder indicate that they would not support such mitigation measures.

The relocation of this supply from RN14360 to a location outside the 5 km spring

exclusion radius could be undertaken, however it would involve significant reticulation

works. Preliminary discussions with the landholder indicate that they would support

such mitigation measures, but that it is not their preferred option. This is the

secondary option for this spring.

The landholder agreement to facilitate monitoring includes provision for the landowner to negotiate in good faith on the preferred mitigation option should that become necessary.

4. Groundwater Bores

The Queensland Water Act 2000 defines obligations for petroleum tenure holders in Queensland to make good any authorised bore that has, or is likely to have, an impaired capacity due to a decline in groundwater levels because of the exercise of underground water rights, and because of this decline, can no longer provide a reasonable quantity or quality of groundwater for its authorised use or purpose.

The Queensland Water Commission, (QWC – now Office of Groundwater Impact Assessment (OGIA)) released the Underground Water Impact Report (UWIR) for the Surat Cumulative Management Area (CMA) on 1 December 2012. Groundwater flow modelling was undertaken using current production schedules and predicted water-take volumes across industry, to assess and predict impacts to groundwater levels.

Under the UWIR, affected areas were defined based on trigger thresholds specified in the Water Act 2000. These trigger thresholds are 5m for consolidated aquifers, and 2m for unconsolidated aquifers. Immediately Affected Areas (IAA) (less than 3 years) and Long-term Affected areas (LAA) (great than 3 years) were defined. The Walloon Coal Measures are the only formation predicted to be impacted within APLNG tenure during the upcoming 3 year period. Accordingly the areas shown as IAA only reflect landholder bores constructed to tap the Walloon Coal Measures.



There is a two-step process for assessing and implementing make good measures:

1. Bore Assessments are required, under the Water Act 2000, to be undertaken by the petroleum tenure holder to help establish if the exceedance of trigger levels constitutes impaired capacity. They are undertaken for each immediately affected bore that is not already the subject of a make good agreement, or by direction of the chief executive.

2. For each bore assessed as requiring make good measures, a Make Good Agreement must be entered into by the responsible tenure holder and the bore owner.

The statutory delivery timelines for the various actions are listed below.

Make Good measures, according to the Water Act 2000, can be any of the following:

a. ensuring the bore owner has access to a reasonable quantity and quality of water for the bore’s authorised use or purpose;

Examples —

bore enhancement by deepening the bore or improving its pumping capacity

constructing a new bore

providing a supply of an equivalent amount of water of a suitable quality by piping it from an alternative source

b. carrying out a plan to monitor the bore, including, for example, by undertaking periodic bore assessments;

c. giving the bore owner monetary or non-monetary compensation for the bore’s impaired capacity.

An outline of the Make Good Agreement schedule showing project progress to date, is provided below:

Delivery Timeframe Date

Bore Assessment 60 business days 28/2/2013

Make Good Agreement 40 Business days following Bore Assessments 29/4/2013

Action agreements Within current UWIR period Before Dec-2015



Action Target

Completion Date

Status

Review Baseline Assessment data for all bores within IAA and properties bisected by IAA. Conduct supplementary investigations to refine formation assignments. Derive list of IAA bores.

December 2012 Complete

Discuss provisional APLNG Bore Assessment results and proposed make good measures with landowners and discuss landowner suggested alternatives.

January 2013 Complete

Complete Bore Assessments, including an outline of the proposed make good measures.

28/2/2013 Complete

Finalise Make Good agreements with signoff by APLNG and landholder. 29/4/2013 Not completed (5/23 agreements finalised)

Implement make good agreements. December 2015 Not commenced

The current scope of make good activities for the first iteration of the UWIR is outlined in the following table. In addition to bores which were judged to be at risk of impaired capacity, a significant number of bores were identified during the Baseline Assessment program that were producing elevated methane as a result of historical landowner groundwater use. Decommissioning of these bores has been included in the make good scope for social and safety reasons.

Make-good activity Refined Estimate

Number of make good agreements 26

Number of make good bores 41

Number or replacement bores 12, or compensation for equivalent replacement bore

Number of bores to decommission 40

Number of bores to monitor 5

*Unauthorised bores have been included if they have or are likely to have elevated gas.

4.1 Compromised Bores

A compromised wellbore is one which may provide a pathway between two aquifers by by-passing the intervening aquitard, and may include bores where the open interval directly connects two aquifer, or there is no cement seal behind the casing. They may include both water bores and petroleum wells. The UWIR numerical groundwater flow model does not currently assess the effects of compromised wellbores on the propagation of drawdown from petroleum production.

A risk assessment was included by APLNG in the development of its groundwater monitoring program (APLNG, 2014a), and has been further assessed herein (Appendix A). The APLNG groundwater monitoring network is considered sufficient to monitoring the potential increase in drawdown propagation as a result of compromised wellbores on its tenure. Should the drawdown occur, it would trigger a response action in accordance with the response process identified in the groundwater monitoring plan and the JIP.



Should compromised wellbores be identified as part of the response process, the compromised wellbore would be decommissioned. The decommissioning procedure would follow the same process outlined in Section 4. APLNG has already decommissioned and replaced one bore which was identified to connect the Walloon Coal Measures and the Hutton Sandstone, and is investigating a second.

5. Aquifer Drawdown Mitigation - Aquifer Injection

Aquifer injection can be used to increase aquifer pressures. Due to the highly confined nature of GAB aquifers, aquifer injection is likely to result a sub-regional to regional scale increases to groundwater levels within the target (receiving) aquifer. Injection is not currently required to achieve any spring impact or groundwater bore mitigation outcomes, however the APLNG’s aquifer injection feasibility studies (APLNG, 2013c) will provide an understanding of the feasibility of increasing formation pressures via injection into the following formations:

Precipice Sandstone;

Hutton Sandstone; and

Gubberamunda Sandstone.

Injection is the primary element of the operational water management strategies at Spring Gully and Reedy Creek.

Injection trials, including hydraulic and geochemical assessment, were completed at Spring Gully in late 2012/early 2013. The technical feasibility assessment and injection management plan, which included a geochemical compatibility assessment was submitted to the Department of Environment and Heritage Protect (DEHP) in February 2013. Approval to inject up to a rate of 9.3ML/day into the Precipice Sandstone at Spring Gully was gained in May 2013 The assumed water profile for Spring Gully injection is shown in Figure 1 (Treated CSG water outflows). Should the water profile be realised, approximately 20GL will be injected into the Precipice Sandstone. Injectate will comprise reverse osmosis permeate with an operational target electrical conductivity of 300µS/cm. The injection site is approximately 15km east of the Bandanna Formation subcrop, which is the source of potential CSG-related drawdown impacts to the Precipice Sandstone (APLNG, 2013d; QWC, 2012). The operational scheme is currently under construction and is scheduled to commence operation in March 2014, Additional injection bores installed for the operational scheme have been constructed to comply with the Queensland Water Act 2000, which is a condition of the Environmental Authority.

Injection trials were successfully completed at Reedy Creek and an operational scheme is currently being constructed. The primary injection target is the Precipice Sandstone, with the technical feasibility of injection into the Hutton Sandstone and Gubberamunda Sandstone currently under assessment. The conceptual basis of design for the Reedy Creek scheme is to match the water quality of the Precipice Sandstone based on total dissolved solids, to deoxygenate the water and to match the Precipice Sandstone native pH. Up to twenty bores will be used to manage the treated CSG water outflows shown on Figure 2 up to 2022. The bores will be constructed to comply with the Code of Practice for Constructing and Abandoning Coal Seam gas Wells in Queensland (DEEDI, 2011). Applications for Environmental Authority approvals have been submitted to DEHP. Injection is scheduled to commence in late 2014.



Regional scale numerical groundwater flow modelling has been undertaken in support of the Reedy Creek aquifer injection scheme management plan. This modelling was originally undertaken using the Surat CMA UWIR cumulative groundwater model (QWC, 2012), however it was found that the UWIR model did not represent the Precipice Sandstone in the vicinity of Reedy Creek at an appropriately local scale. Because the Precipice Sandstone was represented by a layer of only 2m thick modelled pressure increases were unrealistically large.

In lieu of the UWIR model, APLNG commissioned SKM to construct a regional scale numerical groundwater flow model of the Precipice Sandstone to model the hydraulic changes associated with injection and Spring Gully and Reedy Creek (SKM, 2013b, Appendix B). Key aspects of the model include:

The model was constructed to represent the Braided Stream Facies of the Precipice

Sandstone across its extent in the Surat Basin, approximately 350km in the east-west

direction and 450km in the north-south direction. The BSF is the permeable

component of the Precipice Sandstone;

The thickness of the BSF was mapped from drilling logs. A clear relationship between

the total Precipice Sandstone thickness and the BSF thickness was observed, which

allowed the data set to be extended where only total Precipice Sandstone thickness

was available. Actual BSF thickness data was used where available, transitioning to

the calculated thickness when not.;

The model was developed in the FEFLOW Version 6.1finite element software code.

The finite element model mesh consists of interconnected triangles. In general these

triangles have sides in the order of 1500 to 2000 m. In areas of particular interest

such as the springs and Reedy Creek injection borefield the triangles are much

smaller with sides in the order of 400 to 600 m.

The upper and lower boundaries were assumed to be impermeable. This would tend

to over-predict pressure build-up because the pressure could not disperse vertically.

The model was allowed to discharge to the Dawson River, as observed through

pressure surface mapping.;

The hydraulic conductivity of the aquifer was adjusted during calibration The best

calibration was obtained with the hydraulic conductivity of 5 m/d assumed for all of

the model domain except for the Spring Gully area which has an assumed hydraulic

conductivity of 100 m/d. The hydraulic conductivity of 5 m/d corresponds well with

pumping test results obtained by APLNG.

The model of the Precipice Sandstone BSF aquifer is best characterised as a Class 2

model at this stage. It is founded on a large data set obtained from drilling of

numerous wells and from various surveys of the groundwater discharge features

(springs) located in the north of the model domain. It does not reach the highest

classification (Class 3) because it has been calibrated in steady state mode alone

and has not been calibrated to time varying (transient) groundwater responses. There

is little or no useful data on which to base a transient calibration exercise across the


commercial-in-confidence Q-LNG01-10-MP-0019 Australia Pacific LNG Pty Limited ABN 68 001 646 331 L l 3 135 C ti D i Milt Qld 4064

regional extent of the model. Model updates will be in accordance with the Reedy

Creek Precipice Aquifer Injection Management Plan (Q-4255-95-MP-004) (APLNG,

2013e) and will initially be annually. These updates are expected to upgrade the

model to Class 3; and

Five different injection scenarios were modelled to assess pressure changes resulting

from Reedy Creek and spring Gully injection. Partcile tracking was ulso modelled to

assess the movement of the injectate during and for 1,000 years after injection.

Figure 3 shows the predicted head change after 5 years of injection at Reedy Creek (following the water profile shown in Figure 2). This Figure shows that a positive head change could be expected at the Lucky Last and Yebna spring complexes, with continued injection likely to result in sustaining head changes to the springs in the northeast of the Surat Basin. The model does not consider long term decline in water levels in the Precipice Sandstone nor does it consider the potential drawdown associated with CSG production.

Figure 1 Spring Gully Water Profile



Figure 2 Reedy Creek Water Profile



Figure 3 Modelled head rise resulting from five years of injection at Reedy Creek, based on the water profile shown in Figure 2 (SKM, 2013b)



Figure 4 Modelled head rise resulting from ten years of injection at Reedy Creek, based on the water profile shown in Figure 2 (SKM, 2013b)

Injune

Taroom

RomaYuleba

MilesChinchilla

Goondiwindi

Wandoan

Wallumbilla

600000 650000 700000 750000 800000 850000 900000

Predicted Hydraulic Impact Zone (10 year) - 5 m

Predicted Hydraulic Impact Zone (10 year) - 1 m

Predicted Hydraulic Impact Zone (10 year) - 0.1 m

Baseflow Reach

Spring Vent

Landholder Bore

APLNG Lease

Roads

Reedy Creek Injection Site

Rivers

Towns

Precipice Sandstone Outcrop



6. References

APLNG, 2013a. Desktop Assessment of Relocation, Surrender, Substitution Options to Prevent or Mitigate Spring Impacts, report Q-LNG01-95-RP-2134 Rev 1, February 2013

APLNG 2013b Surat Underground Water Impact Report Springs: Evaluation of Prevention or Mitigation Options Report (EPMOR), report number Q-LNG01-95-RP-2201, August 2013

Australia Pacific LNG, 2013c. Reedy Creek Precipice Aquifer Injection Management Plan (Q-4255-95-MP-004)

Australia Pacific LNG, 2014a. Groundwater Monitoring Plan Q-LNG01-10-MP-0005. March

2013. Included as Component 2 of Stage 2 CSG WMMP.

Australia Pacific LNG, 2014b. Aquifer Injection Feasibility Studies Q-LNG01-10-TR-0060.

Queensland Water Commission, July 2012. Underground Water Impact Report for the Surat Cumulative Management Area. Queensland Water Commission, 18 July 2012.

DEEDI 2011. Code of Practice for Constructing and Abandoning Coal Seam Gas Wells in Queensland, Version 1.0. Department of Employment, Economic Development and Innovation.

Hemker and Post (2014) MLU for Windows, Version2.25.58. Aquifer test analysis for Unsteady-State Flow in Multiple-Aquifer Systems.

JIP (2013). Joint Industry Plan for an Early Warning System for the Monitoring and Protection of EPBC Springs, 30 September 2013.

Santos 2013b, EPBC Spring Hydrogeological Conceptual Model, report submitted to the Department of Environment, Document Number: 3301-GLNG-4-1.3-0060, 1 November 2013

SKM 2013a Surat Basin Quarterly Spring Baseline Monitoring Program - Future Baseline Monitoring Recommendations, report number QE06816.700, 13 December 2013

SKM 2013b. Injection into the Precipice Sandstone – Groundwater Modelling Report, October 2013.



Appendix A - Wellbore Pathway Risk Assessment



Wellbores that transect multiple aquifers have the potential to transmit drawdown effects between aquifers if they possess some form of pathway (e.g., screens extending across multiple aquifer layers, poorly sealed wellbore annuli, or failure of the casing). The potential for compromised wellbores is therefore a function of its construction and its condition.

There are an estimated 6,500 bores currently in the study area within the Surat Basin. These bores range in depth from 1.5 m to up to 8,500 m. Many of the deeper wells were established for petroleum exploration, and were plugged and abandoned following their completion.

The potential for a compromised well to act as a conduit is directly related to the number of units it transects. That is, if it is screened in the shallowest aquifer (Cainozoic) and fails it could not act as a conduit as there are no overlying units. However, if a well screened in a deeper aquifer (e.g., Precipice Formation) fails, this could inadvertently cause connection with one of up to six other overlying units (i.e., Evergreen, Hutton, Eurombah, Walloons, Springbok, Westbourne, Gubberamunda, BMO, Rolling Downs Group, or Cainozoic). Total depth, or if this was not available the deepest constructed interval, of 3,420 bores was compared with each geological layer and the number of units which the bore transected was determined. This included CSG, other petroleum wells and water bores. A maximum score of ten was applied, which corresponded to a bore that intersected the Precipice Sandstone or deeper. Bores that did not intersect the Walloon Coal Measures were also included, because CSG induced drawdown in an upper aquifer could transmit through a compromised wellbore to an even shallower aquifer.

The ages of the bores date back to the early twentieth century. Because well construction techniques and materials have improved over time, older bores were assessed a higher potential for failure, thereby providing a pathway for inter-aquifer flow. To allow for this changing potential, well age was also used as an input parameter to the vulnerability mapping. Although construction standards were enacted in about the nineteen nineties which in theory would improve bore construction, this scoring was not weighted. Well age was rated on an equal scale of zero to ten, with zero representing ages from 2000 to 2009.

The ranking criteria are shown in Table A1.

The number of units was then multiplied by its age ranking to obtain an overall indicator of risk of the wellbore acting as a pathway for pressure transmittal. The product of the depth and age ranking was then reclassified to a ranking of between 1 and 10, with 10 being the highest risk, to provide a relative risk ranking. The ranked locations are shown on the map below (Figure A1).

From the map, it can be seen that the majority of bores score a classified ranking of 1 or 2, and are therefore a low risk of providing a pathway. The highest risk ranked wellbore on APLNG tenure is ranked as 6, which is considered to constitute a medium risk as it falls within the middle of the range. The risk category tends to be skewed to the depth ranking, with most of the higher risk bores being old exploration wells.

A simple analytical model was set up using MLU for Windows (Hemker and Post, 2014), which represents CSG extraction from the Walloon Coal Measures and two boreholes that connect multiple aquifers. The compromised boreholes connect the Walloon Coal Measures with the Hutton Sandstone and the Hutton and Precipice Sandstones.



The aquifers were parameterised with average hydraulic parameters for each of the Hutton Sandstone and Precipice Sandstone (APLNG, 2014b). These aquifers were selected as they are source aquifers for springs which host MNES. The intervening aquitards were parameterised to provide no leakage between the aquifer, which forces all water to flow through the compromised wellbores, and does not reduce the predicted drawdown through aquitard leakage. (Figure A2 and A3) The extraction rate from the layer representing the Walloon Coal Measures was adjusted to result in approximately 1,000m of drawdown, which approximates the maximum anticipated drawdown in the Walloons for the APLNG gasfields. This equated to a continuous extraction rate of 1ML/day.

Pseudo-monitoring bores were included in each of the layers representing the Hutton and Precipice to assess the drawdown propagation away from the site. The monitoring bores were located at 1,000m, 2,000m, 5,000m, 10,000m and 50,000m.

Two scenarios were run varying the offset distance between the compromised bores and the producing wells. Scenario 1 had a distance of 100m which represents the distance to the edge of a drilling lease, and Scenario two used a distance of 350m, which is the approximate distance between two CSG wells in the Walloons fields.

The results of the modelling show little discernable difference between the two scenarios. The model predicts maximum drawdowns of approximately 7 and 0.7m at 50km in the Hutton and Precipice Sandstone respectively. One meter of drawdown is predicted in the Hutton Sandstone between 80 days and 300 days at 1km and 50km respectively. In the Precipice Sandstone, 1m of drawdown in predicted after 10 years.

All higher risk bores are with 10km of a APLNG Hutton Sandstone monitoring bore. The rate of drawdown, and distribution of monitoring bores, suggests that the monitoring network will be adequate to assess the potential effects of compromised wellbores on the Hutton Sandstone. Similarly the monitoring network, has Precipice monitoring bores within 10km of most high risk bores, with the exception of one in the Carinya field. Carinya is not currently in the field development plan which extends out to 2025.

Table A1 Wellbore Pathway Risk Criteria Ranking

Well age (years) Deepest Surat Basin Unit Intersected

Category Ranking

100-110 Precipice 10 90-100 Evergreen 9 80-90 Hutton 8 70-80 Eurombah 7 60-70 Walloons 6 50-60 Springbok 5

40 – 50 Westbourne 4 30 – 40 Gubberamunda 3 20 – 30 BMO Grouping 2 10 – 20 Cainozoic 1

<10 - 0



Figure A1 Wellbore pathway risk ranking for each groundwater bore

148.

8 1

48.8

149.

3 1

49.3

149.

8 1

49.8

150.

3 1

50.3

150.

8 1

50.8

151.

2 1

51.2

-28.1 -28.1

-27.6 -27.6

-27.1 -27.1

-26.6 -26.6

-26.1 -26.1

-25.6 -25.6

-25.4 -25.4

BLYTHDALE

CHINCHILLA

CONDAMINE

KOGAN

MILES

SURAT

TARA

TAROOM

WANDOAN

YULEBA

LEGEND

APLNG GWMB

APLNG PL

APLNG ATP

ROAD

STREAM

TOWN

Wellbore PathwayRisk Ranking

1

2

3

4

5

6

7

8

9

10



Figure A2 MLU Aquifer parameterisation

Figure A3 MLU Aquitard parameterisation

Figure A4 MLU prediction: compromised wellbores at 50m

10 100 1000 10000

1

10

100

1000WCM1, layer: 1

Hutton1000, layer: 2










Drawdown - time

Time [d]

Drawdown [m]



Figure A5 MLU prediction: compromised wellbores at 350m

10 100 1000 10000

1

10

100

1000WCM1, layer: 1











Drawdown - time

Time [d]

Drawdown [m]



Appendix B - Precipice Sandstone Modelling Report (SKM, 2013)

Documents

Australia Pacific LNG Upstream Phase 1 Groundwater ...€¦ · Australia Pacific LNG Upstream Phase 1 Groundwater Mitigation Plan commercial-in-confidence Q-LNG01-10-MP-0019 Australia