ARROW ENERGY GROUNDWATER MODELLING INFORMATION ·  · 2014-06-12GROUNDWATER MODELLING INFORMATION. October 2011. ... system (geometry, material ... CSIRO 2008, upper Condamine groundwater

ARROW ENERGY GROUNDWATER MODELLING INFORMATION

October 2011

GROUNDWATER MODELLINGPRESENTATION SUMMARY

• What is groundwater modelling?

• What did the peer review say?

• What were the predictions from the model?

• What are we doing to understand more?

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ObjectivesWhat are “groundwater models”?

What do we mean by: “conceptual model”

“water balance”

“numerical groundwater flow model”

Calibration

Prediction and uncertainty

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First, a refresher… Groundwater occurs in pores and fractures in rock and

soil. Aquifers are layers that transmit groundwater, mainly

horizontally. Aquitards impede the movement of groundwater.

Flow in aquitards is mainly vertical. Groundwater flow is driven by differences in head,

which is a measure of potential energy The rate of flow of groundwater is controlled by

hydraulic conductivity, which can be different in different directions.

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Shale (aquitard)

Alluvium

Aquifers, aquitards, pressure, head

Groundwater flows due to differences in “head”

water table elevation

piezometric head

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Water tableWater table

What is a groundwater model?A “groundwater model” is a representation in

computer software of a regional scale hydrogeological system: based on a complete description of the natural

system (geometry, material properties, recharge etc.)

including proposed changes (e.g. pumping)with which we can predict water levels,

piezometric heads and flows in space and time

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Purpose of modellingModelling is the only methodology that allows

us predict future behaviour

Models can have different levels of detail (“complexity”) To illustrate or explain

To predict potential environmental impacts

To predict short-term operational response (an “aquifer simulator”)

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Stages in modelling1. Conceptual model Sketch how a hydrogeological system is believed to

work

2. Mathematical model Use equations to represent the physics of

groundwater flow

3. Numerical model Convert to a form suitable for computers

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Conceptual model The first stage in understanding a

hydrogeological system is the development of a conceptual model Regional geology, including faults and shear zones

Layering, and hydrostratigraphy

Hydrogeological properties (Sy, S0, Kh, Kv)

Recharge, pumping, rivers, streams

Initial heads

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Water balance numerical modelConsider a small volume of aquifer or aquitard:

Qin Qout

Qin

Qout Qin

Qout

Water balance allows us to compute

h(x,y,z,t) at any time

Calibration versus prediction Important distinction between simulating

the past and the future

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PresentPast Future

Calibration: adjust parameters until simulated heads match historical observations

Prediction: simulate future behaviour

Calibration

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Time series plot

Contour plot

Results of Peer Review

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The conceptual hydrogeological model is supported by a detailed geological model

Some aspects of calibration are very good

Predicted impacts are of the right order of magnitude

Consistent with models developed by other CSG proponents

Model needs to evolve from an “impact assessment model” towards an “aquifer simulator”

Recommendations

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Some aspects require further testing/refinement: Representation of regional faults

Representation of connections between key hydrostratigraphic units

Representation of recharge and evapotranspiration

SURAT GAS PROJECT EIS GROUNDWATER MODELLING

October 2011

ARROW ENERGYOVERVIEW

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Scope of groundwater impact assessment

Key assumptions

Projected groundwater abstractions from Walloon Coal Measures

Modelled impacts of depressurisation

Proposed mitigation measures and studies

ARROW ENERGYSCOPE OF GROUNDWATER IMPACT ASSESSMENT

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Develop a regionalgroundwater model based on most accurate data

Calibration to the best available data

Predict groundwater abstraction that simulates the operations of Arrow and other CSG proponents

To understand the resilience of groundwater systems and how they will recover

Area 120,000 km2 15 layers

1.8 million cells

ARROW ENERGYKEY ASSUMPTIONS

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Deeper aquifers Comprise extensive thicknesses of

consolidated rock Mainly sub-artesian through project

study area Recharged through infiltration along

Great Dividing RangeCondamine Alluvium

Forms a surface unconfined aquifer in some parts of the basin

Recharged mainly from Condamine River seepage

Groundwater movement Movement of groundwater will occur

based upon the properties of the aquifers and aquitards.

ARROW ENERGYABSTRACTION VOLUMES

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Groundwater abstraction from coal measures (Walloons)

Model development scenarios for proposed CSG projects

• Arrow only 25GL/yr

• Condamine 40~60 GL/yr “allocated”

• Walloons 7~13 GL/yr “allocated”

Aquifers influenced by multiple CSG projects.

Arrow Surat Gas Project only

Arrow , Origin, QGC & Santos Projects (cumulative)

COAL SEAM AQUIFERS (WALLOON COAL MEASURES)

Peak impact in 2024 with recovery occurring as abstraction winds downWith no mitigation

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Recovery occurring as abstraction winds downWith no mitigation

COAL SEAM AQUIFERS (WALLOON COAL MEASURES)

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INTERMEDIATE AQUIFERS (SPRINGBOK SANDSTONE)

Peak drawdown of 40 to 50 m

Recovery so that drawdown is generally reduced to 20 m by 2061

With no mitigation

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DEEP AQUIFERS(HUTTON SANDSTONE)

Peak drawdown of 50 to 75 m Recovery to 20 to 30 m by 2061 With no mitigation

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DEEP AQUIFERS(PRECIPICE SANDSTONE)

Peak drawdown of 30 to 40 m in 2042 Recovery to 20 to 30 m by 2061 With no mitigation

ARROW ENERGYSTUDIES TO ADDRESS POTENTIAL IMPACTS

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Preventative Measures Recovery Actions

Impaired capacity

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Monitor changes in

groundwater vs

predictions

Substitute InjectLower pump

Modify pump

Deepen bore

Replace water supply

New bore

SHALLOW AQUIFERS(CONDAMINE ALLUVIUM)

Cumulative impact of all CSG proponents without mitigation

Maximum incremental impact in 2065 of ~2.5m (potential uncertainty range of 1 to 4 m)

Impact in western portion of Condamine Alluvium

With no mitigation

Substitution to maintain water balance

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CONDAMINE ALLUVIUM HIGH LEVEL STUDIES

Past Future?

Recharge Landholder off-take Recharge Net off-take after substitution

CSG Leakage

46.4 GL/yr1

1. DERM 2010, central Condamine Alluvium data availability review2. CSIRO 2008, upper Condamine groundwater model calibration report

Average of 1.8 GL/y

A cumulative volume of 90 GL by 2065

< 46.4 GL/yr?

12-20 GL/yr1

36 GL/yr2

Alluvium Alluvium

12-20 GL/yr1

36 GL/yr2

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Monitor abstraction from bores

Measurement at base of Alluvium and below

Measurement within Alluvium

CONDAMINE ALLUVIUM DETAILED STUDIESCONNECTIVITY TO THE WALLOON COAL MEASURES

Monitor: Abstractions in the Condamine Responses in water levels Alluvium Underlying coal measures

Geochemistry including: Naturally occurring Isotopes:

Rn 222, Kr, Sr, Ar, delta O18 CFC, SF6 Anion/cation ratios

Isotope and isotope/ion ratios to assess mixing of waters

The rate of exchange can be used in future model simulations

HIGH LEVEL STUDIESOTHER AQUIFERS

Modelling expanding calibration datasets & including allocations for aquifer

simulation modelling substitution & injection scenarios uncertainty analysis

Analysis of model predictions to 90-95% confidence intervals assess both the rate of change and the scale of future changes via hypothesis testing

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Hydrochemistry Use of hydrochemistry and isotope hydrology to test hydraulic

connectivity between aquifers and Walloon Coal Measures

Connectivity studies of Walloons and intermediate and deep aquifers via hydraulic testing

Deep injection - Tipton injection study scanning electron microscope results

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DETAILED STUDIESOTHER AQUIFERS

HUTTON SANDSTONESCANNING ELECTRON MICROSCOPE IMAGES

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PP = pore spaceK = kaolinite

PP

K

K

PP

PRECIPICE SANDSTONESCANNING ELECTRON MICROSCOPE IMAGES

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PP = pore spaceQO = quartz

PP

QO

SUMMARY

Initial Impact Assessment Model results completed for EIS

Aquifer Simulation Model for mitigation scenarios in preparation

Field studies are progressing to support mitigation development

Overarching mitigation measure planning is progressing

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Questions

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