Studies on Groundwater Impacts by CSG Productions in Australia

Surat Basin

Ming Li

1,*

, Quan Wang

, Ming Zhang

, Xiangwen Kong

, Zhaohui Xia

, Hongjun Wang

, Zehong

Cui

and Jietang Lv

Research Institute of Petroleum Exploration & Development, Beijing, China;

China's oil and gas exploration and development company, Beijing, China;

China Institute of Geological Environment Monitoring, Beijing, China.

liming211@petrochina.com.cn,

Keywords: Coal seam gas (CSG), Surat Basin, groundwater, aquifer, hydraulic connection

Abstract: The Surat Groundwater system include shallow, intermediate, coal seam and deep groundwater system. The

shallow groundwater resources in Surat basin has been developed over the years for irrigation, stock,

domestic and other uses. Extraction water from this aquifer is critical to support the local irrigation. With

the large-scale CSG production beginning in the Surat basin, the hydraulic connection between the shallow

groundwater and coal seam water become a key problem. This paper first gives an introduction on geology

and hydrogeology of the region and then gives a brief view of CSG production affects the groundwater level

based on the Condamine interconnectivity test analysis, the monitor results of groundwater level and

groundwater level drawdown numerical model predictions. Results show that groundwater levels provide

little to no effect relative to CSG production. Further study and simulation work will continue to research

CSG and groundwater connections.

1 SURAT BASIN CSG

INTRODUCTION

The Surat basin is part of the Cretaceous-Jurassic

Great Artesian basin (GAB). The basin overlies the

Permo-Triassic Bowen Basin and is a relatively

undeformed intra-cratonic basin with overall layer-

cake stratigraphy (Exon, 1976). The regional seismic

section illustrates that the Surat basin is draped over

basement highs and separated by an unconformity

from the underlying Permian-Triassic sediments of

the Bowen Basin (SRK Consulting 2005). Coals

intersected in the Surat Basin are a member of the

Walloon Coal Measures (Figure 1). Most CSG

blocks are in the eastern margin of the Surat Basin.

AA Block is one of CSG blocks in the eastern most

of Surat basin. Most groundwater analysis comes

from AA CSG blocks.

The Walloon coal measures are Low-rank coal

measures with R

of 0.6% and are further divided

into the Juandah coal measures and the Taroom coal

measures. The Walloon coal measures are underlaid

by the Eurombah Formation and Hutton Sandstone

and overlaid by the Springbok Sandstone and its

equivalents, such as Kumbarilla Beds (Figure 2).

The complex architecture of Walloon Coal Measures

is a result of the highly variable depositional

environment. The relatively stable alluvial flood

plain allowed river channels to freely migrate and

disturb coal swamp development rapidly and

laterally (Scott, 2004).

Many LNG projects are being constructed in

Australia. Among them, The CSG-LNG projects are

located in the east Australia (Figure 3). The gas

resources come from the Wallon Coal measures of

Surat Basin. This paper provides interconnectivity

analysis between the coal seams and the shallow

Condamine aquifers, the monitor results of

groundwater level and groundwater level drawdown

numerical model prediction.

214

Li, M., Wang, Q., Zhang, M., Kong, X., Xia, Z., Wang, H., Cui, Z. and Lv, J.

Studies on Groundwater Impacts by CSG Productions in Australia Surat Basin.

In Proceedings of the International Workshop on Environment and Geoscience (IWEG 2018), pages 214-218

ISBN: 978-989-758-342-1

Figure 1: Regional seismic line across the center of

the Surat Basin.

Figure 2: Stratigraphy and groundwater systems in

Surat Basin.

Figure 3: CSG Blocks in Surat Basin.

2 SURAT BASIN

HYDROGEOLOGY REVIEW

AND GROUNDWATER

IMPACTS ANALYSIS

The Surat Basin is located on the eastern margin of

the GAB (Great Artesian Basin), which is

Australia’s largest contiguous groundwater resource.

The formations are exposed along this eastern

recharge zone include the Gubberamunda Sandstone,

Hutton Sandstone and Precipice Sandstone, and they

are found within the project development area. From

the recharge zone, subsurface groundwater flow

within the GAB is generally towards the southern,

southwestern, western and northern margins of the

GAB. In some areas, natural groundwater discharge

occurs via flowing artesian springs (Barnett and

Muller, 2008).

The aquifers in Surat Basin can be classified as

four aquifer units: shallow, intermediate, coal seam

and deep groundwater systems according to the

stratigraphy features. (Figure 2).

Shallow Groundwater Systems are quaternary

unconfined or water layer aquifers. They are named

as the Condamine Alluvium aquifers. Condamine

Alluvium aquifers generally have some general

characteristics that make good resource aquifers,

such as high permeability, high hydraulic

conductivity, substantial thickness, sandstone-like

storage characteristics, consistent characteristics

over large distances, and good quality groundwater,

but still they have some claystones as heterogeneous

layers in (Figure 4). The shallow groundwater

system provides the primary source of irrigation

water.

Figure 4: Surat Basin schematic groundwater model.

Basement

Studies on Groundwater Impacts by CSG Productions in Australia Surat Basin

215

Intermediate Groundwater Systems include

confined aquifers located above the coal seam

formations.

Coal Seam Groundwater Systems are confined

aquifers associated with coal seam formations. It

include Walloon Coal Measures, but are variable

and have commonly with low permeability and/or

low water quality.

Deep Groundwater Systems: confined porous

aquifers located below the Walloon Coal Measures

formation. They include the Marburg Formation,

Hutton Sandstone and Precipice Sandstone (Arrow

Energy 2012; CSIRO 2008; Henning, 2005).

Groundwater movement in the major confined

aquifers of the Surat Basin is predominantly

horizontal. The lower permeability units between

these aquifers (aquitards) restrict vertical

interconnection between the groundwater systems.

In this situation, there is no impact to groundwater

by CSG production; however, vertical inter-aquifer

flow may occur in areas where the aquitards are

thinner or eroded. In addition, if significant

groundwater pressure differences occur across

different formations, then inter-aquifer groundwater

flow can occur. In these cases, groundwater

influence by CSG production should be calculated

and taken actions to ensure the safety of irrigation,

stock, and domestic uses of groundwater. Three

analysises of observing groundwater impacts by

Surat CSG production shows in the following

sections.

2.1 The Condamine Interconnectivity

Analysis

The groundwater resources of the Condamine

Alluvium Aquifer been used for irrigation, stock and

domestic uses. Communities have expressed concern

that groundwater extraction from the CSG wells

could lead to reduced groundwater availability from

the Condamine Alluvium aquifer. The objective of

investigations is to provide scientific evidence about

whether CSG development near Condamine

Alluvium would have impact on groundwater

supplies for irrigation (Scott et al., 2004).

Four underground water-monitoring bores were

drilled on two separate intensively farmed properties

in the Condamine Alluvium area. Aquifer pumping

tests in the bores were undertaken at two locations:

‘A’ in 2013 and ‘B’ in 2014, adjacent to the existing

irrigation bores.

The analysis on the core porosity, permeability,

mineralogy and geophysical logs of groundwater

monitoring bores showed the formation layers and

the lithology type. Then the density, porosity and

permeability of the layers can be determined. The

result shows the vertical permeability of “transition

zone “of A and B is about 3.5x1E

-6

-1.0x1E

-6

m/day

and 2.0x1E

-7

m/day-1.6x1E

-4

-1.6x1E

-4

m/day

respectively (Figure 5).

The results from A and B are consistent with the

vertical permeability used in the current numerical

model and vertical permeability from B indicates the

site is less permeable than A. These results verified

that there is only a low level of hydraulic connection

between the Condamine Alluvium and the

underlying Walloon Coal Measures.

Figure 5: The comparison plot between Model and

core analysis.

2.2 Groundwater Level Monitor

Analysis

There are many water monitor wells drilled to

survey the water level alteration. Since 2009, the

potentiometric elevations of 15 wells have been

draw down little by little. Figure 6 (different color

lines are different coal seams) shows two CSG fields

potentiometric elevation drawdown results. D11 and

D12 well are from D Field of Block AA, S5 well is

from S Field in Block AA. Noticeable

potentiometric elevation drawdown(20m-135m) in

the different coal seams of Wallon coal measures

appears according to Figure 6a and Figure 6b results,

which indicate the produced water only come from

Walloon confined aquifer, not from the flux between

the underlying and overlying aquifers. The Walloon

Coal Measures are low permeability sediments and

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216

there are shale zone between different groundwater

systems (Schlumberger 2011).

2.3 The Groundwater Level Drawdown

Predication Analysis

In order to know the groundwater level alternations,

the numerical groundwater model was analyzed to

provide estimates of drawdown in response to the

abstraction of groundwater associated with CSG

activities.

The MODFLOW EVT software packages are

used to model the cumulative groundwater case. The

cumulative case models all current and proposed

water extraction from CSG activities from 1995

onwards.

Total modelled extraction from CSG projects

showed in Figure 7. The extraction include CSG

water extraction from block AA and other

company’s CSG extractions by considering their

CSG development plans. The result suggests a

cumulative peak extraction of around 550 ML/d in

2015, or around 20 years into the ‘predictive’

simulation, which runs from 1995 onwards

(Department of Natural Resource and Mines 2012).

Figure 8 identifies areas where the predicted

cumulative maximum impact drawdowns based on

the predication simulation result exceed 5 m in each

of the affected aquifers. As expected, the impacted

area is greatest in the WCM and gradually reduces

in the various underlying and overlying aquifers.

Predicate result suggest predicted maximum

cumulative drawdown impacts of more than 5 m in

the Springbok Sandstone, Walloon Coal Measures,

Hutton Sandstone, Precipice Sandstone (GHD 2013;

Geoscience Australia and Habermehl M.A 2010). The

cumulative drawdowns of other aquifers are

indistinct. The cumulative model result shows there

are no pronounced impacts for the groundwater

alteration in Surat Basin by considering all the CSG

activities from 1995 onwards.

Figure 6a: D Field groundwater monitor map.

Figure 6b: S Field groundwater monitor map.

Figure 7: CSG and other extraction in Surat Basin.

Studies on Groundwater Impacts by CSG Productions in Australia Surat Basin

217

Figure 8: Maximum 5m Drawdown Contours.

3 CONCLUSIONS

There are a low level of hydraulic connection

between the Condamine Alluvium and the

underlying Walloon Coal Measures according to

core analysis and Condamine Interconnectivity

study result.

The potentiometric elevations drawdown result

from water monitor wells near CSG fields shows the

produced water only from Walloon confined aquifer,

not from the flux between the underlying and

overlying aquifers.

According to predicating result from

groundwater model based on CSG and other

extraction in Surat basin, there are no pronounced

impacts for the groundwater alteration in Surat

Basin. Further study and simulation work will go on

with the change of CSG and other activities.

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