Bowen and Surat Basins
The coal fields of Bowen Basin are primarily located in Queensland, although the southern portion of the basin lies in New South Wales. Structure and stratigraphy of the area is complex with the Bowen Basin unconformably underlying the Surat and Duaringa Basin and unconformably overlying the Drummond Basin all of which are generally covered in Tertiary and Quaternary sediments.
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Bowen and Surat Basins on top of OZSEEBASE™ showing the coplex structural nature of the basement.
The Bowen and Surat Basins are also located within the headwaters of the Murray-Darling Basin
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Location of the Bowen and Surat Basin relative to each other and to the headwaters of the Murray-Darling Basin, Australia.
Most of the groundwater produced by CSG in the Surat Basin comes from coal seams located within the Walloon Coal Measures. Long term average water production from the Walloon Coal Measures is estimated to be about 200-400 ML/PJ. As the Walloon Coal Measures are conservatively estimated at containing over 30,000 PJ this equates to ~6000-12,000 GL of potentially co-produced water (http://www.dme.qld.gov.au/zone_files/None_Zoned_Files/csg_water_m_s_final_7.pdf).
The current volume of co-produced CSG water (CSG water) is about 13.5 GL/yr which could rise to 281 GL/yr depending on the volume of LNG production (http://203.210.126.185/dsdweb/v4/apps/web/secure/docs/ 3895.pdf). To put this volume of water into perspective, total groundwater recharge into the Great Artesian Basin is 323 GL/yr with current groundwater use is estimated to be 549 GL/yr (http://water.gov.au/ RegionalWaterResourcesAssessments/SpecificGeographicRegion/TabbedReports.aspx?PID=QLD_GW_AP12072x). The additional impact of CSG water could place a large additional impost upon an already stressed system.
The Walloon Coal Measures is located between two major aquifer systems with the Surat Basin: the overlying aquifers of the Cadna-owie – Hooray Aquifer and the underlying Hutton Sandstone. The connection between these aquifers and the Walloon Coal Measures is not well-known across the region but it is generally thought to be low (http://www.dme.qld.gov.au/zone_files/None_Zoned_Files/csg_water_m_s_final_5.pdf).
Stratigraphic column of the Surat Basin showing the relative position of the Walloon Coal Measures (primary target for CSG) and the Cadna-owie - Hooray Aquifer (aquifers coloured blue) and the Hutton Sandstone aquifer (modified from http://www.dme.qld.gov.au/zone_files/None_Zoned_Files/csg_water_m_s_final_7.pdf).While this may be true under steady state conditions (although this assumption may be questioned too), the effects of abstracting such large volumes of water from the Walloon Coal Measures and the subsequent reinjection of groundwater back into the coal seams is not known. Over or under pressuring of the Walloon Coal Measures could result in increased interaquifer leakage via faults/fractures or from stratigraphic thinning of aquitard layers. This could result in contamination of commercial aquifers by low quality groundwater, decrease in artesian pressure within these aquifers and/or interference of important GAB spring complexes such as the Springsure and Bogan River Groups. In addition, there could also be effects on the head waters of the Murray-Darling Basin.
Without fully understanding the geofabric, it is possible that managers and producers will not have enough information to both manage the effects of co-produced water and to maximise methane production.