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Concurrent 5. Presentation for: Multiple tracers for dis-connectivity of shallow aquifers, alluvium, and coal seam gas wells in the Great Artesian Basin

J. K. Pearce A B *
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A Centre for Natural Gas, University of Queensland, Qld, Australia.

B School of Earth and Environmental Sciences, University of Queensland, Qld, Australia.

* Correspondence to: j.pearce2@uq.edu.au

The APPEA Journal 62 - https://doi.org/10.1071/AJ21315
Published: 3 June 2022

Abstract

Presented on Tuesday 17 May: Session 5

The potential for connectivity between water supply aquifers and gas reservoirs raises community, government, and scientific concerns. Methane can occur naturally, making it difficult to determine whether water bore methane levels are being influenced by nearby gas operations. This poses a challenge in the Surat Basin, where coal seam gas production operates alongside groundwater using industries (including feedlots, agriculture, mines). Water and gas samples were taken from water bores and coal seam gas (CSG) wells in the Walloon Coal Measures and from overlying aquifers (nominally, the Springbok, Gubberamunda, Orallo, and Mooga sandstones) and the Condamine Alluvium, for stable isotopes of gases, groundwater and dissolved inorganic carbon, as well as strontium isotopes. Most of the sampled water bores had isotopic signatures distinct from CSG wells, though a minority from gassy Springbok Sandstone and Walloon Coal Measure water bores could not be distinguished from CSG wells. In those few cases, neither connectivity or dis-connectivity could be confirmed. Alluvium and shallow aquifer samples have higher R36Cl values distinct from the older CSG production waters, as is the case with most 14C measurements. Waters from the Condamine River indicate potential surface water connectivity with the alluvium. The use of multiple tracers has shown that groundwater in some aquifers can be differentiated from groundwater in the coal seam gas reservoir and hence are useful tools in identifying where groundwater connectivity occurs. Understanding this connectivity forms another line of evidence to improve impact prediction models on a regional scale as well as providing information on connectivity in local groundwater investigations.

To access the presentation click the link on the right. To read the full paper click here

Keywords: coal seam gas, Condamine Alluvium, Great Artesian Basin, groundwater, isotopic tracers, methane, Springbok Sandstone, Surat Basin, Walloon Coal Measures.

Dr Julie Pearce is a geochemist with international experience in the UK, Japan, and Australia on interdisciplinary projects. She is currently a Research Fellow with the University of Queensland Centre for Natural Gas, and School of Earth and Environmental Sciences. Pearce is an expert on gas–water–rock interactions with a focus on the Surat Basin, QLD, Australia, and geochemical processes in gas and oil shales. She is currently working on field monitoring techniques for measurement of gases and waters, and understanding processes through geochemical and isotopic techniques. She has collaborated in research projects with the gas and CCS industries, and provided expert opinion to the Queensland Government.