The Springbok Sandstone (Surat Basin, Australia) overlies the Walloon Subgroup, which is a significant target for Coal Seam Gas (CSG) production. In order to assess and mitigate possible groundwater impact of CSG production, it is critical to define groundwater flow units. This is challenging for the Springbok Sandstone due to the significant heterogeneity of its mineralogy and lithology as well as hydrogeological properties. The main objective of our research is to reduce the uncertainty of the hydrogeological characterisation of the Springbok Sandstone through a comprehensive comparison with a well-understood aquifer in the Surat Basin: the Precipice Sandstone. For the systematic comparison of both formations new geochemical, mineralogical, and porosity and permeability data has been acquired. Here we present the results from over 200 samples. The laboratory results are used to calibrate petrophysical models for the Springbok and Precipice Sandstones. Our results show, that a petrophysical model of the Springbok Sandstone needs to take into account a suite of minerals (in particular clays) in order to accurately predict the porosity of the formation. Such petrophysical models can be used to identify zones of high and low permeability and therefore help improve the accuracy of groundwater impact assessments and mitigation strategies.

Open-Access Online Publication: March 28, 2023