Petroleum Systems Modelling for Unconventional Play Analysis in the Cooper Basin

The Cooper Basin is a late Carboniferous - Middle Triassic intracratonic basin in north-eastern South Australia and south-western Queensland. The basin is currently Australia's premier onshore hydrocarbon producing province and hosts a range of unconventional gas play types, including the extensive basin-centred and tight gas accumulations in the Permian Gidgealpa Group, deep dry coal seam gas associated with the Patchawarra and Toolachee formations, as well as the shale gas plays in the Murteree and Roseneath shales. This study uses petroleum systems modelling as a tool to investigate the prospectivity of each unconventional gas play type across the basin. Existing published structure surfaces were updated to incorporate new seismic and well data interpretations and combined into a regional 3D basin model, ensuring seamless data integration across the state border. All publicly-available total organic carbon (TOC) and RockEval data were compiled and used to review source rock distribution and quality, demonstrating the abundance of viable source rock intervals across the basin. Cooper Basin-specific kinetic relationships allowed the estimation of oil and gas windows. All datasets were integrated into a multi-1D petroleum systems model, which was calibrated using vitrinite reflectance and corrected temperature for 90 wells. Petroleum system model outputs, including thermal maturity and hydrocarbon generation, expulsion and retention maps by source interval, were then used to characterise possible play fairway extents for each play type. The hydrocarbon generation maps and play fairway areas for the basin centred gas and deep dry coal seam gas plays of the Toolachee and Patchawarra formations highlight that these play types are both more extensive and more prospective than the Roseneath and Murteree shale gas plays. However, the overlapping nature of all three play types makes it more convenient to consider them collectively as a composite Gidgealpa Group unconventional gas play. The composite Gidgealpa Group gas play fairway map shows that the Nappamerri and Allunga troughs are highly prospective, along with the deepest areas of the Patchawarra and Arrabury troughs. Results also indicate prospectivity potential for unconventional gas further to the northeast, including areas of the Windorah Tough and Ullenbury Depression, consistent with recent drilling results. Further potential may exist in shallower coal plays outside the composite resource play area.