Cooper Basin Unconventional Gas Prospectivity Review

The Cooper Basin is a late Carboniferous - Middle Triassic intracratonic basin in north-eastern South Australia and south-western Queensland. The basin is Australia's premier onshore hydrocarbon producing province and, by providing domestic gas for the East Coast Gas Market, is nationally significant. Exploration activity in the region has recently expanded with numerous explorers pursuing newly identified unconventional hydrocarbon plays. While conventional gas and oil prospects are more clearly identified by 3D seismic, the undiscovered unconventional gas resources in the basin remain poorly defined.
This study reviews the hydrocarbon prospectivity of the Cooper Basin, with a focus on unconventional gas resources. Regional basin architecture is characterised through compilation and integration of seismic and well data, indicating the wider extent of the Permian Toolachee and Patchawarra formations further north in Queensland. Source rock distribution and quality are reviewed demonstrating the abundance of viable source rock intervals across the whole basin. The Toolachee and Patchawarra formations are the richest sources; however organic-rich rocks are also present in the Nappamerri, Daralingie and Epsilon formations, and the Roseneath and Murteree shales. Petroleum systems modelling, incorporating new compositional kinetics, source quality and Total Organic Carbon (TOC) maps, highlights the variability in burial, thermal and hydrocarbon generation histories between depocentres. Although hydrocarbon generation began in the Permian, peak oil and gas expulsion across the basin occurred during the Cretaceous. 
The Cooper Basin hosts a range of unconventional gas play types, including the very extensive basin-centred and tight gas accumulations in the Gidgealpa Group, deep dry coal gas associated with the Patchawarra and Toolachee formations, as well as the less extensive shale gas plays in the Murteree and Roseneath shales.  However, the overlapping nature of these plays makes it more convenient to consider them collectively as a composite Gidgealpa Group unconventional gas play. The possible extent of the composite Gidgealpa Group gas play fairway is defined using a common risk segment mapping workflow. Low and high confidence play fairway extents are also calculated.
In South Australia and the south-western most areas of Queensland, the composite Gidgealpa Group gas play fairway maps show that the Nappamerri and Allunga troughs are highly prospective, along with the deepest areas of the Patchawarra and Arrabury troughs. The play fairway maps also show the prospectivity potential for unconventional gas further to the northeast in Queensland, including areas of the Windorah Tough and Ullenbury Depression. 
The prospectivity of the Cooper Basin for composite unconventional gas plays exceeds its currently known conventional resources. Whilst additional work is required to better characterise key petroleum systems elements, the play fairway area estimated for the combined Gidgealpa Group gas play is significantly larger than that of the Roseneath and Murteree shale gas plays alone, suggesting very large volumes of gas in-place and highlighting the Cooper Basin's status as a world class unconventional gas province.

Tags: Earth Sciences, GA Publication, Other Publication, Published_External, QLD, SA
Organization: Geoscience Australia Data