Source Rocks of the Cooper Basin

The Cooper Basin is a late Carboniferous-Middle Triassic intracratonic basin in northeastern South Australia and southwestern Queensland. The basin is one of Australia's premier onshore hydrocarbon producing provinces and, by providing domestic gas for the East Coast Gas Market, is nationally significant. This study reviews the distribution, quality and maturity of source rocks across the Cooper Basin and forms part of Geoscience Australia's source rock program. All publicly-available total organic carbon (TOC) content and Rock-Eval pyrolysis data for the Cooper Basin were compiled into a single database, quality checked and compiled by well and formation to highlight the multiple viable source rock units throughout the Permian. The Toolachee and Patchawarra formations represent the principal source rocks in the basin. These comprise coals and carbonaceous shales deposited in fluvial deltaic and peat swamp environments and show good to very good oil and gas source potential. Additional source intervals include the gas prone lacustrine Roseneath and Murteree shales, as well as coals and carbonaceous shales of the Daralingie and Epsilon formations. Permian source rock distribution was investigated using lithofacies mapping combined with geochemistry data. Lithofacies maps published for South Australia were integrated with electrofacies data from Queensland to produce new, internally consistent, net source thickness maps for key intervals, including coals and carbonaceous shales of the Toolachee and Patchawarra formations, and the Roseneath and Murteree shales. Pyrolysis data that indicate the presence of an in-situ source rock with remaining hydrocarbon generation potential (i.e. TOC > 2% and S1+S2 > 3 mg hydrocarbons/g rock) were mapped by formation, demonstrating the broad extent of Permian source rocks across the basin. Toolachee and Patchawarra source rocks are present in most major depocentres, including the Windorah Trough and Ullenbury Depression in the northern part of the basin, where maximum coal thicknesses still reach more than 10 m. Source rocks within the Roseneath and Murteree shale are generally restricted to the southern Cooper Basin.