Oil-source correlations as a tool in identifying the petroleum systems of the southern Taroom Trough, Australia

A geochemical study of crude oils and samples of various Permian, Triassic and Jurassic organic-rich rock units from the southern Taroom Trough was undertaken to test the prevailing Permian-source hypothesis for the petroleum reserves of the Bowen/Surat Basin. Seventy three core and cuttings samples were screened using organic petrography, total organic carbon analysis, Rock-Eval pyrolysis, and solvent extraction. Saturated and aromatic hydrocarbon fractions of selected source rocks, kerogen hydrous pyrolysates, and thirteen oils were then analysed by gas chromatography, gas chromatography-mass spectrometry and isotope ratio mass spectrometry, for the purpose of oil-to-source correlation. On the basis of their bulk carbon isotopic compositions and terpane, sterane and aromatic biomarker signatures, two oil families were identified. Those oils sourced by the Snake Creek Mudstone and reservoired in the Showgrounds Sandstone (both the Middle Triassic age) at Roswin North and Rednook are assigned to the “Snake Creek-Showgrounds” petroleum system. The remaining oils belong to the “Blackwater-Precipice” system. These originated in the Late Permian coal measures of the Blackwater Group but are produced from the Precipice Sandstone and other reservoir rocks of Permian to Jurassic age along the southeastern and southwestern margins of the trough.