ORIGIN OF PETROLEUM IN THE BOWEN AND SURAT BASINS: GEOCHEMISTRY REVISITED

Abstract

A detailed regional geochemical study of over 70 oils and condensates, eleven natural gases and over a hundred core samples from potential source rocks enable resolution of the generation and migration history of petroleum in the Bowen and Surat Basins. Biomarker analysis confirms a pre-Jurassic source for the petroleum. Stable carbon-isotope analysis further indicated a Permian-sourced petroleum and was able to differentiate a very minor and localised Triassic source contribution. The dominant source for the petroleum is terrestrial land plants as well as a minor contribution from bacteria and marine algae. In the north, Late Permian lower delta plain and alluvial Permian coals show the higher liquid potential compared with upper delta plain facies, while in the Taroom Trough, coals in the Blackwater Group have the highest liquid potential compared with mudrocks of the Blackwater Group, and sediments of the Back Creek Group. Initial liquid expulsion from the source rock occurred at vitrinite reflectance (Ro) of 0.65-0.7 per cent and continued to Ro of 1.05 per cent. This was followed by the main phase of gas generation between 1.05 per cent