A GEOCHEMICAL INVESTIGATION OF OILS AND SOURCE ROCKS FROM THE SURAT BASIN

A series of twelve oils and five source rocks and potential source rocks from the Surat Basin have been subjected to detailed geochemical analyses. Particular attention has been given to determining the distribution of various classes of biomarkers such as the steranes and triterpanes. The results from this study have shown that the Cabawin oil is derived from the Permian Back Creek Formation and has a high content of marine organic source material. The Triassic/Jurassic oils have a different source from the Cabawin oil and are dominated by land plant source material. Within the Triassic/Jurassic oils there are subtle variations in biomarker distributions suggesting that some oils may have small but additional amounts of different source materials. A number of Cretaceous and Jurassic potential source rocks (i.e. Walloon) have biomarker parameters clearly indicating levels of maturity at which oil generation is impossible. A number of the oils in this basin are extensively biodegraded. In particular biodegradation has been very heavy in the Riverslea/Yapunyah area. With the exception of Conloi oil, all the oils appear to have been exposed to similar levels of maturity. A biomarker migration parameter has provided some tentative evidence to suggest that, in general, oils in the southern part of the basin have migrated further than those in the northern part. In summary, the biomarker data from oils and source rocks of the Surat Basin have been used to provide a new insight into the origin of the Surat Basin oils and their post-formation history.