Distribution of Dibenzothiophenes in Crude Oils from Tarim Basin and Identification of Major Source Rock Types

Commercial oils drilled in most parts of the North Tarim Uplift and Central Tarim Uplift have been characterized and corn firmed as oils derived from marine Lower Paleozoic source rocks. The marine oils might have, however, originated from blask shale beds or carbonate sequences of the same age. That brings difficulties in oil-source correlation by biomaker approaches. In this paper, dibenzothiophene distributions of typical marine carbonate-sourced oils and siliciclanic sourced oils with different maturity have been studied in detail. It is revealed that the dibenzothiophene demethylation index(DDI) and dibenzothiophene methyl-isomeration index(DMI) could distinguish two types of oils effectively and suffer from little influence of maturity. According to the relative amounts of DBTS and DDI vs DMI values of Tarim oils, the major source rocks in Tarim Basin are identified as the dark and black laminated micrite and marlite deposited in the Ordovician continental shelf zone.