Geochemical application of tricyclic and tetracyclic terpanes biomarkers in crude oils of NW China

Abstract

Composition and distribution of tricyclic terpanes, tetracyclic terpanes and hopane in crude oils from Tarim, Turpan, Ordos and Qaidam basins, NW China, were investigated, and some new source dependent parameters were developed and evaluated. C19 and C20 tricyclic terpanes are more abundant in terrigenous oils, with C24 tetracyclic terpane dominant. Relatively higher carbon number tricyclic terpanes, especially C23 tricyclic terpane, are often the dominant homologues in crude oils from saline lacustrine and marine sources. On the whole, the relative content of C23 tricyclic terpane of crude oils follow the order of saline lacustrine oils > marine oils > freshwater lacustrine oils > terrigenous oils for C19–23 tricyclic terpane. Some new parameters based on the tricyclic/hopane and tetracyclic/tricyclic terpane as well as tetracyclic/hopane ratios, could be used to distinguish the oils and source rocks with similar maturity deposited in different sedimentary environments.