Geochemical characteristics of aromatic hydrocarbons in saline lacustrine crude oils and their significance as exemplified by the south area of western Qaidam Basin

Based on quantitative GC-MS analysis of 40 crude oil samples collected from the south area of western Qaidam Basin, one of the largest saline lacustrine basins in China, the geochemical characteristics of aromatic hydrocarbons in oils were studied systematically in this paper. Among those constitutes, naphthalene (43%?C59%), phenanthrene (12%?C21%) and taromatic-sterane series (6%?C28%) were the main ones of aromatic hydrocarbons. The ratio of aromatic hydrocarbon maturity parameter vs. saturated hydrocarbon maturity parameter C₂₉20S/(20S+20R) shows that some aromatic hydrocarbon maturity parameters are not suitable for low-mature oils, including MPI, MNR, DNR, etc. Meanwhile, maturity parameters for dibenzothiophene and taromatic-sterane series are more appropriate for low maturity saline lacustrine crude oils. Based on the ratio of 4, 6-DMDBT/1, 4-DMDBT, the Rc values are within the range of 0.59%?C0.72%. However, the abundance of dibenzothiophene (DBT) is low, and the dibenzofuran (DBF) content is even lower, suggesting that the crude oils were formed in a saline lacustrine anaerobic environment. The high abundance of C₂₆ triaromatic steroid also indicates that the source material is brackish water-saline water with strong reducibility.