Occurrence and Geochemical Significance of Phenylnaphthalenes and Terphenyls in Oils and Condensates from the Yakela Faulted Uplift, Tarim Basin, Northwest China

A total of 32 oils and condensates were collected from four gas/oil fields (Dalaoba, Luntai, Kuqa, and Yakela) in the Yakela Faulted Uplift (Tarim Basin, northwest China). The composition of biomarkers and a previous study show that oils and condensates in the Dalaoba, Luntai, and Kuqa gas/oil fields originated from lacustrine mudstone/shale source rocks deposited in an oxic environment. Oils and condensates from the Yakela gas/oil field are of typical marine carbonate origin. Some phenyl-substituted polycyclic aromatic hydrocarbons, including phenylnaphthalenes (PhNs) and terphenyls (TrPs), were unequivocally detected in most of these oils and condensates. They are present in significant abundance in oils and condensates from the Dalaoba, Luntai, and Kuqa gas/oil fields. However, the concentrations of PhNs and. TrPs are relatively lower or below the detection limit in oils and condensates from the Yakela gas/oil field. The ratios of 2-PhN/2-MN and m-TrP/3-MBP are used in this study to describe the abundance of PhNs relative to, their alkylated counterparts, i.e., methylnaphthalenes (MNs), and that Of TrPs to methylbiphenyls (MBPs), respectively. Oils and condensates from the Dalaoba, Luntai, and Kuqa gas/oil fields have relatively higher 2-PhN/2-MN and m-Trp/3-MBP ratios. However; oils and condensates, from the Yakela gas/oil field have Comparably lower 2-PhN/2-MN ratios (<5.0) and low m-Trp/3-MBP ratios (<0.10). This shows that the occurrence and formation of PhNs and TrPs in oils are probably relative to the lithology and/or depositional environment of:their corresponding Source rocks. PhNs and TrPs, are potential molecular markers for oil-Source correlation in organic geochemistry.