Oil-source correlation in the Yangjiang Uplift, South China Sea: A comparative analysis of mathematical and fingerprint methods

Abstract

In recent years, significant exploration breakthroughs have been achieved in the Yangjiang Uplift. However, the source of crude oil is ambiguous, and the prevailing view suggests a remote hydrocarbon supply. To clarify the source of the crude oil in the Yangjiang Uplift, 30 source rocks and 15 crude oil samples collected from the Wenchang A Sag and Yangjiang Uplift are subjected to Rock-Eval pyrolysis, maceral analysis, vitrinite reflectance, and biomarker analysis, among other experiments. Principal component analysis and hierarchical cluster analyses are performed. The results indicate that the source rocks in the Yangjiang Uplift exhibit robust hydrocarbon-generating potential, with S1 + S2 values ranging between 0.04 and 140.5 mg/g (averaging: 13.54 mg/g), indicative of reaching the oil generation period. Using 13 biomarker compounds, two types of biomarkers are selected to compare the sources of the crude oils: pristane/phytane (Pr/Ph) representing the depositional environment and tricyclic terpanes (TTs) representing the source input. The crude oil in the Yangjiang Uplift can be divided into two types: one with high values of bicadinane-T (T)/C30 hopane and ΣC30-4 methyl sterane/ΣC29 regular sterane and another with a low ratio of (C19TT + C20TT)/C23TT according to the charting method. The investigated crude oil is mixed with the source rocks of the Wenchang A Sag and the Yangjiang Uplift. Furthermore, owing to the differences in the mixing ratios, the crude oil in the study area exhibits two distinct characteristics. Type A is characterized by a higher proportion of the Wenchang A Sag crude oil in the mixture, whereas type B is characterized by a higher proportion of local crude oil. This study establishes that the Yangjiang Uplift boasts large petroleum resources.