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 were subjected to Rock-Eval pyrolysis, maceral analysis, vitrinite reflectance, biomarker analysis, among other experiments. Principal component analysis (PCA) and hierarchical cluster analyses (HCA) were performed. The results indicate that source rocks in the Yangjiang Uplift exhibit robust hydrocarbon-generating potential, with S1 + S2 values ranging between 0.04–140.5 mg/g (averaging: 13.54 mg/g), indicative of reaching the oil generation period. Using 13 biomarker compounds, two types of biomarkers were selected to compare the sources of the crude oils: Pristane/Phytane (Pr/Ph), representing the depositional environment, and tricyclic terpanes, 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 (C19tricyclic terpane + C20tricyclic terpane)/C23tricyclic terpane according to the charting method. The investigated crude oil was mixed with the source rocks of the Wenchang A Sag and the Yangjiang Uplift. Furthermore, owing to differences in the mixing ratios, the crude oil in the study area exhibited two distinct characteristics. Type A is characterized by a higher proportion of Wenchang A sag crude oil in the mixture, whereas type B is characterized by a higher proportion of local crude oil. This study established that the Yangjiang Uplift boasts large petroleum resources.