Distribution patterns and geochemical implication of bicadinanes in crude oils from Baiyun Sag, Pearl River Mouth Basin

Bicadinanes (W, T) are abundant in crude oils in the Baiyun Sag of the Pearl River Mouth Basin. The distribution patterns and geochemical implication of bicadinanes in crude oils from the study area were investigated based on the gas chromatography-mass spectrometry of 35 oil samples. The relative content of bicadinanes in crude oils is relatively higher in the north but lower in the east of the sag. Maturity and gas washing exert a minor impact on the relative contents of bicadinanes in mature to high-maturity crude oils, while hydrocarbon sources play an important role. The relative content of bicadinanes is positively related to Pr/Ph and tricyclic terpane (C₁₉TT+C₂₀TT)/C₂₃TT ratios, which shows that an oxidizing environment with high terrestrial input is more favorable for the enrichment of bicadinanes. Therefore, the relative content of bicadinanes can be used to define biological source, depositional environment and oil-source correlations. In addition, bicadinane T/W ratios may serve as an index for evaluating maturity in low to medium-maturity crude oils.