Geochemical characteristics and oil source correlation of reservoirs in Lufeng 15 drape structural belt, Pearl River Mouth Basin

The north and south parts of Lufeng 15 drape structural belt in the Pearl River Mouth Basin are adjacent to Lufeng 22 Sag and Lufeng 15 Sag, respectively. Conventional oil source correlation indicators cannot determine the oil source of the S2-1 and S5-1 reservoirs in the structural belt, and the two adjacent sags may supply hydrocarbons to them. To reveal the origin and source of crude oils, the biomarkers, carbon isotopes and nitrogen-containing compounds of crude oils and source rocks in this area were compared. Four C₂₄ tetracyclic terpanes were detected from crude oils and source rocks in the study area: des-A-oleanane, des-A-lupane, new C₂₄ tetracyclic terpane and C₂₄17,21-secohopane. The distribution of C₂₄ tetracyclic terpanes in crude oil from S2-1 and S5-1 reservoirs are more consistent with the source rocks of Wenchang Formation in Lufeng 22 Sag in a close relationship. In addition, the carbon isotopes of whole oil and n-alkane monomers indicate that the S2-1 and S5-1 reservoirs are significantly different from those in the Lufeng 15 Sag, indicating that they are contributed by the source rocks of Lufeng 22 Sag. The tracer parameters of nitrogen-containing compounds indicate that the S2-1 reservoir has the characteristics of near-source charging, which further verifies the conclusion that the S2-1 and S5-1 reservoirs have important contributions from the Lufeng 22 Sag source rocks.