珠江口盆地陆丰15披覆构造带油藏地球化学特征及油源对比

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

珠江口盆地陆丰15披覆构造带南、北部分别与陆丰22洼、陆丰15洼毗邻,常规的油源对比指标无法确定构造带上S2-1和S5-1油藏的油源,2个洼陷都有可能向其供烃。为揭示原油的成因来源,对该地区原油及烃源岩开展了生物标志物、碳同位素及含氮化合物等特征的精细对比。在研究区原油及源岩中新检测出4个C_(24)四环萜烷:脱-A-奥利烷、脱-A-羽扇烷、新C_(24)四环萜烷及C_(24)17,21-开环藿烷。研究对比发现,S2-1和S5-1油藏原油中C_(24)四环萜烷分布特征与陆丰22洼文昌组烃源岩更加吻合,具有更强的亲缘关系。此外,全油碳同位素和正构烷烃单体烃碳同位素指示S2-1和S5-1油藏明显区别于陆丰15洼生成的原油,预示着其原油具有陆丰22洼烃源岩的贡献。含氮化合物示踪参数指示S2-1油藏具有近源充注特征,进一步验证了陆丰22洼烃源岩对S2-1和S5-1油藏的重要贡献。

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 C_(24)tetracyclic terpanes were detected from crude oils and source rocks in the study area:des-A-oleanane,des-A-lupane,new C_(24)tetracyclic terpane and C_(24)17,21-secohopane.The distribution of C_(24)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.