准噶尔盆地玛东斜坡区百口泉组–下乌尔禾组混源油地球化学特征及定量判识

Geochemical characteristics and identification of mixed crude oil of the Baikouquan Formation Lower Wuerhe Formation on the East slope of the Mahu Sag,Junggar Basin

混源油的定量判识是当前石油地质地球化学研究的热点与难点。本次研究以准噶尔盆地玛东斜坡区百口泉组–下乌尔禾组的混源油为典型研究实例,通过有机地球化学与化学计量学相结合的方法,对研究区混源油进行了定量研究,取得良好效果。原油地球化学研究结果表明,研究区原油混源现象普遍存在。综合分析后认为,现今混源油中可划分出3个端元,其中端元A和B可能主要代表了二叠系风城组早期和晚期烃源岩的贡献,并以晚期充注原油为主,而端元C差异较大,可能为二叠系下乌尔禾组烃源岩生烃或风城组不同岩相、不同沉积环境的烃源岩生烃。研究区以风城组生烃聚集为主,虽然晚期生烃占比不高,但对油气运聚成藏却起到非常关键的作用。这一综合对比研究表明,化学计量学方法在混源油的比例计算、端元分析等方面具有重要作用,是对传统地球化学方法研究的有效补充,值得推广应用。此外,研究认识还为区域油气勘探提供了新的参考信息。

Studies on the quantificational discrimination of mixed oils have generally been difficult to perform;however,they are extremely important for petroleum,geology,and geochemistry research.This article includes a case study based on the East slope of the Mahu Sag,Junggar Basin,which was performed through a combination of geochemistry and chemometrics analyses.It indicates that oil accumulated in the East slope of the Mahu Sag is characterized by multistage hydrocarbon generation and mixed sources.Results show that three end-member oils contributed to the mixed oils in this region.End-members 1 and 2 indicate that the Fengcheng Formation comprises early or late Permian source rocks.However,end-member 3 is vastly different;it may indicate the Lower Wuerhe Formation source rocks or the Fengcheng Formation,but through different lithofacies and depositional environments.Oil generated from the later Fengcheng Formation source rock is not plentiful but important.Oil generated from the Lower Wuerhe Formation only exists north of the study area.This comparative research shows that chemometrics analyses play a significant role in calculating the proportions of mixed oils and identifying end-member oils.Moreover,multivariate data analyses should be popularized as an effective complement to traditional geochemistry studies.