涠洲油田油气地球化学特征及成因类型探讨

中石化涠西探区2015年获重大突破,涠西南D洼东部斜坡发现了涠洲油田。为揭示原油的成因和来源,此文采用地质地球化学技术,通过GC、GC-MS分析表明,原油中链烷烃组分以低碳数正构烷烃为主,平滑分布;甾萜烷异构化程度较高,富含重排甾烷,具丰富的C₃₀4-甲基甾烷以及低碳数甾烷,C₂₇、C₂₈、C₂₉规则甾烷呈"V"型或"L"型分布。油-油、油-源对比表明,涠洲油田原油与流沙港组优质的深湖-半深湖相烃源岩具有成因联系。原油成熟度参数C₂₉甾烷αββ/（αββ+ααα）、C₃₁升藿烷22 S/（S+R）等表明原油已达成熟阶段,利用甲基菲指数MPI1折算原油成熟度分布在0.79~0.97之间,原油成熟度与涠西南D洼流沙港组烃源岩热演化程度相当。综合以上分析认为,涠洲油田的原油表现为典型湖相特征,主要来源于涠西南D洼流沙港组烃源岩。

Geochemical Characteristics and Genetic Type of the Oils in Weizhou Oilfield

In 2015, it achieved an important breakthrough for the petroleum exploration in Weixi exploration area of SINOPEC. Weizhou Oilfield located in the east slope of Weixinan Sag was discovered.In order to reveal the cause of crude oil, Geochemistry and Geology methods have been used to study the genesis and source of crude oil in this paper. The analysis by GC and GC-MS shows that the crude oil is mainly composed of alkanes distributed smoothly with low carbon number. The crude oil is also characterized by high degree of sterane isomerization, rich in C₃₀4-methyl steranes and low molecular steranes. The abundance of C₂₇, C₂₈, C₂₉-regular steranes of the crude oil samples show a "L" or "V" shape distribution. The correlation between oil-oil and oil-source rock shows that the crude oil of Weizhou Oilfield has a genetic relationship with the high-quality deep to semi-deep lacustrine source rocks of Liushagang Formation (El₂). The crude oil maturity parameters, C₂₉ αββ/(αββ+ααα) -sterane and C₃₁22S/(S+R)-homohopane, indicate that the crude oil has reached the matured stage. The maturity of the crude oil is equivalent to the thermal evolution of source rocks of Liushagang Formation in D sub-sag,estimated to be 0.79~0.97 by the parameter MPI1. Based on the above comprehensive analysis, the crude oil of Weizhou Oilfield is characterized by typical lacustrine facies, mainly from the El₂ source rock in D sub-sag of Weixinan.