渤海海域沙西北地区潜山油源及成藏特征

综合地质与地球化学方法，探讨了渤海海域沙西北地区潜山的油气来源及成藏特征。生物标志物参数表明沙西北地区已发现的原油位于沙河街组。曹妃甸2-1油田的潜山储层岩性为碳酸盐岩，潜山的原油具有高的伽马蜡烷指数（G/H）以及相对低4-甲基甾烷参数（4MSI），具有相对轻的正构烷烃碳同位素值（整体轻于-29‰），主要为沙河街组一段（沙一段）的油源。曹妃甸1-6油田为花岗岩潜山储层，潜山的原油具有相对高的4MSI（>0.4），正构烷烃的碳同位素值偏重（重于-29%），可能指示着以沙三为主的油源。曹妃甸2-1潜山直接披覆沙一段，沙一段源岩生成的原油可近距离充注至潜山储层中，为披覆式的源储对接成藏模式。曹妃甸1-6油田上覆为东营组，其丰度与热演化程度低，主要作盖层。歧口凹陷的原油侧向通过砂体运移侧向充注至曹妃甸1-6潜山圈闭中，表现为侧向砂体输导油气成藏特征。通过岩心观察和铸体薄片实验分析了CFD2-1-2井潜山风化壳结构特征，揭示了沙西北地区潜山风化壳结构可能不具备侧向长距离输导油气的能力，与潜山直接披覆接触的有效烃源岩或者发育沟通源储的砂体是潜山油气成藏的基础。

Origin and accumulation characterization of petroleum in buried hill reservoirs in Shaxibei area,Bohai Sea

The study discussed the origin and accumulation characteristics of hydrocarbon in buried hills in Shaxibei area,Bohai Sea,through geological and geochemical research methods.Analysis of biomarker parameters reveals that the proved buried hill oil samples in Shaxibei area originate from the Shahejie Formation source rocks.Oil samples from the CFD2-1 buried hill carbonate reservoir have a high G/H index and relatively low 4MSI,and are characterized by depleted ¹³C for n-alkanes(less than -29‰ as a whole).Such characteristics may be an indicator of the oil origin from the Es¹ source rocks.Oil samples, taken from the granite reservoir of the CFD1-6 oil fields,are typified by relatively higher 4MSI (more than 0.4) and heavier carbon isotope of n-alkanes (more than -29‰), which may indicate that CFD1-6 buried hill oil is dominated by the Es³-derived oil. The CFD2-1 buried hill is overlain by the Es¹ formation unit,and the mature Es¹ source rock may supply adequate petroleum for charging the carbonate reservoirs without long migration distance.This accumulation model can be referred to as the assemblage of generation from the draped source rock and vertically charging to the underlying carbonate reservoir.CFD1-6 granite buried hill is covered by the Ed shale,being characterized by low organic matter abundance and thermal maturity,which can be served as a seal for oil accumulation.Oil generated from the source rock in the Qikou Sag can be transported through the laterally distributed sand body and charge the CFD1-6 buried hill traps,exemplifying a hydrocarbon accumulation model of migration through lateral sand body.On the basis of core observation and casting thin section experiments,we analyzed the textural characteristics of weathered crust from Well CFD2-1-2.The results show that the weathered crust structure in Shaxibei area may not be able to receive the laterally transporting petroleum from sags to buried hill traps,while the overlying effective source rocks on the surface of buried hills or the occurrence of sand bodies communicating source and reservoir are fundamental for hydrocarbon accumulation in buried hills.