渤中西洼东三段烃源岩特征与油气成藏模式

Source Rock Characterization and Hydrocarbon Accumulation of Dong3 Member in West Bozhong Sag

渤中西洼东营组烃源岩埋深较浅、成熟度相对较低,其生烃潜力一直未受重视。为了明确东营组烃源岩特征及其与油气成藏关系,对东营组烃源岩有机质丰度、类型、成熟度、油源对比及其对油气成藏的影响进行了一系列研究。结果认为:渤中西洼东三段烃源岩有机质丰度高,在埋深大于3500 m的东三段有机质成熟度R_o>1.0%,达到了生油高峰,是渤中西洼重要的烃源层系。通过油源对比分析,认为东三段烃源岩原油主要环绕渤中西洼主洼槽呈环带状分布。断层、砂体是渤中西洼东三段烃源岩有效的输导体系要素,主要发育烃源岩-断层、烃源岩-砂体、烃源岩-砂体-断层复合接触型3种油气高效输导类型。根据烃源岩的发育特征,结合输导体系与烃源岩的配置关系研究,认为东三段主要为自生自储油气成藏模式。在渤中西洼的北部,东营组烃源岩可以作为浅层油气成藏的有效烃源岩,油气主要通过沟通东营组烃源岩的大断裂垂向运移至浅层成藏,因而浅层油气具有较大的勘探潜力。东三段烃源岩生排烃能力及油气成藏模式的重新认识,对该区深化勘探及目标区的优选有一定的指导意义。

The source rocks in Dong3 Member of west Bozhong Sag is featured by shallow buried depth and relative- ly low maturity and the corresponding hydrocarbon generation potential has been neglected in the past. The effects of organic matter abundance, type, maturity and oil-source are researched to characterize the source rocks in Dongy- ing Member and identify their correlation with hydrocarbon accumulation. Research demonstrates that the source rocks in west Bozhong Sag is featured by high organic matter abundance. The organic matter maturity （ Ro ） of source rocks with buried depth exceeding 3 500 m is greater than 1.0%, which has reached oil generation peak and can be considered as an important source rock series. Oil-source comparison indicates that the oil within Dong3 Member source rocks mainly distributes in a zonal pattern around the main subsag of west Bozhong Sag. Fault and sandbody are considered as the effective palhway systems in the Dong3 Member source rocks of west Bozhong Sag. There are three efficient pathway patterns, including source rock-fault, source rock-sandbody and source rock- sandbody-fauh with compound contaction. It is concluded that the Dong3 Member is self-generation and self-pres- ervation pattern according to the characterization of source rocks and the configuration patterns between path system and source rocks. The source rocks of Dong3 Member in the northern part of west Bozhong Sag can bc taken as ef- fective source rocks for shallow hydrocarbon accumulation. The hydrocarbon mainly migrates from source rocks to shallow reservoirs vertically by large-scale faults, which results in a great exploration potential. The re-understand- ing of hydrocarbon generation, expulsion and accumulation pattern could provide certain guidance for the further ex- ploration and target-area selection.