渤海湾盆地南堡凹陷原油成因类型及其分布规律

Genetic Type and Distribution of the Oils in the Nanpu Depression,Bohai Bay Basin

南堡凹陷近年油气勘探取得了重大突破,为揭示该区滩海与陆地油气成因及分布规律,对67个原油和油砂样品进行了详细的地球化学研究。南堡凹陷原油具有低硫、中高蜡含量特征,陆相成因特点显著。共分为4种类型原油:(1)陆地沙三段深部层系原油,具有高4-甲基甾烷丰度、低奥利烷丰度与低甲基菲指数值和轻微偏高成熟度特征;(2)陆地Es1—Ed原油与Ng和Nm原油,其特征与第一类原油相反;上第三系原油普遍遭遇生物降解;(3)滩海东营组原油,以较高伽马蜡烷/C30藿烷和高甾烷/藿烷值区别于陆地原油;(4)滩海奥陶系潜山原油,具有低丰度甾萜类生物标志物、相对高丰度孕甾烷、三环萜烷与重排甾烷系列等特征,显示较高成熟度。上述4种成因类型原油指示南堡凹陷陆地、滩海均存在多层导有利烃源岩;同层位中滩海Es1-Ed存在较陆地更为优越的有利烃源岩,南堡滩海地区具有广泛的油气勘探前景。

A great quantity of oils were discovered recently in both the foreshore and onshore of the Nanpu Depression, Bohai Bay Basin. Totally 67 oil and oil sand samples were collected to perform detail conventional geochemical analysis to unravel differential characteristics and classify genetic types for the oils. Four groups of the oils in the depression are recognized, including （1）onshore oils produced from Es3 interval, characterized by high abundance of 4-methyl steranes but low level of oleanane and low methylphenanthrene indices. Also the oils have a relatively higher degree of thermal maturity ; （2） onshore oils produced from Es1 to Ed and Ng to Nm. They have converse features of the group-Ⅰ with widely secondary alteration by water washing and biodegradation for most of the oils from Ng to Nm; （3）offshore oils from Ed interval, which are differentiated from onshore oils with relatively high ratios of gammacerane to C30 hopane and steranes to hopanes; （4） oils from Ordovician burial hill, which have apparent low contents of steranes and terpanes but high content of pregnane, tricyclic terpane and diasteranes, indicate relatively high thermal evolution of the oils. It is expected that there are several favored source rocks developed in both onshore and offshore regions of the Nanpu Depression, and there is a better quantity of Es1 to Ed source rocks offshore than to onshore. Great petroleum potential in the depression was suggested after our study.