渤海湾盆地上第三系油藏形成与勘探

渤海湾盆地是一个新生代裂谷盆地，其演化具有早第三纪断陷，晚第三幼坳陷的特点，烃源层位于下第三系，上第三系为河流相沉积，受盖层控制，上第三系油藏主要分布在盆地中部（黄骅，渤中和济阳坳陷），多数上第三系油藏位于凸起上和凹陷内大断层下降盘逆牵引构造中，大量勘探实践表明，小规模的低凸起比大规模的高凸起更有利于油气富集，凹陷内聚烃条件差，则利于凸起上聚集油气，断层的运移条件决定了上第三系逆牵引构造油气富集程度，与主断层相交的次数断层晚期活动强，断层密度大且断至层位深，有利于油气运移至上第三系富集成藏，地层与断层的组合关系控制了油气富集部位，海域内的低凸起及富生烃凹陷边缘大断层下降盘的逆牵引构造是上第三系勘探的有利地区。

NEOGENE OIL ACCUMULATIONS AND THEIR EXPLORATION IN BOHAI BAY BASIN

As a Cenozoic rift basin,Bohai Bay experienced 2 stages of evolution,i, e. Paleogene rifting and Neogene depressing. There are source rocks in Paleogene Shahejie and Dongying Formations,and the Neogene sequences are fluvial deposits. Under control of seals ,most Neogene oil accumulations occur in the center of the basin. It has been proved by wide exploration that lower uplifts with smaller area are more favorable for oil accumulation than higher uplifts with larger area ,and that poor trapping conditions in sags contribute to hydrocarbon accumulation in adjacent uplifts. In the Neogene rollover structures,abundance of hydrocarbon largely depends on communication of various faults ,and secondary faults cutting across major ones promote hydrocarbon migration into the Neogene reservoirs,because of their strong later activities, dense spacing and deep extension. Therefore, hydrocarbon accumulations are controlled by assemblage of formations and faults. For future exploration in Neogene,the lower uplifts and roll-over structures on down-thrown side of petroliferous-sag boundary faults are most prospective.