Abstract: The overpressure in Zhanhua Sag of Bohai Bay Basin was distributed in the large series of mud in the middle and lower parts of the third member of Shahejie Formation and gypsum-salt rock in the forth member of Shahejie Formation.The distribution of overpressure in the various formations was different.There formed the binary structure on the section.The normal-compaction or normal-pressured (low pressured) system was formed at the formation above 2 500 m in depth,and the over-pressured system was formed at the formation below 2 500 m.The over-pressured system corresponds to the main source rocks.Hydrocarbon generation was an important mechanism for genesis of the overpressure system,but the suppression of overpressure on the hydrocarbon generation was not obvious.There are two kinds of fluid dynamics systems in Zhanhua Sag,including the normal-pressured opening fluid-dynamics system and over-pressured fluid-dynamics system,which result in two types of accumulation dynamic mechanisms.One is the self-sourced and sealed dynamic mechanism,and the other is the outward-sourced and opened mechanism.The former provided the oil-gas source and reservoir-forming driver for hydrocarbon accumulation.Faults and ruptures are important pathways for episodic hydrocarbon-expulsion.So the sandstone-bodies communicated by faults and anticlines are the favorable prospects for exploration,and the sand lens reservoirs around the over-pressured source rocks are the latent targets for the exploration of subtle trap reservoirs.

Key words: Zhanhua Sag, faulted basin, overpressure system, fluid flow mechanism, fault, hydrocarbon accumulation

摘要： 渤海湾盆地沾化凹陷古近系的超压在渤南洼陷和五号桩洼陷的沙三段中—下亚段大套泥岩和沙四段灰色膏盐岩段中分布,但在不同层位超压分布略有差别;常压—低压系统发育于上部层段,剖面上形成二元结构.从埋深上看,2 500 m以上地层基本为常压或低压,2 500 m以下地层开始出现较明显的压力异常.沾化凹陷超压系统对应主力烃源岩系沙三中、下亚段及沙四上亚段,生烃作用是超压的重要成因,但超压对生烃的抑制作用不明显.超压体系构成了准封闭的超压封存箱型自源油气成藏动力学系统,同时也通过幕式排放为浅层的新近系及古近系的沙三段上亚段—东营组常压开放性它源油气成藏动力学系统提供油源及成藏动力.断裂是超压体系泻压的重要渠道,也是油气幕式排放的主要途径,与断裂沟通的砂岩体及背斜构造是有利的勘探目标,超压泥岩体周围的透镜状砂体是潜在的目标.

关键词: 沾化凹陷, 断陷湖盆, 超压系统, 流体流动机制, 断裂, 油气成藏