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

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