断陷湖盆超压封存箱形成机理与油气成藏机制——以渤海湾盆地东营凹陷为例

东营凹陷的超压分布于沙河街组三段中-下亚段大套泥岩和沙四段灰色膏盐岩段中,常压—低压系统发育于上部层段,包括沙二段上亚段、东营组、馆陶组、明化镇组和更新统,形成二元结构。这些发育程度不同的超压体系可以构成不同级别的超压封存箱系统,控制着油气的运移和聚集。超压封存箱的形成是一个地球化学自组织过程,与系统内的流体对流运动及成岩作用密切相关。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,同时也可以通过幕式排放为浅层的新近系及古近系的沙三段上亚段至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。超压不但是油气运聚的主要动力,而且在其产生与演化的过程中能形成微裂缝型油气运聚隐蔽输导体系,是形成岩性等隐蔽油气藏的重要条件。超压和断裂形成陆相断陷湖盆断—压双控流体流动机制。断裂是超压体系卸压的重要渠道,也是幕式排放的主要途径;与断裂沟通的砂岩体及构造背斜等是有利的勘探目标,超压泥岩体周围的透镜状砂体是隐蔽油气藏的潜在目标。

Mechanism of overpressured fluid compartment and its controlling on hydrocarbon migration and accumulation in faulted lacustrine basin: A case study from the Dongying Sag, Bohai Bay Basin

The overpressure in the Dongying Sag was distributed in mudstones of the middle and lower parts of 3rd Member,Shahejie Formation and gypsum-salt layer of the 4th Member,Shahejie Formation.The normal and lower pressure developed in the above strata,and the both made up a binary structure.The over-pressured systems formed over-pressured fluid compartments(OPC)in varied levels,which controlled hydrocarbon migration and accumulation.The geochemical characteristics of OPC demonstrated the geochemical self-organized course,and it included the phenomena of nucleus formation,growth,diffuse,convection,dissolution,deposition,and cementation under a situation of non-equilibrium.These courses were controlled under the coupling of stress,temperature,chemistry and pressure field.The active heat fluid in the deep formation provided dynamical condition for the functions.The two series of seals were distributed at the depth of 2 200 m and 4 000 m respectively,corresponding to the abnormal high content of Ca2 .With an exception of the stagnant fluid dynamic system there were two kinds of fluid dynamic systems in the Dongying Sag:normal-pressured opening fluid dynamic system and OPC fluid dynamic system,which resulted in two accumulation dynamic mechanisms:one was self-sourced and sealed dynamic mechanism,another was outward-sourced and opened mechanism,and the former provided the oil-gas source and drived for hydrocarbon accumulation.Faults and rupture were important pathway for episodic hydrocarbon-expulsion,so the sandstone bodies communicated by faults and conformation-anticlines were favorable prospects for exploration,and the lens-shaped sandbodies around the overpressured source rocks were potential targets for the exploration of subtle trap reservoirs.