东营凹陷流体超压封存箱与油气运聚

东营凹陷古近系由于压实不均衡和生烃作用导致超压的广泛发育,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。东营凹陷超压封存箱中的地质地球化学特征显示封存箱可以划分为三部分:箱缘成岩地带(封隔层),对油气起着封闭作用;烃类的有利释放带,其中超压得到一定程度释放,烃类较大程度上排出,可以称为排烃的高峰带;烃类滞留带,该带中超压未能得到很好释放,烃类也多滞留于其中,为排烃的不利地带。幕式排放是超压封存箱排液的一种重要排液方式,存在“压力幕”和“构造幕”两类方式。“构造幕”的机制是外部构造活动的破坏,其排烃方式主要是沿着断裂面及构造裂缝运移;“压力幕”的机制是超压体系内部“剩余”能量的积累和释放,其排烃方式主要是沿着压裂形成的微裂缝排放。在发生幕式排烃作用的超压体系内,排烃效率、烃指数分别较上下层段明显增大和减小。幕式排烃具有的高能量、快运移的特征,使得其在油气勘探中具有重要的意义。东营凹陷可以划分为浅层的常压开放性流体动力学系统和中部的超压封存箱流体动力学系统两类流体动力学系统(排除深层滞留系统),分别对应常压开放性它源油气成藏动力学及超压封存箱型自源油气成藏动力学两类不同成藏机制。

Over-pressured Fluid Compartment and Hydrocarbon Migration and Accumulation in Dongying Depression

Rapid and continuous deposition and large thickness,as well as high heat flow,high geotherm and high content of organic matters characterize source rocks in Dongying depression.Large thickness of mudstones are developed in the main source rock intervals(3rd and 4th of Shahejie Formation).Source rocks are mainly deposited in the forms mudstone inlaid with sandstone,sandstone enclosed within mudstone and pure mudstones.As a result,over pressured systems are well developed in the main source rock intervals,and episodic expulsion becomes the fundamental mode of hydrocarbon expulsion in Dongying depression.The over-pressured systems form over-pressured fluid compartments(OPC) in vary levels that control the hydrocarbon migration and accumulation.The compartments could be divided into three parts according to the geochemical characteristics: the edge of compartment(seal),which hold up the hydrocarbon migration to outside;the favorable releasing zone for hydrocarbon,in which over-pressure was released to some degree and hydrocarbon was expelled efficiently;the stagnant zone for hydrocarbon,in which the over-pressure remains and the hydrocarbon is stagnant relatively.The episodic hydrocarbon-expulsion can be classified as "tectonic episode" and "pressure episode" based on the different mechanisms.The mechanism of "tectonic episode" is a destruction caused by tectonic activities,and hydrocarbons migrate along fault planes,while the mechanism of "pressure episode" is the accumulation and release of the "residual energy" in the over pressured systems,and hydrocarbons migrate along microfissures induced from fracturing.Episodic hydrocarbon-expulsion of OPC has important significance in petroleum exploration in Dongying depression,due to its characteristics of high energy and rapid migration.With the exception of the stagnant fluid dynamics system,there are two kinds of fluid dynamic systems in Dongying depression: normal-pressured open fluid dynamics system and OPC fluid dynamics system,which results in two accumulation dynamic mechanisms: one was self-sourced and sealed dynamic mechanism,another was outward-sourced and opened mechanism.OPC is moving and changing at all times, so all the geological behaviors should be investigated by historical and developmental eye.