东营凹陷超压系统的幕式排烃

东营凹陷烃源岩具有沉积速度快、连续沉积厚及高热流、高地温、高有机质含量的特征;同时,主力烃源岩段(沙河街组三段、四段)发育大套的泥岩,烃源岩主要以砂岩嵌入式、泥包砂及纯泥岩形式存在。这些条件导致在成熟的烃源岩段超压系统十分发育,同时也使得幕式排烃成为东营凹陷烃源岩一个重要的排烃方式。东营凹陷超压体系幕式排烃分为"构造幕"和"压力幕"两种方式。"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。

Episodic expulsion of hydrocarbons in overpressured systems in Dongying depression

Source rocks in Dongying depression are characterized by rapid and continuous deposition and large thickness, as well as high heat flow, high geotherm and high content of organic matters. Large thickness of mudstones are developed in the main source rock intervals(3rd and 4th members 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, overpressured systems are well developed in mature source rock intervals, and episodic expulsion becomes the fundamental mode of hydrocarbon expulsion in Dongying depression. The episodic expulsion of hydrocarbons in the overpressured systems in the depression can be classified into "tectonic episode" and "pressure episode" .The mechanism of "tectonic episode" is destruction caused by tectonic activities, and hydrocarbons migrate along fault planes and tectoclase, while the mechanism of "pressure episode" is the accumulation and release of the "residual energy" in the overpressured systems, and hydrocarbons migrate along microfissures induced from fracturing. Hydrocarbon expulsion efficiency and hydrocarbon index in the overpressured systems with episodic expulsion are remarkably higher than that in the upper source rock interval, and they are remarkably lower than that in the lower source rock interval. Episodic expulsion of hydrocarbon has important significance in petroleum exploration, due to its characteristics of high energy and rapid migration.