大民屯凹陷超压的发育演化及油气运聚的动力学机制

Evolution of overpressure and dynamic mechanism of hydrocarbon migration and accumulation in Damintun depression

关键词:  超压  幕式油气成藏  动力学机制  水力破裂  大民屯凹陷

Key words:  overpressure  episodic petroleum accumulation  dynamic mechanism  natural hydraulic fracture  Damintun depression

摘要:

通过186口探井545组实测储层压力数据的统计分析,采用等效深度法对65口井泥岩段声波时差进行压力计算,并利用数值模拟技术对大民屯凹陷超压的发育演化进行研究,结合应力场演化与断裂发育分布和活动强度性分析,探讨大民屯凹陷厚层烃源岩排烃的动力学机制。结果表明:凹陷内超压普遍发育;快速沉降沉积和生烃作用是超压发育的主控因素;沙四段沉积期超压开始发育并迅速增大,在沙一段沉积期达到最高,随后逐渐泄放降低,断裂发育少的地区超压发育,断裂密集发育区超压发育相对较弱;在超压的作用下地下流体以幕式流动为主;阐明了大民屯凹陷超压主导型和构造活动-超压联控型两种幕式成藏的动力学机制。

Abstract:

Based on 545reservoir pressure measurements in 186boreholes and the calculated shale pressure of 65boreholes using equivalent depth method, the evolution and distribution characteristics of overpressure in Damintun depression were studied by using numerical simulation method. The dynamic mechanism of hydrocarbon expulsion from the thick source rock was discussed through the integrated analysis of the evolution, distribution and activity of faulting in the depression. The results show that overpressure is extensively developed in the depression. Compaction disequilibrium resulted from high sedimentary rate and hydrocarbon generation are the main controlling factors for the development and evolution of overpressure. The numerical simulation shows that overpressure increased gradually from the period of Es_4and reached maximum at the period of Es₁. The development of overpressure is relatively slower in the faulting zone. It is suggested that overpressured fluid is mainly episodically expulsed from geopressured sediments. The dynamic mechanism of overpressure-dominated and tectonic-overpressure controlled episodic petroleum accumulation includes natural hydraulic fracture, mud diapir, faulting dominated and overpressure promoted.