大民屯凹陷压力场特征及其成因机制探讨

异常地层压力是沉积盆地中的常见现象,其与成烃成藏关系密切。本文以欠压实带的有无、欠压实的幅度大小、持续的深度范围,将大民屯凹陷泥岩压实类型分为4种,即强烈欠压实型、欠压实型、局部欠压实型以及正常压实型。利用测井、地质和钻井资料,运用等效深度法分析了该区现今异常压力的展布特征并探讨了其成因机制。5条超压分布剖面揭示大民屯凹陷的超压体系在凹陷内分布较广泛,纵向上基本可分为上、中、下3套压力体系。①纵向上,上部即Es23段及其以上地层基本为正常压力系统;中部即Es33段为弱超压系统;下部即Es43和Es4地层为强超压系统。②横向上,超压在洼陷中心强烈发育,到斜坡和隆起带渐渐演变为正常压力。压实不均衡和生烃作用是大民屯凹陷超压发育的主要机制。

Characteristics and Genetic Mechanism of the Pressure Field of the Damintun Depression

Abnormal geopressure widely existent in the sedimentary basin is of great significance in the study of hydrocarbon generation and accumulation. There are four types of shale compaction, namely, strong undercompaction, undercompaction, local undercompaction and normal compaction. With the equivalent depth method, the authors calculated the overpressure along five profiles with sonic log data and discussed its origin. The results show that overpressure is widely distributed in damintun depression. Vertically, there exist three geopressure systems, i.e., the normal geopressure system within and above Es3_2, the weak overpressure system in Es3_3 and the overpressure system in Es4_3 and Es_4. Horizontally, overpressure is strong in the center of the sag and turns into normal pressure on the slope. Unbalance compaction and hydrocarbon generation constitute the main mechanism of overpressure.