廊固凹陷异常高压与油气成藏的关系

SURPRESSURE AND ITS RELATIONSHIP WITH HYDROCARBON POOLING IN LANGGU SAG

油气藏的形成和分布与异常高压的关系非常密切。廊固凹陷异常高压主要发育在下第三系渐新统沙河街组沙三、沙四段,以沙三下段最为明显,压力系数逾1.7,平面上异常高压主要发育在凹陷中心,向凹陷边缘压力系数逐渐降低。快速沉积导致的欠压实作用、烃类的生成以及岩浆侵入导致的流体热增压效应是异常高压形成的重要原因。对该凹陷异常高压与油气成藏关系进行了研究,结果发现,异常高压对油气运聚有着重要的影响:一方面,异常高压是油气运聚的一种重要动力来源;另一方面,在一定地质背景下其也是控制油气分布的重要因素。油气藏多分布在超压层内或者邻近超压区,同时异常高压形成的流体势能驱动流体从凹陷中心向凹陷边缘流动,最终形成油气藏围绕生油凹陷分布的格局。该区油气藏主要分布在廊东、柳泉—曹家务等异常高压发育区。

Formation and distribution of oil and gas reservoirs are closely related to surpressure.In Langgu sag,surpressure mainly occurs in the third and the fourth members of the Shahejie Formation of the Lower Tertiary Oligocene,especially the lower interval of the third member of Shahejie Formation with a pressure coefficient over 1.7.Laterally,the surpressure mainly occurs in the central part of the sag and lowers progressively to the edge of the sag.The major causes of the surpressure include undercompaction resulted from rapid deposition,hydrocarbon generation and thermal boosting of fluid pressure caused by igneous intrusion.Study of the relationship between surpressure and hydrocarbon pooling in Langgu sag shows that surpressure has very important influences on hydrocarbon migration and accumulation.On the one hand,surpressure is an important driving force of hydrocarbon migration.While on the other hand,surpressure is also a major factor controlling hydrocarbon distribution in a certain geologic setting.Oil and gas reservoirs are mainly distributed in the surpressure layers or in the vicinity of the surpressure zone.Meanwhile,the fluid potential resulted from surpressure can drive the fluid to migrate from the center to the edge of the sag,resulting in the scattered distribution of oil and gas reservoirs around hydrocarbon kitchen.The oil and gas reservoir in the study area are mainly distributed in surpressure zones such as Langdong and Liuquan-Caojiawu.