南八仙构造带水文地质演化与异常高压形成机理

Hydrogeological evolution and formation mechanism of abnormal pressure in Nanbaxian structure zone

柴达木盆地北缘新生代构造活动剧烈,断层十分发育,但是位于该区中部的南八仙构造带在深层发育异常高压。弄清异常高压的形成机制,对该区油气成藏研究有重要意义。根据地层温度、压力及流体地球化学资料,分析了该区压力分布特征。从沉积埋藏史和流体演化史的角度,探讨了异常高压的形成机理。研究表明,南八仙深层异常高压是在构造挤压作用背景下,泥岩压榨离心流的快速充注引起的邻源型高压;该异常高压的分布,明显受沉积相带和区域封隔体范围的控制;该异常高压的存在,有利于深层油气藏的持续充注及浅层油气藏的垂向运移聚集。

Structure movement was very fierce in Cenozoic era,and the faults were well developed in northern Qaidam Basin.Abnormal pressure universally exists in the deep formation of Nanbaxian structure zone which is located in the central area of northern Qaidam Basin,so it is very meaningful to study the mechanism of abnormal pressure for the research of oil and gas pool formation.According to the measured pressure data,temperature data and fluid geochemistry data,distribution characteristics of pressure are analyzed in the zone.The formation mechanism of abnormal pressure is discussed from the respect of sedimentary burial history and fluid evolution history.The research shows that the abnormal pressure is caused by the rapid injection of centrifugal flow of compacted mudstones in Nanbaxian structure zone where the tectonic compression is very serious.The abnormal pressure belongs to adjacent source type.The distribution of abnormal pressure is mainly controlled by sedimentary facies and the distribution range of regional compartments.The abnormal pressure not only can facilitate the continuous injection of hydrocarbon in deep formations but also can provide the power for the vertical migration and accumulation of oil and gas in shallow formations.