桂中坳陷及周缘油气保存条件分析

Study of hydrocarbon preservation condition in Guizhong depression and the margin

桂中坳陷经历多期构造运动,油气藏改造破坏强烈,油气保存条件是制约其勘探决策的关键因素之一.基于盖层和构造条件对油气成藏保存具有重要的影响,从宏观与微观角度对盖层封闭性进行了综合评价,对后期构造作用与油气保存条件的改造进行了探讨,就构造断裂活动导致桂中坳陷及周缘的油气保存条件遭到破坏提出了流体地球化学方面的证据,综合分析了桂中坳陷及其周缘地区油气保存条件.结果表明:中、下泥盆统泥质岩是桂中坳陷及其周缘主要的区域盖层,上泥盆统和下石炭统的有效匹配可组成有效的局部盖层,盖层封闭性由"中等"到"好",且坳陷东部泥质岩更发育;燕山—喜山运动使得桂中坳陷尤其是坳陷东部、东南部遭受强烈抬升,断裂发育,大气水下渗强烈,且剥蚀时间长、面积广、强度大,导致中泥盆统普遍出露地表,由东往西剥蚀厚度逐渐减小.桂中坳陷及周缘现今油气保存条件整体已遭遇一定的破坏,相对而言,坳陷中西部比东部好.

There have been experienced several period tectonic actions in Guizhong depression and the margin,which induced hydrocarbon preservation condition to be damaged seriously.The hydrocarbon preservation condition is one of key factors for exploration in Guizhong depression and the margin.Based on the important effect of cap rock and tectonic condition on the hydrocarbon preservation,a comprehensive evaluation of cap rock＇s sealing capacity from the macro and micro point of view was conducted.The subsequent tectonism was discussed.The evidence of fluid geochemistry was presented,which indicates that the hydrocarbon preservation conditions of Guizhong depression and the margin were damaged by tectonic-fault action.The hydrocarbon preservation conditions of Guizhong depression and the margin were evaluated synthetically.The results show that the Middle-Lower Devonian argillaceous rocks are the main regional cap rock of Guizhong depression and the margin,while the valid combination of Upper Devonian and Lower Carboniferous can form an effective local cap rock.The cap rock sealing is improved from medium to good,and argillaceous rocks are more developed in the east of the depression.During the period of Yanshan-Himalayan movement,Guizhong depression,especially the eastern and south-eastern areas had suffered a strong uplift and erosion,faults developed and meteoric water infiltrated intensively,which leaded to the Middle Devonian generally exposed surface and the erosion thickness decreased from east to west.The present hydrocarbon preservation conditions have been destroyed to a certain extent,and that of midwest of depression is better than that of the east.