川西坳陷须家河组二段致密砂岩储层成岩作用与孔隙演化——以大邑地区为例

Diagenesis and porosity evolution of tight sand reservoirs in the 2^(nd) member of Xujiahe Formation,western Sichuan Depression:an example from Dayi region

低渗透气藏产气量在我国天然气总产量中所占比例越来越大,但由于其气藏分布复杂、预测难度大等因素,阻碍了该类气藏的勘探开发进程。四川盆地川西坳陷上三叠统须家河组二段储层物性总体较差,属于低孔、低渗储层。以储层特征与成岩作用研究为基础,结合大量镜下薄片鉴定成果,确定了胶结物充填的序次及各期胶结物相对含量;并在各期胶结物中找出特征包裹体进行温度检测,结合储层埋藏史、热史等资料,确定了各期胶结物的形成时间与油气充注的时间及次序;此外,描述了储层孔隙在不同历史阶段的变化率与变化原因,从而再现了储层的形成历史,确定了储层致密化时间。最后,结合油气充注史,提出下一步有利勘探方向,为进一步油气勘探奠定了基础。

The percentage of gas production from low-permeability gas reservoirs is increasing in China.However,the low-permeability gas reservoirs are geologically complex and can not be predicted easily,impeding their exploration and development.The second member of the Upper Triassic Xujiahe Formation in western Sichuan depression of Sichuan basin has poor poroperm characteristics as a whole and belongs to low porosity and permea-bility reservoirs.Based on the study of reservoir characteristics and diagenesis,this paper determines the filling sequence and relative content of cements of each stage through microscopic observation of thin sections.Characteri-stic inclusions are identified in cements of each stage and used to measure temperature.The results in combination with burial history and thermal history are used to determine the forming time of cements of each stage,hydrocarbon charging time and their sequences.In addition,the paper describes the rate and causes of porosity change in different periods,reconstructs the reservoir forming history and determines the time of reservoir tightening.Finally,this paper presents further exploration targets according to the analysis of hydrocarbon charging history.