致密砂岩储层成因及其孔隙演化过程--以杭锦旗十里加汗地区下石盒子组为例

Genesis and pore evolution of tight sandstone reservoir:taking Lower Shihezi Formation in the Shilijiahan block of Hangjinqi area as an example

对杭锦旗十里加汗地区下石盒子组储层复杂的成岩及孔隙演化过程认识不清,严重制约了致密气的高效勘探开发。文中运用铸体薄片分析、扫描电镜、X衍射及物性分析等方法,对研究区下石盒子组低渗透致密储层成因及孔隙演化过程进行了研究。结果表明:研究区下石盒子组优质储层发育受控于断裂带、煤系地层、沉积相、埋藏深度及溶蚀作用强度;辫状河比冲积扇更有利于储层发育,断裂带有利于储层溶蚀孔隙发育;储层储集空间类型包括残余原生孔隙、粒间溶孔、粒内溶孔及微裂缝,次生孔隙数量明显高于残余原生孔隙;压实作用和胶结作用破坏了储层原生孔隙,早期方解石胶结对储层具有双重作用,溶蚀孔隙是储层的主要孔隙类型;研究区下石盒子组主要处于中成岩阶段A期,少量达到中成岩阶段B期,溶蚀作用主要发生在中成岩阶段A期,有利于优质储层发育。

The unclear complex diagenesis characteristics and pore evolution of Lower Shihezi Formation in the Shilijiahan block of Hangjinqi area restricted the exploration and development of tight gas.Genesis and pore evolution of low permeable tight sandstone reservoir of Lower Shihezi Formation was studied by the means of thin-section,scan electron microscope,X-ray diffraction and physical property analysis.The result shows that the high-quality reservoir of Lower Shihezi Formation was controlled by the fault zone,coal-bearing stratum,sedimentary facies,burial depth and dissolution intensity.Braided river is more beneficial to development of high-quality reservoir than the alluvial fan,and the fault zone was in favor of dissolved pore development.The pore space types consist of residual primary pore,intergranular dissolved pore,intragranular dissolved pore and micro-fracture,and the number of secondary pores is obviously higher than the residual primary pores.Mechanical compaction and cementation destroyed primary pore of reservoir,but early calcite has destructive and protective effect on reservoir pore.Dissolved pore is the main pore type of the reservoir.Lower Shihezi Formation of the study area is mainly in the stage A of middle diagenesis phase and minor in the stage B of middle diagenesis phase.Dissolution,which mainly occurred in the stage A of middle diagenesis phase,is in favor of development of high-quality reservoir.