川西坳陷南段中侏罗统沙溪庙组Ⅱ段储层控制因素

Reservoir controlling factors of the second member of Middle Jurassic Shaximiao formation in the south of western Sichuan depression

川西坳陷南段中侏罗统沙溪庙组Ⅱ段是侏罗系气藏重要的产层段,储层纵横向上变化大,非均质性强,其控制因素与孔隙演化规律尚不清晰使得勘探开发效果不理想。通过对岩心及岩屑薄片观察,结合粒度、物性、薄片等分析化验资料,分析了控制储层的主要因素。沙溪庙组Ⅱ段以分流河道砂体和河口坝砂体为储层,储层物性受控于沉积因素和成岩作用。沉积因素主要通过粒度、沉积微相及岩屑成分等影响储层物性,高长石、粒度较粗的三角洲前缘水下分流河道及河口坝砂体物性最佳。成岩作用则控制孔隙演化,压实作用和胶结作用对储层物性起到破坏性作用,减小的孔隙占原生孔隙的80.4%,压实作用对孔隙的破坏大于胶结作用,溶蚀作用是改善储层孔隙的重要成岩作用,最终因溶蚀作用增加的孔隙度为1.8%。

The second member of Middle Jurassic Shaximiao formation in the south of western Sichuan depression is the important producing interval of Jurassic gas reservoir. Due to the great variation of reservoir in vertical and horizontal direction and the strong heterogeneity, its unclear controlling factors and pore evolution rule make the unsatisfactory effects of exploration and development. By observing core and cuttings thin slice, and analyzing assay data of size, physical property and thin slice, the main factors of controlling reservoir are analyzed. The second member of Shaximiao formation is composed of distributary channel sandbody and mouth bar sandbody, and its reservoir physical property is controlled by sedimentary factors and diagenesis. Sedimentary factors mainly affect the physical properties through grain, sedimentm7 microfacies and debris composition, in addition, sand body physi- cal property is best distributary channel and mouth bar sandstone of the front-delta deposition with high feldspar content and coarse grain. Diagenesis controls porosity evolution, and compaction and cementation have destructive effects on reservoir physical property. In addition, 80.4 % of the primary pores are decreased, and the effect of compaction on porosity is greater than that of cementation. Dissolution is an important diagenesis to improve the porosity of reservoir, accordingly, the porosity increases 1.8 % by dissolution.