川东北地区石炭系成岩作用及储集性

川东北石炭系为一套蒸发性局限海潮坪沉积 ,仅残存中石炭统黄龙组。残厚在通江—南江—巴中地区为2 0 -m左右 ,且分布零星 ;开县—大竹—垫江一带为主要分布区 ,达县地区最厚 ,局部可达 70 -m。岩性主要为含粒屑微—粉晶白云岩、角砾状白云岩、膏岩及泥晶灰岩等。经历了白云石化、重结晶、溶蚀等成岩作用和构造作用 ,地层的溶蚀孔、晶间孔和裂缝发育 ,其储集性能得到了较大改善 ,成为川东北乃至川东地区碳酸盐岩地层中最重要的一套储集层。孔隙度大于 3%的储层分布范围也在开县—大竹—垫江构造上 ,呈北东向展布。宣汉以北 ,主要是由于双石庙、通江—南江—巴中地区石炭系地层变薄 ,因而储集性能较差。高产的沙罐坪气藏预示本区石炭系具良好的油气远景。

Diagenesis and Reservoir Characterization Carboniferous Sediments in Northeastern Sichuan

The Carboniferous strata are a set of vaporized tidal flat sediments in northeastern Sichuan. Though they only exist in Huanglong Formation with a thickness of 20～70m, they are the most important carbonate reservoirs in this area. The rocks mainly consist of dolomicrite, powder-crystal dolomite, dolosparite, brecciate dolomite and anhydrite rock. As experiencing diagenesis of dolomitization, recrystallization and dissolution and other geological and structural processes, solution porosity, intergranular porosity and fractures are developed well so as to good reservoir condition in them. The reservoirs with more than 3% of porosity are mostly distributed in Kaixian-Dazhu-Dianjiang area and the strata are thinning up and reservoir characterization is getting poor toward the north of Xuanhan to Shuangshimiao area and Tongjiang-Nanjiang-Bazhong area. The Carboniferous Shaguanping Anticline is the most high-yield gas reservoir, which implies that there are good oil and gas potential in this area.