鄂尔多斯西部长6砂岩成岩演化与优质储层

对鄂尔多斯盆地西部盐池—姬塬地区三叠系延长组长6砂岩成岩作用特征的研究表明,该套砂岩目前处于晚成岩阶段A期的早期,受酸性成岩环境控制,长石类易溶颗粒普遍发生溶蚀,石英次生加大发育,特别是早期形成的绿泥石粘土膜非常发育。对砂岩组分的统计和计算表明,机械压实作用是造成该区原生孔隙消亡的最主要原因,其次为胶结作用,而由溶蚀作用增加的孔隙约为初始孔隙度的10%。结合沉积相分析成果,在研究区可划分出3个典型的沉积-成岩相带,即:台型三角洲前缘-绿泥石胶结+晚期铁方解石交代相,坡型三角洲前缘-绿泥石胶结+晚期铁方解石交代相,三角洲前缘末端-绿泥石胶结+晚期铁方解石交代相。优质储层主要受控于绿泥石胶结相带,分布在研究区东部安边至铁边城的一个不规则的区域内。

Diagenetic evolution and high-quality reservoir in Chang 6 sandstone in the western Ordos Basin

The diagenetic characteristics of Chang 6 sandstone of the Upper Triassic in Yanchi-Jiyuan area of the western Ordos Basin show that this set of sandstones are in the early A period of the late diagenetic stage at present and controlled by the acidic diagenetic environment,where the abundant diagenetic phenomena including widespread dissolution of feldspar and lithoclast,secondary enlargement of quartz and well-developed early chlorite film can be observed.The quantitative statistics and calculation show that the mechanic compaction is the main cause resulting in the disappearance of primary porosity,and the next one is cementation.The increasing porosity by dissolution accounts only a little proportion of the initial porosity(lower than 10 percent).According to the sedimentary facies analysis,three types of the typical sedimentary-diagenetic facies zones could be recognized,including platform delta front-chlorite cementation-late ferrous calcite replacement facies,slope delta front-chlorite cementation-late ferrous calcite cementation facies,delta front end-chlorite cementation-late ferrous calcite replacement facies.The high-quality reservoir is controlled by chlorite cementation facies zone distributed in an irregular area from Anbian to Tiebiancheng region.