内蒙古索伦地区中二叠统哲斯组碎屑岩成岩作用及其对储层物性的影响

Diagenesis and its influences on reservoir properties of clastic rocks from Middle Permian Zhesi Formation in Soren region,Inner Mongolia

利用薄片确定砂岩类型、扫描电镜观察碎屑岩微观特征并划分成岩阶段以及对岩石储层进行物性测试分析等方法,系统地探究了内蒙古索伦地区中二叠统哲斯组碎屑岩成岩作用及其对储层物性的影响。研究表明该地区砂岩胶结物有钙质胶结物、硅质胶结物、黏土矿物胶结物和凝灰质胶结物,其中钙质胶结物多为方解石,硅质胶结主要表现为石英次生加大,黏土胶结物以伊利石为主,凝灰质胶结物在该地区出现较少。地化数据显示哲斯组泥岩有机质镜质体反射率值(Ro)在2%~4%之间、最高热解温度(T_(max))>490℃、伊利石/蒙皂石(I/S)的蒙皂石层<15%;薄片镜下观察发现碎屑颗粒间以线接触为主,扫描电镜观察石英次生加大级别为Ⅲ—Ⅳ级。综合分析确定内蒙古索伦地区哲斯组碎屑岩处于晚成岩阶段B期—C期。压实和胶结作用一定程度上降低砂岩的孔隙度和渗透率;而溶蚀溶解作用提高砂岩的孔隙度和渗透率。

Diagenesis in the clastic rocks from Mid-Permian Zhesi Formation in the Soren region of Inner Mongolia and its influences on reservoir properties were systematically studied by means of thin section,scanning electron microscope observation and analysis,diagenetic stage identification,and reservoir physical property testing.The results show that the sandstone cements mainly consist of calcareous,siliceous cements,clay mineral and tuff.The calcareous cement comprises mostly calcite,siliceous cement mainly occurs as quartz secondary growth,while illite is the primary clay cement,with small amount of tuff cement.The geochemical data of Zhesi Formation show that the vitrinite reflectance（Ro）is ranging from 2%to 4%,the highest pyrolysis temperature（Tmax）is above 490℃,and the smectite content of illite/smectite（I/S）is〈15%.The main contact between particles is linear contact,and the grade of secondary growth of quartz isⅢ-Ⅳ.Comprehensive analysis confirmed that the clastic rocks from the Zhesi Formation in the Soren region of Inner Mongolia are in the late diagenetic stages B-C.Compaction and cementation reduce the porosity and permeability of sandstone to a certain extent,whereas the dissolution and dissolution increase the porosity and permeability of sandstone