鄂尔多斯盆地合水地区长7致密油储层伊利石成因

Genesis of illite in Chang 7 tight oil reservoir in Heshui area,Ordos Basin

田建锋 高永利 张蓬勃 王秀娟 杨友运

Tian Jianfeng Gao Yongli Zhang Pengbo Wang Xiujuan Yang Youyun

鄂尔多斯盆地合水地区长7油层组为典型的致密油储层,伊利石平均含量高达9.1%是其重要特征,也是控制储层性能的关键因素。扫描电镜、铸体薄片、能谱分析、X-衍射等分析表明,合水地区长7油层组发育浊流沉积的极细砂岩,孔隙类型以长石溶蚀孔为主,且发生溶蚀的长石均为钾长石;伊利石化学成分复杂,以分散杂乱片状为主,仅分布于残余粒间孔隙内,且岩石粒度越细伊利石含量越高;与相邻泥岩相比,粘土矿物相对含量相似,但砂岩中钾长石/斜长石比值小于泥岩。合水地区长7沉积时期火山活动强烈,具有早期蒙脱石形成的地质条件,同时伊利石产状具有蒙脱石化的特征,且镜下可见大量的杂基伊利石化,表明研究区伊利石主要由大量蒙脱石等杂基转化而来;而研究区最高古地温一般不超120℃,也无外来富钾热流体的加入,不具备其他成因伊利石大量生成的地质条件。

Chang 7 reservoir in Heshui area,Ordos Basin is a typical tight oil reservoir with high content of illite up to 9.1%,which is the key factor controlling the quality of reservoir.Analyses of the composition,distribution and occurrence of illite through SEM,EDS,cast thin section and X-diffraction show that the Chang 7 reservoir is very fine turbidity sandstones.The pervasive dissolution of K-feldspar yield lots of secondary pore which is the main pore type.The illites are complex in chemical composition and are mainly in scattered,chaotic sheet-like shape.They only occur in residue intergranular pores.And their content increases with the decreasing of grain size.In comparison with the adjacent shales,the relative content of clay mineral is similar,but the K-feldspar/plagioclase ratio is smaller.Volcanic activities were very intense during the deposition of Chang 7,which provides the favorable condition for semctite development at the early diagenetic stage.The semctites were transformed to illites subsequently.This process may be the main genesis of illite in Chang 7,as illitization of smectite is very common.In addition,the palaeo-geotemperature in the study area is generally lower than 120 ℃ and there are no external potassium-rich hot fluid input,making it impossible for the formation of illite of other genesis.

10.11743/ogg20130518