鄂尔多斯盆地西南部延长组长7致密砂岩伊利石成因初探

鄂尔多斯盆地延长组长7为典型的致密砂岩储层,粒度细,填隙物含量高,物性差.最主要的黏土矿物为伊利石,占填隙物总量的60%.根据大量的铸体薄片、扫描电镜、包裹体测试等分析资料,探讨了伊利石的产状、成因,以及对储层物性的影响.认为:伊利石呈片状、蜂巢状和丝缕状3种方式产出.第一种为原生沉积形成;第二种为早期形成的蒙脱石转化而来;第三种是由钾长石溶蚀形成的高岭石在深埋期间通过伊利石化作用形成.高岭石的伊利石化能促进钾长石的溶解,其形成的长石溶孔是本区最主要的孔隙类型,长石溶孔发育区即为相对优质储层发育区.

Study on origin of illite in Chang 7 tight sandstone of Yanchang Formation in the southwest of Ordos Basin

Chang 7 reservoir in Ordos Basin is typical tight sandstone reservoir.Its physical property is poor due to fine grain size and high pore-filling substance content.The pore-filling substance of 60% is illite,which is the main clay mineral.The occurrence forms and origin of illite are studied according to the analysis of casting thin-section,scanning electron microscope and inclusion data.It is shown that the illite occurs in three forms: flake,honeycomb and wire strands.The flake illite is origin sediment;the honeycomb illite came from smectite in early stage;the wire strand illite is formed by the illitization of kaolinite during the deep burial period of kaolinite,and the kaolinite was produced by the dissolution of potash feldspar.The illitization of kaolinite can accelerate the dissolution of potash feldspar and form secondary pores,and the area where the secondary pores are formed is the region where relatively high quality reservoir develops.