陇东地区延长组长7致密砂岩伊利石成因初探

Preliminary Discussion of Illite Genesis of Chang7 Tight Sandstone of Yanchang Formation in Eastern Gansu Region

鄂尔多斯盆地延长组长7为典型的致密砂岩储层，粒度细，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、包襄体测试等分析资料，探讨了伊利石的产状、成因，以及对储层物性的影响。研究认为：伊利石呈片状、蜂巢状和丝缕状3种方式产出。第一种为原生沉积所带来：第二种为早期形成的蒙皂石转化而来：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该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。

The Chang7 reservoir of Yanchang Formation, Ordos Basin, is a typical tight sandstone reserw）ir, with line grain size and poor physical properties. The main clay minerals are illite, accounting for 60% of the total amount of the interstitial materials. According to lots of data analysis of casting thin sections, scanning electron microscopy, and inclusions testing, illite occurrence, genesis, and its impact on the reservoir properties are dis- cussed. The study concludes that the illite was formed by assuming three ways of schistose（flaky or sheet）,scro- biculate （honeycomb-like） and silk-thread-like. The first was brought by the primary sedimentation or connate. deposits; the second was transformed from the early formed montmorillonite; the third was formed through deep- buried illitization of kaolinite which was formed by the dissolved potash feldspar. The illitization of kaolinite can promote the dissolution of potash feldspar. The dissolved pores instead of feldspar formed through the illitization are the main-body of pore types of this region. The feldspar dissolved pores-developed areas are relatively high- quality reservoir-developed areas.