鄂尔多斯盆地致密砂岩储层伊利石膜特征

Features of Illite Films in Tight Sandstone Reservoir of Ordos Basin

利用铸体薄片和带有能谱仪的扫描电镜对鄂尔多斯盆地延长组致密砂岩储层伊利石膜的赋存状态和化学组分进行了细致观察与测试分析,进而讨论了其成因和生长过程及对储层物性的影响。研究认为,伊利石膜生长于压实作用之后,起因于假杂基化的蒙皂石蚀变提供的物质来源和生长空间,形成Ⅱ型伊利石膜;随着骨架颗粒溶蚀产物的参与,Ⅱ型伊利石膜发展为Ⅰ型伊利石膜。伊利石膜具有内、外2层结构,单体特征标示出外层膜的形成时间早于内层膜,在内层膜的片状或长条状单体形成时,外层膜原有的片状或长条状单体丝状化。在伊利石膜的生长和伊利石单体丝化过程中,产生大量次生孔隙,有效地改善了致密砂岩油储层的物性。

The occurrence and chemical composition of the illite films in Yanchang Formation tight sandstone reservoir in Ordos Basin were observed and analyzed by means of thin section analysis and scanning electron microscopic analysis with energy disperse spectros- copy, and the genesis and the growth process of the illite films and their impact to the reservoir physical properties were systematically discussed. The study shows that the growth of the illite films was after the compaction of the early diagenetic phase, the hydrolysis of smectite as pseudomatrix provided the substance and the space for the illite films, and II -type illite film was formed. With the participa- tion of the material produced by the dissolution of the skeleton particles, the I1 -type illite film developed into I -type illite film. The illite film is of the structure of double layers, and the features of the illite crystals illustrate that the growth time of the outer layer is earlier than that of the inner layer. When the flake-shaped and long stripe-shaped illite crystals in the inner layer were formed, the flake-shaped and long stripe-shaped illite crystals in the outer layer became filaceous. A large number of secondary pores have been produced in the process of the growth of illite films and the filamentation of illite crystals ,which can effectively improve the physical properties of tight sandstone reservoir.