鄂尔多斯盆地正宁地区长6段储层成岩相与孔隙演化

Diagenetic facies and pore evolution of Chang-6 reservoir in the Zhengning area,Ordos Basin,China

研究鄂尔多斯盆地正宁地区三叠系延长组第6段(简称"长6段")成岩相及孔隙演化过程,探讨长6段储层的主控因素。通过铸体薄片、扫描电镜、X射线衍射、阴极发光及薄片染色技术研究长6段成岩相,结果表明:长6段处于中成岩A-B段,主体为A段,关键成岩作用有压实作用、胶结作用、溶蚀作用和交代作用。考虑成岩矿物、成岩阶段、孔隙演化及关键成岩作用等要素划分出5种成岩相:绿泥石薄膜-粒间孔成岩相、长石溶蚀-溶孔成岩相、泥岩压实成岩相、碳酸盐胶结相和黏土矿物胶结相,其中绿泥石薄膜-粒间孔成岩相与长石溶蚀-溶孔成岩相为建设性成岩相。以关键成岩作用指标为基础,定量计算长6段孔隙演化过程:压实作用使原始孔隙消失74%,胶结作用后孔隙仅剩6.6%,溶蚀作用使孔隙增加至9.86%左右。

Zhengning area is one of the popular exploration regions of Triassic Yanchang Formation reservoir in the southern Ordos Basin. However, the Chang 6 section reservoir in the area possesses ambiguous controlling factors over the formation of oil and gas, which makes the energy exploration more complex. The diagenetic facies and pore evolution of Chang 6 section reservoir are studied by means of application of casting thin section observation, scanning electron microscope, X ray diffraction, cathodoluminescence and thin film dyeing technologies, so as to provide clear geological understanding of the reservoir and guide the further oil gas exploration in this region. It shows that the diagenesis in the Chang 6 reservoir is in the A B segment of the middle diagenesis, with A as the main segment. The main ＂types metasomatism. Diagenetic facies of of ＂the diagenetic minerals, diagenetic of diagenesis include compaction, cementation, erosion and Chang 6 section reservoir can be divided into 5 ＂types on ＂the basis of the diagenetic minerals,diagenetic events, diagenetic stages, porosity evolution, key diagenesis and other factors. These ＂types are chlorite film-intergranular pore diagenetic facies, feldspar erosion dissolved pore diagenetic facies, mudstone compacted diagenetic facies, carbonate cementation diagenetic facies and clay mineral cementation diagenetic facies. Of the diagenetic facies, chlorite film-intergranular pore diagenetic facies and feldspar erosion dissolved pore diagenetic facies are constructive diagenetic facies. The pore evolution process of Chang 6 reservoir is quantitatively calculated in terms of key diagenesis index. It shows that compaction caused 74% lose of original pores, only 6. 6% pores remained after cementation, and later erosion increased the porosity up to 9.86% again. The above calculated result agrees well with measured porosity one.