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鄂尔多斯盆地东部上古生界致密气储层主要以岩屑石英砂岩和石英砂岩为主,总体石英含量较高,在镜下观察中经常发现该区上古生界储层发育石英溶蚀现象,因此分析该区石英溶蚀特征、探讨其形成机理对储层评价具有重要的意义。通过铸体薄片鉴定、扫描电镜及X-射线衍射分析等测试手段,对鄂尔多斯上古生界致密气储层石英溶蚀特征、成因机理进行了详细研究。石英溶蚀表现为石英颗粒及硅质胶结物溶蚀成港湾状、锯齿状,部分颗粒表面发育溶蚀坑,可分为石英颗粒边缘被溶蚀、石英次生加大边被溶蚀及石英颗粒部分或整体被溶蚀这3种型式;石英溶蚀表现出2种伴生胶结物特征:一种是多酸性黏土矿物高岭石的石英溶蚀;另一种为富伊利石的石英溶蚀。石英溶蚀机理有2种:一种是有机酸条件下酸性孔隙水及游离水中的Al 3+对石英的溶蚀,主要伴生以高岭石为主的酸性黏土矿物,对高岭石含量较高的本溪组及山2段储层孔隙改善明显;另一种是偏碱性成岩环境下碱性孔隙水对石英的溶蚀,主要伴生以伊利石为主的偏碱性—中性黏土矿物,对伊利石大量发育的太原组储层孔隙改善明显。
The Upper Paleozoic tight gas reservoirs in the eastern Ordos Basin are dominated by lithic quartz sandstone and quartz sandstone with high overall quartz content. Quartz erosion of the Upper Paleozoic reservoirs is often found in microscopic observations. Therefore, It is of great significance to study the dissolution characteristics of quartz in the area and to discuss its formation mechanism on reservoir evaluation. Through the identification of thin castings, scanning electron microscopy and X-ray diffraction analysis, the quartz dissolution characteristics and genetic mechanism of tight gas reservoirs in the Upper Paleozoic of the Ordos Basin were studied in detail. The quartz dissolution shows that the quartz grains and the siliceous cement dissolve into a bay-like, jagged and some corrosion pits on the surface of the grains, which can be divided into the dissolution of the quartz grain edge, the dissolution of the quartz secondary enlarged edge and the partial or whole quartz grain There are two types of associated cementation: quartz dissolution of kaolinite with polyacid clay minerals and quartz dissolution of kaolinite. There are two kinds of dissolution mechanism of quartz: one is dissolution of quartz in acidic pore water and free water under organic acid conditions, mainly associated with kaolinite-based acidic clay minerals, and high content of kaolinite The porosity of Benxi Formation and the Member 2 of the reservoir has been obviously improved. The other is the dissolution of quartz by alkaline pore water in the alkaline diagenetic environment, mainly associated with illite-dominated alkaline-neutral clay minerals, The porosity of the Taiyuan Formation reservoir improved significantly.