鄂尔多斯盆地山2段砂岩储层的孔隙类型与孔隙结构

Pore Types and Pore Texture of Sandstone Reservoir of 2^(nd) Member of Shanxi Formation,Ordos Basin

在铸体薄片鉴定、粒度分析、压汞曲线及物性分析统计的基础上,对鄂尔多斯盆地山2段砂岩储层的孔隙类型、孔隙结构等微观特征进行了深入分析,结果表明:山2段储集空间主要为粒间溶孔、原生残余粒间孔、岩屑粒内溶孔、杂基溶孔和高岭石晶间孔,局部发育微裂隙;渗透率随孔隙度的增大而增大,而孔隙度和渗透率的大小又与砂岩的孔隙结构有关。根据砂岩的压汞参数及物性特征,划分出4类储层:Ⅰ类——优质储层,主要发育粒间溶孔,具有较好的颗粒支撑,孔隙连通性好;Ⅱ类——较好储层,其储集空间为粒间溶孔—粒内溶孔—高岭石晶间孔组合;Ⅲ类——较差储层,主要发育残余粒间孔—高岭石晶间孔组合;Ⅳ类——差储层,仅发育孤立微孔。指出粗粒结构与含砾支撑结构的石英砂岩储层物性较好;含砾支撑结构储层具有双众数粒度分布特征,有利于孔隙水的流动,促进填隙物溶蚀和粒间溶孔的形成,使得储层的渗透率得到提高。

Based on the identification of cast slice, granularity analysis, mercury penetration curves and physical property statistics, microscopic features such as pore types and structure in the sandstone reservoirs of 2^nd member of Shanxi Formation in Ordos basin are studied. The result shows that the gas reservoir spaces of the 2^nd member of Shanxi Formation mainly include inter-granular dissolution pores, survived original inter-granular pores, debris intragranular dissolution pores, filling ingredient dissolution pores, kaolinite intercrystalline pores and a few of micro-crevasses. The permeability is correlative with the porosity, but they both are related with the pore structure. Four kinds of reservoirs are identified by the mercury penetration parameters and physical properties of the reservoirs. Class Ⅰ has high permeability, mainly contains inter-granular dissolution pores, which has good underpropping structure and good communication. Class Ⅱ is a kind of fair quality reservoir, containing inter-granular dissolution pores, intragranular dissolution pores and kaolinite intercrystalline pores. Class Ⅲ is of lower permeability and contains survived original inter-granular pores and kaolinite intercrystalline pores. Class IV only contains isolated micropores. It indicates that quartz-sandstones with coarse granular texture and pebbled underpropping structure are of high permeability. Sandstone reservoir of pebbled underpropping structure is characterized by double-peak ggrain distribution, which could accelerate the pore water flowing and conduce to dissolution of filling ingredients, improving the reservoir permeability.