致密砂岩储层成岩相类型划分——以鄂尔多斯盆地环县西部地区长33储层为例

Classification of diagenetic facies in tight sandstone reservoirs:a case study of Chang 33 reservoir in the west of Huanxian,Ordos Basin

通过铸体薄片、扫描电镜等分析资料,明确了鄂尔多斯盆地环县西部地区长33储层特征,确定了成岩作用类型及强度。在此基础上,对研究区成岩相类型进行划分,并探讨其与产能之间的关系。研究表明:强烈的胶结作用使砂岩储层原生孔隙遭到严重破坏,是致密储层形成的主要原因;以成岩作用强度为要素,结合三端元将研究区储层成岩相划分为溶蚀-胶结(充填)相、胶结(充填)相2类成岩亚相,根据胶结物对储层物性的影响关系,储层成岩亚相进一步划分为溶蚀-伊利石+绿泥石胶结相、溶蚀-高岭石+碳酸盐+硅质胶结相、高岭石+碳酸盐+硅质胶结相3种成岩微相;结合实际产能分析,溶蚀-伊利石+绿泥石胶结相产能效果最好,是有效的油气富集储层;溶蚀-高岭石+碳酸盐+硅质胶结相产能效果较差;高岭石+碳酸盐+硅质胶结相储层物性极差,以产水为主,难以形成有效的油气藏。

Through analysis data such as cast slices,scanning electron microscope,the characteristics of Chang 33 reservoir in the west of Huanxian,Ordos Basin were clarified,and the type and intensity of diagenesis are determined.Based on this,the types of diagenetic facies in the study area are divided and its relationship with productivity is discussed.The research shows that strong cementation has severely damaged the primary pores of sandstone reservoirs,which is the main reason for the formation of tight reservoirs.Using the diagenetic intensity and the three-end-member,the diagenetic facies of the reservoir is divided into two subfacies:dissolution-cementation(filling)facies and cementation(filling)facies.According to the relationship between cement and physical properties the reservoir is further divided into three microfacies:dissolution-illite+chlorite cementation phase,dissolution-kaolinite+carbonate+siliceous cementation phase and kaolinite+carbonate+siliceous cementation phase.Combined with productivity analysis,the dissolution-illite+chlorite cementation phase has the best productivity and is an effective oil-rich and gas-rich reservoir;the dissolution-kaolinite+carbonate+siliceous cementation phase has a poor productivity;the kaolinite+carbonate+siliceous cementation phase has the very poor physical properties and mainly produces water,and it is difficult to form an effective oil and gas reservoir.