鄂尔多斯盆地东西部长2低渗透储层微观特征对比研究

Comparative Study on Microscopic Characteristics of Chang-2 Low Permeability Reservoir in the East and West of Ordos Basin

综合铸体薄片、扫描电镜、高压压汞和常规物性等实验结果,研究对比了鄂尔多斯盆地东部和西部长2低渗透储层微观特征。结果表明,东西部均表现为低渗透,但西部长2储层孔隙度总体好于东部。东部长2储层为中-细粒长石砂岩,方解石和绿泥石为主要的胶结物;西部长2储层以中-细粒长石砂岩为主,次为岩屑长石砂岩,高岭石、绿泥石及铁白云石为主要胶结物。孔隙类型主要以原生粒间孔为主,次为长石溶孔;西部长2储层平均孔喉半径及退汞效率均优于东部,反映出孔喉的连通性好。物源与沉积环境不同是造成东西部长2储层原始孔隙差异的主因。深埋藏、强压实作用是控制东西部长2低渗透储层形成的主因之一,压实平均减孔率西部长2储层高于东部;胶结作用是促使长2储层物性进一步变差的主因之二;溶蚀作用造成的孔隙度增加是长2低渗透储层形成的关键。

Based on the results of casting thin section,scanning electron microscope,high pressure mercury injection and conventional physical properties,the microscopic characteristics of Chang 2 low permeability reservoirs in the eastern and western Ordos Basin ware studied and compared.The results show that the eastern and western parts are low permeability,but the porosity of Chang 2 reservoir in the western part is generally better than that in the eastern part.The eastern Chang 2 reservoir is medium-fine feldspar sandstone,calcite and chlorite are the main cements;the western Chang 2 reservoir is dominated by medium-fine feldspar sandstone,followed by lithic feldspar sandstone,kaolinite,chlorite and iron dolomite as the main cement.The pore types are mainly primary intergranular pores,followed by feldspar dissolved pores;the average pore throat radius and mercury removal efficiency of Chang 2 reservoir in the west are better than those in the east,reflecting good pore throat connectivity.The difference of provenance and sedimentary environment are the main cause of the original porosity difference of the east and west Chang 2 reservoir.Deep burial and powerful compaction are one of the main factors controlling the formation of low permeability reservoirs in the western and eastern Chang 2 low permeability reservoir,and the average porosity reduction rate in the west is higher than that in the east.Cementation is the main reason for further deterioration of Chang 2 reservoir physical properties;the increase of porosity caused by dissolution is the key to the formation of Chang 2 low permeability reservoir.