鄂尔多斯盆地东北部奥陶系马五1+2储层特征及成因

基于岩心、薄片和分析化验资料，研究鄂尔多斯盆地东北部奥陶系马五¹⁺²亚段的储层特征及成因。结果表明，研究区马五¹⁺²亚段具有多样性的储集岩类和储集空间类型。储集岩类包括含膏模孔泥粉晶云岩、颗粒云岩、砂糖状中-粗晶白云岩、微生物碳酸盐岩和溶洞充填砂质角砾云岩。相应的储集空间有膏模孔、渗流物间微孔、粒间（溶）孔、粒内溶孔、晶间（溶）孔、窗格孔和砾间残余孔洞。研究区储集层整体表现为低孔、低渗孔隙型。其中，储集性能以含膏模孔泥粉晶云岩最佳，但发育频率及规模一般；而颗粒云岩和溶洞充填砂质角砾云岩储、渗性能略低于前者，但分布频率及发育规模更大。储层成因分析发现，研究区储层发育主要受沉积微相、多期叠合型岩溶的控制，为典型的相控岩溶型储层。砂屑滩和膏云坪是储层发育和后期岩溶叠加改造的物质基础，未成熟期表生岩溶对膏质团块的溶蚀以及岩溶水沿早期砂屑滩孔渗层顺层流动溶蚀是储集层形成的关键，而成熟期表生岩溶叠加改造未成熟期表生岩溶及其混合充填作用则使得先期储集层遭到破坏或消失。

Characteristics and genesis of Ordovician Ma51+2 sub-member reservoir in northeastern Ordos Basin

Characteristics and genesis of Ma5¹⁺² sub-member reservoir (the 1^st and 2^nd sub-member of the 5^th member of Ordovician Majiagou Formation) in the northeastern Ordos Basin are studied based on core,thin section and physical property analysis.The result shows that diverse types of reservoir rocks and reservoir spaces occur in Ma5¹⁺² sub-member in the study area.The reservoir rock types include gypsiferous micritic to very fine crystalline dolomite,grain dolomite,saccharoidal medium-coarse crystalline dolomite,microbial carbonate and sandy rubble dolomite with caverns filled.And the corresponding reservoir space types are gypsum mould pore,micropore between pore fillings,intergranular (dissolved) pore,intragranular dissolved pore,intercrystalline (dissolved) pore,fenestral pores,inter-breccia residual vuggs.The reservoirs in Ma5¹⁺² sub-member are typical porous reservoirs with low porosity and low permeability as a whole.The micritic and very fine crystalline dolomite with gypsum mold pores have the best reservoir properties but fair frequency and scale of occurrence.In contrast,the grain dolomite and sandy breccia dolomite have poorer reservoir properties but larger frequency and scale of occurrence than the former.Reservoir genesis analysis indicates that the formation and distribution of the Ma5¹⁺² sub-member reservoirs in this region are mainly controlled by sedimentary microfacies and multi-stage superimposed karstification,thus they are typical facies-controlling karst reservoirs.The psammitic banks and the gypsiferous dolomite flat provided the material foundation for the reservoir development and later karst reformation.The dissolution of gypsum clumps via epigenic karstification in the immature stage,the dissolution caused by layer-parallel flowing of karst water along the porous beds of early psammitic banks played a key role in the formation of the reservoirs.However,the overprint of epigenic karstification in the mature stage on that in the immature stage and the hybrid filling destroyed the earlier reservoirs or made them disappear.