鄂尔多斯盆地南部马家沟组孔隙类型及其演化

经数百片岩心薄片观察和扫描电镜分析认为,鄂尔多斯盆地南部马家沟组发育微缝、晶间缝、溶缝、破裂缝以及微孔、粒间孔、晶间孔、晶间溶孔、溶孔和溶洞等多种储集空间类型,其中晶间孔和晶间溶孔是主要的孔隙类型。在孔隙演化过程中白云石化、去膏化和溶蚀作用对形成孔隙有利,而胶结作用、岩溶压实作用、膏化作用及去白云石化作用使孔隙消失,为破坏性成岩作用。低重结晶及中等重结晶作用有利于孔隙的形成,但强重结晶作用不利于孔隙的形成。据盆地南部马家沟组碳酸盐岩经历的成岩环境、成岩阶段及相应成岩作用特征,将其孔隙演化分成早期原生孔隙形成与减少、中期和晚期次生孔隙形成及充填三个阶段。从演化过程来看,中期表生成岩阶段及晚期深埋藏成岩阶段对有效储集空间的最终形成具有决定意义。

Pore Types and Evolution of Ordovician Majiagou Formation in the Southern Part of Ordos Basin

Based on observation of hundreds of thin sections and SEM analysis,ten types of the reservoir space was found in Ordovician Majiagou Formation in the southern part of Ordos Basin,such as dissolved fracture,dis-solved pores,intergranular pores,and intercrystalline pores,etc.,in which intercrystalline dissolution pores and intercrystalline pores are the main types. During evolution of pores,dolomitization,corrosin and degypsification are favourable to formation of pores while cementation,compaction-pressolution,gypsification and dedolomitization are unfavourable and ruinous. Recrystallization is dualism. Analysis of environment,stages and characteristics of diagenesis has shown that pore evolution came through three stages:the formation and decrease of primary pores in early stage,the formation and filling of secondary pores in middle and late stages. Evolutionary process reveals that hypergene and embedding diagenesis stages are significant to form effective reservoir space.