鄂尔多斯盆地陇东地区延长组砂岩储层孔隙成因类型及其控制因素

陇东地区延长组砂岩储层属于典型的低孔低渗储层，分析孔隙成因类型及其控制因素，对于寻找相对高孔渗储层具有重要指导意义。通过大量孔隙铸体薄片鉴定认为，陇东地区延长组砂岩发育原生与次生两大类孔隙类型，其中原生孔隙包括压实剩余原生粒间孔和胶结剩余原生粒间孔；次生孔隙包括粒间杂基及胶结物溶孔、长石和岩屑粒内溶孔及铸模孔、粒间高岭石绿泥石胶结物晶间孔；另外还存在少量构造成因的微裂缝。现今孔隙多为部分原生与部分次生组成的混合孔隙。孔隙成因类型受沉积条件和成岩作用双重因素控制，沉积条件决定了砂岩沉积时的水动力条件，从而决定了砂岩的岩石学特征和原生粒间孔的发育程度，压实作用决定了压实剩余粒间孔的大小与多少，胶结作用决定了胶结剩余粒间孔的多少，溶蚀作用控制了各种溶蚀孔隙的类型及发育程度，如粒间杂基和碳酸盐胶结物溶孔、长石及岩屑粒缘与粒内溶蚀孔隙的发育程度。原生孔隙在长8、长9、长4+5粒度较粗的层段中较明显，次生孔隙在长6、长7粒度细层段和顶部不整合面附近的长1-3中占的比例较多。系统运用大量薄片和物性资料首次明确指出陇东地区延长组砂岩储层孔隙为混合成因，且次生孔隙特征明显，原生孔隙由于压实和胶结作用大量损失。

Pore genetic types and their controlling factors in sandstone reservoir of Yanchang Formation in Longdong Area.Ordos Basin

The reservoir of Yanchang Formation in Longdong Area is of typical low porosity and low permeability.The analysis of pore types and their controlling factors is instructive for the prospecting of relatively high porosity and permeability reservoir.The pore types of Yanchang Formation in Longdong area are divided into primary pores and secondary pores based on thin section identification.Primary pores include post compaction residual porosity and post cementation residual porosity,and secondary pores include miscellaneous matrix solution pores,cement solution pores,solution pores within feldspar or detritus,mouldic pores and intergranular kaolinite and chlorite matrix crystal pores,and besides,there are small amout of microfractures of tectonic origin.The present pores are almost mixed pores consisted of primary pores and secondary pores.Pore genetic type is closely related to the sedimentary conditions and diagenesis.Sedimentary conditions control the hydrodynamics during the deposition,and further control the characteristics of the rock and the development of primary pores.Compaction process is decisive for the remnant pore sizes and pore volume left by the compaction,and cementation controls the content of residual pores after cementation.Dissolution controls the development of all kinds of dissolution pores,such as miscellaneous matrix solution pores,carbonate cement solution pores,solution pores in feldspar or detritus grain or of grain margin.Primary porosity are important in some coarser grain size members in Chang 8—9 and 4+5,while secondary porosity are important in finer grain size members as in Chang 6—7 and the top of Chang 1—3 near to the unconformity.On the basis of large amount of informations from rock thin sections and petrophysic studies,the present paper firstly proposed that the pore genetic type of the sandstone reservoir of the Yanchang formation in Longdong area is of mixed porosities,and the secondary porosity is probably superior to the primary porosity.