Gas productivity of the Lower Permian Shanxi and Xiashihezi Formations in the Ordos Basin is controlled mainly by reservoir property. Understanding the porosity origin and its controlling factors is a critical step in predicting the distribution of reservoir. Integrated analysis of porosity characteristics, mineral solubility and pore textures shows that reservoir space for sandstones and conglomerates in the Member 2 of Shanxi Formation is mainly primary porosity, while that for the Member 8 of Xiashihezi Formation is mainly dissolution porosity. Reservation of primary porosity and creation of dissolution porosity are constrained by detrital component, grain size, and silica origin, i. e. coarse quartzose sandstones and conglomerates in the Member 2 of Shanxi Formation are favored by their strong resistance to compression, absence of dissoluble components, and multiplicate origin of silica; coarse lithic sandstones and conglomerates in the Member 8 of Xiashihezi Formation are prone to be dissolved due to their abundant dissoluble components and organic acid. This study indicates that reservoirs with 8%~18% of dissoluble components possess the highest dissolution porosity. Porosity genetic types correlate well with pore textures, i.e. reservoirs with primary pores are of higher permeability than those with dissolution pores at the same porosity.%鄂尔多斯盆地中部横山—靖边—安塞地区山西组和下石盒子组发育低孔低渗至特低孔特低渗砂(砾)岩储集层,其物性控制了气层产能的大小.文中通过对显微镜下的孔隙形态特征、易溶碎屑组分含量和孔隙结构特征3个方面的分析,提出山西组二段砂(砾)岩储集层主要发育原生孔隙,而下石盒子组八段砂(砾)岩储集层以溶孔为主.在研究区内储集层埋藏深度差异不大的情况下,砂(砾)岩原生孔隙的保存程度和溶孔的发育规模主要受粒径、碎屑组分、石英次生加大和有机酸来源的影响,粒径是山西组二段和下石盒子组八段储集层孔隙发育的基本影响因素,储集层渗透率大于0.2×10-3μm2的有利储集层均发育于中粗砂岩及以上粒级的砂(砾)岩中.山西组二段石英砂(砾)岩的强抗压性、缺少易溶碎屑组分是原生孔隙保存较多的主要原因,而丰富的硅质来源是原生孔隙减少的重要因素.对下石盒子组八段而言,易溶物质含量适中、有机酸来源丰富是岩屑砂(砾)岩溶孔发育的主要原因.进一步的研究表明,储集层的孔隙成因与孔隙结构之间有良好的相关性,原生孔隙储集层的孔隙结构要优于溶孔储集层,表现为在相同孔隙度时,前者的渗透率明显高于后者.
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