The reservoir rock types of member 2 - 3 of Lower Shihezi Formation in Daniudi gas field mainly include lithic quartz sandstone and lithic sandstone. Their compositional maturity and textural maturity are low. Research shows that diagenesis stage of the reservoir is at A-substage and the diagenesis types are mechanic compaction, cementation, dissolution and metasomatism. The mechanic compaction and cementation are the most popular and typical destructive diagenesis in the study area, which are the main causes of low physical property. The dissolution is constructive diagenesis with relatively low degree of development, but relatively high in some areas, and it is one of the primary factors which improve the reservoir physical property. The physical property changes regularly with the burial depth. At the depth scale of 2,670 to 2,750 meters, the abnormal high values of porosity and permeability is due to the comprehensive action of various diagenesis, in which the organic acid produced by hydrocarbon migration and accumulation makes clastic particles and carbonate cement dissolved. It makes a great contribution to the formation and preservation of abnormal porosity zones.%鄂尔多斯盆地大牛地气田二叠系下石盒子组盒2-3段储层砂岩类型以岩屑石英砂岩和岩屑砂岩为主,岩石结构成熟度和成分成熟度均较低.研究表明该区目的储层的成岩阶段处于早成岩A期,主要发育机械压实、胶结、交代和溶解4种成岩作用.机械压实、胶结和交代作用为破坏性成岩作用,发育程度普遍较强.其中,压实作用和碳酸盐胶结作用是本区储集层中发育最普遍、最典型的两种成岩作用,也是导致储层物性变差的主要因素;溶解作用作为主要的建设性成岩作用,发育程度不高,但在局部区带发育相对较强,是引起该地区储层改善的主要成岩因素之一.储层物性随深度增加呈有规律变化,在2 670～2 750 m深度段孔隙度和渗透率出现异常高值区,该孔隙异常发育带是多种成岩作用综合的结果,油气运聚高峰期产生的有机酸引起的碎屑颗粒和碳酸盐胶结物等的溶蚀对其形成和保存有重大贡献.
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