Thin section and scanning electron microscope (SEM) observations, X-ray Diffraction (XRD) measurements, and mercury intrusion capillary pressure were selected to systematically research the lithology, physical properties, pore structure, and diagenetic features of member-7 of Yanchang Formation (Chang-7 Fm) in Qingcheng Area, Ordos Basin, NW China. The influences of pore structure and diagenetic processes of physical properties were revealed, and the gradual evaluation standard was proposed. The results show that the Chang-7 Fm sandstones are dominated by feldspathic litharenites. The average porosity and permeability are 9.7% and 0.06 mD, respectively, which can be classified as a set of tight sandstone reservoir. The reservoirs stay in mesodiagenesis B stage, and the physical properties are primarily controlled by mechanical compaction and dissolution. The coarser particle size and higher content of quartz and feldspar improve the anti-compaction ability of relatively high-quality reservoirs. Meanwhile, quartz and feldspar also provide material basis for dissolution, and are important control factors for the development of relatively high-quality reservoirs. The pore type and structure also have influences to the physical properties. The primary pore has excellent connectivity. The development of secondary pores is conducive to porosity increasement, but has little effect to permeability. Based on the fractal theory, the heterogeneity of reservoir’s pore network is quantified, and the results show that the heterogeneity is negative correlate with the porosity and permeability, which means that the complex pore network is not conducive for the development of high-quality reservoirs. According to the pore structure and physical properties, three categories can be identified of the Chang-7 Fm tight sandstones. Class I and II reservoirs have large particle size, and the pore system is dominated by primary pores with less heterogeneity, therefore, they are favorable exploration targets. Type III reservoir has small particle size, and mainly develops intercrystalline pores of clay minerals, possess strong heterogeneity of pore structure and poor physical properties, which is not the target of tight oil and gas exploration. 

利用薄片观察、扫描电子显微镜(SEM)观察、X射线衍射(XRD)分析和高压压汞实验等手段, 系统地研究鄂尔多斯盆地庆城地区三叠系延长组七段(长7段)致密砂岩的岩性、物性、孔隙结构以及成岩作用特征, 揭示孔隙结构和成岩作用对储层物性的控制作用, 进而提出针对研究区长7段致密砂岩油储层的分级评价标准。长7段致密砂岩以长石岩屑砂岩为主, 平均孔隙度和渗透率分别为9.7%和0.06 mD, 整体上是一套致密砂岩储层。长7段成岩演化处于中成岩B阶段, 其物性主要受控于压实作用和溶蚀作用。较好的颗粒结构、较高的石英和长石含量提升了相对优质储层的抗压实能力, 石英和长石则为溶蚀作用提供物质基础, 是相对优质储层发育的重要控制因素。储层的物性取决于孔隙类型和孔隙结构, 原生孔具有较好的联通性, 次生孔有利于提高孔隙度, 但对渗透率影响较小。应用分形理论的定量计算结果表明, 孔隙网络的非均质性与储层物性负相关, 复杂的孔隙网络不利于优质储层的发育。根据孔隙表征和物性分析结果, 将长7段致密砂岩储层分为3类。I和II类储层岩石颗粒较大, 以原生粒间孔为主, 非均质性较小, 物性较好, 是有利的勘探目标层。III类储层岩石颗粒较小, 主要发育黏土矿物晶间孔, 非均质性强, 物性较差, 不是致密砂岩储层油气勘探目标层。