###### Abstract  
The unconventional tight oil and gas resources in the Xinzhao East belt of the Hangjinqi Prospect area in the Ordos Basin of China are abundant. However, the reservoir's internal storage space is complex, and the microscopic pore throat structural features are not well recognized, which has led to some trouble in the deployment of oil and gas exploration. To reveal the microscopic characteristics of the dense sandstone gas layer in the first member of the Lower Stone Box Formation of the D-well Zone in the Xinzhao East belt of the Hangjinqi Prospect area, a three-dimensional space digital core was built, and the stored set spatial data were extracted, based on rock sheet and coring data and X-CT scanning technology. Quartz grain size was segmented and analyzed based on an adaptive approach. The microscopic characteristics of the gas layer in the studied section and the factors influencing its development were studied, combining the use of a field emission scanning electron microscope, helium porosimeter, and gas permeability meter. We found that in the studied section, the porosity is relatively high, the pore throat size is large, and the pore permeability correlation is good. The reservoir space, which consists of intergranular pores, intragranular pores, and microcracks at the grain edges in the study area, is characterized by a complex distribution pattern. Within the gas layer, isolated pores are connected by microcracks to form a network of reservoir spaces, which increases the pore throat size, enhances the connectivity of the pore throat, and makes the microscopic characteristics of the reservoir space better. The first member of the Lower Stone Box Formation could be an advantageous reservoir. Hole-throat connectivity is poor because of the gas layer having underdeveloped primary pores, the blockage of pores by unstable minerals (kaolinite, etc. ), and poorly connected pore throats based on insoluble mud cementation. The high content of quartz brittle minerals and the development of natural microcracks within the gas formation are favorable conditions for fracking development. The quartz grain size within the gas layer is positively correlated with the pore throat size, which suggests that the quartz grain size somewhat influences the microscopic characteristics of the reservoir space. This comprehensive study shows that the methodology of the study is more advantageous than traditional methods in the fine and three-dimensional spatial characterization of the microstructure of dense sandstone reservoirs. The research results of this paper have certain guiding significance for further reservoir evaluation and advantageous reservoir prediction in the Hangjinqi Prospect area in the Ordos Basin. We also provide the basis for the subsequent efficient development of the gas reservoir. unconventional oil and gas reservoirs; X-CT scanning technology; three-dimensional spatial structure; microscopic characteristics of gas layers; Hangjinqi Prospect area; Ordos Basin; China  
20241739910 ing shale and tight gas, accounts for more than 47% of global natural gas reserves [1; 2]. Unconventional reservoirs are becoming an increasingly important source of natural gas. Unconventional hydrocarbon reservoirs are mainly located in the Paleozoic strata, including the Lower Ordovician, Silurian, Devonian, and Permian [3; 4]. Tight sandstone gas reservoirs are one of the unconventional reservoir types, which are widely distributed around the world [5; 6]. The Ordos Basin, China, is subject to the composite superposition of three generations of Mesozoic and late and early Paleozoic large-scale craton, forming the present \"Middle (Biocene) oil and ancient\" \"basin full of gas, half of oil\" oil and gas distribution patterns [7]. The Ordos Basin in China is one of the major enrichment areas for tight sandstone gas reservoirs, with tight gas production reaching 256 \(\times\) 108 m\({}^{3}\) in 2019 [8]. The first member of the Lower Stone Box Formation is the main reservoir of tight gas in the Ordos Basin.