###### Abstract
In recent years, the natural gas exploration results obtained in the first member of the Lower Stone Box Formation of the Hangjinqi Prospect area in the northern Ordos Basin have been remarkable [9]. In 2021, four appraisal wells were deployed in the Xinzhao belt, and 13 billion cubic meters of proven natural gas reserves were discovered, which proved that the Xinzhao belt has huge exploration potential. The formation of large gas reservoirs in this zone is closely related to the extensive and continuous distribution of sandstone reservoirs. So, it has become particularly important to investigate the microstructural characteristics and influencing factors of the dense sandstone gas layer in the studied section. A lot of research has been carried out on reservoir characterization in the studied section by previous researchers. They found that the studied section is predominantly clastic sandstone in a braided river setting [10], and it is a typical low-permeability sandstone or dense sandstone reservoir [11]. However, there are relatively few studies on the microscopic characterization of the gas layer in the studied section. [PERSON] proved the longitudinal stacking relationship, pore penetration characteristics, and influence of the sedimentary phase and diagenesis on the non-homogeneity of the reservoir in the studied section [12], and [PERSON] studied the reservoir characteristics and influencing factors in the studied section by using particle size analysis, thin-section identification, and mercury compression experiments [13]. In existing studies, reservoir characteristics are mostly characterized by traditional 2D image techniques. However, the study of the three-dimensional spatial microscopic features of dense sandstones and the factors affecting them has been neglected. The three-dimensional spatial microscopic characterization of dense sandstone reservoirs is not well understood. Tight sandstone reservoirs are characterized by a small pore throat size, a complex pore structure, and strong non-homogeneity [14], and the study of their microscopic characteristics, especially the quantitative characterization of microscopic pore throats, is of great significance to the evaluation of reservoir quality and capacity. Current techniques for characterizing pore microstructure include cast thin sections, scanning electron microscopy, constant-velocity mercury pressing, high-pressure mercury pressing, nitrogen adsorption, and X-CT scanning. The cast sheet method can effectively identify the type of reservoir space in tight sandstone gas formations and calculate the face porosity, but it cannot reflect the three-dimensional pore space characteristics of the samples [15]. A scanning electron microscope can observe the characteristics of pore distribution on the surface of rock samples, and analyze the mineral morphology and the content of various elements [16], but what is reflected is only two-dimensional spatial characteristics [17; 18]. Constant-velocity mercury pressure can be used to obtain pore and throat size parameters, based on the pressure drop during the mercury feed process, but the field of view of the pore and throat that can be recognized is small, because of the limitation of the pressure of the mercury [19]. High-pressure mercury pressing can quantitatively determine the spatial size and distribution of pore throats in dense sandstones, but the pore structure of rock samples may be damaged due to high pressure [20]. X-CT digital coring is an unconventional testing technique for characterizing rock structures with X-rays, and can be used to characterize the three-dimensional spatial structure of pores and to quantitatively study the microscopic characteristics of reservoir pore throats [21; 22]. In the 1990s, [PERSON] et al. used CT technology in petroleum engineering to improve the resolution of pore identification [23]. In 2004, [PERSON] et al. constructed micrometer-scale digital cores, which promoted the application of this technology in the petroleum industry [24].