Abstract: ObjectiveThe Longdong Area is located in the southwestern part of the Ordos Basin. Previous studies have conducted extensive research on the quantitative evaluation of the microscopic pore structure of tight sandstones in this area, while relatively few studies have focused on the characteristics of full pore-size distribution and the fractal characteristics under different pore-throat scales. MethodsThis study employed the dense sandstone reservoirs from Chang 7 member of Yanchang formation in Longdong area of Ordos Basin as the object of study, drilled 9 core samples from different wells, and utilized the means of casting thin section, scanning electron microscope, high-pressure mercury compression, and nuclear magnetic resonance (NMR), etc. Based on the analysis of reservoir characteristics, the NMR saturated water T₂ spectrum was converted to a full aperture pore-throat size distribution curve using high-pressure pressurized mercury pore-throat distribution to analyze the fractal dimensions of different pore-throat types and their influencing factors. ResultsThe results show that the pore types of the Chang 7 reservoir in the study area are mainly feldspar solution pores, intergranular pores and rock chip solution pores. The pore structure of the reservoir can be categorized into three types: Type I, Type II and Type III, corresponding to the deterioration of physical properties, storage performance and seepage capacity in that order, with an increase in the proportion of micro-miniature pore throats, and the enhancement of non-homogeneity. ConclusionsAccording to the full pore size distribution, the pore throats are categorized into micro pore throats (<0.01 µm), small pore throats (0.01~0.1 µm) and medium pore throats (0.1~1 µm), corresponding to the fractal dimensions increasing in order. As the main contributor to reservoir physical properties and reservoir space, the fractal dimension of the mesopores and small pores correlates well with the pore structure parameters, the mineral composition and content influence the complexity of the pore structure, and the clay minerals exacerbate the pore throat surface roughness and non-homogeneity, all of which correlate well and positively with the fractal dimension of the mesopore.