The clastic rocks of the late Triassic Xujiahe Formation in the Sichuan Basin of southwestern China are typical unconventional tight sandstone reservoirs with proven natural gas reserves of up to one trillion cubic meters. In particular, the Xu-6 member of the Xujiahe Formation in the Guang'an area of the central Sichuan Basin is a gas reservoir with great exploration and development potential. In this study, we studied the petrography, measured the geophysical properties, and performed mercury injection tests and calculations based on fractal theory on a suite of tight gas sandstone samples from the Xu-6 member to evaluate the pore types and volumes, permeability, and heterogeneity of the reservoirs. The results show that the sandstone reservoirs of the Xu-6 member of the Xujiahe Formation can be divided into the following three types. Type I reservoirs, which are generally of high quality (an average porosity of 12.59% and an average permeability coefficient of 6.8231 × 10^-3 μm²), are dominated by macroscale pores and a uniform distribution of mesoscale and microscale pores; the fractal dimension is 2.45 to 2.59. Type II reservoirs (an average porosity of 8.9% and an average permeability coefficient of 1.3504 × 10^-3 μm²) are dominated by mesoscale pores, followed by microscale pores, whereas the macroscale pores are poorly developed; the fractal dimension range is 2.42–2.69. Type III reservoirs, typically of low quality (an average porosity of 4.67% and an average permeability coefficient of 0.2947 × 10^-3 μm²), are dominated by microscale pores, followed by mesoscale pores with poorly developed or undeveloped macroscale pores; the fractal dimension is 2.46 to 2.81. The varying distribution of pore types leads to significant differences in pore heterogeneity for the three types of reservoirs, suggesting that type III reservoirs are more heterogeneous than type I reservoirs. Our correlation analysis reveals that the physical properties are related to the reservoir heterogeneity, as proxied by the fractal dimension. When the fractal dimension is between 2.45 and 2.6, porosity is variable, but generally high, whereas permeability shows no obvious relationship to the fractal dimension. When the fractal dimension is greater than 2.6, there is a decreasing trend in porosity, and permeability remains at a constant low value as the fractal dimension increases. Based on our quantitative study of physical properties and fractal characteristics of the Xu-6 member sandstone reservoir, microscopic pore characteristics such as fractal dimension hold great theoretical and practical significance as evaluation criteria for unconventional high-quality natural gas reservoirs and can potentially be used for guiding their exploration and development.