The tight sandstone gas reservoir in the second section of the Xujiahe Formation in the western Sichuan Depression is characterized by deep buried, ultra-low porosity, high density, strong heterogeneity, and significant differences in the development of planar fractures. Because the reservoir has been tight before the main reservoir formation period, faults and fractures have become advantageous migration channels for highly mature gas, as a result, the relationship between gas and water is complex, and the identification of logging fluid properties is difficult. Due to the significant impact of reservoir complexity on resistivity, and acoustic waves, traditional fluid identification methods based on resistivity-porosity intersection can not effectively distinguish gas and water layers. However, the existing nuclear magnetic resonance logging fluid property identification technology, which uses relaxation time cut-off values to identify "bound water" and "movable water" as the core idea, suffers from the contradiction between "deep invasion of mud filtrate" and "shallow radial detection depth of instruments" caused by overbalanced drilling, resulting in ineffective differentiation between water and filtrate on the relaxation spectrum and reduced reliability of fluid identification. To deal with this issue, a calibration is conducted between the results of 2D NMR and constant-rate mercury injection experiments on core samples, the microscopic geological significance of the T₂-T₁ relaxation spectrum is clarified, by correlating the degree of natural gas charging during accumulation with the distribution of gas and water, research is carried out based on the layout of signals in the relaxation spectrum, the relative magnitude of signal intensities, and their correspondence to gas well production conditions. It is shown that throats occupy a considerable proportion of the reservoir space in tight sandstone reservoirs, the first independent peak on the right side of the clay water signal in the two-dimensional relaxation spectrum is the throat retention water signal, the ratio of natural gas signal to throat retention water signal can reflect the degree of natural gas injection during the reservoir formation period, the reservoir formation characteristic coefficients calculated using the two-dimensional relaxation spectrum have a good correlation with the production characteristics of gas wells, thus a new thinking for identifying fluid properties in tight sandstone gas reservoirs with the core of characterizing the degree of natural gas injection during the reservoir formation period is formed. The method is used for gas-bearing evaluation for the second section of Xujiahe Formation in the western Sichuan Depression, favorable result is achieved. It effectively overcomes the issue of low distinguishability between gas and water layers' conventional logging response, which confirms the rationality and accuracy of T₂-T₁ spectra in characterizing the microscopic geological features of reservoirs.