Abstract: The carbon isotope composition of natural gas provides significant insights into the preservation conditions of oil and gas. This study focuses on the Wufeng-Longmaxi Formation in the Changning, Fuling, and Zheng'an areas, analyzing shale gas components and the carbon isotopes of monomer hydrocarbons to understand the variation in alkane carbon isotope reversal (δ¹³C₁－δ¹³C₂) in different areas. We reconstruct the spatial and temporal evolution of preservation conditions in the Wufeng-Longmaxi Shale of the Yangtze Block and explore how preservation conditions affect shale gas enrichment. The results show that: (1) Carbon isotope reversal of hydrocarbons is commonly observed in the Wufeng-Longmaxi Shale, primarily caused by the mixing of secondary cracking gas with primary cracking gas during the high or post-maturation stage. (2) The mixing ratio of these two types of cracking gases is the major factor controlling the degree of carbon isotope reversal. As the proportion of secondary cracking gas increases, the extent of carbon isotope reversal and shale gas content gradually increase from the periphery towards the interior of the Sichuan Basin, indicating relatively good sealing conditions within the basin. (3) A quantitative evaluation model based on δ¹³C₁ shows that the system openness (θ) of the Wufeng-Longmaxi shale ranges from 66% to 82% in the Zheng'an area, 70% to 77% in the Fuling area, and 65% to 70% in the Changning area. (4) Differential structural deformation of the Meso-Cenozoic strata in the Upper Yangtze Region has severely damaged the sealing conditions outside the Sichuan Basin, facilitating hydrocarbon migration and expulsion, and the preservation conditions are relatively poor. Therefore, good preservation conditions are crucial for shale gas enrichment, particularly in regions that have undergone extensive deformation.