Zhigen Zhao, A H Li, Jiajie Zhang, Mo Chen
China hosts a large number of closed coal mines containing abundant residual resources. Driven by resource recycling, mine safety, environmental protection, and the dual-carbon goals, research on gas resources in closed coal mines has expanded rapidly. In some closed mines, substantial unmined coal resources remain with high gas content, making in situ gas resources a key focus of investigation. Given the Xinzhuangzi closed coal mine as a case study, this study analyzed the distribution of coal resources based on the monitoring results of coal extraction and remaining reserves, and the distribution of gas content based on regression equation. Furthermore, it applied a volumetric calculation method to estimate the gas resources of any a certain unit, all units, and summarize the gas resources across different coal seams, structural divisions, mining levels and the entire coal mine, thereby characterizing the in situ gas resources. The results indicated that the area below −412 m in the closed Xinzhuangzi coal mine was favorable for in situ gas resource development, containing 20,061.1 × 104 t of coal resource and 2250.32 × 106 m3 of gas resources, with a gas resource abundance of 1.96 × 108 m3/km2. C13, B11b, B4, B7a, B6, and B8 were favorable targets for in situ gas resources, each containing over 100 × 106 m3 of gas resources, and these seams were thick and stable. Levels 6 and 7 were favorable zones for in situ gas resources, each containing abundant coal resources with high gas content, holding 644.94 × 106 and 1407.77 × 106 m3 of gas resources, respectively. These findings provided not only a scientific basis for the future evaluation and development of gas resources in this coal mine, but also important references for the study of in situ gas resources in other abandoned mines. And, several suggestions were given about the development prospects of gas resources.