Research status and reduction strategies of methane emissions from closed/abandoned coal mines

With the global transition to a low-carbon energy structure, coupled with the depletion of coal mine resources, gas disasters, and other problems, the number of closed/abandoned coal mines is increasing rapidly. After the coal mine closes, the residual methane in the goaf escapes to the ground continuously, becoming an essential source of greenhouse gas emissions. In view of a series of issues such as methane residual stock, emission rate and emission reduction measures in closed/abandoned coal mines, the number of closed/abandoned coal mines and the distribution of high-gas mines at home and abroad were clarified through a large number of literature review, and the sources and estimation methods of methane residual stock were summarized. At the same time, the theory and research method of methane geological leakage in the field of natural gas accumulation was used for reference, and the emission mechanism and monitoring means of residual methane were analyzed. Finally, the countermeasures and challenges of residual methane emission reduction were put forward. The study found that there are many closed/abandoned coal mines in Shanxi, Guizhou, Chongqing, Hunan, Jiangxi, etc., and the residual coal is mainly anthracite with strong methane adsorption capacity, resulting in a large amount of residual methane in the mine, which will become a critical methane emission source. Methane from closed/abandoned coal mines is desorbed and released to the goaf, and then discharged to the atmosphere through channels such as wellhead and mining-induced fractures. Methane monitoring in coal mines can be realized by means of satellite remote sensing, flux chamber method, geochemical probe method, micro-meteorological technology, etc. Based on the methane emission prediction model of closed/abandoned coal mines, the methane emissions from closed/abandoned coal mines may account for more than 20% of total methane emissions from coal mining operations by 2050, so it is urgent to solve the problem of methane emissions from closed/abandoned mines. Therefore, the countermeasures of emission reduction, such as extraction and utilization, in-situ deflagration power generation, microbial degradation of methane, water flooding, and methane emission channel closure are put forward. Considering the limitations of cost, treatment time, groundwater contamination, and other limitation factors, it is concluded the mineralized remediation method can be used to seal large-scale mining-induced fractures in overlying rocks, which can achieve the methane emission reduction goal of closed/abandoned coal mines at a low cost. © 2023 China Coal Society. All rights reserved.