Abstract: Enhancing the recovery rate of coalbed methane is an essential requirement for achieving large-scale and effective development of coalbed methane. Existing studies have shown that microwaves have the feasibility of improving coalbed methane recovery rate at the core scale, but relevant studies at the mine scale are relatively scarce. For this reason, a microwave heating well model at the mine scale is established to couple the electromagnetic field, temperature field and mechanical field within the coalbed, to explore the influencing factors of microwave heating parameters, and to optimize the process parameters, thereby ensuring the effectiveness and stability of microwave heating wells. The study shows that: Microwave heating wells are mainly vertical or horizontal wells, which are made of copper waveguides (BJ 22 or BJ 26 type) and ceramic casing materials, the temperature and thermal stress in the coalbed and wellbore are positively correlated with microwave power and heating time. The coalbed in the vicinity of the well generates heat by its own dielectric loss, while the coalbed in the area far from the well mainly relies on contact heat transfer to increase temperature. A microwave operating mode of 500 W to 100 W over 33 days has improved the effectiveness and operational stability of the coalbed. Optimizing process parameters alone cannot meet practical application requirements; therefore, a combination of intermittent cyclic variable power microwave heating patterns, microwave-absorbing medium enhanced coalbed thermal conduction technology, and hydraulic fracturing techniques should be employed to enhance the practical effects of microwave heating of the reservoir. The study results can provide technical support for the promotion and application of microwave-enhanced coalbed methane mining technology.

Key words: coal rock, coalbed methane, microwave heating, thermal stress, finite element software