Study on coalbed methane production and transportation law under in situ microwave irradiation condition

Low permeability of China’s coal reservoirs and the high adsorption capacity of coalbed methane represent core constraints on coalbed methane extraction. Microwave heating technology has enhanced recovery rates in low-permeability reservoirs. However, existing studies typically simplify coal’s dielectric constant as a fixed value and adopt a single-point heating injection pattern. This study proposes a novel coalbed methane enhancement technique, based on directional drilling and continuous tubing technology, enabling large-scale coal seam heating. A fully coupled electromagnetic-thermal-fluid-solid model, incorporating the actual temperature-dependent dielectric properties of coal seams, was established. This model simulates and thoroughly investigates the enhancement and migration patterns of coalbed methane under varying microwave power levels. Results show microwave heating significantly promotes methane desorption and enhances reservoir permeability. 1600 W heating for 120 days, the effective desorption radius exceeded 3.6 m, with maximum permeability increases near the wellbore reaching 18.4%. Under 2400 W microwave irradiation, cumulative gas production reached 5781.5 m3, 15.7% higher than the 4996.3 m3 produced under the non-microwave heating. Due to excessively high power may cause overheating, 1600 W was determined as the optimal power level, balancing efficiency and safety. The study provides both theoretical foundations and practical strategies for optimizing microwave-enhanced coalbed methane recovery rates.