Research on coalbed methane extraction technology based on in-situ microwave heating

Microwave heating, as a fast and controllable heating method, can quickly increase the temperature and permeability of coal seams, and thus enhance the recovery rate of coalbed methane. The transmission of microwaves to underground coal seams and the temperature response of coal seams are the key to developing a new coalbed methane extraction technology. The influence of temperature on the real dielectric constant of coal seams is considered, and an electromagnetic-thermal bidirectional coupling mathematical model for microwave intermittent heating of the whole coal seam is established. Using COMSOL Multiphysics, the temperature field distribution of the whole coal seam under different parameters of microwave intermittent heating is simulated, and the effects of microwave intermittent heating duration, microwave frequency, and input power on the temperature distribution of coal seams are explored. Finally, based on the directional drilling and continuous tubing technology in petroleum engineering, a coalbed methane production enhancement extraction technology that can achieve a large range of coal seam microwave heating is proposed. The results show that: When microwave heating thick coal layers, employing a short-cycle intermittent heating method—four days of heating followed by two days of rest—results in superior heating effects and significantly reduces energy waste; The frequency has a minimal impact on the average and maximum temperatures of the coal layer but is inversely proportional to the penetration depth, when heating coal layers with microwaves, the microwave at 260 MHz balances penetration depth and temperature field uniformity; The microwave power has a significant and positive correlation with the temperature of the coal layer and the effective penetration depth, at 6 000 W, the maximum temperature gradient is 581.3 K/m, which easily induces thermal fracturing in the coal layer, enhancing its permeability. The effective penetration depth also reaches its maximum at 6 000 W; The novel coalbed methane enhancement and extraction process addresses the issues of microwave transmission loss over long distances and the backflow in microwave transmission pipelines for coalbed methane. By utilizing the characteristics of continuous tubing, extensive microwave heating of the coal layer is achieved.