Investigation on the microwave heating technology for coalbed methane recovery

Abstract Microwave heating is an efficient thermal stimulation approach in developing coalbed methane (CBM). In this paper, a new microwave heating technology for CBM is proposed and two structure schemes of waveguide antennas for heating are designed. After characterizing the mathematical model of the microwave coaxial antenna radiation, the numerical model of coal reservoir heated by microwave is established, which couples both the electromagnetic field and the heat transfer. The electromagnetic field distribution and the temperature changing law in coal reservoir during microwave heating process are solved numerically and verified by the designed experiment. A parametric study on heating effect yields an optimized structure of the microwave antenna, which is SD 6 × R8 and α = 15°. After irradiated by the optimal antenna for 120 min, the average temperature rises to 62 °C (from 20 °C) and the energy efficiency reaches 85%. In different coal reservoirs, the maximum temperature ranges from 169 °C to 1586 °C and the maximum temperature gradient ranges from 2.52 °C/mm to 37.19 °C/mm, which are beneficial to the crack propagation. The microwave heating technology can provide fast and sufficient energy to raise the temperature of coal reservoir and is feasible for enhancing the CBM recovery.