Sensitivity analysis on the microwave irradiation enhancing coal seam gas recovery: A coupled electromagnetic-thermo-hydro-mechanical model

Abstract

Microwave irradiation (MI) technology is a potential effective method to improve the efficiency of coal seam gas recovery. However, the research on how to increase coal seam gas production by microwave heating is rare. In this paper, microwave stimulation technology is introduced in coal seam gas extraction area for the first time. Based on the gas extraction technology with directional long borehole, a new coupled electromagnetic-thermo-hydro-mechanical model for coal seam gas recovery is established. The heat and gas transfer characteristics of coal seam under MI heating is analyzed. What's more, the impacts of key parameters on gas production, temperature distribution, gas pressure distribution and permeability ratio are discussed. Under the MI power 1000 W, numerical simulation results show that the cumulative gas production increased by 80%, which indicating the great effective of microwave heating for improving gas extraction rate. Furthermore, it reveals that the daily gas production will decrease rapidly with the attenuation coefficient λ. And with the greater of attenuation coefficient λ, the faster the permeability ratio decays. Comparing with the case of λ = 1 × 10−8, the permeability ratio decreases by 26% when λ = 5 × 10−8. And we also found that the initial permeability k0 is negatively correlated with the peak pressure in matrix. Overall, microwave heating can effectively reduce the methane adsorption capacity of the coal matrix and significantly increase the gas extraction production from coal seam.