A fully coupled electromagnetic-thermal-mechanical model for coalbed methane extraction with microwave heating

Realized by the conversion of the electromagnetic energy into thermal energy, microwave heating can be a sound method to enhance coalbed methane (CBM) recovery. Although the effects of microwave heating on the petrophysical characteristics of coal have been comprehensively investigated, few studies considered the complex coal-gas interactions under non-isothermal conditions. In this study, a fully coupled electromagnetic-thermal-mechanical model was developed to investigate the influence of coal compaction, thermal expansion, thermal-induced gas desorption, and sorption-induced coal deformation on CBM extraction. The results indicated that the sorption-induced coal deformation makes the predominant contribution to the porosity evolution. In addition, microwave heating can enhance the cumulative gas production by 43.9% by promoting gas desorption and seepage. The sensitivity analysis showed that the microwave operating at 2450 MHz under lower powers is preferred to maintain efficient stimulation and to avoid overheating. Furthermore, the stimulation efficiency of microwave heating increases with the initial permeability and gas pressure. Outcomes of this study can provide valuable insights into microwave-assisted CBM recovery.