Microwave-Induced Microstructure Evolution of Coal and Its Effects on the Methane Adsorption Characteristic

Coalbed methane (CBM) reservoirs usually require stimulation to enhance the permeability. Characterized by the transformation of electromagnetic energy into thermal energy, microwave heating may be a promising CBM stimulation approach. In this work, the microstructure evolution of coal affected by microwave heating was investigated by Fourier transform infrared spectroscopy (FTIR), low-temperature nitrogen adsorption (LT-N 2 GA), and scanning electron microscopy (SEM). In addition, the methane adsorption property of coal was evaluated using a high-pressure adsorption instrument. The results indicate that microwave heating would cause the pyrolysis of ether groups, oxygen-containing groups, and aliphatic hydrocarbon in coal. After microwave treatment, the volume and connectivity between mesopores and micropores increase. The decrease in the methane adsorbability of coal may be attributed to the reduction of the methane adsorption site induced by microwave heating. The outcome of this study implies that microwave heating can be used to promote CBM recovery.