Effects of microwave heating on coal seam property for full-cycle in situ exploitation

Microwave-heating enhances coalbed methane recovery via rapid thermal response and controllability. This study defines a three-stage development lifecycle: conventional fracturing, external energy-enhanced recovery (e.g., microwave), and in-situ conversion. Systematic investigations quantify microwave-induced structural modifications in coal matrices, characterizing porosity, permeability, fracture networks, and surface morphology evolution under varied parameters. Experimental findings reveal: 1) Microwave heating can effectively induce coal sample thermal fracture and improve the permeability of coal. 2) The permeability of coal sample decreases first and then increases with the increase of microwave heating time. After microwave-induced fracture of coal sample, the permeability of coal sample increased from 5.01 mD to 444 mD, and the permeability increased by two orders of magnitude. 3)Thermogravimetric analysis identifies substantially lower volatile content in high-power treated specimens compared to low-power counterparts, accompanied by distinct variations in combustion characteristics, pyrolytic behaviors, and char combustion properties with differing heating durations, with prolonged microwave irradiation duration, all tested samples demonstrated a 5 %–10 % mass loss during pyrolysis, significantly lower than the 15 % mass loss observed in control groups. The environmental protection and controllability of microwave-heating provide a new path for the green development of fossil energy.