Influence of microwave irradiation on the permeability of coal with different bedding dip angles

Microwave irradiation (MI) is a prospective method for increasing CBM production. Due to the permeability anisotropy caused by bedding structural plane, the spatial relationship between underground microwave irradiation drillings (MID) and the coal bedding plane has become an important factor affecting the effect of MI on enhancing production. The self-developed MI device numberer WY3S02 was used to carry out the MI experiment on samples with different bedding angles (BDA). The permeability of coal before and after MI was tested by the steady-state seepage method. The surface temperature and ultrasonic data of samples during the test were collected, and the influence of MI on the permeability of coal with different BDA was studied. The experiments indicate that the permeability of samples with different BDA increases by 30.2–100.1 times after MI under external axial load, and the increase of permeability is positively correlated with the BDA. The permeability after MI shows the variation law of K (90°) > K (60°) ≥ K (45°) > K (30°) > K (0°), showing an obvious bedding effect. The standard deviation of the lateral surface temperature of the specimen increases with the increase of the BDA, which makes the thermal fracture degree of the sample with large BDA higher, resulting in more dominant seepage channels, which is manifested as greater permeability growth. These results provide a scientific basis for the design of MID in the method of enhanced coalbed methane by microwave irradiation (MI-ECBM).