Study on the effect of penetration enhancement and energy change of coal samples pretreated with different microwave powers

In order to investigate permeability and destructive deformation energy evolution of the loaded coal body under different power microwaves, the high-pressure three-dimensional visual mechanics experimental equipment to carry out the triaxial compressive percolation experiments of the coal samples after microwave pretreatment with different power. Results show that the modulus of elasticity of coal samples after microwave treatment with different powers shows a decreasing and then increasing trend, while the peak stress and Poisson's ratio show a decreasing trend; the increase of microwave power leads to easier compact of coal samples, larger overall strain values of radial and body stress-strain curves, and significant expansion; the permeability of the coal samples increases as power rises, which is consistent with the logarithmic function fitting relationship; the increase of microwave power leads to decreasing total energy U and elastic energy U^e at the peak stress of different pretreated coal samples, and the ability of coal samples to accumulate elastic energy U^e in the elastic stage is weakened. When we compare 200 W and 600 W microwave pretreatment under the same irradiation time, it is found that the change of each energy was more significant in 400 W microwave pretreatment, and the coal samples have the smallest dissipated energy U^d as a proportion of total energy U, at 24%. The study could provide references for gas extraction in microwave fracturing coal seams.