SEM and permeability enhancement experiment study on thermal damage characteristics of coal-rock under infrared radiation

China is rich in coalbed methane resources. In order to improve the efficiency of CBM extraction and reduce disasters such as coal and gas outbursts in the process of mining, a new technology principle of CBM production enhancement- infrared heating extraction of CBM is proposed. Using a self-made infrared heating seepage tester, the method of combining scanning electron microscopy and Matlab image post-processing was used to study the development and expansion of pores and fissures and the change characteristics of permeability of coal samples before and after different infrared temperatures. The results show that the effect of infrared radiation can damage the coal and rock mass, and the higher the infrared temperature, the more obvious the thermal damage. With the increase of infrared temperature, the porosity of coal samples increases. The primary micro pores and cracks are interconnected, the new cracks gradually increase, and then the mineral particles attached to the surface of the sample decrease accordingly. The pore structure changes from narrow and long to elliptical, the equivalent diameter of pores in each interval is greatly increased, and the volume of small pores to large cracks expands synchronously. When infrared heating at 150 ℃, the change of pore volume in the transition stage of 8-15 μm fluctuates the most, which is 4.35 times that of the original state, and the total pore volume increases by up to 99.5%. With the increase of infrared temperature, the permeability of coal also increases. The permeability of the samples with low original porosity in the low temperature stage increases slightly, but the permeability of the samples with high original porosity can increase up to 130%. The permeability of the samples in the high temperature stage jumped significantly, it can reach more than 9 times compared with the lower temperature stage, and 30 times compared with the original state. The statistics between the change of pore structure of coal samples before and after infrared action and the increase of macroscopic permeability are established, and the response coefficient of pore structure of coal under infrared action is proposed. The increase of infrared radiation temperature can effectively promote the increase of coal and rock sample pores and the expansion of cracks, which in turn leads to the increase of permeability and the improvement of CBM extraction.