Effect of cyclic hot/cold shock treatment on the permeability characteristics of bituminous coal under different temperature gradients

This study aimed to investigate the influence of cyclic hot/cold shock on the change in the permeability of coal sample under different temperature gradients. The low permeability of Chinese coal seams has always hindered the exploitation and use of coalbed methane resources. In the present study, bituminous coal produced from the Xutuan Mine was selected as the test coal sample. The hot/cold shock experiments of single, multiple cycles treatment under the same temperature gradient, different temperature gradients were carried out by heating of samples in a drying oven, followed by a low-temperature treatment using liquid nitrogen. The fixed-point photography and nitrogen percolation tests were carried out on the coal samples at various stages of exposure. The results showed that the cracking effect of coal was proportional to the number and the temperature gradient of the cycle hot/cold shock treatment. After two treatments, the maximum increment of the permeability of coal samples reached 1129.79%. The permeability increment of coal sample with heating temperature of 100 degrees C is 2.89-6.44 times that of coal sample with 20 degrees C. This paper used a quadratic function to fit and discuss the seepage results of coal samples. The influence of hot/cold shock treatment on the Klinkenberg effect of nitrogen flow in coal was also analyzed.