Gas migration law of gas-bearing rock strata under the influence of repeated mining

Under the influence of repeated mining, the gas endowed in the rock strata adjacent to the coal seam desorbs and gushes out, becoming one of the gas sources in the working face.In order to study the gas migration law of gas-bearing rock strata under the influence of repeated mining, the No.5 coal seam in Shaqu No.1 Coal Mine and its adjacent coal rock layers were taken as the engineering background.On the basis of measuring the basic parameters of gas in coal and rock mass, numerical simulation was used to study the range of pressure relief and antireflection of coal and rock mass under the influence of repeated mining, and the spatial distribution of the permeability of gas-bearing rock strata was obtained, then the gas migration law of gas-bearing rock strata was simulated.The research results show that the L5 limestone strata has the highest gas occurrence among the adjacent strata, and the gas content is about 14.3% of the No.5 coal seam. Repeated mining leads to increased pressure relief degree of coal and rock mass, and the pressure relief area of L5 limestone strata is distributed in the edge area of permanent coal pillar.The maximum permeability in the pressure relief area of the L5 limestone strata can reach 4.8×10^-15 m², which is 7.7 times of the initial permeability.The distribution of the high permeability area is consistent with the pressure relief area.The gas in L5 limestone strata is desorbed and gushed up to the working face, resulting in the gas concentration in the upper corner rising from 6.1% to 7.1%.Influenced by the roadway ventilation, the gas in L5 limestone strata mainly gathers in the back of the rock layer and the side of the return airway, which is the key area that should be paid attention to during gas extraction.