Uneven stress and permeability variation of mining-disturbed coal seam for targeted CBM drainage: A case study in Baode coal mine, eastern Ordos Basin, China

Abstract

The permeability of coal reservoirs is generally low in most of the mine areas in China. Using the stress-relief effect of the foremost-mined coal seam mining to increase the permeability of coal reservoirs is great significance for coalbed methane (CBM) drainage. Based on the engineering practice in Baode coal mine, the numerical model of coal seam group mining was established. The plastic zone evolution law of the mining-disturbed coal seam was analyzed after the foremost-mined coal seam has been mined. The stress and permeability uneven distribution characteristics of the mining-disturbed coal seam were studied, and the unloading effect of the mining-disturbed coal seam was obtained. Based on this, the adjacent mining-disturbed coal seam was divided into 5 areas on the plane. Field measurements of the mining stress, expansion deformation, and coal seam permeability coefficient evolution of the mining-disturbed coal seam during the mining of the foremost-mined coal seam show that the results of field experiment and numerical simulation are basically consistent. The method of targeted CBM drainage which combines the strike directional boreholes and cross-seam boreholes was proposed from engineering point of view. The method was carried out engineering application in Baode Coal Mine, and achieved good CBM drainage results.