Research and application of hydraulic slotting gas extraction technology in coal seams containing gangue

In order to study the application of hydraulic slotting enhanced gas extraction technology in coal seams containing gangue, theoretical analysis shows the following points. Compared with ordinary drilling, hydraulic slotting borehole can enhance gas extraction by increasing coal seam permeability, coal body exposure area, and gas flow channels. A coal seam gas flow control equation has been established considering changes in porosity and permeability. Taking the 21218 working face of Dongpang Mine as the engineering background, a numerical model for hydraulic slotting gas extraction in coal seams containing gangue is established by using COMSOL numerical simulation software. By solving the control equation of coal seam gas flow, the gas pressure distribution law of hydraulic slotting gas extraction borehole under different slotting heights and drilling spacing conditions is studied. The construction parameters for hydraulic slotting gas extraction borehole with a slotting of 0.3 m in the upper coal seam, a slotting of 0.1 m in the lower coal seam, and a borehole spacing of 7.5 m are determined. Based on the above parameters, 28 groups of 7 hydraulic slotting borehole are constructed on-site at the 21218 working face of Dongpang Mine to extract gas from coal seams containing gangue. The results show that compared with ordinary borehole, the construction quantity of hydraulic slotting borehole per 100 meters of roadway decreases by 28.51%. The net amount of gas extraction increases from 115300 m³ to 214300 m³ with an increase of 85.86%. The average gas volume fraction of the excavation working face during the roadway excavation period decreases from 0.06% to 0.01%. The gas extraction effect is good and the gas extraction efficiency is effectively improved.