Research on gas control in unexploited protective layer areas of high outburst mines

To solve the problem of gas concentration exceeding the limit in the unmined protective layer area of the high outburst mine test working face, the influence of extraction parameters on the pre extraction effect of coal seam gas was analyzed based on COMSOL numerical simulation.The gas diversion channel for pressure relief during mining was clarified through physical similarity simulation.Based on the actual mining progress of the project, the gas prevention and control work was divided into two steps: the "excavation period" and the "recovery period".The three-dimensional gas drainage technology was adopted to carry out the "layer by layer+through layer" drilling combined gas drainage.The pre extraction effect of high negative pressure layer drilling and through layer drilling (non depressurized area) during the excavation period was analysed.The gas concentration relationship of through layer drilling (replenishment) near the fault during the recovery period was compared, and the relationship between gas extraction effect and recovery mileage was studied.The results show that under different drilling conditions, the effective gas extraction radius on the outer side of the borehole is about 5 meters, and the spacing between boreholes is set at 10 meters.This could be more reasonable.During the excavation period, the gas content in the coal seam is reduced from 24.37 m³/t to 6.76 m³/t.The coal seam gas pressure decreased from 1.62 MPa to 0.47 MPa.During the mining period, low negative pressure and high pressure drilling were carried out on the side of the track to extract gas from the upper goaf, with a maximum gas concentration of only 8.7%.The combination of gas extraction and pressure relief gas extraction technology in the unexplored protective layer area has successfully eliminated the risk of coal and gas outburst in the M18 coal seam.