Improvement of Gas Drainage Efficiency of Low-Permeability Coal Seams Using Ultra-High Pressure Hydraulic Cutting Technique

With the increase in the coal mining depth, the dynamic disasters of deep coal seam under the combined effects of high crustrals stress and high gas pressure seriously restrict the safety production of the coal mines. Moreover, it is very difficult to lower the gas content of the low-permeability coal seams. Even though numerous boreholes have been drilled inside the coal seam and gas drainage have been performed for a long period. High-pressure water jet cutting technology can effectively increase the exposure area of coal seams, improve the gas flow state in coal seams, so that the coal can be evenly and fully discharged in a certain range, and then the goal of rapid discharge and permeability enhancement can be achieved. After cutting the coal seam between 1m and 2m interval, a uniform pressure relief space is formed inside the boreholes to increase the permeability of the coal seam and improve the gas drainage efficiency The field test results shows that the equivalent diameter of boreholes with cutting is about 5 times that of boreholes without cutting. The gas drainage radius of boreholes with cutting is 2.8 times that of boreholes without cutting, which significantiy shortens the gas drainage time of the coal lane strip, and then attributes to relizing the rapid and safe excavation of coal seam roadway. This technique can provide reference significance for the modification of low-permeabilety coal seans in the similar condition area. (paper)