Experimental study on gas extraction with intensive hydraulic punching and penetration enhancement

Efficient gas extraction from outburst coal seams with high gas and low permeability is the main problem of gas control in working faces with complex geological conditions. In order to increase the permeability of this type of coal seam, based on the results of testing the influence radius of hydraulic punching by the gas flow method, the coal seam floor roadway was used to arrange dense drilling holes through the seam, and hydraulic punching was carried out on the working face to enhance and increase the permeability, so as to achieve the purpose of high-efficiency pre-extraction of coal seam gas. The research results show that the pores formed in the coal body by hydraulic punching promote the continuous expansion and deformation of the coal body around the borehole, the in-situ stress of the coal body decreases within the range of about 1.8 times the diameter of the pores, the compression degree of the coal body decreases, and the coal body permeability increases;hydraulic punching accelerates the desorption of coal body gas, and achieves the effect of high-concentration gas pre-drainage with an average single hole concentration greater than 52.64% for 18 consecutive days;after 60 days of pre-extraction, the coal seam gas content is reduced from the original 9.09 m3/t to 4.03 m3/t. It can be seen that the use of intensive drilling and hydraulic punching improves the effect of pre-draining gas in the coal seam, realizes the elimination of outbursts in outburst coal seams with low air permeability, and ensures the safe production of working faces.