Study On Enhanced Penetration Technology Of Hydraulic Fracturing In High Gas Coal Seam

The application result on Hydraulic fracturing in the C13 coal seam of Xinzhuangzi coal mine is investigated in this paper,using the methods of theoretical research,numerical simulation and field test.Facts proved that,after Hydraulic fracturing,the gas concentration of the coal seam is greatly reduced,the gas drainage rate is greatly improved,and the permeability is improved obviously.The possibility of Coal and gas outburst is reduced effectively.After the study on the theory of hydraulic fracturing,the range of pressure relief around the drill hole can be enlarged,the exposed coal around the drill hole can be increased greatly,the mobility of gas in the coal can be enhanced,and the Air permeability also can be improved substantially.The simulation experiment using RFPA2D software shows that,initiation pressure of the coal seam is 30MPa.After fracturing,the extension length of crack extension can reach 35?40m;Coal seam stress shows some change.According to the stress distribution of the fractured coal seam,the coal seam around the fracture hole can be roughly divided as follows:Taking fracturing hole as the center,within the scope of the radius 35m named pressure relief area,the range between 35m and 50m is stress concentration area,the range between 50m and 62.5m is stress transition zone,beyond this range,the area is named original stress area.Single hole hydraulic fracturing can reach 35m.Within the influence scope of fracturing,the permeability of coal seam has been greatly improved,approximately 25 times.During fracturing,the water flow in the coal seam can be up to 400m3/(d*m),the permeability of coal seam has been obviously enhanced.The variation rule of moisture content in coal seam show that fracture radius is greater than 50m;The regularity of gas content of the coal in fracturing area show that fracture radius keeps between 30 and 50m.Within 40 meters around drilling,the fracturing effect is obvious,and the gas content decreases obviously.lt indicates that the influence scope from fracturing hole reaches 40m,Before fracturing,gas pressure of coal is measured as 4.9MPa,and the gas permeability of coal seam is measured as 0.032 m2/MPa2.d.After fracturing,the gas pressure decreases sharply to1MPa,and the gas permeability increases to 0.840 m2/MPa2 d.It indicates that fracturing effect is very obvious.To some extent,permeability of coal seam has shown some improvement.The accuracy of numerical simulation is proved by field test.And the study also show that permeability of coal seam can be improved exactly,gas drainage rate can be increased,and the risk of coal and gas outburst can be reduced by the implementation of hydraulic fracturing technology.On this basis,the security of coal mining gets guarantee.