Research on gas drainage hydraulic fracturing improvement technology for soft and low permeability coal seam
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Abstract
In order to solve the difficulty and low efficiency of gas extraction in soft and low permeability coal seam, taking 3# coal seam of Xinjing Coal Mine as the research object, using PFC2D particle flow numerical simulation software and control variable method, the influence of different water injection flow rate and fracturing time on hydraulic fracturing radius, maximum fracture opening and fracture number of coal seam is studied.The results show that the hydraulic fracturing radius, maximum fracture opening and fracture number of coal seam are proportional to the power function of the water injection flow rate and the fracture time in soft and low permeability coal seam.Based on the characteristics of soft and low permeability coal seams, the fracturing fluid efficiency was introduced to modify the calculation formulas of fracturing radius, maximum fracture opening and fracture number.According to the actual engineering geological conditions of the 3# coal seam in Xinjing Coal Mine, an on-site hydraulic fracturing test is carried out in the south 5th bed plate roadway.The results show that the hydraulic fracturing radius is about 50 m during the pump injection pressure and the water injection volume is from 20 MPa to 25 MPa and from 90 m3 to 100 m3, respectively; the air permeability coefficient, average gas drainage concentration, gas drainage volume of per 100 meter roadway and single hole average gas drainage scalar volume of the coal seam in hydraulic fracturing area is 22.0,2.2, 2.4 and 2.7 times than that in unfractured areas, respectively, which provide technical support for selecting the hydraulic fracturing parameters and gas drainage design for the 3# coal seam of Xinjing Coal Mine.
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