松软低透气性煤层水力压裂增透瓦斯抽采技术研究

Research on gas drainage hydraulic fracturing improvement technology for soft and low permeability coal seam

为解决松软低透气性煤层瓦斯抽采难度大、效率低的难题,以新景煤矿3#煤层为研究对象,采用PFC2D颗粒流数值模拟软件和控制变量法,研究不同注水流量和压裂时间对煤层水力压裂半径、裂缝最大开度和裂缝数目的影响。研究结果表明:松软低透气性煤层水力压裂半径、裂缝最大开度和裂缝数目与注水流量和压裂时间均呈幂函数形式增长。基于松软低透气性煤层的特点,引入压裂液效率,得到了压裂半径、裂缝最大开度和裂缝数目的修正计算公式。基于新景煤矿3#煤层实际工程地质条件,在南五底抽巷进行了现场水力压裂试验。试验结果表明:当泵注压力为20~25 MPa、注水量为90~100 m^(3)时,水力压裂半径约为50 m;水力压裂区域煤层透气性系数、平均抽采瓦斯浓度、百米巷道瓦斯抽采量和单孔平均抽采瓦斯纯流量分别为未压裂区域煤层的22.0、2.2、2.4、2.7倍,为新景煤矿3#煤层水力压裂参数选取和瓦斯抽采设计提供了技术指导。

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 m^(3) to 100 m^(3),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.