煤层穿层钻孔水力割缝卸压增透数值模拟及应用

Simulation and Application of Pressure Relived and Permeability Enhanced Law of Perforated Hydraulic Slotting Borehole in Coal Seam

为研究水力割缝穿层钻孔缝槽直径和钻孔倾角对卸压增透效果的影响,以典型低透气煤层为背景,采用FLAC^(3D)数值模拟方法对缝槽直径为1.1,1.2,1.3,1.4,1.5 m,钻孔倾角为50°、60°、70°、80°、90°的水力割缝模型卸压效果及应力场进行计算和对比分析。结果表明:割缝钻孔周围塑性破坏面积与缝槽直径正线性相关;割缝影响范围与缝槽直径成对数函数关系。割缝钻孔周围塑性破坏面积与钻孔倾角成正相关关系,在钻孔倾角为60°至70°时发生突变;割缝影响范围与钻孔倾角成幂函数关系;缝槽直径对割缝效果影响较大。根据研究结果进行了现场实践,现场数据验证了数值模拟结果,割缝钻孔的平均抽采瓦斯流量为常规钻孔的1.4~2.2倍,瓦斯抽采浓度为常规钻孔的3~4倍,瓦斯抽采纯量为常规钻孔的4.5~10.5倍。研究结果为穿层钻孔水力割缝参数的确定提供了理论依据。

In order to study the influence of slot diameter and borehole inclination of perforated hydraulic slotting borehole on the pressure relived and permeability enhanced law,taking the typical coal seam with low permeability as a background,FLACnumerical simulation method was used to calculate and analyze the pressure relief effect and stress field of hydraulic slotting models with slot diameter of 1.1,1.2,1.3,1.4,1.5 m and borehole inclination of 50°,60°,70°,80°,90°.The results show that there is a positive linear correlation between the plastic failure area around the slotting borehole and the slot diameter.The influence range of slotting is a logarithmic function of the slot diameter.There is a positive correlation between the plastic failure area around the slotting borehole and the borehole inclination,and a sudden change occurs when the borehole inclination is 60°to 70°.The influence range of slotting is a power function of the borehole inclination.The slot diameter has a great influence on the slotting effect.According to the research results,the field practice was carried out,and the field data verified the numerical simulation results.The average gas drainage flow of slotting boreholes was 1.4-2.2 times that of conventional boreholes,the gas drainage concentration was 3-4 times that of conventional boreholes,and the gas drainage purity was 4.5-10.5 times that of conventional boreholes.The research results provide a theoretical basis for the determination of hydraulic slotting parameters of perforated boreholes.