低透气煤层超高压水力割缝与水力压裂联合增透技术

Combined permeability enhancement technology of ultra-high pressure hydraulic slot and hydraulic fracturing in low permeability coal seam

为了解决矿井瓦斯预抽中存在的问题,提高矿井瓦斯抽采利用效率,杜绝瓦斯灾害事故发生,以新集二矿瓦斯预抽工艺为研究背景,针对矿井采掘接替紧张、煤层透气性差、瓦斯抽采率低等技术难题,提出了超高压水力割缝与水力压裂联合增透技术。基于岩石力学与流体力学理论,分析了超高压水力割缝与水力压裂联合增透机理。并采用数字模拟方法研究确定了沿槽缝延伸方向,缝槽至煤体深部依次形成破碎区、塑性区、弹性区及原岩应力区,被冲割煤体受高压水射流剪、割应力作用影响,原岩应力区向煤体深部转移,煤体渗透率增大。得出水力压裂钻孔布置在超高压水力割缝形成的塑性区范围内能够达到较好的增透效果,并设计了超高压水力割缝与水力压裂一体化联合增透技术工艺:割缝水压为95~100 MPa,旋转水尾转速为40 r/min,割缝间距为1.0~1.2 m,单刀冲割时间为12 min;水力压裂钻孔直径为95 mm,并采用100 mm的钻孔洗扩装置冲、扩钻孔。通过在新集二矿2201采区220108底板巷2号上钻场的应用结果显示:超高压水力割缝与水力压裂协同增透技术能够明显改善煤层透气性,瓦斯抽采30 d以后,协同超高压水力割缝钻孔平均瓦斯抽采纯量为普通钻孔的10.3倍;协同水力压裂钻孔平均瓦斯抽采纯量为普通钻孔的6.4倍,且能够持续保证较高流量和浓度的瓦斯抽采效果。

In order to solve the problems existing in the mine gas pre-drainage,improve the mine gas drainage utilization efficiency,and prevent the occurrence of gas disaster accidents,aimed at the technical problems of tight replacement of mining and excavation,poor permeability of coal seam and low gas drainage rate,taking gas pre drainage technology of Xinji No.2 Coal Mine as the research background,the joint permeability enhancement technology of ultra-high pressure hydraulic cutting and hydraulic fracturing is proposed.Based on the theory of rock mechanics and fluid mechanics,the combined permeability enhancement mechanism of ultra-high pressure hydraulic slotting and hydraulic fracturing was analyzed.A numerical simulation method was used to determine the fracture direction,fracture zone,plastic zone,elastic zone and original rock stress zone along the slot extension direction from the slot to the deep part of the coal body.Under the influence of high pressure water jet shear and cutting stress,the original rock stress zone transfers to the deep part of coal body,and the permeability of coal body increases.The results show that the arrangement of hydraulic fracturing boreholes in the plastic zone formed by ultra-high pressure hydraulic slits can achieve better permeability enhancement and the combined technology of ultra-high pressure hydraulic cutting and hydraulic fracturing was designed:The hydraulic pressure of cutting is 95~100 MPa,the rotating tail speed is40 r/min,the gap spacing between the slits is 1.0~1.2 m,and the single punching time is 12 min,the diameter of hydraulic fracturing borehole is 95 mm,and the hole expanding device with the diameter of 100 mm is adopted.The application results of No.2 drilling field of No.220108 floor roadway in No.2201 mining area of Xinji No.2 coal mine show thatthe ultra-high pressure hydraulic cutting and hydraulic fracturing synergistic permeability enhancement technology can significantly improve the permeability of coal seam.After 30 days of gas extraction,the average gas extraction volume of ultra-high pressure hydraulic slotted boreholes is 10.3 times that of ordinary boreholes,and the average gas extraction volume of collaborative hydraulic fracturing boreholes is 6.4 times of that of ordinary boreholes,and it can continuously guarantee higher flow and concentration of gas drainage effect.