中硬煤层长钻孔“射孔−压裂”复合增透区域瓦斯治理技术

Regional gas control technology using long-borehole perforation–fracturing composite permeability enhancement in medium-hard coal seams

  • 摘要: 针对常规水力压裂技术用于中硬煤层瓦斯治理时存在的起裂压力高、裂缝扩展不可控等技术难题,以陕西黄陵二号煤矿有限公司区域瓦斯治理为工程背景,运用理论分析、数值模拟与现场试验等方法,系统研究了定向长钻孔“射孔−压裂”复合增透区域瓦斯治理技术,构建了从参数优化、分段压裂施工到效果验证的完整技术体系。该技术核心是利用高压水射孔形成定向导向缝槽,将后续水力压裂的起裂压力降低约30%,并诱导裂缝沿射孔方向稳定扩展。通过数值模拟与现场试验,确定了射孔与压裂的匹配参数为喷嘴直径3.0 mm、射流压力5 MPa。在工程现场采用分段压裂段间距30~50 m、单段注液量不小于80 m³的压裂参数与工艺,完成4个压裂钻孔的水力压裂现场作业。应用结果表明:采用“射孔−压裂”复合增透技术后,煤层起裂压力被有效控制在11.5~13.7 MPa,整体低于常规压裂技术的起裂压力;裂缝径向延伸距离最大达50 m;百米钻孔瓦斯抽采纯量平均值达0.226 m³/(min·hm),分别为割缝钻孔和普通钻孔的2.9倍,3.8倍,且瓦斯抽采体积分数长期稳定在67%以上。

     

    Abstract: To address technical problems such as high fracture initiation pressure and uncontrollable fracture propagation when conventional hydraulic fracturing is used for gas control in medium-hard coal seams, a regional gas control technology based on directional long-borehole perforation–fracturing composite permeability enhancement was systematically investigated against the engineering background of regional gas control at Shaanxi Huangling No. 2 Coal Mine Co., Ltd. through theoretical analysis, numerical simulation, and field tests, and a complete technical system covering parameter optimization, staged fracturing operations, and performance verification was established. The core of this technology was to use high-pressure water-jet perforation to form directional guide slots, thereby reducing the initiation pressure of subsequent hydraulic fracturing by approximately 30% and inducing stable fracture propagation along the perforation direction. Numerical simulations and field tests determined the matching perforation and fracturing parameters as a nozzle diameter of 3.0 mm and a jet pressure of 5 MPa. Field hydraulic fracturing operations were completed in four boreholes using a fracturing-stage spacing of 30–50 m and a fluid injection volume of at least 80 m3 per stage. The application results showed that after the perforation–fracturing composite permeability enhancement technology was applied, the coal-seam fracture initiation pressure was effectively controlled at 11.5–13.7 MPa, lower overall than the conventional fracturing initiation pressure. The radial fracture propagation distance reached 50 m; the average pure gas drainage rate per 100 m of borehole reached 0.226 m3/(min·hm), 2.9 and 3.8 times those of slotted boreholes and ordinary boreholes, respectively. The gas drainage volume fraction remained above 67% over the long term.

     

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