煤矿井下硬煤层顺层长钻孔分段压裂强化瓦斯抽采技术及应用

针对硬煤层瓦斯抽采衰减快，抽采周期长、效率低等问题，提出了中硬煤层顺层长钻孔分段压裂增加煤层透气性瓦斯强化抽采技术。以陕西彬长矿区4号煤层为研究对象，在实验室采用SEM高分辨率电子显微镜对比分析了水力压裂前后煤体微观孔隙结构变化特征；利用Abaqus软件模拟了封隔器受力特征及钻孔的稳定性；在彬长矿区大佛寺煤矿井下4号煤层进行水力压裂工业性试验。结果表明：煤层在加载压力15 MPa，保压48 h，煤体的孔隙、裂隙数量增多，孔径尺寸增大，且连通性增强，裂隙间的连通性明显提升。压裂过程中，封隔器同时受到内压和外压载荷产生膨胀变形，内压15 MPa、外压10 MPa时，可保持硬煤钻孔结构完整同时，产生最大的封隔摩擦力。工程试验完成3个顺煤层定向长钻孔分段压裂施工，孔深540～568 m，每孔分8段压裂，单孔注液量910～1 154 m³，累计注液量3 011 m3；压裂后，利用孔内瞬变电磁测试确定压裂影响半径34～46 m。压裂钻孔平均瓦斯抽采纯量0.72～1.73 m³/min，平均抽采瓦斯体积分数42.60%～67.48%；对比试验区常规钻孔，瓦...

Enhanced gas drainage technology by staged fracturing in long bedding borehole in hard coal bed of underground coal mine and its application

In view of the problems of rapid attenuation, long period and low efficiency of gas drainage in hard coal bed, the enhanced gas drainage technology of increasing the permeability of coal bed by staged fracturing in long bedding borehole was put forward for the medium-to-hard coal bed. Herein, research was conducted on No.4 coal bed of Shaanxi Binchang Mining Area. Specifically, the change characteristics of micro-pore structure of coal body before and after hydraulic fracturing were comparatively analyzed by high-resolution electron microscope (SEM) in the laboratory. Meanwhile, the stress characteristics of packer and the stability of borehole were simulated with Abaqus software, and the industrial test of hydraulic fracturing was carried out in the No.4 coal bed of Dafosi Underground Coal Mine in Binchang Mining Area. The results show that the pores and fractures in the coal body are increased in number, enlarged in size and enhanced in connectivity under the conditions that 15 MPa pressure is applied to the coal bed and held for 48 h. In particular, the connectivity between fractures is significantly improved. During fracturing, the packer will expand and deform under the joint action of the internal and external pressures. Besides, the borehole structure of hard coal could be kept intact and the maximum sealing friction would be generated when the internal pressure is 15 MPa and the external pressure is 10 MPa. In the engineering test, 3 long directional bedding boreholes with a depth of 540?568 m for each were fractured by stage. Specifically, each borehole was divided into 8 stages, with a liquid injection volume of 910?1 154 m3 for each single borehole and a cumulative liquid injection volume of 3 011 m3. After fracturing, the fracturing influence radius was determined through the transient electromagnetic test in the borehole to be 34?46 m. The net amount of gas drained from the fractured boreholes is 0.72?1.73 m3/min, with a volume fraction of 42.60%?67.48%. Compared with the conventional boreholes in the test site, the volume fraction of gas drained is increased by 1.29?2.49 times, and the net amount of gas drained in every 100 m boreholes is increased by 3.93?10.03 times, realizing the advanced permeability improvement and pre-drainage of gas in the coal bed area of the test site. Generally, this process technology provides a technical reference for the advanced treatment of gas in large areas with similar geological conditions.