Study on staged hydraulic sand-propped fracturing technology for gas drainage via long boreholes in coal seam roof

Gas hazards pose one of the most significant threats to coal mine safety production, and improving gas drainage efficiency while reducing gas concentration is critical for ensuring mine safety. Aiming at the issues of high gas content, high gas pressure, and poor permeability in No. 8 coal seam of Luling Coal Mine in the Huaibei Mining Area, a study was conducted on the technology of staged hydraulic sand-propped fracturing for gas drainage via directional jetting in long boreholes drilled in the roof. Based on comprehensive geological characterization, theoretical framework development, numerical simulation coupled with computational modeling, and field validation campaigns, a systematic technical framework for enhanced gas drainage and stress relief in fractured, soft, and high-gas-outburst-prone coal seam zones was established. During field trials, the staged hydraulic sand-propped fracturing technology in roof long boreholes was successfully implemented, achieving a borehole depth of 520 m, 9 fracturing stages, and a cumulative injection of 2214 m3 fracturing fluid and 40.34 t quartz sand. After fracturing, the maximum gas drainage concentration reached 75%, the daily pure gas drainage volume peaked at 3542.4 m3, and the cumulative gas drainage approached 451 600 m3. The results indicate that this technology significantly improves coal seam permeability and effectively reduces gas pressure, providing valuable technical references and practical experience for gas control in mines with similar geological conditions.