Research on Pressure Relief and Anti-impact Technology for Segmental Hydraulic Fracturing in Directional Long Borehole in Roof

Abstract

After large-scale underground mining operations in coal mines, the stress of the overlying strata above the goaf is transferred to the surrounding support areas, creating support pressures. These pressures can easily trigger dynamic disasters such as gas outbursts and roof collapses, seriously threatening mine safety and production. To ensure the safety of underground mining operations, directional long borehole segment hydraulic fracturing technology was used in the roof strata of the 2305 comprehensive caving working face of Cuijiagou Coal Mine in Shaanxi Province to conduct experimental research on the technology of directional long borehole segment fracturing for pressure relief and anti-impact. The hydraulic fracturing of the roof’s directional long borehole reduced the stress peak coefficient of the coal body in front of the working face (K≈2.9), blocked the propagation of mining stress and high stress in the goaf to the mining roadway, reduced the deformation of the mining roadway, and reduced the average working resistance of the working face support by 22% compared to the working face without any measures. The effective reduction of the length of the hanging roof, the improvement of the support resistance, and timely roof collapse during the working face mining period helped ensure the initial pressure did not form a strong impact. The initial pressure interval of the thick hard roof calculated theoretically was shortened by 53%, and the periodic pressure interval during normal mining was reduced by 27% compared with the 2303 working face under the same geological conditions. The experimental results show that the coverage of the directional long hole on the roof is extensive, with the utilization rate of segmented hydraulic fracturing wells reaching up to 80%. This technology effectively diminishes the strength of the roof above the coal seam on a large scale, thereby reducing the periodic pressure interval and intensity. As a result, it prevents the impact caused by the hanging roof during the mining period of the working face, ensuring a safe working environment for underground workers and facilitating the safe and efficient progress of mining operations.