低渗煤层分段水力造穴钻孔卸压增透技术研究

    Research on segmented hydraulic cavitation borehole for pressure relief and permeability enhancement in low permeability coal seams

    • 摘要: 为了系统揭示分段水力造穴技术在低渗煤层瓦斯抽采中的作用机制及参数优化路径,建立了煤体损伤−应力−渗流耦合模型。结合数值模拟与现场试验,探究了造穴半径、造穴间距等关键参数对煤层卸压范围及瓦斯抽采效率的影响。结果表明:分段水力造穴技术能够有效降低钻孔周围煤层的应力,在孔壁附近诱发煤体损伤破坏,形成明显的应力扰动区和孔隙率提升区,进而提高煤层的渗透率,并显著提升瓦斯抽采效率;造穴形成的孔穴对煤层的卸压增透效果明显,造穴半径的增大可显著扩大应力扰动范围和渗透率提升程度,但造穴半径超过0.6 m后,效益增幅趋缓且孔壁稳定性下降;当造穴间距减小时,相邻孔穴间形成应力叠加区,渗透通道贯通,抽采效果显著增强。现场试验结果与模拟趋势具有良好的一致性:最优造穴半径为0.5~0.6 m,最优造穴间距为6 m。

       

      Abstract: To systematically reveal the mechanism and parameter optimization path of staged hydraulic cavity creation technology in gas drainage from low-permeability coal seams, a coal damage-stress-seepage coupling model was established. Combining numerical simulation with field tests, numerical simulation experiments were conducted to investigate the influence of specific engineering parameters such as cavity radius and spacing on coal seam pressure relief area and gas drainage effect. The spatio-temporal evolution law of coal seam gas under staged hydraulic cavity creation technology during drainage activities was systematically discussed. Field experiments were conducted for comparative verification and analysis of gas drainage effects. The simulation results show that staged hydraulic cavity creation technology can effectively reduce the stress in coal seams around boreholes, induce coal damage and failure near borehole walls, forming obvious stress disturbance areas and porosity improvement areas, thereby increasing coal seam permeability and significantly improving gas drainage efficiency. The cavities formed by hole-making have a significant pressure relief and permeability enhancement effect on coal seams; the expansion of the cavity radius can significantly enhance the stress disturbance range and permeability improvement degree, but after exceeding 0.6 m, the benefit increase slows down and the risk of hole wall instability increases; when the cavity spacing decreases, stress superposition zones form between adjacent cavities, permeability channels are formed, and gas drainage effects are significantly enhanced. Field tests further confirm the consistency of simulation trends, indicating that the optimal cavity radius is 0.5 m to 0.6 m, and the optimal spacing is 6 m.

       

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