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煤层钻孔脉动空气爆冲致裂煤体数值模拟研究

Numerical simulation study of coal cracking caused by pulsating air burst in coal seam borehole

  • 摘要: 针对深部煤层低渗难抽的问题,提出一种脉动空气爆冲高效增透技术,可以显著提升煤层渗透率及瓦斯抽采效率。主要阐述了高压脉动空气爆冲卸压机理,利用LS-DYNA软件,在不同强度煤体、埋深、起爆压力、脉动次数等条件下进行数值模拟,并分析高压脉动空气爆冲致裂效果。结果表明:通过对RHT模型中p-a状态方程、RHT本构方程的参数进行理论研究与计算,得出RHT模型参数,使得RHT损伤本构模型能更好反映煤的动力变形与破坏过程。对于脉动空气爆冲致裂,通过控制单一变量,得出有效致裂范围整体上与煤体强度呈负相关关系,对中硬煤体的致裂效果最佳,其有效致裂范围为2.52 m; 有效致裂范围与煤体埋深呈负相关关系,其在埋深为300 m时对硬煤体的有效致裂范围为0.47 m; 有效致裂范围与煤体起爆压力呈正相关关系,其在起爆压力为100 MPa时对硬煤体的有效致裂范围为2.83 m; 有效致裂范围与煤体脉动次数呈正相关关系,其在脉动3次时对硬煤体的有效致裂范围为2.72 m。建立各因素对影响有效致裂范围的回归模型,进一步分析了不同因素对有效致裂范围影响的相关性。

     

    Abstract: In order to solve the problem of low permeability and difficult pumping in deep coal seams and significantly improve the permeability of coal seams and the efficiency of gas extraction, a pulsating air blast high-efficiency permeability enhancement technology was proposed.The mechanism of high-pressure pulsating air burst flushing and pressure relief was expounded.The numerical simulation was carried out under the conditions of different coal strengths, buried depth, initiation pressure and pulsation times by using LS-DYNA software.The cracking effect of high-pressure pulsating air burst was analyzed.The results indicate that through theoretical research and calculations of the parameters of the p-a equation of state and the RHT constitutive equation in the RHT model, the parameters of the RHT model are derived, allowing the RHT damage constitutive model to better reflect the dynamic deformation and failure process of coal.For fracture caused by pulsating air blasts, with controlling a single variable, it was found that the effective fracturing range is generally negatively correlated with coal strength.The best fracturing effect was observed in medium-hard coal and effective fracturing range is 2.52 m.The effective fracturing range is negatively correlated with coal seam depth.With a depth of 300 m, the effective fracturing range for hard coal is 0.47 m.The effective fracturing range is positively correlated with coal initiation pressure.With an initiation pressure of 100 MPa, the effective fracturing range for hard coal is 2.83 m.The effective fracturing range is positively correlated with the number of pulses.At three pulses, the effective fracturing range for hard coal is 2.72 m.Regression models were established for each factor affecting the effective fracturing range, and the correlation of the influence of different factors on the effective fracturing range was further analyzed.

     

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