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

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.