Numerical analysis on CSW fracturing behavior of coal seam under constraint of geological and engineering conditions

As a revolutionary technology for rock stratum reformation, the controllable shock wave(CSW) fracturing technology has achieved remarkable effect in coal seam reconstruction, and application exploration in the field of coal safety mining has been carried out. However, the previous understanding of the basic CWS fracturing rules under the constraints of geological engineering factors is insufficient due to the limitation of experimental and field monitoring conditions, which restricts the exploration of the fracturing mechanism and the optimization of the field operation parameters. In view of this, based on the description of CSW coal seam reformation and its engineering scientific problems, the CDEM method is used to carry out numerical simulation in order to further reveal the behavior and basic rules of CSW coal seam fracturing under the constraints of geo-stress, mechanical properties of coal and rock, and shock wave loading conditions. The results show that the influence of CSW loading conditions on the fracturing effect has an optimal range, and excessive loading will lead to coal disintegration near the wellbore, which increases the yield of pulverized coal and cause coal reservoir damage. At the same time, the wave impedance and shock wave attenuation increase due to coal fragmentation, which limits the expansion of fracturing radius. There are critical values of fracturing radius and fracturing degree with the increase of geo-stress and the horizontal principal stress difference significant effects on the morphology, expansion direction and connectivity of CSW-induced fractures. It is revealed that the fracturing effect has a selective response to the mechanical properties of coal:there is a critical value of inflection point in the plots of the elastic modulus to fracturing radius and fracturing degree; with the increase of cohesion, the brittleness of coal becomes smaller, and the fracturing effect becomes worse; the tensile strength seems to have no obvious effect on the CSW fracturing effect. Based on the above, there will be good references for the coal seam optimization and parameter optimization measures of CSW operation.