Numerical Simulation on Gas flow in Coal Seam Enhanced by Controlled Blasting

Controlled blasting for loosening coal seam is one of the most important measures to enhance the gas drainage and thus to prevent coal and gas outburst. The formation and development of blasting-induced damage zone, as well as the gas flow in damaged coal seam, can be considered as a coupled process among gas flow, solid deformation and damage. In this work, a coupled multiphysical model for the interaction of blasting damage of coal seam and gas flow is proposed, based on which, the effect of loosening blasting on draining gas in coalbed is numerically simulated and the associated mechanisms for enhanced gas drainage induced by blasting damage is clarified. In this model the loosening of coal seam induced by blasting is considered as damage process that is dominated by the combined contribution of blasting stress wave and blasting-induced gas pressure. Then, by considering the effect of coal seam damage on the gas permeability, the gas drainage enhanced by blasting damage is quantified based on the numerical simulations. It is demonstrated that, the blasting damage around the borehole can not only alleviate the stress concentration at the perimeter of borehole, but also enhance the gas drainage due to the increase of the gas permeability in the damaged coal seam.