Numerical modeling on destress blasting in coal seam for enhancing gas drainage

Controlled blasting for loosening coal seams is one of the most important measures to enhance gas drainage and thus prevent coal and gas outbursts. The formation and development of blasting-induced damage zone, as well as the gas flow in damaged coal seams, can be considered as a coupled process among gas flow, solid deformation and damage. In this work, a coupled multiphysical model for the interaction between blasting damage of coal seam and gas flow is proposed, based on which, the effect of destress blasting on draining gas in coal seam is numerically simulated and the associated mechanisms for enhanced gas drainage induced by blasting damage are clarified. The loosening of coal seam induced by blasting is considered as a damage process that is dominated by the combined contribution of blasting stress wave and blasting-induced gas pressure, in this respect, the blasting damage of rock and coal seam is numerically simulated and compared with the existing experimental observations. 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 the borehole but also enhance the gas drainage due to the increase of the gas permeability in the damaged coal seam.

► A coupled coal–gas interaction model before and after destress blasting is proposed. ► Evolution of damaged and permeability after destress blasting is numerically examined. ► The coalbed gas drainage enhanced by destress blasting is numerically quantified.