Nitrogen injection for enhanced coal seam gas extraction (N2-ECGE):A simulation study

As energy demand increases, the depth of mining is increasing, and methane disasters grow more serious, efficient extraction of methane is the ultimate method of preventing and controlling methane disasters. The objectives for this research are to explore the efficiency of N 2 injection to enhance gas extraction from coal seams (N 2 -ECGE) and its impact on coal seam permeability. By developing a fluid-solid coupling model and using COMSOL Multiphysics to perform numerical simulations, the changes in gas pressure, methane content, gas production, output rate and permeability of coal seams were comparatively analyzed under the two methods of direct extraction and N 2 -ECGE. The research results show that N 2 -ECGE can significantly improve the coal seam gas pressure and reduce the coal seam CH 4 content, and the larger the N 2 injection pressure the more significant the reduction effect. Meanwhile, N 2 -ECGE can significantly increase the CH 4 extraction and output rate, and the increase of N 2 pressure further improves the extraction efficiency. In addition, the pressure of nitrogen injection has a remarkable effect on coal seam permeability, high pressure of nitrogen injection can increase the permeability in the time of no disturbance, but the rate of permeability decreases more quickly after disturbed. The effect of strain due to adsorption desorption on coal seam permeability dominates. Despite model construction limitations, this research offers essential theoretical and practical direction for N 2 injection to enhance the permeability evolution law of coal seam gas extraction process.