Effect of gas pressure on the creep and seepage characteristics of low permeability coal

Abstract

Coal, as a complex gas-bearing medium, exhibits unique rheological behavior under mining disturbance. However, with increasing mining depth, the creep and seepage mechanisms of low permeability coal remain unclear. Therefore, to investigate the coupled relationship between creep and gas seepage in low permeability coal, time-dependent triaxial experiments were conducted in this study. To consider the effects of gas, a modified creep model based on the Nishihara creep model was developed and validated by numerical simulations and experimental results. The correlation between coal creep and seepage was then analyzed under different gas pressure conditions, showing a significant reduction in Young’s modulus during creep. This reduction indicates a strong correlation between creep and gas seepage, which is supported by the agreement between creep strain and permeability curves. In addition, the results show a significant attenuation effect in the seepage process at different gas pressures due to pore pressure and adsorption. It is worth noting that unlike conventional soft coal, no permeability reduction was observed in the initial stage due to the low permeability and stiffness of the coal. And it was shown that the presence of methane accelerated the creep behavior of the coal, resulting in a decrease in permeability. Overall, this study provides important insights into the rheological behavior of low-permeability coal under mining disturbance and sheds light on the mechanisms governing gas seepage in coal.