Experimental study of gas flow and coal deformation at different levels of axial/radial stress ratio

CH₄ flow dynamics in coal, governed primarily by adsorption, desorption, and seepage processes, are critical for determining gas extraction efficiency. Coal seam deformation under varying stress conditions further significantly impacts CH₄ flow. Utilizing a self-developed coal solid-gas coupling test apparatus, this study conducted simultaneous measurements of CH₄ flow and coal deformation under different axial-to-radial stress ratios. The temporal relationship between CH₄ flow and coal deformation was analyzed, establishing a quantitative correlation between the two. The influence of stress on both phenomena was examined. A model incorporating residual strain was developed to evaluate coal strain throughout the entire CH₄ flow process. Results demonstrated that both CH₄ flow and coal deformation exhibit Langmuir-like relationships with time. Similarly, a Langmuir-like relationship was observed between the amount of CH₄ adsorbed and coal deformation during adsorption. Within the experimental stress range, an increase in the axial-to-radial stress ratio inhibited CH₄ flow, consequently reducing coal deformation. Volumetric strain exhibited greater sensitivity to changes in the stress ratio compared to radial or axial strain. Residual strain was identified in coal during both CH₄ adsorption and desorption, with its prominence inversely related to the axial-to-radial stress ratio. The model, accounting for residual strain alongside isothermal flow and deformation characteristics, accurately represented the temporal evolution of coal deformation during CH₄ flow. This research provides a theoretical foundation for enhancing the efficacy of gas extraction.