A new anisotropic coal permeability model under the influence of stress, gas sorption and temperature: Development and verification

Modeling approach to permeability especially anisotropic permeability of coal in front of working face is of significance for gas extraction in coal mining. Considering three-dimensional stress condition and multi-field influence, in this study, an anisotropic permeability model was suggested for coal in front of working face. The anisotropic permeability was assumed to be controlled by the directional fracture strain under the condition of multi-field influence caused by effective stress, adsorption-desorption and thermal stress. The directional fracture strain induced by effective stress was governed by the generalized Hooke constitutive model. Based on the matrix-fracture interaction, the constitutive model of directional fracture strain induced by adsorption-desorption was established from the improved Langmuir equation. Assuming that the coal matrix was connected by the matrix bridge, the constitutive model of directional fracture strain induced by thermal stress was constructed by proposing the thermal internal swelling coefficient. Consequently, a new anisotropic coal permeability model was developed based on the directional fracture strain under the influence factor of stress, gas sorption and temperature. Moreover, the new permeability model was verified by laboratory tests under different effective stresses, gas pressures, temperatures and their combined influence. The theoretical results of proposed anisotropic permeability model may provide a better understanding of permeability evolution in multi-field coupling geological environment during coal mining.