Experimental analysis and model study on effective stress sensitivity of coal rock permeability

Using the unsteady pressure drop method, permeability measurements of coal samples were conducted across various bedding directions under different effective stresses. Mercury injection, SEM, and micro-CT techniques were employed to analyze pore/fracture structures. By integrating experimental data, existing stress-sensitive permeability models were validated and refined. The results demonstrated that gas permeability in cores from different directions exponentially correlates with effective stress. During decompression, the permeability exhibited limited recovery and irreversible damage. Stress sensitivity assessments with varying parameters indicated high sensitivity of coal permeability to effective stress, both perpendicular and parallel to bedding planes. The revised permeability model predicts permeability with an error margin of less than 15%.