Abstract
Permeability of coal reservoirs is a key determinant of coalbed methane well productivity. The evolutionary behavior of permeability in response to stress and mechanical properties is fundamentally linked to the optimization of development schemes and the augmentation of production capacity. Dry and wet high-rank coal specimens were obtained in the southern Qinshui Basin and subjected to permeability measurements under confining pressure, as well as uniaxial compression and Brazilian splitting experiments. These experiments systematically investigated the relationships among permeability, stress, and mechanical properties. Stress sensitivity was quantitatively evaluated; the mechanisms by which stress and mechanical properties affect permeability were revealed. The results show that gas permeability in both dry and wet high-rank coal decreases exponentially with increasing effective stress. Higher water saturation accelerates this decline, thereby strengthening the effect of effective stress on permeability. High-rank coal is typically characterized by low uniaxial compressive strength, tensile strength, and elastic modulus, together with a comparatively high Poisson’s ratio. With increasing vitrinite reflectance (Ro), coal exhibits higher uniaxial compressive strength, tensile strength, and elastic modulus; Poisson’s ratio decreases. The average stress sensitivity coefficient and permeability damage rate of coal specimens exhibit an overall gradual decline with increasing compressive strength, tensile strength, and elastic modulus, despite minor variations. Both parameters increase linearly with Poisson’s ratio, providing a practical basis for permeability evaluation in high-rank coal reservoirs.