Abstract: In order to reveal the influence of permeability anisotropy on coal seam gas extraction, an anisotropic permeability equation was derived after assuming that the coal seam is an elastic continuous medium with pore-fracture structure and a hydraulic-mechanical coupling model considering two-phase flow was built for gas extraction, on the basis of the multiple-field coupling theory. Based on the permeability in different directions of coal seam measured by experiment, both the reasonable drilling spacing and the arrangement direction of coal seam gas extraction were determined by numerical simulations. The results show that a pressure reduction zone with elliptical shape is formed near the borehole due to the permeability anisotropy, and then the pressure reduction zone becomes drum shape with the limitation of coal seam thickness, that when taking 120 days as the deadline for gas extraction, the rational space is 2.346-2.598 m under the condition of simulated working face, that the gas extraction volume increases with the rising of the angle between borehole direction and maximum permeability direction, and that for the sake of increasing the gas extraction, the direction of drilling arrangement should keep a larger angle with the maximum permeability direction of coal seam.

Key words: gas extraction, coal permeability, anisotropy, hydraulic-mechanical coupling model, effective radius, drilling direction