Permeability of coal associated with cleat and bedding structure: measurement and modeling

Abstract

ABSTRACT The permeability of coal shows anisotropic features due to its cleat and bedding structures. This work measured methane permeability of three cylindrical coal specimens, which represents the three orthogonal axes of the coal seam about bedding plane and cleat (face cleat and butt cleat). Twenty-seven permeability measurement tests were conducted under the different confining pressures and axial compression (4, 6, and 8 MPa) at different gas pressures (0.5, 1, and 1.5 MPa). Results clearly revealed the anisotropy in permeability of the tested coal specimens under test conditions. The specimen parallel to the bedding plane in face cleat direction shows the highest permeability while the specimen perpendicular to the bedding plane shows the lowest permeability. Within gas pressure range from 0.5 to 1.5 MPa, the lower the gas pressure the higher the measured coal permeability. Spatial permeability distribution around coal mine methane drainage borehole is obtained through a three-dimensional permeability model. The spatial permeability around drainage borehole parallel to butt cleat direction is much higher than that parallel to face cleat direction. In-mine methane drainage boreholes parallel to bedding plane in the butt cleat direction are recommended to use in engineering application.