Influence of effective drainage radius by borehole orientation along seam with anisotropic permeability

In order to improve gas drainage efficiency along seam, the key is to determine borehole orientation and effective drainage radius.Based on the gas permeability test results of anisotropic coal seam, the gas-solid coupling seepage model in gas anisotropic permeability coal seam is established to numerically simulate the time variation laws of effective drainage radii of different borehole orientations, and to analyze the influence of drainage effect by borehole orientation.The results show that the gas permeabilities at the directions of face cleat and butt cleat are about 2.6 times and 1.5 times respectively larger than that on the direction vertical to the bedding plane.In any direction, effective dranage radii increases with gas drainage time increasing, but increasing rates gradually decrease, which the relationship of effective drainage radii and gas drainage time can be expressed by power exponent.Effective drainage area is an ellipse under any gas drainage time in gas anisotropic permeability coal seam, and the ellipse center is drainage borehole, its long axis and short axis are maximum drainage distance (parallel bedding direction) and minimum extraction distance (perpendicular to the direction of the bedding) respectively.The gas drainage effect of drainage hole parallel bedding along butt cleat derection (perpendicular to face cleat) is better than that of drainage hole parallel bedding along face cleat derection (perpendicular to butt cleat).This research provides the basis for the selection of borehole orientation and reasonable arrangement of boreholes, which has significance to improve gas drainage efficiency and ensure mine safe production.