Study On Effects Of Coal-permeability Anisotropy On Gas Drainage Performance:a Case Study In Baode Coalmine

The no.8 coal seam of Baode coal mine has high gas content and poor permeability,and the distribution of coal seam fractures has obvious directionality.The extraction efficiency of pre-extraction borehole arranged in the conventional way is low,which seriously affects the safety of mine production.Therefore,in this paper,by combining laboratory test,numerical simulation and field test,the microscopic crack distribution of no.8 coal seam in Baode coal mine is analyzed,the anisotropic characteristics of coal permeability and its influence on gas flow are studied,the layout plan of pre-drainage borehole in working face is optimized,and the field verification is carried out.(1)The basic geological data of no.8 coal seam in Baode coal mine were investigated and analyzed,and the occurrence and main fracture development directions of coal seam were determined.The micro-fracture zone of no.8 coal seam in Baode mining area is distributed in groups,and the main direction of development shows an included Angle of about 23 °with the coal wall of 81310 working face.(2)The bulk coal was retrieved from the working face of the 81310 air return trough,and the standard coal sample was processed in the laboratory,and the permeability anisotropy test was carried out.The results show that the permeability of coal decreases linearly with the increase of airflow direction and bedding Angle.With the increase of confining pressure,the permeability of coal body decreases exponentially.There are obvious easy zone and difficult zone in the flow direction in the coal body,and the width of the difficult zone increases with the increase of the flow direction and the included Angle of the microscopic crack.When the included Angle is 90°,the whole coal sample is a difficult zone for gas flow.(3)Based on the actual conditions of Baode coal seam,COMSOL Multiphysics was used to simulate and analyze the gas migration law of coal seam.The results show that under the condition of high in-situ stress,the decreasing trend of coal seam gas pressure is obviously less than that under the condition of low in-situ stress.The larger the Angle between the drill hole and the strike of the coal seam,the larger the effective radius and the better the extraction effect.(4)Based on the anisotropic characteristics of coal permeability,the layout plan of pre-extraction borehole in working face was optimized,and field tests were carried out on the 81310 working face in Baode coal mine,the drilling angle of-6° is the best.The results show that when the angle between the gas extraction borehole and the strike of the coal seam is 90°,it is the optimal placement position of the borehole.The permeability of no.8 coal seam in Baode coal mine has the anisotropy characteristic.The results of this study are of great value in guiding and applying the arrangement of pre-drainage borehole in Baode coal mine.Figures[59]Tables[8]References[73]...