Experimental Research On Gas Seepage Characteristics Of Coal Seam With Cross-measure Borehole Based On Bedding Effect

The geological conditions of coal seams in my country are complex.Under the background of gradually entering the deep mining mode,the possibility of underground gas dynamic disasters has increased sharply due to the large in-situ stress,low coal seam permeability and high gas content.The method of reducing coal seam gas pressure is currently an effective and common gas control method in underground mines.Coal rock is a typical sedimentary rock with obvious bedding structure,which makes the gas seepage performance and mechanical properties of coal in different bedding directions in the same coal seam vary greatly.It is comprehensive,and it is often assumed that coal is a homogeneous medium in the study of coal seam gas extraction through layer drilling,which is quite different from the actual underground production.Therefore,considering the influence of bedding effect on the mechanical deformation and damage characteristics of coal body and the law of gas seepage,it is of practical value to study the effect and law of gas drainage in through-bed drilling,which is of practical value for efficient and precise control of underground gas disasters,and also for revealing coal seams.The mechanism of gas dynamic disaster provides scientific basis and experimental reference.In this paper,coal samples with obvious bedding taken from the 9# coal seam of Guandi Mine were taken according to the included angles of 0°,15°,30°,45°,60°,75° and 90° with the bedding plane,respectively.First,the coal samples were subjected to uniaxial loading and failure,and at the same time,the acoustic emission characteristics during the loading process were monitored to fully understand the influence of the bedding angle on the mechanical deformation and damage characteristics of the coal samples under uniaxial loading.The mechanical seepage experiment under loading explores the change law of the mechanical seepage characteristics of the coal body with the bedding angle under different confining pressures and different gas pressures.The influence of mining area provides theoretical basis and scientific method for solving engineering problems.The main research conclusions are as follows:(1)The uniaxial compressive strength of the coal body generally shows a "V"-shaped change trend with the increase of the bedding angle,and the elastic modulus increases with the increase of the bedding angle,but the growth rate gradually slows down;The failure mode of coal samples changed from tensile failure to shear failure with the increase of the bedding angle.The 75° and 90° bedding coal samples showed composite failure of tension and shear,and the damage degree gradually increased;the acoustic emission during the loading process The signal characteristics are basically consistent with the deformation and failure characteristics of coal samples.The distribution of signal positioning points and the amplitude of the signal source can also reflect the actual damage and damage of coal samples.The method of underground dynamic disaster is feasible and reliable.(2)Under triaxial loading,the compressive strength and elastic modulus of coal body are much higher than those under uniaxial compression,and they also show a "V" shape with the increase of bedding angle;coal samples with different bedding angles under the action of confining pressure The failure mode of 30° and 45° bedding angle is different from that under uniaxial.The near-parallel bedding coal samples have shear and expansion tension deformation failures.Coal management samples showed irregular "X" type conjugate shear failure.The compressive strength and elastic modulus of coal body increase with the increase of confining pressure,and the degree of fragmentation of coal samples after instability and failure increases with the increase of confining pressure.(3)In the triaxial loading mechanical seepage experiment,the seepage characteristics of coal samples with different bedding angles under different confining pressure conditions were measured,and the permeability first decreased and then increased with the axial loading.,the permeability reaches the minimum value from the end of the elastic deformation stage of the coal sample to the early stage of the yield stage,and then with the yield failure of the coal body,the permeability begins to gradually rise.The functional relationship between the bedding angle and its initial permeability of coal samples under different confining pressures was obtained by fitting respectively,and the permeability distribution law of one point in all directions in the vertical section of the coal seam was obtained by expanding in polar coordinates.The principle of permeability vector synthesis algorithm is compared and analyzed.The permeability of coal samples first decreased and then increased with the increase of gas pressure.Due to the influence of the Klinkenberg effect,the permeability was relatively large when the gas pressure was low,and the minimum permeability appeared at about 1MPa.The confining pressure sensitivity coefficient was introduced to evaluate the influence of the change of confining pressure on the permeability of coal samples with different bedding angles.(4)The construction and solution of the gas-solid coupling mathematical model of coal body and the coal seam gas model of drilling through layer drilling were carried out.Under the condition of anisotropy,the effective drainage radius and area of the drilled hole with a smaller dip angle are significantly smaller than those of the isotropic permeability,which proves that the bedding effect affects the drainage effect of the drilled hole.In addition,the variation law of the drainage effect of through-bed drilling under different initial permeability and different initial gas pressure of coal seam was simulated,and it was found that the initial permeability of coal seam had the most significant influence on the drainage effect of through-bed drilling.