Experimental Study On Micro Pore Structure And Gas Adsorption Desorption Seepage Of Anisotropic High-rank Coal

This paper takes the high-rank coal from the Zhongmacun Mine of the Coking Coal Group as the research object.Firstly,the microscopic pore structure characteristics of the coal samples are analyzed qualitatively and quantitatively by scanning electron microscopy,high-pressure mercury intrusion method,low-temperature liquid nitrogen adsorption method and low-field nuclear magnetic resonance（LNMR）method.Secondly,the mechanical properties and acoustic emission characteristics of anisotropic high-rank coal are tested by uniaxial compression and acoustic emission device.The low-field nuclear magnetic resonance system is used to analyze the adsorption law of anisotropic high-rank coal under different confining pressures.Finally,the evolution law of permeability of anisotropic high-rank coal under different path conditions is analyzed by using the coal-rock triaxial adsorption-desorption-seepage experimental system.The main research results are as follows:（1）Through qualitative and quantitative analysis of the microstructure of high-rank coal in Zhongmacun Mine,uniaxial compression and acoustic emission experiments,it can be seen that:the total pore volume of high-rank coal of coking coal group is 0.0316ml/g,the volume of micropore,pore,mesopore and macropore are 0.0129ml/g,0.0016ml/g,0.0026ml/g and 0.0145ml/g,respectively.The adsorption pore is the most developed,and the seepage pore and fracture are undeveloped relatively.The T_2C（T₂cutoff value）of anisotropic high-rank coal is different to some extent,and the relationship between bedding angle and T_2Cis in line with the exponential function.vertical bedding coal sample ZM5（stratified angle 90°）has the largest compressive strength and deformation modulus,followed by parallel bedding coal sample ZM1（stratified angle 0°）,and oblique bedding coal sample ZM2,ZM3and ZM4（stratified angle 30°,45°and 60°）have the smallest average value of compressive strength and deformation modulus.（2）Through the experiment of gas adsorption law of anisotropic high-rank coal under different confining pressures,it can be obtained:The gas adsorption capacity of anisotropy high-rank coal increases with time.In the process from low confining pressure to high confining pressure,the gas adsorption average increment of oblique bedding coal sample ZM2,ZM3 and ZM4 is the largest,followed by vertical bedding coal sample ZM5.The gas adsorption increment of parallel bedding coal sample ZM1is the smallest.The relationship between adsorbed gas quality of anisotropic high-rank coal and confining pressure conforms to the linear function of y=a-bx.The relationship between the free gas peak area and confining pressure is y=a+bexp（cx）.The area of adsorption peak increases first and then decreases with the increase of bedding angle,generally in an"inverted V"shape.The area of the free peak decreases first and then increases with the increase of the bedding angle,which is in a"V"shape in general.In addition,when the confining pressure increases,the free peak keeps moving to the left,and the large pores of anisotropic high-rank coal shrink with the increase of the confining pressure.（3）According to the experiment of gas seepage characteristics of anisotropic high-rank coal under different mechanical path conditions,it can be known that:The relationship between permeability and effective stress of anisotropic high-rank coal in mechanical path 1 and 2 is y=aexp（bx）exponential function.The permeability of mechanical path 1 under constant axial pressure and relief of confining pressure gradually increases with the decrease of confining pressure,and gradually increases with the increase of differential stress（σ₁-σ₃）.Under mechanical path 1,the initial permeability of ZM1 under loading axial confining pressure is the largest,which is5.41 times of that of ZM5,followed by ZM2,ZM3 and ZM4,which is 3.69 times of that of ZM5.In mechanical path 2,the initial permeability of coal samples under loading axial confining pressure stage is similar to that in mechanical path 1.In mechanical path 2,the permeability of coal samples in loading axial pressure and unloading confining pressure stage increases gradually with the increase of differential stress.In mechanical path 1,constant axial pressure and relief of confining pressure stage and mechanical path 2,loading axial pressure and unloading confining pressure stage,the average increase of permeability of ZM2,ZM3 and ZM4 is the largest.