Research On Microstructure And Pore Characteristics Of Medium And High Rank Coal Bodies In Guizho

Guizhou area is rich in coal resources,with many kinds of coal and a large proportion of medium and high rank coal bodies,but there are problems such as complex coal seam occurrence conditions,high gas content and low coalbed methane production.Therefore,it is of great significance to study the microstructure and pore characteristics of medium and high rank coal for gas control and coalbed methane exploitation in Guizhou.In this paper,the pore characteristics and adsorption characteristics of medium and high rank coal in Guizhou Province are comprehensively analyzed from the micro level through multiple sets of experiments such as industrial analysis,elemental analysis,maceral determination,vitrinite reflectance test,pore structure characteristics analysis and gas emission initial velocity determination.The results show that:（1）Through the analysis of the composition of coal samples and the analysis of coal petrological characteristics,it can be obtained that the moisture content in coal samples is between 0.92%and 4.3%,the volatile content is between 4.7%and 32.26%,the C element content is between 68.40%and 84.61%,the vitrinite content is between55.82%and 71.86%,and the maximum vitrinite reflectance is between 1.09%and3.67%,covering medium and high rank coal samples.（2）According to the microcrystalline morphology analysis of coal samples,there is a sharp and narrow absorption peak near 1600cm^-1 in the infrared spectrum of coal samples,which is attributed to the skeleton vibration and stretching vibration of C=C in aromatic hydrocarbons and polycyclic aromatic layers.With the increase of coalification degree,the aromatic hydrogen ratio(f _Ha)and aromatic carbon ratio（f _C）showed an increasing trend.With the increase of coal rank,the aromatic layer spacing d₀₀₂ generally shows a decreasing trend.Compared with the coalification index P of coal samples,with the increase of coal metamorphism,it is found that the coalification degree P of high-order coal body is slightly higher than that of medium-order coal body,indicating that the content of side chain in high-order coal body is lower than that of medium-order coal body,which leads to the increase of relative aromatic ring number of high-order coal body.（3）Through the analysis of the pore structure characteristics of coal samples,it is found that there are many staggered cracks and holes on the surface of coal samples,and the combination of cracks is complex.For coal samples with medium and high metamorphic degree,as the metamorphic degree of coal increases,the fractal dimension of seepage increases and the fractal dimension of adsorption pore decreases.Based on the comprehensive pore characteristics analysis of low temperature liquid nitrogen adsorption and high pressure mercury injection experiments,with the increase of metamorphic degree,the comprehensive fractal dimension of coal samples increases,the pores of coal samples become more complex,and the pore surface area becomes rougher.（4）By combining the initial velocity,metamorphic degree,industrial analysis,coal macerals and pore characteristics of coal samples,the influence of each variable on the diffusion characteristics of coal was analyzed.Based on the low temperature liquid nitrogen adsorption experiment and high pressure mercury injection experiment,the gas diffusion model in coal samples was analyzed.It is found that with the increasing degree of metamorphism,the moisture and volatile matter show a decreasing trend;the proportion of exinite is inversely proportional to the degree of coal metamorphism and the initial velocity of gas emission.As the degree of metamorphism increases,the content of exinite decreases.The comprehensive fractal dimension is proportional to the degree of metamorphism and the initial velocity of release.Based on the high pressure mercury injection experiment,the methane gas mode of coal sample is excessive and Fick type diffusion.Based on the low temperature liquid nitrogen adsorption experiment,the methane gas diffusion model of coal samples is mainly Horvath-Kawazoe diffusion and excessive type.