Research On Microscopic Pore Structure And Gas Adsorption Characteristics Of The Low Rank Coal For Aiweiergou Mining Area In Xinjiang With Low-Field NMR

In recent years,the exploration and development of many coalbed methane in China has gradually been carried out into low-rank coalbeds in western Xinjiang.Coalbed methane（gas）is not only a clean and efficient high-quality energy source,but also a dangerous source that affects the safety of coal mines.Gas drainage is one of the main measures for preventing and controlling gas disasters in mines and utilizing gas resources.As China’s coal mining depth continues to increase,the increase in in-situ stress and gas pressure has an impact on the pore structure and gas adsorption characteristics of coal bodies.Therefore,research on the pore structure and gas adsorption characteristics of low-rank coal in Xinjiang has been carried out.The pore structure of low-rank coal and the gas adsorption characteristics under different gas pressures and confining pressures are necessary to improve the development efficiency of Xinjiang’s low-rank coalbed methane and the underground gas recovery rate.（1）This paper uses a combination of qualitative and quantitative research methods to analyze the micro-pore structure of low-rank coal in Aiweigou,Xinjiang.With scanning electron microscope experiments,low-rank coal has many types of pores and good connectivity.The pore size distribution characteristics and pore type of coal samples were obtained by means of mercury intrusion,liquid nitrogen adsorption and low-field nuclear magnetic resonance.The results show that low-order coal has a higher porosity more than of 7.0%,most of the pore types are open,and the connectivity between pores is relatively high.Good;small pores and large pores occupy large proportions,about 21.0%and 54.0%,respectively;micropores and small pores occupy large proportions,about 58.0%and 34.0%,respectively.Micropore specific surface area is the pore ratio The main contributor to surface area,which constitutes the main site for low-order coal gas adsorption.（2）Carry out low-level coal gas adsorption experiments under different gas pressures,and study and analyze the influence of gas pressure on low-level coal adsorption.Under different gas pressures,the gas content of low-rank coals gradually increases with the increase of gas filling time until it tends to be constant,and the amount of gas absorbed in the micro-pores gradually increases with the gas filling time until it stabilizes.Inflatable gas pressure promotes coal gas adsorption,and the larger the initial gas pressure,the faster the coal gas adsorption gas rate,and the more accumulated gas volume,when the gas pressure gradually increases from 0.31MPa to0.74,1.11,1.46MPa:Within the first hour of filling with gas,the mass of adsorbed gas gradually increased from 0.05653g to 0.11117,0.18023,0.28731g,and the cumulative mass of adsorbed gas increased from 0.28189g to 0.42892,0.52313,0.60523g during the 11h cumulative charge.Within the first hour of inflation,the mass of the adsorbed gas linearly increases with the gas pressure.With the increase of the inflation time,the mass of the adsorbed gas conforms to the form ofy=(abp^1-c)/(1+p^1-c)gas pressure;the mass of the free gas increases linearly with the gas pressure.According to the change of the lateral relaxation time of the adsorbed gas with the gas pressure,the gas pressure has no significant effect on the micropore structure of low-order coal.（3）Carry out gas adsorption experiments of low-rank coal samples under different confining pressures,and study and analyze the influence of confining pressure on the adsorption of low-rank coals.When coal samples adsorb gas under different confining pressures,the gas content gradually increases with the increase of aeration time until it becomes constant,and the amount of gas adsorbed in micropores gradually increases with the increase of aeration time until it stabilizes.From the change of lateral relaxation time of adsorbed and free gas,it can be known that increasing the confining pressure has no obvious effect on the micropore structure of low-rank coal,but it will cause the larger pores of coal to close.The increase in confining pressure leads to the closure of large pores in low-rank coals,which makes it difficult for gas flow from the cavity to enter the coal pores.The amount of adsorbed gas during the same inflation time decreases as the confining pressure increases.When the confining pressure is gradually increased from 3 MPa to 4,5,7 MPa:Within 1 hour of the initial charge of gas,the mass of adsorbed gas gradually decreases from 0.27664 g to 0.25758,0.22531,0.1827 g,and the cumulative mass of adsorbed gas is 0.51334g gradually decreased to0.48469,0.4243,0.36617g.