Study on influence of coal seam water content on effect of CO2 isobaric diffusion displacing CH4

CHEN Liwei; WANG Dongjie; BIAN Le; LIU Yuan; LI Xiaohua

doi:10.12438/cst.2024-0061

Abstract：In order to study the influence of moisture on the effect of CH4 replacement by CO2 injection in coal beds,a gas-containing multi-gas replacement experimental system developed independently was used to conduct CH4 and CO2 adsorption experiments on coal with different water content.The results show that:the presence of moisture in coal does not affect the pattern of CH4 and CO2 isothermal adsorption curves and the ranking of the magnitude of the capacity of coal adsorption of CH4 and CO2;under the same adsorption equilibri-um pressure,the amount of CH4 and CO2 adsorbed gradually decreases with the increase of the water content of coal samples.Under the same adsorption equilibrium pressure,the adsorption amount of CH4 and CO2 gradually decreased with the increase of the water content of the coal samples,and the inhibition rate of CH4 adsorption by water was larger than that of CO2 adsorption by coal,which indicated that the inhibition degree of water on the adsorption of weakly adsorbable gases by coal is larger.In the experiments of CH4 replacement by CO2 injection in coal with different water contents under isobaric diffusion conditions,it was found that,under the same water content con-ditions,with the increase of adsorption equilibrium pressure,the replacement amount and replacement rate of CH4 kept increasing,while the CO2 injection ratio kept decreasing,and the replacement effect of CH4 was better,while the utilization rate of CO2 was lower.Under the same adsorption equilibrium pressure,with the increase of the water content of coal samples,the CO2 storage quantity decreased con-tinuously,and the comparison with the CH4 replacement quantity found that,under the same conditions,the storage quantity of CO2 in the coal body was always higher than the replacement quantity of CH4 when the water content of coal samples was unchanged,and the adsorp-tion equilibrium pressure was increased,the CO2 storage quantity and CH4 replacement quantity of coal samples were both enlarged,and the storage quantity of CO2 in the coal body was also always higher than the replacement amount of CH4.Under the same adsorption equi-librium pressure,with the increase of water content of coal samples,the replacement amount and rate of CH4 and CO2 injection ratio showed a decreasing trend,and the moisture inhibited the replacement of CH4 in coal by CO2,and the larger the water content of coal samples was,the worse the replacement effect was,and the higher the degree of inhibition was;the gradient of the decrease of the CO2 in-jection ratio was small,and the degree of the decrease was not obvious,and the moisture had less influence on it.The research results fur-ther improve the theoretical analysis of the factors affecting the adsorption and desorption of coal on gas,which will provide a theoretical basis for the engineering application of gas injection and extraction of coalbed methane.