Study On The Replacement Effect Of CO₂ On CH₄ In Coal Based On Equal Injection Condition

In this paper,the characteristics and differences of CH₄ in equal volume of CO₂replacement coal were studied.First,the adsorption experiments of coal on CH₄ and CO₂were carried out,and the law of gas adsorption between different metamorphic grade coal was studied.On this basis,the replacement CH₄ experiment of the injected CO₂ under different gas injection conditions was carried out,and the replacement law and the replacement effect were analyzed.The isothermal adsorption experiments of CH₄ and CO₂ were carried out in anthracite coal,lean coal and gas-fat coals.The experimental results show that the adsorption volume of CH₄ and CO₂ increases with the increase of adsorption equilibrium pressure in the same metamorphic grade coal,and the adsorption volume of CO₂ in coal is larger than the adsorption volume of CH₄;the adsorption volume of CH₄ and CO₂increases with the increase of the degree of coal metamorphism under the same adsorption equilibrium pressure.This research lays the foundation for gas injection replacement experiments.In this paper,the method of controlling the volume of injection was used to inject the same volume of gas under the conditions of isobaric diffusion and high pressure gas injection to carry out displacement experiments.The results show that CH₄ replacement volume of increases with the increase of the CO₂ replacement pressure or the increase of the degree of metamorphism of coal.With the increase of coal metamorphism degree,CH₄ replacement rate and CO₂ replacement efficiency increased under the conditions of isobaric diffusion and high pressure gas injection.However,in the same metamorphic grade coal,there are different rules for CH₄ replacement rate and CO₂ replacement efficiency under isobaric diffusion and high pressure gas injection conditions.That is,with the increase of CO₂ replacement pressure,the CH₄ replacement rate increased and the CO₂ replacement efficiency decreased under isobaric diffusion;CH₄ replacement rate and CO₂ replacement efficiency increased under high pressure gas injection.The difference between replacement rate and replacement efficiency under the two conditions is mainly affected by the change of cavity pressure,the difference of free space volume and the adsorption of gas in coal.The results of isobaric diffusion and high pressure gas injection show that isobaric diffusion replacement effect is better than high pressure gas injection in low pressure stage,and the effect of high pressure gas injection is better than that of isobaric diffusion with the increase of pressure.As isobaric diffusion to enhance the replacement effect is to reduce the CO₂ replacement efficiency of the cost,and high pressure gas injection in the high-pressure stage by raising the pressure to enhance the replacement effect is not significant,indicating that the pressure is not the greater the higher.The guidance of the study on practical application is to balance the relationship between gas injection volume and replacement effect,and save resources under the control gas.In addition,the change of pressure in low metamorphic grade coal is better.