DESORPTION CHARACTERISTIC CURVES OF CARBON DIOXIDE AND METHANE IN COAL AND THEIR APPLICATION

Mechanisms of adsorption and desorption of carbon dioxide and methane determine the chelation capacity of carbon dioxide in coal.How to enhance the deliverability of methane is the focus of research at present.Based on study of a large amount of adsorption/desorption isotherms and adsorption characteristic curves of methane and carbon dioxide,their mechanisms of adsorption/desorption are discussed in the context of adsorption potential,and desorption curves are concluded into 3 types:① when their adsorption/desorption curves do not intersect and the adsorption potential of carbon dioxide is equal to or larger than that of methane,intermediate pressure at which their potential values are close is unfavorable for displacing methane through injection of carbon dioxide,while both high and low pressure are favorable;② when their adsorption curves intersect due to the intersecting of adsorption/desorption curves of methane,high pressure is favorable for displacement of methane through injection of carbon dioxide;③ when their adsorption curves intersect due to the intersecting of adsorption/desorption curves of carbon dioxide,high pressure is favorable for displacement of methane through injection of carbon dioxide.These understandings have been verified by experiment of methane displacement by injecting carbon dioxide.The introduction of adsorption potential theory provides a methodology for evaluation of process parameters of displacing methane through injection of carbon dioxide and selection of favorable reservoirs.