Adsorption Characteristics Of CH₄ And CO₂ On Shale And Property Change Of Shale Gas Reservoir Caused By CO₂ Injection

Under the double pressure of natural gas energy shortages and increasingly severe natural disasters and social harm caused by the emission of greenhouse gases which are composed mostly of carbon dioxide,enhanced shale gas recovery and CO₂ storage in geological reservoirs by CO₂ injection into low permeability shale reservoir which has the similar occurrence mechanism to that of coalbed methane are hopefully to be met through competitive adsorption mechanism because of the different sorption capacity of gases on shale consulting the theoretical research achievement of enhanced coalbed methane recovery?CO₂-ECBM?and CO₂ storage in geological reservoirs by CO₂ injection into coalbed reservoir.However,the scientific issues that are related to enhanced shale gas recovery by CO₂ injection such as how CO₂ enhances shale gas recovery through competitive adsorption and how CO₂ affects the shale reservoir property and so on need to be solved urgently.Scientific investigation and answer will provide theoretical basis and scientific guidance for enhanced shale gas recovery by CO₂ injection and will make significant contributions to green utilization and effective exploitation of shale gas resource and environmental protection.Therefore,from the view of adsorption characteristics of shale,the adsorption characteristics of pure CH₄,CO₂ and their mixtures on shale are studied using manometric method at 50? and pressures up to 5MPa.Then reservoir property change caused by CO₂ injection is investigated through permeability measurements.The main results obtained from this study are as following:1.The results show that the preferential adsorption of CO₂ on shale is observed for pure CH₄,CO₂.However,the preferential adsorption of CH₄ is observed in the process of adsorption and preferential adsorption of CO₂ occures in the process of desorption for CH₄ and CO₂ mixtures.Whether CH₄ is adsorbed on shale in advance has no effect on the adsorption characteristics of CH₄ and CO₂ mixtures on shale.2.Enhanced shale gas recovery depends on the process of CH₄ and CO₂ mixtures desorption other than their adsorption process.Although CH₄ is not replaced by CO₂ and adsorbed more instead during the process of adsorption?whether or not CH₄ is adsorbed on shle in advance?,desorption of CH₄ is accelerated eventually taking advantage of preferential adsorption of CO₂ during the process of CH₄ and CO₂ mixtures desorption,and shale gas recovery is enhanced in the end.3.By comparing the results of GRI permeability measurements using CH₄ and CO₂,separately,no obvious influence on shale permeability is observed by CO₂ injection.So CO₂ injection will not induce differential swelling of shale.