The Effect Of Supercritical Carbon Dioxide On Shale Adsorption

The CO₂ improve shale gas recovery which can achieve CO₂ geological storage and reduce greenhouse gas emissions.In the process of CO₂ flooding to improve shale gas recovery,the adsorption and competitive adsorption of CO₂,CH₄ and other gases in shale are involved,which has an important impact on the effect of gas displacement and the safe storage of CO₂.Under the actual reservoir conditions,CO₂ is in a supercritical state.Therefore,the analysis of the preferential adsorption characteristics of supercritical CO₂ in shale reservoir provides an important theoretical basis for improving the recovery of shale gas by CO₂ and CO₂ sequestration.In this paper,the pure CO₂ adsorption experiment is carried out by volume method under the condition of 323³53K and maximum pressure of 16MPa.The adsorption data were fitted by different equations,so that the most suitable adsorption model for supercritical CO₂ was selected.The influence of pressure and temperature on supercritical CO₂ adsorption on shale is also analyzed.Through thermodynamic equation,the isosteric adsorption heat of supercritical CO₂ for shale adsorption is between 20.68 and 25.65KJ/mol.Comparing the adsorption characteristics of CO₂ and CH₄,the selection coefficient of CO₂/CH₄ is between 2.5 and 5.6.The mixed adsorption experiments of CO₂ and CH₄ on shale were carried out by using the improved high-pressure adsorption device.The results showed that the adsorption capacity of mixed gas was between pure CO₂ and pure CH₄.The concentration of CO₂ in free gas is always lower than that in CO₂ of source gas,indicating that shale preferentially adsorbs CO₂.The separation coefficient of CO₂ is always greater than 1,and the greater the separation coefficient,the better the replacement effect.Finally,from the two aspects of adsorption capacity and CO₂partial pressure effect,we discuss the influence of supercritical CO₂ on CH₄adsorption.on shale.