Competitive adsorption characteristics based on partial pressure and adsorption mechanism of CO2/CH4 mixture in shale pores

Abstract

• Gas partial pressure is the decisive factor under certain temperature and pore size. • Each adsorption layer of mixture gas can be explained by monolayer adsorption theory. • Appropriate timing and amount of CO 2 injection were proposed for CS-EGR technology. In the context that CS-EGR technology has received more and more attention, molecular dynamics simulation method was used to analyze the competitive adsorption characteristics and mechanism of CO 2 /CH 4 mixture in graphene-MMT heterogeneous surface pores. In the case of certain temperature and pore size, the gas partial pressure of mixture is found to be the decisive factor of the competitive adsorption behavior. It’s better to describe the competitive adsorption behavior by gas partial pressure. Langmuir equation was applied to fitting adsorption isotherm in the first adsorption layer and the second adsorption layer. The good fitting results indicate that although the competitive adsorption mechanism of CO 2 /CH 4 mixture can’t be considered as monolayer adsorption due to the existence of multiple adsorption layers, each adsorption layer can be explained by Langmuir adsorption theory. To enhance the CH 4 recovery and CO 2 storage, the appropriate timing and amount of CO 2 injection were proposed. The pressure should be reduced to as low as possible in the first pressure drawdown process, because the first pressure drawdown is obviously beneficial to CH 4 production. The Ratio should be controlled not to exceed 1.11 ∼ 1.21 when injecting CO 2 . The operation recommendations can effectively enhance the shale gas recovery and CO 2 storage and may help to optimize the design of CS-EGR technology.