Molecular Insight Into the Replacement Behavior of CO2CH4 Hydrate in Porous Media: Implications for CH4 Recovery and CO2 Storage

ABSTRACT CO 2 replacement method is an auspicious method for the CH 4 extraction from gas hydrate and the CO 2 geological storage into sediments. The replacement of CO 2 CH 4 hydrate in porous medium system is jointly affected by many factors such as heat transfer, mass transfer, and reaction. It is of great significance to deeply understand the mechanism and dynamics of different factors influencing the replacement characteristics of CO 2 CH 4 hydrate in porous media. In this study, the molecular dynamics simulation method was employed to study the replacement characteristics and kinetic process of CO 2 CH 4 hydrate in porous medium system with varying conditions expecting to offer significant theoretical direction and a point of reference for the CO 2 replacement method of natural gas hydrate extraction in permafrost regions in reality. The quantitative influence and internal mechanism of different factors on the replacement process of CO 2 CH 4 hydrate were revealed. The results show that, in the porous medium system, when the temperature was ranged of 265–270 K and the pressure was ranged of 10–20 MPa, the replacement effect of CO 2 CH 4 hydrate is the best under the initial concentration of CO 2 of 100%. It was further indicated that the replacement effect is appropriate when the initial concentration of CO 2 was ranged of 40%–60% under the case of 265 K and 10 MPa. Moreover, the result also indicated that the effects of some certain factors, including temperature, pressure, and initial concentration of CO 2 on the replacement process of CO 2 CH 4 hydrate, exist slightly different. Owing to the adsorption effect of porous media on CO 2 molecules, it reduced the replacement efficiency between CO 2 CH 4 hydrate. Additionally, the initial concentration of CO 2 imposed a more significant influence on the replacement of CO 2 CH 4 hydrate in porous medium system considering the adsorption effect of porous. It does not mean that the higher the initial concentration of CO 2 , the better the replacement effect of hydrate. The diffusion capacity of CO 2 depends on the concentration of H 2 O molecules and the adsorption effect of porous media.