Evolution of bubbles in decomposition and replacement process of methane hydrate

YN Liu and L Zhao and S Deng and DS Bai, MOLECULAR SIMULATION, 43, 1061-1073 (2017).

DOI: 10.1080/08927022.2017.1359745

Nanobubbles have been proved to play an important role for the extraction kinetics of CH4 hydrates. Existing investigations on nanobubbles mainly focus on the hydrate melting. However, the mechanism and effect of bubble evolution during the replacement of CH4 hydrates by CO2 are still elusive. Therefore, molecular dynamics simulations on melting and replacement of CH4 hydrate are performed with the same initial system size, pressure and amount of CH4 hydrates. It is proved the two processes move layer by layer but with different features. Moreover, despite the different composition of gas phases, behaviours of nanobubbles are similar during the two processes except that the gas film is not formed during the replacement. In addition, a quantitative analysis of molecules in each nanobubble during the decomposition is conducted preliminarily. Also a remarkable effect of mixed nanobubble on the replacement is revealed based on the analysis of bubble behaviour. It is found that CH4 molecules are surrounded by some dense CO2 molecules in the mixed bubble during the replacement. Moreover, CO2 molecules in the solution can assist the bubble formation of CH4 molecules at an initial stage and prevent their further escape and reoccupation by encompassing them afterwards.

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