Molecular dynamics study of the influence of water molecular phase state on the replacement of CO2-CH4 hydrate in porous media

XM Zhang and TT Huang and T Shan and Q Yuan and SQ Yin and JP Li and QB Wu and P Zhang, JOURNAL OF MOLECULAR LIQUIDS, 391, 123401 (2023).

DOI: 10.1016/j.molliq.2023.123401

Natural gas hydrates mainly occurs in sediments and the hydrogen bond networks composed of H2O molecules have saturation and directivity. Consequently, it is necessary to understand the influence of water molecules on the replacement process of CO2-CH4 hydrate. In this work, molecular dynamics simulation method was used to study the influence of H2O molecular phase state on CH4-CO2 hydrate replacement process in porous media. The consequences indicate that at the condition of 270 K and 20 MPa, the replacement characteristics of CH4-CO2 hydrates in pure water systems are generally unaffected by the phase state of H2O molecules, whereas the replacement characteristics of CO2-CH4 hydrates are significantly affected in porous medium systems. Besides, the effects of porous medium system below freezing point on the replacement characteristics of CH4-CO2 hydrate are compared in this study. The results show that compared with pure water system, the porous medium system makes it easier to realize the replacement of CO2-CH4 hydrate. However, due to the "self-protection effect" and the adsorption of SiO2 on small molecules of gas, the replacement effect of CH4-CO2 hydrate is not satisfactory. The findings are crucial for providing a theoretical guidelines and references for the efficient extraction of natural gas hydrates in permafrost zones.

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