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

• Published in: Journal of molecular liquids Vol. 391; p. 123401
• Main Authors: Zhang, Xuemin, Huang, Tingting, Shan, Tao, Yuan, Qing, Yin, Shaoqi, Li, Jinping, Wu, Qingbai, Zhang, Peng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2023
• Subjects: H2O molecular phase; Molecular dynamics; Porous media; Replacement characteristics; Porous media; Molecular dynamics; H2O molecular phase; Replacement characteristics
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2023.123401

•Point out the effect of the phase state of H2O molecules on the displacement characteristics of CO2–CH4 hydrate in porous medium system.•Point out the effect of the phase state of H2O molecules on the displacement characteristics of CO2–CH4 hydrate in pure water system.•Point out the synergistic mechanism of CO2–CH4 hydrate displacement between the porous medium and H2O molecules.•The shortcomings of MD simulation of CO2–CH4 hydrate replacement process in porous media and the future development direction are pointed out. 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.