期刊
SCIENCE OF THE TOTAL ENVIRONMENT
卷 852, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.scitotenv.2022.158454
关键词
Methane hydrate; Molecular dynamics simulation; Hydrate formation; Seawater salinity; Pressure; Temperature
资金
- National Natural Science Foundation of China [41976203, 21506178]
- National Key Research and Development Program of China [2018YFE0126400]
- Department of Natural Resources of Guangdong Province Project [GDNRC [2020] -047]
- Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) [CUGGC09]
This study investigates the formation of CH4 hydrates in clay nanopores under the influence of marine environmental factors such as seawater salinity, pressure, and temperature. The results reveal that high salinity hinders diffusion, high pressure promotes diffusion, and high temperature causes phase separation.
In nature, CH4 hydrates are mainly buried in marine sediments. The complex marine environments on the seafloor continuously affect hydrate formation. Herein, systematic molecular simulations have been performed to investigate CH4 hydrate formation in clay nanopore, mainly affected by several marine environmental factors, including seawater salinity, pressure and temperature. Simulation results show that these factors exert different effects on hydrate formation in the nanopore and the outside bulk solutions by affecting the mass transfer and phase separation inside and outside of the nanopore. Specifically, high salinity hinders the diffusion of CH4 molecules from nanopores into the outside bulk solutions, promoting hydrate formation in nanopore and inhibiting hydrate formation in bulk solution; salinity has a dual effect on hydrate formation in the whole system by changing the local CH4 concentration via the formation of the hydration of salt ions. High pressure favors the diffusion of CH4 molecules from nanopore into outside bulk solutions, promoting hydrate formation in bulk solution and inhibiting hydrate formation in nanopore; high pressure promotes hydrate formation at the nanopore throats by increasing CH4 concentration and reducing ion concentration therein. In contrast, temperature significantly affects hydrate formation in the system by causing phase separation, i.e. high temperature promotes the aggregation of CH4 molecules to form nanobubbles and inhibits hydrate formation. Under high temperature conditions, the nanobubble in the nanopore gradually decomposes, while the nanobubble in the outside bulk solution grows an extra-large cylindrical nanobubble. These molecular insights into the formation behavior of CH4 hydrates in clay nanopores are helpful for understanding the formation process of natural gas hydrates in marine sediments and the development and utilization of CH4 hydrates.
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