In order to alleviate the world energy resources crisis,
the research
and development of natural gas hydrates has a very important economic
value and strategic significance. The CH4–CO2 replacement method can not only achieve geological storage
of carbon dioxide but also more effectively mine natural gas hydrates.
Based on molecular dynamics theory and the properties of natural gas
hydrates, this paper delves into the replacement of methane hydrate
with carbon dioxide under different temperatures, pressures, and concentrations
of ethylene glycol (EG). We established a CO2–Hydrate
model and three CO2/EG–Hydrate models with different
concentrations of EG, and we simulated the radial distribution function
(RDF), mean square displacement (MSD), and relative density distribution
of each particle in the system in different conditions. The higher
the temperature, the more unstable the methane hydrates are, and the
methane hydrates are more prone to decomposition. Compared with 280
and 290 K, the temperature of 270 K is more favorable for carbon dioxide
molecules to enter the hydrate layer and form carbon dioxide hydrates.
The changes in pressure have little impact on the decomposition of
methane hydrates, the rupture of water cages of methane hydrates,
and the number of carbon dioxide molecules entering the hydrate layer
under temperatures of 280 K and pressures of 1, 4, and 7 MPa. But
overall, a pressure of 1 MPa is more conducive for carbon dioxide
molecules to enter the hydrate layer and form carbon dioxide hydrates.
Adding EG to CO2 molecules can inhibit the decomposition
of methane hydrates. However, the higher the concentration of EG,
the faster the decomposition of methane hydrates. The degree of fracture
of the water cages in methane hydrates is greater under pure CO2 conditions. Adding EG to CO2 molecules is more
conducive for CO2 molecules to enter the hydrate layer
and form carbon dioxide hydrates. This review is of great significance
to improve the mining efficiency and CO2 storage efficiency
of the replacement of natural gas hydrates with CO2.