Re-definition of the region suitable for CO2/CH4 replacement into hydrates as a function of the thermodynamic difference between CO2 hydrate formation and dissociation

The replacement of methane with a theoretically equal quantity of carbon dioxide, probably represents the most promising solution for natural gas hydrate exploitation. However, the real efficiency is far from the ideal value. This article aims to focus the attention on the thermodynamic area considered suitable for replacement. Because the formation and dissociation of hydrates always show differences between each other and, in particular, the formation always requires more severe conditions to occur, the region effectively suitable for replacement is still more narrow than what currently believed and consists of the area between the dissociation curve of methane hydrates and the formation curve of CO2 hydrates. The present hypothesis was confirmed by carrying out the replacement process both above and below this latter curve. It was found that the methane recovery was more than one order of magnitude higher in the first case: 43.32 against 4.19 vol%.