Methane replacement by using CO2/C3H8 mixtures for carbon storage and enhanced methane recovery in gas hydrates

The storage of gases via hydrates formation can be enhanced with several different techniques; for instance, the addition of promoting additives helps in reducing the pressures required for the process. However, most of strategies used for gas storage cannot help during replacement processes. This article deals with the hypothesis that the usage of moderate concentrations of small – chain hydrocarbons can absolve both the purposes at the same time. In particular CO2 storage and CH4 replacement were tested with the addition of propane. Three different concentrations of propane in mixture with carbon dioxide were selected, or 0.05, 0.10 and 0.15 mf. Hydrates were formed with each of them and the results discussed in order to identify the better solution in terms of hydrates produced and, mostly, quantity of CO2 stored. The selected concentration was then used for the replacement of methane and the results discussed in order to reveal the benefits obtained in terms of both CO2 stored and CH4 recovered, in comparison with the maximum results theoretically achievable in replacement tests carried out exclusively with pure carbon dioxide.