Usage of a Binary CO 2 /C 3 H 8 (85/15 vol%) Mixture for Hydrate Production: The Role of the Memory Effect and Phase Boundary Conditions of the System

Since it was proposed, the replacement process, in natural gas hydrate reservoirs, has been considered as one of the most promising options to obtain an alternative and potentially carbon-neutral energy source. However, such a process shows high complexity, and its maximum efficiency cannot exceed 75% if carried out with pure carbon dioxide. The addition of minor quantities of other guest species in mixture with carbon dioxide allows higher efficiencies to be reached. This study deepens the production of hydrates with a binary mixture containing carbon dioxide and propane, with corresponding concentrations equal to 85/15 vol%. Several experiments were carried out consecutively and with the same gas–water mixture in order to ensure the system retains memory of previous formations. The results were then discussed in terms of the quantity of hydrates produced and the evolution of the formation process as a function of time. The data collected during the dissociation of hydrates were finally used to define the phase boundary of the system.