How methane release may affect carbon dioxide storage during replacement processes in natural gas hydrate reservoirs

Methane replacement with carbon dioxide molecules in natural gas hydrate reservoirs mainly occurs in two different methods. The first is based on initial CH4 hydrate dissociation and a following CO2 hydrate formation, with all related problems for sediment deformation and so on. With the second method, the direct CO2/CH4 exchange occurs in already present cages, thus avoiding environmental problems and ensuring an exchange ratio close to 1. Because of practical difficulties in perfectly applying the second method, the initial methane release may produce a binary gaseous phase over the hydrate sediment, whose concentration may affect hydrate formation, till favouring CH4 hydrate re-formation rather than CO2 hydrate formation. The present experimental work analysed such aspect, by showing how that concentration may modify the formation trend, mainly in terms of carbon dioxide storage, and also proving the importance of thermodynamic conditions in this sense.