Interdisciplinary results of an Italian research project on methane recovery and carbon dioxide storage in natural gas hydrate reservoirs

Natural gas hydrates (NGH) are found in marine sediments on continental and island slopes, in deep-water sediments of lakes and seas inland, and in polar sediment on continents and continental shelves. NGH constitute the biggest hydrocarbon resources on earth, representing a reservoir of sustainable fuel, thanks to the possibility of the so-called CO 2 -CH 4 replacement process. If CO 2 is injected into NGH sediments, it causes CH 4 release and CO 2 hydrate formation. The extraction of gas from NGH, combined with carbon capture, presents significant potential advantages in energy infrastructure and in various economic and political contexts, aligning with future green policies. This paper contributes to the advancement of knowledge by reviewing the findings of a three-year Italian research project focused on methane recovery and carbon dioxide disposal in NGH. The consortium comprises seven multidisciplinary italian partners. The paper introduces a novel process wherein the CO 2 -CH 4 replacement process is integrated with methane purification and CO 2 recirculation, which has been experimentally tested and represents a new advancement in gas hydrate science. Experimental tests at microscopic and macroscopic levels, show that the efficiency of the process strongly depends on the mutual influence among the properties of water, sediment and the involved gaseous species. Energy evaluations show that the ratio between the energy spent to complete an entire cycle of replacement and recirculation over the stored energy in the recovered methane is 17%, resulting in a beneficial energy balance, while economic analysis show that the transition could generate, even in the short term, large high-impact cash-out.