Investigating CO2–N2 phase behavior for enhanced hydrate-based CO2 sequestration

Storing CO2 in underwater sand sediments as hydrates offers vast capacity and minimal leakage risk. But direct CO2 injection can clog the surrounding area, reducing the flow. One solution is injecting CO2–N2 mixtures. This study investigated the movement and transformation of this gas mixture, with a focus on the formation rates and main factors of hydrate-based CO2 storage. Results revealed two distinct gas seepage-phase transition processes. In freshwater conditions, there was an initial temperature spike followed by localized hydrate formation, which then spread outward. In memory water, multiple hydrate formations occurred simultaneously. Freshwater conditions led to more blockages due to the concentration of hydrates, while the memory conditions maintained better flow due to more evenly distributed hydrates. Gas composition analysis showed that as CO2-rich hydrates formed, the CO2 level in the flowing gas dropped, which could stop further hydrate formation. This finding indicates that mixed gas injections could prevent excessive hydrate formations and maintain flow. The saturation of hydrates varied between 10 % and 50 %, with differences attributed to the unpredictable nature of initial hydrate formation. Overall, this research will guide efforts to optimize CO2 storage as hydrates and re-evaluate the viability and safety of this storage method using CO2–N2 mixtures.