Towards hydrate-based CO2 storage in marine environments: salinity effects in CO2-H2O binary systems

This study investigates CO2 hydrate formation in marine environments using controlled experiments in pure water, 3 wt% NaCl, and 4 wt% NaCl solutions. Gas uptake decreased from 31.51 % in pure water to 13.97 % and 5.30 % in 3 wt% and 4 wt% NaCl solutions, respectively, as well as formation density (from 19.36 kg/m3 to 8.71 kg/m3 and 3.61 kg/m3). A non-linear effect was observed wherein 4 wt% NaCl solutions with slightly higher hydrate formation than 3 wt% under certain conditions, suggesting complex interdependencies between salinity, pressure and temperature. The pressure decline rate (Delta P/Delta t) varies with pressure and salinity, demonstrating a direct correlation between formation pressure, water conditions and hydrate growth kinetics. Stability tests conducted at 65 bar in 4 wt% NaCl solutions confirmed CO2 hydrate persistence for over 10 days, reinforcing the feasibility of hydrate-based carbon sequestration in marine settings and providing critical insights for optimizing CO2 storage in deep-sea environments.