Carbon dioxide hydrate kinetics in porous media with and without salts

Highlights: • CO₂ hydrate formation and dissociation kinetics in pure and saline water in porous media. • Slightly lower water conversion to hydrate in presence of salts compared to pure water. • Dissociation investigated at two different temperature driving forces of 4 K and 10 K. • Presence of salts did not impact the kinetics of CO₂ hydrate formation in porous media. - Abstract: Large amounts of methane (CH₄) exist in the earth in the form of natural gas hydrates, an ice-like substance with guest gas molecules trapped within. One proposed method to recover methane from marine natural gas hydrates is to sequester carbon dioxide (CO₂) as hydrates and produce methane. Fundamental understanding of CO₂ hydrate in marine environments – the formation and dissociation behavior needs to be understood first in order to develop techniques to facilitate the exchange process. In this study, CO₂ hydrate formation and dissociation was studied in Toyoura sand (100–500 μm), pure water, saltwater of 1.5 wt%, 3 wt% and natural seawater at formation pressure of 3.5 MPa and driving force of 1.5 MPa. Slightly lower water conversions to hydrate were observed when comparing pure water to saline water, though initial gas uptake in saline water was higher than that in pure water. Multiple nucleation was observed in pure water systems, possibly explaining a slightly higher rate of gas uptake after extended periods of time. Dissociation behavior was investigated at two different temperature driving forces of 4 K and 10 K. The presence of NaCl might have a slight impact on dissociation kinetics, causing slightly quicker dissociation than in pure water systems at the lower driving force of 4 K. We did not observe evidence of kinetic inhibition during hydrate formation due to the presence of NaCl but as expected, we observed thermodynamic inhibition.