Leakage-driven CO₂ hydrate growth kinetics from multiphasic CO₂ unveiled by high-pressure microfluidics coupled with...

Pore-scale CO₂ hydrate growth pathways and kinetics affect the flow behavior of multiphasic CO₂, thereby controlling the efficiency and stability of CO₂ sequestration as clathrates in subsea sediments. Under subsea hydrostatic pressures, injected CO₂ exists in a gaseous or liquid phase, which results in drastically different CO₂ hydrate kinetic behavior in the pore space of sediments. In this study, a novel high-pressure microfluidic platform coupled with in situ Raman is devised to observe pore-scale CO₂ hydrate formation under two designed pressures covering multiphasic CO₂. We identify three co-existing but different CO₂ hydrate formation pathways: (a) interfacial CO₂ hydrate film inward growth wrapping CO₂ bubbles or droplets, (b) dendritic CO₂ hydrate growth into dissolved CO₂, and (c) leakage-driven CO₂ release with cascading rapid CO₂ hydrate formation. For gaseous CO₂, CO₂ hydrate film rupture triggers CO₂ leakage into the aqueous phase, which yields gas-liquid surface renewal and sustained CO₂ hydrate formation with high S_H = 24.7%. For liquid CO₂, a dense CO₂ hydrate crust suppresses CO₂ leakage, which retards interfacial mass transfer and yields relatively low S_H = 8.3%. Results of in situ Raman spectroscopy further confirms that the leakage-driven CO₂ yields rapid encaging of CO₂ into sI hydrate cages. The novel high-pressure microfluidic platform coupled with in situ Raman reveals leakage-driven CO₂ as the primary mechanism controlling CO₂ hydrate formation pathways and kinetics, offering valuable pore-scale insights for understanding CO₂ sequestration as hydrates in marine sediments.