Characteristics of CO2 hydrate formation and dissociation at different CO2-water ratios in a porous medium

Hydrate-based CO2 sequestration (HBCS) is a new concept to store a huge amount of CO2 in geological sediments in the form of crystalline solids. This technique can address several environmental challenges of the current geologic carbon sequestration approaches. This study aims to evaluate and compare the characteristics and ki-netics of CO2 hydrate formation and dissociation in the porous medium (three-phase) and bulk (two-phase) conditions at different CO2-water ratios. The experimental results indicate that the pressure drops and conse-quently hydrate nucleation and growth are limited in the porous medium due to the presence of solid particles, limited CO2 mass transfer, and heat transfer. Calculation of CO2 mass consumption and rate of gas uptake during hydrate formation also support the limited CO2 consumption and gas uptake rate in the porous medium, compared to the bulk condition. The calculated driving force for each test condition suggests its critical importance in the kinetics of CO2 hydrate formation. On the other hand, limited CO2 diffusion to the aqueous phase, hydrate nucleation at the solid-CO2-water interface, and better protection of newly formed hydrates are among the main reasons for the success of hydrate formation at the CO2-limited ratio only in the porous medium. Lastly, three steps during hydrate dissociation via thermal stimulation, such as heat transfer driving, kinetic driving, and fluid flow driving, are no longer discernable in the porous medium due to the limited heat and mass transfer during the process.