Numerical Simulation of Hydrate Formation in Sub-Seabed Sand Sediment to Store CO2 in the Form of Gas Hydrate

Abstract

CO2 capture and storage is a promising strategy against global warming. Although there is concern about the risk of CO2 leakage from deep saline aquifers, it is expected that leaking CO2 forms gas hydrate and this hydrate formation suppresses the CO2 leakage. When the water depth of a storage site is large: say, about 400 m or more, leaked CO2 changes its form to gas hydrate, which may block CO2 rise in the sandy seabed sediment. Therefore, hydrate formation in the sub-seabed sand sediments is one of key factors in lowering the risk of CO2 leakage and it is important to know conditions under which CO2 leakage is suppressed by hydrate formation. On the other hand, using this leakage trap mechanism, it is also possible to store CO2 in the form of gas hydrate without a cap rock in the sub-seabed geological formation. To estimate the sealing effect of CO2 hydrate against CO2 leakage beneath the seabed, it is necessary to evaluate the permeability of the stratum after CO2 hydrate forms. In this study, numerical simulations of hydrate formation in sand sediment are conducted for CO2 injected in the sub-seabed geological formation. When modelling CO2 hydrate formation, it is assumed that the hydrate forms on the CO2-water interface and on the surface of the sand particles after CO2 plume front passes by during its rise. Simulation results suggest that under the given conditions, even if the leakage rate was set to be extremely large, it was shown that the sealing effect due to the hydrate formation was expected, and the differences in hydrate formation depending on the leakage rate were also shown. From these results, it can be said that it was confirmed that the hydrate suppresses CO2 leakage depending on the selected sea area.