Hydrate-based CO2 sequestration is a novel approach that can not only realize permanent CO2 sequestration but can also form an artificial cap to prevent its upward migration. In this work, a self-developed large-scale 3D apparatus was employed to investigate hydrate formation characteristics in hydrate-based CO2 sequestration at a constant liquid CO2 injection rate through a vertical well for the first time. Temperature and pressure evolutions in the sediment were analyzed in detail. Key indicators, including cumulative sequestered CO2, CO2 in hydrate and liquid phases, the instantaneous hydrate conversion, and liquid CO2 retention rates, were calculated. The results show that hydrate continuously forms with increased CO2 injection and exhibits strong heterogeneity due to the variation in hydrate formation rate and quantity. Severe liquid CO2 heterogeneous figuring phenomena occur since hydrate deteriorates the effective pore structure and topology, resulting in relatively small cumulative sequestered CO2 when a large amount of CO2 is released from the outlet. Meanwhile, the instantaneous hydrate conversion and liquid CO2 retention rates have large fluctuations owing to water consumption and variation in the effective contact area between liquid CO2 and water. However, hydrate formation does not cause blockage of wellbore and formation nearby under given experimental conditions, which is beneficial for hydrate formation in deeper sediment. This study provides insights into hydrate formation and liquid CO2 immigration regularity during hydrate-based CO2 sequestration and demonstrates its feasibility at a field scale.
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