Hydrate Distribution and Its Effects on CO₂ Sequestration in Oceanic Muddy-Silt-Type Reservoirs

CO2 hydrate formation during the injection process in an oceanic reservoir offers extended sequestration capacity and extra sealing. However, review of the literature reveals that the role of injection strategy on hydrate distribution remains unclear. Therefore, in this work, the reservoir was rebuilt first using muddy-silt-type marine soil from the station of LW3 in the northern part of the South China Sea. Then, the characteristics of hydrate distribution in the reservoirs using water/CO2 injection mode were compared, and their effects on CO2 sequestration were analyzed. The results show that the hydrate distribution is layered and heterogeneous, with gathering away from the CO2 injection port, and the water injection mode leads to greater heterogeneity compared to the CO2 injection mode. Furthermore, during the CO2 injection process, hydrate formation occurs simultaneously in each layer of the reservoir, whereas during the water injection process, hydrate formation occurs first in the layer near the CO2 injection port. Meanwhile, the injection mode also affects the percent conversion of CO2 to hydrate, and the water injection mode results in a conversion that is twice that of the CO2 injection mode. Finally, to enhance the CO2 storage capacity, a mode of multiple CO2 injections is proposed and experimentally demonstrated to increase the total amount of CO2 stored by 28 times. The findings of this study are significantly helpful to safe and permanent CO2 sequestration in deep-sea sediment.