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.