Geological structure controls CO₂ hydrate sequestration in seafloor sediments: A numerical simulation study of anticline, syncline, and inclined reservoirs

Abstract

Sequestration of CO₂ as hydrates in seafloor sediments is an effective method for reducing CO₂ emissions. However, the efficiency of CO₂ hydrate sequestration can be influenced by the geological structure of seafloor reservoirs. To address this, the authors numerically investigate the effects of four reservoir structures (horizontal, inclined, anticline, and syncline) and dip angle on CO₂ hydrate formation mass and sequestration security. The results show that different geological structures alter the temperature distribution within the reservoir, thereby modifying the stability zone of CO₂ hydrates. At a dip angle of 30°, the hydrate formation mass (F_hyd) in the inclined, anticline, and syncline structures changes by -19.12%, +6.60%, and -7.19%, respectively, relative to the horizontal structure (baseline: 342×10⁶ kg). The distance from the top of the CO₂ hydrate cap to the seafloor mudline (D_H), a key security indicator, varies significantly: Compared to 25 m in the horizontal structure, D_H changes by +160%, -20%, and +20% for the inclined, anticline, and syncline structures, respectively. As the dip angle increases, F_hyd in the anticline structure increases while D_H decreases. In contrast, F_hyd decreases and D_H increases in both the inclined and syncline structures. The temperature variation across structures is a key factor influencing F_hyd, while permeability is a major factor affecting the safety of CO₂ sequestration. Therefore, if F_hyd is the sequestration objective, the anticline structure is the optimal reservoir. If D_H is the objective, the inclined structure is the best reservoir. These findings provide critical insights for site selection in marine CO₂ hydrate sequestration projects.

Keywords

CO₂ hydrate sequestration / Geological structures / Horizontal+inclined+anticline+syncline / Numerical simulation / Structural dip angle / Phase Equilibrium zone / Sequestration capacity / Sequestration safety / Carbon neutrality / CCS

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