Dynamics of Plume Evolution and Safety for CO 2 Hydrate Sequestration: Insights for Injection Optimization

CO 2 hydrate-based sequestration is a promising offshore carbon storage option, yet the long-term evolution of CO 2 plumes and leakage risk remain uncertain. In this study, numerical simulations were employed to investigate the long-term evolution of the CO 2 plumes. The effects of geological factors and injection parameters on vertical plume migration and hydrate formation were systematically analyzed. The proposed safety metrics─the Vertical Storage Safety Margin (VSSM) and the Stabilized-Plume Hydrate Conversion (SPHC)─were jointly used as optimization objectives to determine injection parameters via particle swarm optimization (PSO). The results indicate that CO 2 plume evolution is inherently stage-dependent, comprising (i) an injection stage dominated by injection-induced pressure differentials, (ii) a buoyant plume stage in which upward migration is governed primarily by buoyancy, and (iii) a plume stabilization stage characterized by progressive attenuation and eventual cessation of vertical plume migration. A higher geothermal gradient suppresses hydrate conversion and yields a thinner, flatter hydrate cap. Lower vertical connectivity limits upward migration and conversion, whereas higher permeability enhances late-stage “waist-shrinking” and slightly increases the stabilized migration distance. Increasing injection mass increases both migration distance and conversion, while deeper injection and longer horizontal wells reduce the conversion and flatten the plume. Particle swarm optimization identifies an optimal scheme (1.579 Mt, 260 m injection depth, 260 m horizontal length), yielding VSSM(600 yr) = 50 m and SPHC = 1.12%. This study contributes to the further development of CO 2 hydrate-based sequestration technology.