Pressure and multiphase flow effects on CO2 storage in hydrate-based cap: A comprehensive analysis

Abstract

CO₂ hydrate cap plays a crucial role in the long-term carbon storage in sub-marine reservoirs, and its formation is influenced by various factors, such as storage pressure and flow conditions. However, systematic investigations of the dynamic formation and stability of hydrate caps under multiphase flow process, particularly regarding the coupled effects of storage pressure and flow regimes, are still lacking. Therefore, this study explores the formation dynamics and stability behaviors of CO₂ hydrate sealing cap under varying pressures and flow rates during CO₂ single-phase and CO₂-H₂O two-phase flow. The experimental findings indicated that the hydrate cap was uniformly distributed under CO₂ single-phase flow, while a more dispersed distribution occurred in CO₂-H₂O two-phase flow, particularly at lower gas fractional flow (20∼40 %). Moreover, the formation time of the hydrate cap decreased with increasing storage pressure and CO₂ fractional flow. Notably, storage pressure had a more significant effect on rapid hydrate cap formation. Decreasing the pressure from 5 MPa to 3 MPa resulted in a formation time that was approximately 4 times longer. Furthermore, the hydrate cap formed under CO₂ single-phase flow shows greater stability than that formed under CO₂-H₂O two-phase flow. These insights offer vital guidance for developing the efficient CO₂ storage strategies in submarine environments.