Formation kinetics and MRI visualization of CO2 hydrate with different flow conditions in porous media: Evolution prediction model of stored CO2 leakage

Concern on carbon dioxide (CO2) leakage of geological storage is the most important for global governments and the public. For the subsea scene with the greatest storage potential, possible leakage of stored CO2 can be effectively stopped through the CO2 hydrate formation. It is hence necessary to investigate the formation characteristics of CO2 hydrate, especially under different flow conditions. This study employed a magnetic resonance imaging (MRI) apparatus to observe hydrate formation at 276.15 K and 3.0 MPa. It was found that low flow rates and high water saturation (with a maximum increase in hydrate saturation of nearly 132 %) promoted the formation of CO2 hydrates. This revealed the spatial dispersion of hydrate formation in porous media that was just the most deficiency of traditional kinetic models, and hence this study took nucleation point (Nnuc) and formation amount (Nfor) into consideration for establishing a new formation kinetic model as dN/dt = r(N + Nnuc)(Nfor−N)/(Nnuc + Nfor). Correlation coefficients (standard error) with measurements from previous studies were all greater (less) than 0.96 (0.00041). In addition, r(Nnuc + Nfor) is further employed to evaluate the hydrate formation rate under different flow conditions and then quantitatively predict the minimum requirements of pore water and flow rate for CO2 hydrate formation.