Influence of reservoir properties on the dynamics of a migrating current of carbon dioxide

Storage of carbon dioxide (CO2) in saline aquifers is a promising tool to stabilize the anthropogenic CO2 emissions. At the reservoir conditions, injected CO2 is buoyant with respect to the ambient fluid (brine) and spreads as a current laterally and toward the top cap rock of the aquifer, with the potential risk of a leakage into the upper aquifer layers. However, CO2 is partially soluble in brine and the resulting mixture (CO2 + brine) is denser than both starting fluids. This heavy mixture makes the configuration unstable, producing a convective flow that enhances the dissolution of CO2. Motivated by this geophysical problem, we analyze the influence of the porous medium properties on the evolution of a buoyant current that is weakly soluble with the ambient fluid. A time-dependent large-scale model [C. W. MacMinn et al., Spreading and convective dissolution of carbon dioxide in vertically confined, horizontal aquifers, Water Resour. Res. 48, W11516 (2012)] is used to analyze the evolution of the flow. In this work, we include additional physical effects to this model, and we investigate the role of horizontal confinement, anisotropy, and dispersion of the porous layer in the dynamics of the fluid injected. The effect of anisotropy and dispersion is accounted by changing the dissolution rate of CO2 in brine, which is obtained from experiments and Darcy simulations and represents a parameter for the model. Our results reveal that while the confinement has a remarkable effect on the long-term dynamics, i.e., on the lifetime of the current, anisotropic permeability and dispersion of the medium influence mainly the short-term behavior of the flow. Finally, we outline possible implications for the CO2 sequestration process.

Automated summary

Storage of CO2 in saline aquifers for stabilizing anthropogenic emissions is promising, but poses risks of leakage. The study analyzes the influence of porous medium properties on the evolution of buoyant current behavior. Results show that horizontal confinement, anisotropy, and dispersion affect the flow dynamics, with confinement impacting long-term dynamics and anisotropy/dispersion mainly affecting short-term behavior.