Simulation and Modeling of Convective Mixing of Carbon Dioxide in Geological Formations

Abstract

We perform large-scale numerical simulations of convection in 3D porous media at Rayleigh-Darcy numbers up to o Ra = 8 × 10⁴.. To investigate the convective mixing of carbon dioxide (CO₂) in geological formations, we consider a semi-infinite domain, where the CO₂ concentration is constant at the top and no flux is prescribed at bottom. Convection begins with a diffusion-dominated phase, transitions to convection-driven solute finger growth, and ends with a shutdown stage as fingers reach the bottom boundary and the concentration in the system increases. For Ra ≥ 5 × 10³, we observe a constant-flux regime with dissolution flux stabilizing at 0.019, approximately 13% higher than in 2D estimates. Finally, we provide a simple and yet accurate physical model describing the mass of solute entering the system throughout the whole mixing process. These findings extend solutal convection insights to 3D and high-Ra, improving the reliability of tools predicting the long-term CO₂ dynamics in the subsurface.