Three-dimensional Finger Structure of Natural Convection in Homogeneous and Heterogeneous Porous Medium

Abstract

In carbon dioxide (CO2) geological storage, dissolution of CO2 into brine aquifers has been regarded as one of the effective mechanisms for increasing the storage security against the potential risk of leakage due to buoyancy. In this study, density-driven natural convection between miscible fluids with a nonlinear density property in porous medium with homogeneous and heterogeneous layered structure is visualized three-dimensionally by means of X-ray computer tomography technology. The plastic resin particle with different average diameter has been packed stratified as a heterogeneous porous medium. When fingers pass through the interface of heterogeneous layered structure with an increasing permeability, the finger-extension velocity increases, the diameter of fingers decreases, and the concentration in fingers decreases because of the enhanced dispersion. On the other hand, when fingers pass through the interface with a decreasing permeability, the finger-extension velocity decreases, the finger diameter increases, but the concentration in fingers remains the same, which suggests that the concentration in the finger changes nonlinearly against the permeability. The development of natural convection in the layered heterogeneous structure becomes slower than that in the homogeneous structure.