Dynamics of gravity currents in heterogeneous porous media

We numerically analyze the impact of the porous media heterogeneity in the mixing, migration and spreading of a CO2 gravity current in a saline aquifer. Heterogeneity is represented by multi-Gaussian log-permeability fields of varying correlation length and variance of the log-permeability. We characterize the dynamics of the gravity current using the quantity of buoyant mass, the scalar dissipation rate, and the mixing interface width and length. The results show that, at initial times, heterogeneity favors mixing because of increased the interface length and tortuosity. CO2 gets trapped in low permeability regions and dissolves faster due to high concentration gradients. At later times, low permeability regions prevent the formation and proliferation of fingering instabilities and mixing is similar to homogeneous media. Only for large anisotropy ratio or high variance permeability fields, we observe a more efficient mixing in heterogeneous media compared to the homogeneous media.