Characterization of flow topology is essential to understand the effects of heterogeneity and dimensionality of geological formations on mixing of inert solute clouds in these same geological formations. In this work, we numerically study two indicators of flow topology, the averaged vorticity magnitude |ω|_{av} and the averaged positive second invariant Q_{av} of deformation tensor ∇u, in steady Darcy flows through exponentially correlated lognormal permeability fields K. Our numerical results allow us to establish the relationships between the two indicators considered here and the permeability variance σ² in 2D and 3D, highlighting the role played by the spatial structure of these porous media on flow topology, and indirectly on mixing. This work leads us to assess the maximum dilution index E_{max}, indicator of mixing, theoretically known to increase monotonically in steady Darcy flows through isotropic heterogeneous porous media. Our numerical results allow us to test this hypothesis by establishing the relationship between the slope a of maximum dilution index E_{max} and the averaged positive second invariant Q_{av} of deformation tensor ∇u. The parameters of this relationship depend on molecular diffusion and dimensionality of problem considered.