ABSTRACT
A system of equations for miscible displacement in porous media was constructed by considering the limiting case of immiscible flow with zero surface tension. In that construction it was shown that miscibleflow could be described by a Fokker–Plank equation. Miscible flow predicted that laboratory breakthrough curves should display systematic deviations from the expected breakthrough curves predicted by the convection diffusion theory; these deviations are early breakthrough and long tailing in the breakthrough curve. A flux equation such as diffusional flow at the molecular scale is described by a diffusion equation. It was shown that if the flow is mixed at the macroscale as well, then a megascopic description of that flow requires two coupled Fokker–Planck equations. In the case where molecular scale mixing becomes negligible, this description reduces to one Fokker–Planck equation. Of course, it is straightforward to present identical constructions for other macroscale diffusion processes occurring at the pore scale in porous media.
