Mercury Injection in Porous Media: A Resistance Devil's Staircase with Percolation Geometry

Abstract
The electrical resistance of a porous material during mercury injection decreases in steps on a devil's staircase. These thermodynamically first-order steps result from the filling of pores that short a percolation cluster even though the average conductance is not described by a critical exponent. The consistency of the percolation description is supported by modeling of the devil's staircase and the gravitational influence on injection. The results raise significant questions about applications of percolation theory to the thermodynamics and kinetics of fluid displacement processes in porous media.