Electroosmotic flow and the validity of the classical Darcy equation in silty shales

Abstract

Electroosmotic flow represents the flow of pore water through a porous medium submitted to an electrical field or an electrical current density. A model is developed to describe the coupled electric/hydraulic flow problem in silty shales. The strength of electroosmotic flow is modeled here as a function of porosity, grain shape, pH, and ionic strength of the pore water. In the case of forced flow under a pore fluid pressure gradient, electroosmosis reduces the filtration velocity. This effect can be modeled by introducing an effective or apparent permeability into the classical form of the Darcy equation. This apparent permeability can be much smaller than the intrinsic permeability and becomes very sensitive to the salinity of the pore water.