Flow in Porous Media: Permeability and Displacement Patterns

Porous media represent a broad class of mesoscopically disordered materials that are important in many industrial processes, mostly involving the transport of fluids. For examples, the flow of oil and water in sedimentary rock determines the producibility of oil reservoirs; diffusion and dispersion of molecules in soil govern the spreading of both fertilizers and contaminants; chemical reactors use porous catalysts to enhance the mixing of reagents; the containment of chemical and nuclear wastes depends on the low permeability of concrete barriers. These are just a few problems familiar to our everyday lives. The study of porous media has traditionally been under the disciplines of chemical, mechanical, and petroleum engineering. Only in recent years has the field begun to attract the interest of physicists. The displacement of one fluid by another in a porous medium is now recognized as one of the archetypal systems for studying the physics of pattern formation and interface growth. Fluids transport is known to involve effects due to the microgeometry of the pores, the connectivity of the pore network, and the wetting properties of the pore surfaces. These are all fundamental scientific issues that require the understanding of the physics and chemistry associated with the porous materials. Tackling these problems requires the collaboration of scientists from many different disciplines. Although much work has been done and a great deal has been learned, many interesting and important issues remain. In an article written five years ago, I gave a pedagogical overview of some of the problems in porous media that captivated my own interest.