Recent advances in pore scale models for multiphase flow in porous media

In the last decade, multi‐phase flow in porous media has become a prominent topic in hydrologic research. This has been motivated by the widespread occurrence of subsurface contamination problems involving sparingly soluble liquids, often referred to as non‐aqueous phase liquids (NAPLs). NAPL contamination problems require analysis of the simultaneous movement of at least two fluid phases, NAPL and water. This is somewhat different than the traditional multiphase flow problem in hydrology, namely water movement in unsaturated soils. In the traditional treatment of unsaturated systems, the movement of air, the non‐aqueous phase, is not of interest, and its movement is ignored. Both NAPL‐water and air‐water systems are similar in that capillary forces, acting at the pore scale, usually dictate the pore‐scale distribution of each fluid phase. Pore‐scale fluid distributions then dictate the continuum‐scale properties such as relative saturation and relative permeability.