Three-dimensional modeling of three phase imbibition and drainage

This paper investigates three phase flow in water-wet porous media. From considerations of capillary equilibrium and an analysis of micromodel experiments, the pore scale displacement mechanisms are described. The stability of layers of NAPL between water and gas has an important impact upon the recovery of NAPL to low saturation. The displacement mechanisms and the effects of NAPL layers are incorporated into a three-dimensional network model. The network model calculates capillary pressure, relative permeability, and NAPL recovery. Several types of displacement are analyzed by specifying a series of changes in capillary pressure. Different capillary pressure paths result in drastically different relative permeabilities and NAPL recoveries. In ideal circumstances, the ultimate recovery of NAPL can be virtually 100%, but the recovery time is governed by flow through NAPL layers, which is shown to be very strongly influenced by the boundary condition at the fluid interfaces. The relative permeabilities and capillary pressures we calculate cannot be adequately represented by current empirical models. Copyright (C) 1996 Elsevier Science Limited.