Pore-scale modelling of three-phase flow in mixed-wet porous media: outlet boundary conditions

摘要

Simulations with the present pore-scale network simulator have been carried out to study the effect of various outlet boundary conditions on the course of gas floods, starting at different water/oil saturations in a fractionally wet porous medium. (?) Simulated paths in systems with high phase continuity show good agreement with paths for an analytical model. As expected, agreement decreases when the continuity of one or more of the phases decreases as a result of the absence of wetting films or a lower network co-ordination number. (ⅱ) The analytical model predicts the region of saturation space where the outlet boundary conditions may have a significant effect, i.e. the region where the invading phase is so-called intermediate-wetting. (ⅲ) Implementation of varying outlet boundary differences as a result of reconnections of previously disconnected phase clusters affects paths markedly in the above-mentioned region. Reconnections require a certain lack of phase continuity, causing multiple displacements, but for low phase continuity the effect of the resulting variation in boundary conditions disappears.