A consistent approach for applying numerical boundary conditions for multiphase subsurface flow

The partial differential equations which model multiphase subsurface flow are, in general, of mixed parabolic-hyperbolic type. A consistent and unified approach for handling a wide variety of boundary conditions under all flow conditions is presented. This method is conceptually simple, and numerically efficient. Test computations are presented which demonstrate this method for saturated-unsaturated models, and well as true three-phase simulations. Among the boundary conditions discussed are: seepage face conditions for three-phase problems and multi-node constant-rate pumping wells.