Multiphase flow simulation in fractional flow approach with general boundary condition considering phase configuration change in the system

Abstract

The multiphase flow simulator, MPS, is developed based on the fractional flow approach originated in the petroleum engineering literature considering the fully three phase flow with general boundary condition. The fractional flow approach employs water saturation, total liquid saturation, and total pressure as primary variables. Most existing fractional flow-based models are limited to two-phase flow and specific boundary conditions. Although there appears a number of three-phase flow models, they were mostly developed using pressures based approaches. As a result, these models require cumbersome variable-switch techniques to deal with phase appearance and disappearance. use use of fractional flow-based approaches in MPS makes it unnecessary to use variable switches to handle the change of phase configurations, because the water saturation, total liquid saturation, and total pressure exist throughout the solution domain regardless of whether certain phases are present or not. Also most existing fractional flow-based models consider only specific boundary conditions, which are usually Dirichlet type pressure for water phase, and flux type boundary for NAPL phase or particular combinations for individual phase. The present model considers general boundary conditions of most possible and plausible cases that consist of eight cases. These are the combinations of the phase pressure or phase flux of each of the three individual phases. Thus, the model's capabilities of handling general boundary conditions extend the simulators' usefulness in the field system.