Phase Switching Algorithm for Slug Flows in Wellbores

Well test data might update reservoir model to precise reserves evaluation and field development plan. We consider the cases of gas-liquid flows in a deviated borehole. In order to evaluate the properties of reservoir, one has to be able to filter out the non-linear input of trajectory. Particularly the wellbore flow may have pulses and phase change even under constant reservoir inflow. The evaluation of well tests demands the development of fast and robust numerical techniques for modelling capabilities. The study presents a multi-fluid model and its implementation using the Jacobian-Free Newton-Krylov method. The fully implicit formulation framework described in this work enables to efficiently solve governing fluid flow equations. A reduction of a multi-fluid model in zones of phase disappearance is based on the phase state distribution over the cells. The numerical method implement a novel phase switching algorithm when the single phase cells and multiphase cells are distinguished by solving reduced set of governing equations. A transient two-fluid model is used to verify and validate the phase switching algorithm for conditions of terrain-induced slug flow regime. The algorithm results are in a good quantitative agreement with other multi-fluid simulator, experimental data and well tests.