Drift-flux modeling of two-phase flow in wellbores

Drift-flux modeling techniques are commonly used to represent two- and three-phase flow in pipes and wellbores. Unlike mechanistic models, drift-flux models are continuous, differentiable, and relatively fast to compute, so they are well suited for use in wellbore flow models within reservoir simulators. Drift-flux models require a number of empirical parameters. Most of the parameters used in current simulators were determined from experiments in small-diameter (2 in. or less) pipes. These parameters may not be directly applicable to flow in wellbores or surface facilities, however, because the flow mechanisms in small pipes can differ qualitatively from those in large pipes. In order to evaluate and extend current drift-flux models, an extensive experimental program was initiated. The experiments entailed measurement of water/gas, oil/ water, and oil/water/gas flows in a 15-cm-diameter, 11-m-long plexiglass pipe at eight deviations ranging from vertical to slightly downward. In this paper, these experimental data are used to determine drift-flux parameters for steady-state two-phase flows of water/gas and oil/water in large-diameter pipes at inclinations ranging from vertical to near-horizontal. The parameters are determined using an optimization technique that minimizes the difference between experimental and model predictions for phase in-situ volume fraction. It is shown that the optimized parameters provide considerably better agreement with the experimental data than do the existing default parameters.