In this paper we discuss the multiple solutions of the three-phase flow model and how they can be related to the oil and water accumulation and removal for a low liquid loading case. Under certain conditions, a ramp-up of the flow rates results in the liquid being removed in three sweeps. The time scales of the three sweeps may be very different, having a huge impact on the liquid removal time. By studying a steady-state fully-developed three-phase model we explain the physics behind the liquid removal process. The validity of this steady-state fully-developed flow approximation has been checked against transient simulations of ramp-up cases using OLGA HD 2015.1. Through a Statoil sponsored experimental campaign at the SINTEF Multiphase Flow Laboratory, several transient and pseudo transient two- and three-phase experiments were performed. We have compared the experimental measurements against OLGA HD 2015.1 and the predictions are very good. The theory presented in this paper explains the liquid removal process seen in the experiments.
Multiphase flow simulation of gas-condensate-water pipeline transport with low liquid loading is a challenging task. Important properties are the pressure drop for high rates and oil/water accumulation at low rates; these factors contribute to determining the operational envelope of the field. However, the oil/water content and pressure drop are important not only at steady operating conditions, but also during transient operations such as rate changes and outlet pressure changes. The arrival time and the flow rate of the oil and water surges following ramp-up may be critical factors when designing liquid receiving and separation facilities and operational guidelines.
