Abstract
Observations in deep-water crude oil production systems have suggested that the presence of free water can have a destabilizing effect on the flow, potentially causing large variations in the flow rate and gas/liquid ratio at the outlet. These variations often cause serious operational difficulties with respect to fluid separation, and may also lead to fatigue issues in jumpers and pipe joints. These problems ultimately lead to substantial production loss because of the need for topside choking, as well as increased emissions because of gas flaring.
In this paper we present an experimental study on flow instabilities in three-phase flow in a pipeline-riser system conducted at the SINTEF Multiphase Flow Laboratory at Tiller in Norway. The purpose of the study was to obtain a better understanding of the origin of instabilities in deep-water production systems, and how free water affects these instabilities.
The experimental results show that:
• Large gas volumes upstream the riser has a strong destabilizing effect.
• The system is always stable for sufficiently low or high liquid rates, but unstable for intermediate liquid flow rates.
• The region of unstable flow is larger in three-phase flows than in two-phase flows.
• The amplitude of the pressure fluctuations is larger in three-phase flows than in two-phase flows.
The experiments were simulated using LedaFlow Slug Capturing, and the simulation results were found to be in good agreement with the experiments.