MODELING OF FLOW INSTABILITY IN DEEPWATER FLOWLINES AND RISERS: A CASE STUDY OF SUBSEA OIL PRODUCTION FROM CHINGUETTI FIELD, MAURITANIA

Chinguetti a deepwater oil field development offshore Mauritania is experiencing a rapid
decline in its production that resulted to severe flow instability or slugging in flowlines
and risers of its subsea oil production system. Slugging initiates oscillations and puts field
operator in a demanding situation to manage and control flow instability.
It is crucial to have a model to describe flow instability issues in live field conditions.
Apparently, there is no applicable model to represent flow instability in deepwater
operations. Current available data that represents flow instability in flowlines and risers in
live field conditions has not been published in any literature. The available data is mostly
from laboratory controlled conditions or laboratory scale ideal condition. Model using
laboratory conditions has limited capability that cannot be used to assess severity of
slugging.
A study was undertaken in which integrated production system of the Chinguetti wells,
flowlines and risers were developed using the OLGA transient multi phase flow simulator.
Field validation was performed by tuning the models to match field pressures and phase
flowrates and instability in the systems. The impact of various changes in operating
conditions on the flow instability was examined by simulating the models that included
changes in well routings, gas lift injection rates and location of injection points, riser and
wellhead choke openings. The severity of flow instabilities for the different operating
conditions was categorized by the degree of fluctuations in liquid arrival rates and the
characteristics of its liquid slugs, length and frequency.
Results from field implementation of the recommended changes in operating conditions
indicated improvement in flow stability and oil recovery. From the study, a methodology
has been developed to assess the severity of slugging and strategies to mitigate flow
stability and productivity in the flowlines and risers ofChinguetti oil production system.