Technical Paper: Flow Instability in Deepwater Flowlines and Risers - A Case Study of Subsea Oil Production from Chinguetti Field, Mauritania

Society: SPE
Paper Number: 133188
Presentation Date: 2010
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The Chinguetti field located west of the Mauritania coastline has recently experienced a slugging condition in its flowline and riser systems. A study was undertaken in which integrated production system models of Chinguetti wells, flowlines and risers were developed using OLGA® transient multiphase flow simulator. The field is at a water depth of ~800m and was developed with subsea wells, manifolds, 2 flexible flowlines and lazy “S” shaped risers tied back to a permanently moored turret Floating Production Storage Offloading (FPSO) located 6km away from the furthest drill centre. The main objective of the study was to assess slugging and potential methods to improve flow stability in the Chinguetti systems.

An extensive field validation and benchmarking exercise was performed by tuning the models to match field pressures and phase flowrates in the systems. The goal was to validate the models as closely imitating the conditions in the field. However, uncertainties in the field data made it difficult to reach satisfactory results in the benchmarking exercise. Simulations were then performed to examine the impact of various changes in operating conditions on flow instability. These included changes in well routings, gas lift injection rates and location of injection points, riser and wellhead choke openings. The degree of fluctuations in liquid arrival rates and the characteristics of liquid slugs (length and frequency) were used to categorize the severity of flow instabilities for a range of operating conditions.

Results from field implementation of recommended changes in operating conditions indicated improvement in flow stability. The success of this study was found to be dependent not only upon the inputs and assumptions made in the production system models but also on the outcome of the field validation exercises, and the understanding of pertinent governing factors influencing slugging behavior. The study highlights the methodology and analysis used to assess flow instability, outcome of field implementation, challenges faced and solutions proposed to minimize the flow instability of a deepwater oil field development.

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