Close
Client: CNR International
Location: Offshore Ivory Coast

Preventing process instability caused by slugging.

Xodus Group specialists identify the major causes of slugging in the Baobab field and provide solutions.

Challenge
The Baobab oil field lies in Block CI-40, located about 25km off the coast of Côte d’Ivoire (Ivory Coast). Water depths at the location range from 900m to 1,300m.

The field consists of producing wells and water injectors tied back to four separate subsea manifolds; two for production and two for water injection. The flow lines from these manifolds are tied back to a Floating Production Storage and Offloading (FPSO) vessel.

Operator CNR International experienced hydrodynamic slugging and severe riser based slugging (SRBS) on the FPSO causing excess flaring, compressor trips and unstable exit flows from the High Pressure (HP) separator. Five wells were shut-in due to sand problems with no immediate plans for well intervention. With anticipated declining production rates, Xodus Group were asked to analyse the operational data and solve the slugging control problems.

Assignment scope

  • Review supplied transient model against as-built data
  • Gather and screen production data for use in benchmarking subsea performance
  • Benchmark transient model for a range of operating scenarios
  • Assess suitability of transient model for extrapolation from operating conditions
  • Assess current and future operating envelopes with particular regard to slugging.

The design phase transient model of the system did not predict flow behaviour partly due to the exclusion of the slug control valve at the top of the riser. To model the response of the valve to actual flow conditions, the OLGA dynamic multiphase flow simulator transient flowline model was linked with a HYSYS Dynamics topsides model containing the slug control system and inlet separator.

The model was benchmarked against various production rates and operational modes. Consequently, the major causes of slugging were identified and solutions formulated. Future scenarios of reduced throughput were modelled and provided the client with pipeline operating envelopes that enabled the optimum operating point to be determined.

Results

  • Clear guidance on slugging mechanism
  • Supply of a fully benchmarked hydraulic model for ongoing use by CNR International
  • Clear understanding of slugging operating envelope throughout field life and at various levels of turndown.