Analytical Challenges for Deepwater Flexible Riser Systems in Offshore Brazil

Luiza Ferreira, Senior Engineer, 2H Offshore

26-30 September 2018    |    Beijing, China

Abstract

Somewhat uniquely to other oil producing regions, offshore developments in Brazil typically use flexible risers connected to FPSOs, (Floating Production Storage and Offloading) vessels in water depths ranging from around 2,000m to 2,400m. Obtaining working flexible riser configurations is becoming ever more challenging due to: the quantity of risers and subsea layout used on each field, the FPSO’s geometrical limitations and hang-off balcony positioning, the ultra-deep water depths and the dynamic vessel response under harsh, multi-directional environmental conditions.

All developments require a detailed global analysis of the flexible riser configuration to achieve a thorough understanding of their complex response and to ensure that an acceptable design is obtained. A number of studies are essential, including extreme stress analysis and interference analysis in order to verify the design requirements. Whilst such analyses are commonplace for the industry, the challenging nature of the Brazilian environment demands a level of detail often neglected in other assessments, and complex behaviours such as TDP walking and sliding contact must be addressed in the analysis.

In this paper the authors aim to present an overview of the flexible riser systems used offshore Brazil and the key challenges and considerations that must be made when analysing them. This includes: wave screening, excessive effective tension at the hang-off, compression at the TDP and sag-bend, clashing between adjacent risers, TDP (Touchdown Point) walking and sliding contact.

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