New Approach for Assessment of Flexible Risers Interference in Shallow Waters

Event:
OMAE
Date:
June 2013
Author:
R. Alvim -2H E. Ribeiro, E. Labanca -OGX O. Veras -INSEAD

This paper presents a methodology to analyze the risers interference connected to an FPSO, which is using turret moored system in shallow water.
It is not feasible in shallow water to use riser free hanging catenary configurations, since there is not enough length in order to dissipate FPSO dynamic response due to wave action, which can cause riser damage at TDP. Furthermore, FPSO static offset is very large, around 30% of water depth, when it is compared with deep water, around 11-12% of water depth.
In order to become feasible a large number of risers connected to a FPSO using a turret moored system in shallow water are needed to use compliant configurations, such as: lazy wave, pliant wave and Lazy S.
As mentioned above risers compliant configurations are capable to avoid riser damage at TDP, but they present a large lateral motion. Thus, riser interference becomes a critical issue to be overcome.
As the applicable standards and rules are not entirely prescriptive about this issue, the riser analyst usually have to adopt independent criteria, such as load cases, internal fluid density, hydrodynamic coefficient considering or not wake effect and clashing criteria (allowable, partially allowable or not). Therefore, the proposed methodology is very robust and was used at FEED studies for FPSO OSX-2/3, both belong to OGX, which are planning to install them at the ending of 2013 in Campos Basin, offshore Brazil.

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