Optimization Procedure of Steel Lazy Wave Riser Configuration for Spread Moored FPSOs in Deepwater Offshore Brazil

摘要

The interest in the application of a SCR connected to a FPSO for exploration and production in deep water, has motivated the need to carefully study this concept due to the high offsets and vertical motions imposed by the vessel at the top of the riser. Petrobras has developed through its Research Center the study of different steel riser configurations. For bow turret-moored and spread-moored FPSOs based on VLCC converted hulls, the steel lazy-wave riser (SLWR) has been considered as an adequate solution due to its structural dynamic behavior and costs when compared to other configurations. Although the SLWR furnishes acceptable results for fatigue and extreme environmental conditions, the search for the best configuration is very demanding as any changes to a geometric parameter affect its whole structural dynamic behaviour. The search for configurations that meet all the code criteria for the riser project required meticulous detail that has not always lead to the best results because the number of variables involved is quite significant. Another important aspect is the installation procedure that can also influence the final configuration. In order to reduce the engineering time in generating and analyzing several configurations, optimization tools were studied and used in association with Petrobras in-house software to help define a model that could achieve all design verification phases more easily. This paper presents the experience with the use of an optimization procedure applied to facilitate the design of a SLWR connected to a FPSO unit offshore Brazil. The process of optimization begins with a set of preliminary geometric variables and constraints that are associated with multiple objectives related to economic, construction and safety factors. The result of the optimization process is a set of feasible configurations from which, through careful selection, the "one of the best" configuration is chosen.