Application of an Enhanced Lazy Wave Flexible Riser System in Extreme Shallow Water with an External Turret Moored FPSO

Abstract

This paper presents the design challenges encountered in a flexible riser application with an external turret moored FSO in a shallow water depth around 55m, and the solutions obtained for an improved lazy wave flexible riser system. Extensive dynamic analyses were performed with parametric variations and a model test was also carried out to validate the predicted dynamic responses. The lazy wave flexible riser system is preferred for shallow water applications due to it being cost effective in terms of both fabrication and installation, and high reliability in operational performance. The system relies on the balance of the riser system weight and buoyancy applied, and it is required to accommodate large excursions and dynamic motions of the mono-hull vessel induced by the environmental loadings. The riser system weight varies due to pipe contents changes and heavy marine growth. When the water becomes shallower, the challenges escalate to maintain the riser system to remaining in suspension without clashing with the sea bed or vessel. An enhanced Lazy Wave Flexible Riser solution, a patented technology of BHGE, was adopted. In this technology, the ballast modules were used innovatively to maintain the configuration in suspension by automatically compensating the riser weight variation during entire service period. The paper also summarizes preliminary benefits of the improved lazy wave flexible riser technology over the potential alternative technologies for such shallow water application, for example, the traditional S configuration and the latest middle-water-jacket configuration. Both alternatives involve significant high cost in fabrication and installation.