Interaction Between Flexible Risers and Mooring Lines within a Floating Production System

Abstract

ABSTRACT In any semisubmersible-type or turret-moored tanker-type floating production system (FPS) it is essential to consider interaction between the flexible riser system and mooring system or anchor spread. This is necessary in order to ensure that there is adequate clearance between mooring lines and the closest riser at all depths and that cross-over of lines is avoided. This is a particular problem in supergiant fields utilising many flexible risers, for example the large Campos Basin fields offshore Brasil. Furthermore, a quantitative evaluation of the total dynamic load imposed on the vessel due to the riser system is required for assessment of station keeping and stability and for structural design. This paper demonstrates simultaneous dynamic analysis of flexible riser and mooring systems for a complete FPS. The FPS studied uses a semisubmersible type vessel located in deep water. The vessel is kept on station using a 12-point mooring system. The riser system utilises flexible pipe technology and all risers are designed using a "lazy wave" configuration. The system is subjected to both operational and extreme wave conditions. The effect of variable current direction with depth, which is common offshore Brasil, is demonstrated. The coupled effect of pipe-seabed friction is also demonstrated.