Design of the Greater Plutonio Riser Tower

The Greater Plutonio Riser Tower is installed in Angola in a Water depth of 1310 meters (4300 feet), and gathers 11 risers (two production loops, three water injection, one gas injection and three gas lift lines) and one gas lift umbilical. The total mass of this unique riser system is more than 4000 tons. This paper aims at describing the main challenges associated to the Riser Tower design. After a description of the riser tower main elements (flexible jumpers, buoyancy tank, guiding frames welded to the core pipe, gas lift manifolds...), numerical analyses are presented (in place extreme and fatigue analyses). Assessment of the friction developed by the risers against the guiding frames and associated effects on the global behaviour of the riser tower are detailed. Various sources of conservatism, lessons learned and ways of improvements are also shared for future projects.