NEW ORLEANS -- A new TLP concept for ultra deepwater development was introduced on Tuesday at the Deep Offshore Technology International Conference and Exhibition in New Orleans.
The new concept, 'Pontoon-less TLP' or PLT, was introduced by SBM Atlantia in a paper prepared for the show. It enables the use of a TLP system in ultra deepwater by controlling the natural period of the system by replacing the pontoons from the hull with a rigid top-of-the column frame, which reduces the added mass of the hull and the forces on it, according to author Homayoun A. Heidari.
This reduces the natural period and heave/pitch of the hull, thereby reducing the need for additional tendon steel to adjust the stiffness, resulting in smaller dynamic tensions for the tendons, Heidari says.
A dry tree PLT is compared to a conventional (with underwater pontoons) system, both configured for 2,000 m water depth offshore Brazil. The PLT was found to save over 40% in tendon steel compared to the conventional system.
The savings are due to (1) eliminating the need for additional tendon steel to control the natural period (contrary to the conventional system); and (2) reducing the dynamic tension, therefore resulting in a TLP system that is governed by the offset (as opposed to the conventional system that is typically governed by the minimum tension for that water depth), Heidari explains.
Further work on this concept is planned to follow the current feasibility phase, including coupled hydrodynamic analysis and detailed structural design of the hull.