TOP TENSIONED RISER SYSTEM DESIGN FOR THE FHSB DRY TREE SEMISUBMERSIBLE PLATFORMS

The dry tree production and drilling Top Tensioned Riser (TTR) systems have been extensively used with Tension Leg Platforms (TLPs) and Spar floaters in deepwater applications. However, the large heave response of the conventional Semisubmersible floaters makes this type of platforms not suitable for dry tree applications largely due to the ultra-long stroke tensioner that would be required in this case. The Free Hanging Solid Ballast (FHSB) Semi ([1],[2]) is an innovative new semisubmersible design that is suitable for dry tree applications due to its low heave response that is comparable to that offered by Spar floaters. The new design resembles the conventional Semisubmersibles with an added free-hanging solid ballast tank placed deep below the keel of the Semisubmersible hull and connected to the hull through four groups of chains. The Solid Ballast Tank (SBT) acts as a motion damper that significantly improves the heave motion response. In this paper, the design of the dry tree TTR system for the FHSB Semi is presented. The typical GoM's drilling and production conditions are used in designing the TTR system including the tensioning system and the interface between the SBT and the riser keel joint. The feasibility and performance of the designed TTR system are demonstrated through static and dynamic TTR analyses.