High Performance Semisubmersible Design for Dry Tree Applications in Harsh Environment

The Free Hanging Solid Ballast Semisubmersible (FHSB) Semi is an innovative high performance submersible design that is suitable for the dry tree application because of its extremely low heave motion response. In this paper, the FHSB Semi has been designed to support dry tree application in the Gulf of Mexico (GoM) for similar conditions; payload, environment, water depth and number of risers such as that applied to an existing Spar platform in the GoM. Holstein Spar has been considered for this purpose. Numerical results for the semisubmersible motion response in extreme hurricane and loop current are presented in this paper. The paper also compares the FHSB Semi designs that support certain payload/number of risers in the GoM, in the North West Shelf Australia and in Brazil. Key figures from this comparison are presented in the paper. The paper includes discussions on the proposed project execution plan covering the fabrication, transportation and installation as well as the added risks and risk mitigations associated with the new semisubmersible design and execution.