The Extendable Draft Semi-submersible (EDS) concept is a hybrid design with a truss structure fitted below a semisubmersible hull shape which provides low heave motions to enable dry tree operations. The Dry-tree concept is enhanced by the reduced heave motion characteristics of the Semisubmersible, provided by Second Tier Pontoon (STP) located below the traditional pontoons. The STP is lowered by allowing the extendable columns (e-columns) to slide through sleeves in the hull connectors during offshore installation. The base case EDS configuration is for a 2,200m water depth and consists of 16 Top Tension Risers (TTRs), reserve flexible riser and oil export Steel Catenary Riser (SCR) with a throughput capacity of 90,000 BOPD.
This paper addresses Hull In-place Global performance and E- column sleeve connector strength analysis which are carried out in compliance with DNV design criteria and 100-year extreme conditions. The global performance analysis covers the platform wet-tow, installation, and in place conditions. The four stages for the STP installation depend on the depth of the STP from the column bottom. The extendable column (e-column) and STP are held in place by steel to steel contact conical concept and the grouting is relegated to a secondary structural component if needed. DNV concluded that the evaluated EDS configuration is a feasible concept for Petrobras Offshore Ultra-Deep Water Development.
