Method for installing riser/tendon for heave-restrained platform

Abstract

A Heave-Restrained Platform and Drilling System (HRP/DS) comprises a floating structure having a central buoyance means, at least three out-rigger columns, and a hybrid mooring system in which a spread (lateral) mooring system functions with an array of tensioned production risers (serving as a vertical tension leg) to keep the structure generally over a specified seabed location. The central buoyancy means has supports for upper terminations of a plurality of well production risers. Each riser is comprised of plural concentric tubular structural and pressure containment elements connecting a hydrocarbon well on the sea floor with a pressure containment means located on the floating structure. The risers are connected to the wells on the floor of the body of water upon which the floating structure floats at a locus generally directly below the floating structure, and are connected on the upper end to the floating structure, preferably below the surface of the water and below the center of effective mass of the floating structure, to the central buoyancy means under sufficient tension to function also as tendons to restrain heave of the flaoting structure. An array of at least three lateral mooring lines is attached to the peripheral columns of the floating structure and to the floor of the body of water laterally outwardly of the risers and under sufficient tension to maintain the floating structure generally on horizontal location.