Hybrid buoyant riser/tension mooring system

Abstract

A buoyant hybrid riser/tension (BHRT) member moors a floating body on the sea surface to a pipeline terminated at a submerged structure. The BHRT includes one or more conduits, one or more tension members, and buoyancy. The conduits provide fluid communication from the pipeline at the submerged structure the tension member absorbs the mooring load and the buoyancy cooperates with the tension member to produce a soft restoring force for mooring the floating body to the submerged structure. The BHRT lower end connection allows angular, but not torsional displacement with respect to the submerged structure. In one arrangement of the BHRT lower end, localized flexing is allowed in the separate conductors via bend stiffeners. At the BHRT upper end, several arrangements for the connection between the BHRT and floating body are provided. In one arrangement, a rigid connection is established between a male coupler at an upper end of the BHRT and a female coupler on the floating body. In a second arrangement, the upper end of the BHRT includes a riser end buoy with a mating surface that connects with a female receptacle mounted on a bearing assembly on the floating body. On top of the female receptacle is an ESD valve block and a swivel (in one arrangement) or a manifold block (in another arrangement). The BHRT can “wind up” in torsion when the floating body weathervaning. Such wind up can be undone by temporarily releasing a brake which normally secures the female coupling to the floating vessel and allowing the BHRT and female coupling to rotate backward with respect to the floating vessel.