Abstract: A marine riser system is connected through flowlines and a moonpool plug assembly to a marine vessel. The moonpool plug assembly, when removed from the marine vessel, maintains a fully submerged position due to its having a buoyancy which is less than the net weight of the flowlines to which it is connected.

Abstract: An offshore process vessel is described for connecting service and production hoses to a deepwater production riser system and for performing subsea maintenance thereon without major equipment support. The vessel has a pair of longitudinally aligned moonpools, a derrick above the forward moonpool, a rotary powered turret within the aft moonpool, and tension-maintaining assemblies for terminal hoses in combination with a rotary fluid transfer system for transferring production fluids, electrical power, hydraulic power, and control signals across a rotating interface between the vessel and a flowline bundle of the service and production hoses. The turret supports a coaxially disposed and selectively ejectable plug through which the service and production hoses pass. These hoses are joined together in a linear array along the length of the flowline bundle which hangs as a catenary from the plug while being attached to the riser system.

Abstract: A rotary transfer subsystem is described for transferring production fluids, electrical power, hydraulic power, and control signals across a rotating interface between an offshore process vessel and a flowline bundle of service hoses and high-pressure hoses which are connected to a deepwater production riser system. Tensioning devices are also described for maintaining a selected tension on terminal hoses between the interface and the vessel while the vessel weathervanes during maintenance of position in a watch circle above the riser system. The subsystem and the tensioning devices are mounted on the vessel which is equipped with a powered turret within a circular moonpool and is capable of performing most subsea service functions on the riser system without major equipment support.

Abstract: A marine compliant riser system is provided for attaching a flexible flowline to a buoyed conduit riser section. The improved system includes a yoke assembly for receiving flexible flowline with a means for retaining a terminal portion of the flexible flowline at a substantially normal catenary departure angle. Support means are mounted at the top of the buoyed section, and gooseneck connection means mounted on the support means for establishing fluid communication between the flexible flowline and conduit in the buoyed riser section.An installation method is disclosed for completing the improved riser system in deepwater.

Abstract: A marine compliant riser system is provided for attaching a flexible flowline to a buoyed conduit riser section. The improved system includes a releasable yoke assembly for receiving flexible flowline with a means for holding flexible flowline termination.Quick-disconnect yoke attachment means support and lock the yoke assembly onto horizontal buoy-mounted support means. A fail-safe release means is provided for pulling an unreleased yoke attachment away from the support arm in the event of an opposite end release.The system is particularly adapted for emergency disconnect of a subsea wellhead or production gathering system from a floating vessel.

Abstract: A marine compliant riser system connects a subsea hydrocarbon source to a floating surface facility through a lower multi-conduit riser section to a submerged buoy section located below a turbulent water zone and a flexible flowline. Fluid connection is established between corresponding lower riser conduits and the surface facility by a plurality of flexible conduits. Connection assembly means connects individual upwardly-directed flexible conduits with corresponding upwardly-directed lower riser conduits in fluid flow relationship. A yoke assembly mounted on the buoy section, includes beam means for holding a plurality of spaced apart flexible conduit terminations, with each of the flexible conduits being connected individually in catenary arrangement between the yoke assembly and the surface facility. The flexible conduits are attached to the surface facility in compact, non-linear array and to the yoke assembly in substantially linear array.

Abstract: A marine compliant riser system is provided for attaching a flexible flowline to a buoyed conduit riser section. The improved system includes a novel yoke assembly for receiving flexible flowline with a means for retaining a terminal portion of the flexible flowline at a substantially vertical catenary departure angle. Pivotally-mounted loading gates or a yoke beam support the flexible flowlines during installation and/or replacement on the yoke. Connection means are mounted on the buoy section for establishing fluid communication between the flexible flowline and conduit at the buoyed riser section.An installation method is disclosed for completing the improved riser system in deepwater. This system is particularly adapted for oil and gas flowlines, service lines, hydraulic control and electrical conduits for connecting a subsea wellhead or production gathering eqiupment to a surface facility.