Abstract: A method and system for attaching a TLP to its tendons using pull-down lines to rapidly submerge the hull to installation draft while compensating for inherent hull instability during submergence and to provide motion arrest and aid in station keeping. The system includes tensioning devices mounted on the TLP, usually one for each tendon. Each tensioning device is equipped with a pull-down line which is connected to the corresponding tendon. The TLP hull is submerged to lock-off draft by applying tensions to the pull-down lines connected to the top of the tensions, or by a combination of applying tensions to the pull-down lines and ballasting the hull. As the tensioners take in pull-down line, the hull submerges, i.e. the draft increases.

Abstract: A tendon for mooring a tension leg platform having an uppermost pipe segment with a reduced diameter compared to at least one of the lower pipe segments. The tendon is watertight and sealed from the ocean environment, preferably filled with air at one atmosphere of pressure. One or more interior bulkheads may be included to divide the tendon into multiple compartments. The reduced outer diameter of the uppermost pipe segment provides reduced drag due to waves and currents and accommodates smaller tendon support buoys and vortex fairings, while the greater diameter of the lower pipe segment provides for increased tendon buoyancy.

Abstract: A central pontoon semisubmersible floating platform for use in offshore applications has a hull configuration including vertical support columns, a central pontoon structure disposed inboard of the columns at a lower end thereof, and a deck structure supported at an upper end of the columns. The vertical columns and pontoon structure are constructed substantially of flat plate. The vertical columns are adjoined to the outer periphery of the central pontoon and have a transverse cross sectional shape with a major axis oriented radially outward from a center point of the hull, and a central vertical axis disposed a distance outward from the pontoon outer periphery. Risers can be supported on the inboard or outboard side of the pontoon and extended to the deck, and the structure can be anchored by mooring lines extending along the outboard face of the columns extending radially outward and downward from their lower ends.

Abstract: A method and system for attaching a TLP to its tendons using pull-down lines to rapidly submerge the hull to installation draft while compensating for inherent hull instability during submergence and to provide motion arrest and aid in station keeping. The system includes tensioning devices mounted on the TLP, usually one for each tendon. Each tensioning device is equipped with a pull-down line which is connected to the corresponding tendon. The TLP hull is submerged to lock-off draft by applying tensions to the pull-down lines connected to the top of the tensions, or by a combination of applying tensions to the pull-down lines and ballasting the hull. As the tensioners take in pull-down line, the hull submerges, i.e. the draft increases.

Abstract: An apparatus and method for ballasting and de-ballasting a vessel having a hull with a plurality of watertight ballast compartments wherein each ballast compartment has an individual pump caisson extending vertically to the top of the hull, but the ballast/de-ballast system contains no valves within the hull. An external caisson is used to provide a source of seawater. Several submersible pumps are available for rigging into and out of the internal and external caissons and provide the ballast and de-ballast operations via an installed manifold system at the top of the columns. Venting of the ballast tanks may be accomplished through a connection to atmosphere near the top of the pump caissons.

Abstract: A method and system for attaching a TLP to its tendons using pull-down lines to rapidly submerge the hull to installation draft while compensating for inherent hull instability during submergence and to provide motion arrest and aid in station keeping. The system includes tensioning devices mounted on the TLP, usually one for each tendon. Each tensioning device is equipped with a pull-down line which is connected to the corresponding tendon. The TLP hull is submerged to lock-off draft by applying tensions to the pull-down lines connected to the top of the tensions, or by a combination of applying tensions to the pull-down lines and ballasting the hull. As the tensioners take in pull-down line, the hull submerges, i.e. the draft increases.

Abstract: A system and method for mating risers or umbilicals extending vertically or near vertically from the ocean floor to a floating offshore system such as a TLP or semi-submersible platform. The risers or umbilicals are suspended vertically above the vessel's keel and are supported laterally near the platform's keel by keel guides or riser receptacles positioned along the submerged perimeter of the vessel's hull, or within the hull by production riser slots disposed in the bottom of the hull. The keel guides or production riser slots each receive a keel joint assembly which laterally supports a riser or umbilical passing therein while providing a bearing surface for free vertical movement of the riser.

Abstract: An apparatus and method for ballasting and de-ballasting a vessel having a hull with a plurality of watertight ballast compartments wherein each ballast compartment has an individual pump caisson extending vertically to the top of the hull, but the ballast/de-ballast system contains no valves within the hull. An external caisson is used to provide a source of seawater. Several submersible pumps are available for rigging into and out of the internal and external caissons and provide the ballast and de-ballast operations via an installed manifold system at the top of the columns. Venting of the ballast tanks may be accomplished through a connection to atmosphere near the top of the pump caissons.

Abstract: A passive riser tensioner apparatus for tensioning riser pipes on floating platforms and tension leg platforms utilizes one or more elongate elastic tensioning elements connected at top and bottom ends to the upper end of a riser pipe that are capable of being axially stretched. Each tensioning element has a threaded length adjustment rod and tension preload nut at its top end which adjusts the axial length to produce a predetermined preload tension force in the tensioning element between its connection to the riser pipe. A riser support collar slidably received on the length adjustment rod and riser pipe upper end is configured to be supported on the deck of the platform and allow axial movement of the riser pipe. A tension locking nut on the length adjustment rod releasably engages the length adjustment rod with the riser support collar when it is supported on the deck.

Abstract: An offshore tension leg platform having a deck, a hull, and a plurality of elongate tendons securing the hull to an ocean floor foundation provides full well workover and production capabilities for autonomous operation and can be installed and operated in any water depth and sustains any environmental loading conditions. The hull supports well risers of well trees located below the water surface at an elevation in close proximity to the connections of the tendons to the hull. Alternatively the risers and trees may be supported above water by a deck or the trees may be located on the seabed. A workover platform supported by a perimeter trackway on the deck may be positioned over any of the well risers for workover operations. Liquid products may be exported from the platform via a pipeline or to a floating tanker. The hull is configured to minimize loadings in the tendons. All components are installed by a drilling vessel without the need for special installation vessels and equipment.

Abstract: A compact offshore tension leg platform having a deck, a hull, and a plurality of elongate tendons securing the hull to an ocean floor foundation provides full well workover and production capabilities for autonomous operation and can be installed and operated in any waterdepth and sustain any environmential loading conditions. The hull supports the well risers of well trees located below the water surface at an elevation in close proximity to the connections of the tendons to the hull. Alternatively the risers and trees may be supported by the deck. A well workover platform, supported by a circular perimeter trackway on the deck may be positioned over any of the well risers for workover operations. Liquid products may be exported from the platform via a seabed pipeline or to a floating tanker moored to a mobile offtake on the deck support column. The hull is configured to minimize loadings in the tendons.

Abstract: A system is provided for installing a drilling template in a level orientation over an ocean floor. The drilling template is supported on a plurality of preset piles. The piles extend above the ocean floor. After the piles are set, their elevations are accurately determined, and pile-receiving sockets in the drilling template are finally fabricated to have depths corresponding to the respective piles to be received therein. Once the drilling template is lowered onto the piles, it is supported in a level orientation.

Abstract: A method and apparatus for installing and tensioning mooring tethers or tendons between a subsea foundation and a tension leg platform. Load bearing porch members secured on the platform columns near the hull receive the threaded upper end of tethers which are engaged at their lower ends in the foundation. Movable hoists on the platform deck position the upper ends of the tethers on the porches. A platform arrester through which the hoist lines pass is connected with each hoist to move with the platform during vertical motions thereof and selectively engage the hoist lines to allow only downward movement of the platform arrester relative to the hoist lines. A motorized tether tensioning tool connected to each hoist line has a lock-down nut at its lower which releasably connects to the upper end of each tether such that the nut is vertically movable on the tether.

Abstract: A modular near-surface completion system that positions the production wellheads in a quiescent zone beneath significant wave activity yet within reach of divers for maintenance and inspection. Each subsea well is provided with (a) its own riser, (b) a riser tensioning buoy and (c) a production well tree mounted atop the riser buoy. Produced fluids are transmitted from the well tree to the floating production platform by means of flexible risers suspended in a catenary loop of sufficient length to permit the platform to be maneuvered to position it for drilling or workover of any of the plurality of templates it services.