Abstract: An offshore oil well riser system comprises one or more tubular conduits suspended from a floating platform and having bottom ends extending downward substantially vertically toward the sea floor. A bottom end connection and tensioning assembly is disposed at the bottom ends of the conduits and comprises a jumper for connecting the bottom end of each conduit to an associated sub-sea oil well, a weight for applying a vertical tension in the conduits, and an apparatus for constraining the bottom end of the conduits against horizontal movement, while enabling them to move freely in a vertical direction and to pivot freely at their bottom ends in response to motions of the platform on the water surface. The riser system is useful with a wide variety of floating platforms, and can be employed in either dry tree or wet tree completion systems.

Abstract: An elongated, annular hull of a floating offshore platform includes one or more segmented, helical strakes disposed on an outer peripheral surface of the hull to reduce vortex-induced vibrations resulting from water currents. The hull may comprise a single annular hull or a plurality of parallel, adjacent hulls. Each strake includes a plurality of generally rectangular segments extending substantially radially outward from the hull. Each of the segments includes a pair of spaced-apart radial stanchions supporting a generally rectangular frame to which a corresponding panel is attached. The panels have a radial width that is about 13 percent of the effective diameter of the hull. The segments are arranged in a spaced-apart, end-to-end relationship that defines a discontinuous, but generally helical band extending around the circumference of the hull from about 35 feet (11.7 m) below the mean water line of the hull to its lowermost end.

Abstract: A semi-submersible, multicolumn, deep draft, floating offshore oil and gas drilling and production platform comprises a floating hull having an adjustably buoyant base, a plurality of columns vertically upstanding from the base, and an equipment deck that is supported atop the columns when the platform is operationally deployed. Each of the columns comprises a cellular structure that includes a plurality of elongated tubes having a variety of cross-sectional shapes extending from the base to the top of the column. Each of the tubes defines one or more closed compartments. At least one of the compartments has a buoyancy that is fixed, and at least another one of the compartments has a buoyancy that is adjustable. The buoyancy of the compartments and the base can be controllably adjusted with pressurized air to provide a safer and less costly method for deploying the platform for offshore operations.

Abstract: A semi-submersible floating platform for offshore drilling and/or production of petroleum product from the seabed includes a base having a first moon pool; a plurality of vertical outer buoyancy columns extending upwardly from the base; a deck structure supported by the buoyancy columns and having a second moon pool; a central columnar buoyancy apparatus having a lower portion guided within the first moon pool and an upper portion guided within the second moon pool; and at least one vertical riser passing through the buoyancy apparatus. Each riser has a lower portion that is horizontally restrained within the buoyancy apparatus below the center of gravity thereof. In a preferred embodiment, the platform includes at least two vertical risers attached to a single buoyancy apparatus.

Abstract: In one example embodiment, a floating deep draft caisson vessel for drilling and production is provided. The vessel comprises an outer hull, wherein the outer hull has a hollow centerwell. The vessel further comprises a centerwell buoy guided within the centerwell. At least one tendon assembly secures the centerwell buoy to the sea floor and the tendon assembly is attached along essentially the centerline of the centerwell buoy.

Abstract: A semi-submersible floating platform for offshore drilling and/or production of petroleum product from the seabed includes a base having a first moon pool; a plurality of vertical outer buoyancy columns extending upwardly from the base; a deck structure supported by the buoyancy columns and having a second moon pool; a central columnar buoyancy apparatus having a lower portion guided within the first moon pool and an upper portion guided within the second moon pool; and at least one vertical riser passing through the buoyancy apparatus. Each riser has a lower portion that is horizontally restrained within the buoyancy apparatus below the center of gravity thereof. In a preferred embodiment, the platform includes at least two vertical risers attached to a single buoyancy apparatus.

Abstract: An offshore oil well riser system comprises one or more tubular conduits suspended from a floating platform and having bottom ends extending downward substantially vertically toward the sea floor. A bottom end connection and tensioning assembly is disposed at the bottom ends of the conduits and comprises a jumper for connecting the bottom end of each conduit to an associated sub-sea oil well, a weight for applying a vertical tension in the conduits, and an apparatus for constraining the bottom end of the conduits against horizontal movement, while enabling them to move freely in a vertical direction and to pivot freely at their bottom ends in response to motions of the platform on the water surface. The riser system is useful with a wide variety of floating platforms, and can be employed in either dry tree or wet tree completion systems.

Abstract: A system for establishing fluid communication between a floating body and a wellhead on the seafloor includes a rigid, self-tensioning riser for fluidly connecting the floating body and the wellhead. The riser defines a major axis extending from the floating body to the wellhead. The riser is formed with a series of pre-formed curves that absorb and release energy in response to the heave and surge of the floating-body by flexing in a direction essentially parallel to the major axis. The series of curves may be in a single plane (e.g., sinusoidal), or in multiple planes (e.g., helical).

Abstract: A floating hull for a spar-type offshore oil and gas drilling and production platform comprises a plurality of parallel tubular cells that are subdivided into compartments having a buoyancy controlled by one or both of fixed and variable ballast. The cells may be fabricated in a variety of ways and shapes and include side wall openings for admitting and discharging seawater and petroleum ballast with pumps. Fixed and/or variable ballast may be disposed on or in the cells to adjust buoyancy, trim, and stability. Lower and upper portions of the cells may extend above or below the others for trim or stability. Longitudinal recesses may be formed in an exterior peripheral surface for routing of mooring lines and piping. Stepped helical strakes can be disposed on an outer peripheral surface of the platform or some of the cells to reduce vortex-induced vibrations of the platform. Methods are described for efficient construction of the floating hull in water.

Abstract: An offshore oil well riser system that compensates for the motions of an associated floating platform comprises a vertical pipe section supported by the floating vessel and extending downward from the vessel substantially perpendicular to the sea floor, and a horizontal pipe section connected to the associated sub-sea well equipment and extending away from the equipment substantially parallel to the sea floor. A angled elbow pipe connects the horizontal pipe to the vertical pipe. At least one of the horizontal and the vertical pipes incorporates a flexing portion comprising a plurality of recurvate sections of pipe connected end-to-end with alternating curvatures. In one embodiment, the central axis of the flexing portion lies in a single plane and takes a sinusoid path. In another embodiment, the central axis of the flexing portion takes a three dimensional helical path.

Abstract: An offshore floating platform for the drilling and/or production of petroleum products from the seabed includes a production deck and a buoyancy apparatus vertically guided and restrained within the platform. The buoyancy apparatus includes a well deck on its upper surface on which are mounted at least two surface trees. At least two vertical risers are supported by the buoyancy apparatus and are attached to the well deck. Each of the risers is connected to one of the surface trees and extends down through the buoyancy apparatus for connection to a seabed wellhead. At last one tendon assembly secures the buoyancy apparatus to the seabed. The tendon assembly is constructed with at least two concentric tubular tendon elements, and it is attached to the well deck and extends along the vertical centerline of the buoyancy apparatus.

Abstract: An offshore construction system comprises a work module support vessel having a ballast-down mode, in which a deck of the vessel is submerged below the water surface, and a ballast-up mode, in which the deck is disposed above the water surface. The system further comprises an independently floatable, pontoon-supported work module carried on the deck of the support vessel. The system also includes a draw connected between the work module and the work module support vessel. The draw has a draw-over mode, in which the work module is drawn over the deck of the support vessel, and a remove mode, in which the work module is removed from the deck.