Abstract:
A submerged tubular tower 10 is connected at its lower end 15 to an ocean floor 11 at a site where at least one subsea hydrocarbon well is to be drilled. A riser duct 22 for each well to be drilled extends from an upwardly accessible connection point 20 at the upper end 14 of the tower to the lower end of the tower. The tower is positively buoyant to stand erect in an unguyed manner. The upper end of the tower is located a substantial distance above the ocean floor at a depth sufficiently small to enable wells to be drilled through the riser ducts, through equipment 19 landed on the top of the tower, using floating drilling equipment 12 designed for use in substantially shallower water depths.
Abstract:
A tension leg structure for use with a tension leg platform or the like to interconnect an anchor on the sea floor and platform in which the tension leg structure comprises interconnected buoyant pipe members for transmitting tension forces and for withstanding hydrostatic pressure. Each member has internal watertight bulkheads defining a buoyancy chamber. Tremie pipe extends through the bulkheads of each member and has ends terminating in a slipover coupling provided within a joint interconnecting adjacent tension buoyant members.
Abstract:
A deep draft semi submersible structure wherein the semi-submersible has a center of gravity below its center of buoyancy and the structure is a floating vessel with at least three vertically oriented buoyant columns. Each of the vertically oriented buoyant columns have at least one ballasted compartment and the columns are spaced apart at a sufficient distance to reduce vortex induced vibration amplitude. There are at least two connecting structural sealed trusses connected to the columns below sea level, they are positioned to minimize hydrodynamic wave action on the trusses and to transfer shear loads between the columns while remaining transparent to wave and ocean current motion.
Abstract:
A drilling, production and oil storage caisson for use in deep water offshore well operations in which the caisson has such a deep draft that its bottom end is subject only to minimal excitation forces caused by wave, wind and current acting on the caisson, the caisson including a plurality of oil storage compartments, a plurality of water ballast compartments above said oil storage compartments, a through axial passageway through said compartments; a riser system including a plurality of riser pipes in concentric circular arrangement within the through passageway or center well, each of the riser pipes being supported and tensioned by a buoyant flotation unit connected thereto; a drill string extending axially through said passageway between said riser pipes; and mooring lines connected to the bottom portion of the caisson extending therefrom with relatively low scope of 1:1 or less and providing a small watch circle for anchors for said mooring lines, the mooring lines being tensioned so that the mooring lines are substantially straight. A counterbalance for the drilling string includes a weighted section located near the bottom of the caisson. A deep draft caisson constructed and arranged so that heave motions are minimal.
Abstract:
A marine riser system is provided which extends between a floating offshore platform and well means in a seabed formation and which has riser end portions connected in novel manner to the floating platform and to wellhead structure at the well hole. Each end portion of the riser is adapted to yield axially, laterally, and rotatively during movement of the riser relative to the platform and to the wellhead structure. Each end portion of the riser is provided with fulcrum or pivot contacts with hawse pipe carried by the platform and with hawse pipe or casing means provided in the wellhead structure. Bending stresses at the riser end portions are reduced at the platform and at the wellhead structure.
Abstract:
Methods for developing an offshore field comprising deploying a lead drilling and production vessel to a offshore field to drill and complete at least one well. Production from the at least one well is initiated and evaluated. A secondary production vessel is selected based upon the evaluated production and is deployed to the offshore field to replace the lead drilling and production vessel and support production of the at least one well.
Abstract:
A method for making a deep draft semi-submersible drilling/production vessel having a center of gravity below its center of buoyancy by constructing a plurality of buoyant individual columns. The method connects a pair of columns with at least a first top truss and a first bottom truss. The method additionally floats a connected first and second columns horizontally in water. The method floats the semi-submersible structure to a location for installation. The method concludes by deballasting the semi-submersible structure with connected deck forming a semi submersible drilling/production vessel having a center of gravity below its center of buoyancy with a draft between 300 and 500 feet.
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:
An offshore multiple tendon compliant buoyant tower construction for well operations in which a plurality of tendons are arranged in parallel, vertical, closely spaced assembled relation and have top and bottom ends, the bottom ends being connected to a base module at the sea floor, the top ends being connected to a buoyant structure which includes conductor tubes therein for each of said tendons and which serves to restrict bending of the top portion of said tendons to provide a relatively stiff, unbending, noncompliant tendon top portion which extends below the sea surface, the portion of the assembled tendons below the stiff to portion being relatively compliant; the buoyant structure imparting tension to said plurality of assembled tendons at the top ends thereof whereby the tensioned tendons provide lowering of the effective center of gravity of the tower construction below the center of buoyancy and whereby cyclic stresses in the assembled tendons resulting from roll or bending of the tower construction is reduced.
Abstract:
A jacket tower structure for use in deep water which includes a plurality of tapering jacket sections adapted to be nested, each section including at least three jacket legs. The base and lower jacket sections include cylindrical legs interconnected by box section bracing, the upper jacket sections including cylindrical bracing. The box section bracing is connected to the legs by a unique joint for transmitting stresses to the legs. The box section bracing is floodable for equilizing hydrostatic pressure during and upon installations. Certain transverse box section bracing at ends of adjacent jacket sections include intermediate connection projections for welding during joining of adjacent jacket sections. The cylindrical legs include a plurality of water tight compartments of selected volume, each compartment having one or more check valves for admitting water into the compartments when external water pressure exceeds air pressurization of the compartments. A method of installing the jacket tower includes floating the tower, to the site, on two of the legs; rotating the tower about a longitudinal axis to submerge one leg while at least the other two are at water level and tilting the structure by flooding certain portions of the base and lower sections and continuing such tilting by automatically flooding the legs by preselected pressure conditions in the water tight compartments until the tower reaches a vertical position. Once vertical, the remaining compartments are flooded to settle the tower vertically on the sea floor.