Abstract: The invention is a subsea pump that includes pumping elements, each pumping element including a pressure vessel with a first and a second chamber therein and a separating member disposed between the first and second chambers. The first and second chambers are hydraulically connected to receive and discharge a hydraulic fluid and a drilling fluid, respectively. The separating member moves within the pressure vessel in response to a pressure differential between the first and second chambers. A hydraulic power supply is arranged to pump the hydraulic fluid to the first chamber of each of the pumping elements. A valve assembly is hydraulically coupled to the first chambers of the plurality of pumping elements and to the hydraulic power supply. Volume measurement devices are arranged to measure volumes of each of the first chambers and the second chambers.

Abstract: A buoyancy system for a deep water floating platform includes at least one composite buoyancy module coupled to the a riser having a length greater than 1000 feet and an associated weight. The composite buoyancy module is sized to have a volume to produce a buoyancy force at least as great as the weight of the riser. The composite buoyancy module may include a vessel with a composite vessel wall. The buoyancy module or vessel may have a non-circular cross-section defining an area which is greater than approximately 79 percent of an area defined by a square with sides tangent to the vessel wall to maximize buoyancy. A second buoyancy module may be directly coupled to the first buoyancy module to achieve a desired buoyancy.

Abstract: The present invention relates to a bottom-to-surface link system for an underwater pipe installed at great depth, the system comprising: firstly a vertical tower constituted by at least one float (5, 14) associated with an anchor system (6, 8, 16) and carrying at least one vertical riser (9, 15) suitable for going down to the sea bed (18); and secondly at least one link pipe (4, 3) extending from said float (5, 14) to a surface support (1). According to the invention, said link pipe is a riser whose wall is constituted by a rigid steel tube, and said float (5, 14) is installed at a depth situated below the last thermocline (29).

Abstract: A drilling unit comprises a floating drilling rig, a subsea wellhead, and a riser connecting the subsea drilling rig with the subsea wellhead. A floatation collar encircles the riser so as to reduce deck load on the floating drilling rig. The floatation collar comprises a hollow fabric body filled with gas. The floatation collar has a longitudinal axia and is formed from a sidewall body having a longitudinally extending slit extending through the sidewall body. The slit enables the floatation collar to be transversely mounted onto the marine riser.

Abstract: Two types of isolation tools are disclosed for installation between the upward end of the LMRP and the lower end of a riser string in the drilling of a subsea well using dual gradient techniques, one of which is especially adapted for rotation about a rotating drill sling. Each type includes insert packer adapted to be closed about the drill string to divert drilling fluid in the annulus between the drill string and the subsea wellhead into lines extending along the side of the riser to the surface. The insert is selectively removable to permit conventional drilling.

Abstract: A buoyancy system for a deep water floating platform includes at least one composite buoyancy module coupled to a riser. The module includes an elongate vessel with a vessel wall, and upper and lower ends. The vessel is attached to the riser, vertically oriented, and submerged under a surface of water such that the upper end is disposed at a lower water pressure, and the lower end at a higher water pressure. The vessel wall has a thickness that varies from a thinner wall thickness at the lower end to a thicker wall thickness at the upper end. The vessel may be internally pressurized with air such that an internal air pressure of the vessel substantially equals the higher water pressure at the lower end of the vessel resulting in a lower pressure differential at the lower end with the thinner wall thickness and a higher pressure differential at the top end with the thicker wall thickness. The module is sized to have a volume to produce a buoyancy force at least as great as the weight of the riser.

Abstract: Smooth buoyancy cylindrical elements having a surface roughness coefficient of K/D less than or equal to 1×10−4, where K is the average peak-to-trough roughness and D is the effective outside diameter of said the cylindrical element are affixed about marine elements to decrease vortex induced vibration, thereby decreasing stress and loading on the marine elements.

Abstract: A buoyancy system for a deep water floating platform includes at least one buoyancy module coupled to the a riser. The module may be coupled to a ring structure of an end cap coupled to the riser, or two modules may be coupled to a ring structure to couple them together. The modules have an interior flange extending into the interior cavity and abutting the ring structure. Fasteners couple the interior flange of the module to the ring structure to form an interior attachment. A seal may be formed between the flange of the buoyancy module and the ring structure, and may include a seal member disposed in a groove. A test port extends to the groove to allow testing of the seal. The module may include a material and may have a thickness that together allow a wall of the buoyancy module to expand outwardly under an internal pressure and force the flange against the ring structure to enhance sealing between the flange and ring structure.

Abstract: For a spar type floating platform having risers passing vertically through the center well of a spar hull, there is provided apparatus for supporting the risers from a gimbaled table supported above the top of the spar hull. The table flexibly is supported by a plurality of non-linear springs attached to the top of the spar hull. The non-linear springs compliantly constrain the table rotationally so that the table is allowed a limited degree of rotational movement with respect to the spar hull in response to wind and current induced environmental loads. Larger capacity non-linear springs are located near the center of the table for supporting the majority of the riser tension, and smaller capacity non-linear springs are located near the perimeter of the table for controlling the rotational stiffness of the table. The riser support table comprises a grid of interconnected beams having openings therebetween through which the risers pass.

Abstract: An installation for producing oil from an off-shore deposit has a semi-submersible platform, at least one riser connecting the platform to the sea bed, and devices for tensioning the riser. The tensioning devices include, for each riser, at least one submerged float connected to a point on the main run of the riser for hauling it towards the surface, and a mechanism for hauling the riser. The mechanism is installed on the platform and applied to the top end of the riser.

Abstract: A large bore Christmas tree includes a production outlet that is split into multiple separate outlets, each controlled by a separate, standard sized valve and valve actuator.

Abstract: A mounting system for supporting elongate, metallic structural members used in offshore applications and subject to dynamic forces comprising a support assembly having a socket that at least partially encircles the structural member, an attachment for securing the support assembly to a positioned structure, such as an offshore platform, and a sleeve received in the socket, the sleeve being disposed in surrounding relationship to the structural member and comprising an electrically nonconductive, fiber-reinforced polymer composite.

Abstract: A marine riser has couplings with screw-threads for securing marine riser sections together, and a carousel mechanism for coupling auxiliary lines to the marine riser sections at various locations along the sections to permit the lines to rotate freely relative to the marine riser sections as the sections are rotatably assembled. The marine riser also has a buoyancy module which houses choke and kill lines in buoyancy module fairing portions.

Abstract: A riser for drilling with a subsea wellhead and a method for adjusting the boyancy of a pipe. The riser includes tubular elements (1) linked together by connecting devices (2). The elements include a floating device consisting of a box (6) in which a determined volume of gas can be pumped so as to modify the apparent weight of the element in the water. At least one tubular element comprises detectors (12) for measuring the differential pressure between the inside and the outside of the box, a value device (14) for filling the box with gas, a bleed valve device (15) for discharging the gas from the box, a control transmission and reception unit (13) for controlling the filling valve device and the discharge bleed valve device considering the differential pressure measurement.

Abstract: An apparatus for rapid venting of the compressed air and deballasting of a buoyant air tank in a positively buoyant riser system in the event of a premature drive off or a riser section parting is shown. The buoyancy tank or housing includes an annularly shaped flange positioned on its upper end and retained by explosive bolts. The inner circumference of the flange is sealed to the riser section supported by the buoyancy housing. A sensing means, activated by a parting of the riser, actuates the explosive bolts to release the annularly shaped flange and flood the buoyancy housing while restraining lines limit movement of the buoyancy housing with respect to the riser section.

Abstract: Pipe for great water depths allowing transfer of a fluid between a floating support (1) and a point situated below and at a distance from the water surface, characterized in that it comprises:

Abstract: This application discloses a method of extracting hydrocarbons from a submarine well, which is characterized in that a displacement fluid, e.g. water, is injected under pressure into the submarine well, or into a reservoir connected to the submarine well, from a submerged buoy or from a submerged part of a buoy. Typically, the injection fluid is rawwater. A buoy is also disclosed which comprises an upper section (2) arranged to extend above the sea level; and a lower, submerged section (1), characterized in that the lower, submerged section comprises means for providing a displacement fluid under pressure to an output which is connected or is connectable to a submarine well.

Abstract: Discharge of fluid into or suction of fluid from the boundary region around such structures as offshore marine elements and moored marine vessels to reduce fluid current induced stress to marine elements and low frequency oscillations of moored vessels due to waves and wind striking the vessel is disclosed.

Abstract: A coupling for two pipe sections having integral buoyancy cans, wherein the coupling includes two coupling flanges, each having an inner flange portion configured to couple the pipe stems of the pipe sections and an outer flange portion configured to brace or secure the buoyancy cans of the pipe sections against each other and thereby stabilize the pipe sections. In one embodiment, the inner and outer flange portions of each coupling flange are connected by a plurality of connecting plates. Each coupling flange also includes a plurality of reinforcing plates between the inner and outer flange portions. Each of the inner flange portions is configured as a female box flange. In one embodiment, a pin flange is positioned between the inner flange portions in the assembled coupling to form pin-and-box connections with the inner flange portions. The outer flange portions are bolted together to secure the coupling.

Abstract: The disclosure defined by this invention is a method and assembly for conducting wireline operations in a deep, subsea location, which includes providing a rig on the surface of a body of water, having a riser extending from the rig floor to the floor of the deep body of water; a hydril positioned on the end of the riser on the sea floor; a plurality of blowout preventers positioned below the riser to prevent a blowout into the riser; a wireline subsea blowout preventer control head assembly lowered into the riser to the level above the hydril; pressuring off the assembly by the riser and blowout preventers; lowering a wireline down the riser into the assembly, so that the tool may be lowered beyond the blowout preventers to conduct wireline operations; and pressuring off the side entry apparatus, so that should a blowout occur during wireline operations, any pressure would be prevented from entering the riser, but would be contained by the side entry assembly.

Abstract: An offshore field management system which includes a composite riser, a floating buoy and a service vessel. The riser is extended from a subsea well head to the buoy. Conductors, preferably provided in the riser, are connected with a well telemetry system. The buoy has a floating or semi-submersible hull that includes a hatch covering a moonpool for receiving the riser. The buoy preferably includes satellite communication hardware and computer systems in communication with the well telemetry system via riser embedded conductors. The well environment can be remotely monitored using the buoy communication system. Servicing of the oilfield well is accomplished using the service vessel by docking the buoy in a bay formed in the service vessel. The service vessel is preferably a self-contained facility fitted with the equipment and materials necessary to carry out pre-determined well servicing operations.

Abstract: A tension member comprising a plurality of fiber filaments (21) gathered into a plurality of strands (20). The filaments (21) run close together, and a protective sheath (16) is provided around the strands. Each strand (20) is coated on the exterior thereof with a sheath (22) of a material having a low friction coefficient, permitting the strands (20) to move longitudinally in relation to one another and independently of each other.

Abstract: An installation for producing oil from an off-shore deposit has a semi-submersible platform, at least one riser connecting the platform to the sea bed, and devices for tensioning the riser. The tensioning devices include, for each riser, at least one submerged float connected to a point on the main run of the riser for hauling it towards the surface, and a mechanism for hauling the riser. The mechanism is installed on the platform and applied to the top end of the riser.

Abstract: A device for supplying hydraulic pressure to one or more hydraulically actuable components in a well production system and positioned within the well bore including a reservoir, and electrically powered pump, and a controller each positioned within the well bore and carried on the component. The controller operates the pump to supply fluid from the reservoir to actuate the components. Additionally, valves to route the fluid to the components and sensors to sense when the components are actuated are included.

Abstract: In one embodiment of the invention, there is provided a drilling unit comprising a floating drilling rig, a subsea wellhead, and a riser connecting the subsea drilling rig with the subsea wellhead. A floatation collar encircles the riser so as to reduce deck load on the floating drilling rig. The floatation collar comprises a hollow fabric body filled with gas. The floatation collar has a longitudinal axis and is formed from a sidewall body having a longitudinally extending slit extending through the sidewall body. The slit enables the floatation collar to be transversely mounted onto the marine riser.

Abstract: A device automatically makes up a riser string from riser spools, each having an ancillary line and dog-type connectors. A support member supports a second riser spool for connection. A torque arm above the support member hinges open to accept a first riser spool and hinges close to engage the first spool and rotate the first spool to align its ancillary line with the ancillary line of the second spool. A guide arm above the support member hinges open to accept the first spool and hinges closed to engage and radially position the first spool while allowing vertical movement of the first spool. Connector actuators are positioned around the support member to actuate the connectors when the first spool is lowered onto the second spool.

Abstract: A system for drilling a subsea well from a rig through a subsea wellhead below the rig includes a wellhead stack which is mounted on the subsea wellhead. The wellhead stack includes at least a subsea blowout preventer stack and a subsea diverter. A drill string extends from the rig through the wellhead stack into the well to conduct drilling fluid from the rig to a drill bit in the well. A riser which has one end coupled to the wellhead stack and another end coupled to the rig internally receives the drill string such that a riser annulus is defined between the drill string and the riser. A well annulus extends from the bottom of the well to the subsea diverter to conduct fluid away from the drill bit. A pump has a suction side in communication with the well annulus and a discharge side in communication with the rig and is operable to maintain a selected pressure gradient in the well annulus.

Abstract: A tieback connector comprises a passive lower locking system and an active upper locking system to exert a positive locking force on the connection between a production riser and a high pressure wellhead. The tieback connector is comprised of an outer housing which carries lower locking dogs, upper locking dogs and a piston. The piston is located above the lower end of the production riser and controls the movement of the outer housing. As the piston is stroked the outer housing cams the lower dogs into grooved profile in the wellhead housing. As the piston is stroked further the upper dogs exert a force onto the production riser that locks the riser to the wellhead housing.

Abstract: A method for assembling and delivering a drivepipe to a drill site, the method having the following steps: assembling the drivepipe and driving mechanism at a shoreline assembly station; attaching floatation devices to the drivepipe and floating the drivepipe in the ocean; towing the drivepipe with tow vessels to a drill site; delivering the drivepipe in a horizontal orientation to a drilling vessel at the drill site; attaching a upper end of the drivepipe to the drilling vessel and detaching the tow vessels from the drivepipe; pivoting the drivepipe about its point of attachment to the drilling vessel until the drivepipe is vertically oriented; deactivating the buoyancy function of the floatation devices attached to the drivepipe; removing the floatation devices from the drivepipe; and lowering the drivepipe with a running string from the drilling vessel to the sea bed.

Abstract: An apparatus for rapid venting of the compressed air and deballasting of a buoyant air tank in a positively buoyant riser system in the event of a premature drive off or a riser section parting is shown. The rapid venting of the compressed air ensures that the riser section cannot rapidly ascend to the surface and damage the drilling rig positioned above. In a first embodiment, the buoyancy tank or housing includes a circumferentially shaped channel positioned on its upper end. An annularly shaped ring is placed over the circumferentially shaped channel and sealed in place by a frangible weld. A tether line attaches to the annularly shaped ring and extends to an anchor point on the BOP stack below. In the event of a catastrophic parting of the riser, as the riser sections and attached buoyancy tank or housings begin ascending, the tether line is drawn tight.

Abstract: A riser system connecting a oil or gas well head and a surface vessel comprises a first riser section maintained substantially vertically under tension, attached for example by a tension cable to a constant load tensioner means mounted on the vessel, and a flexible second riser section arranged above the first riser, the second riser being able to flex to accommodate movements in the surface vessel. The second riser section includes a curvature limiter, achieved for example by making the riser from a material of variable stiffness along the riser's length. An emergency disconnect valve is provided between the lower riser section and the upper flexible section. An alternative curvature limiter comprises a plurality of discrete collars which are connected together and surround the outer diameter of the second riser.

Abstract: A subsea production system is provided for producing a number of subsea wells which may be arranged in groups. Each of the groups of subsea wellheads is connected to deliver production flow to a subsea manifold and each subsea manifold is connected to deliver production flow to a production riser. A plurality of production risers each being connected to receive production flow from one of said subsea manifolds extend from the subsea manifolds for groups of wells. A deep draft floating spar is located generally above the subsea wellheads with mooring lines and has a production platform located above the sea surface and has buoyancy and ballast chambers to control floatation. The spar structure defines a riser bore receiving the production risers extending from the subsea wellheads to the production platform. The spar is also capable of being shifted laterally by its mooring lines for positioning above a selected well to thus permit well intervention activities as needed.

Abstract: A dynamically positioned, concentric riser, drilling system comprising a dynamically positioned drilling unit operable to float at least partially above the surface of a body of water, a first, outer, low-pressure, marine riser extending from the drilling unit into the body of water, a tensioning system to support the first marine riser, a second, inner, high-pressure, marine riser concentrically extending within the first, outer, low-pressure, marine riser, a surface blowout preventor, a lower marine riser package, a subsea blowout preventor, and a connector at the base of the lower marine riser package to release the risers from the wellhead in the event of a loss of station of the drilling unit.

Abstract: A riser bundle comprising a number of risers (2) extending in a wave configuration from the bottom of a body of water up to a floating vessel or the like, the riser bundle (1) along its length being provided with means giving different portions (5, 6 7) along the wave configuration different submerged weight and net buoyancy. The risers (2) are arranged around a centrally extending tube (3) and are surrounded by a tubular outer casing (4), the central tube (3) and the interspaces (8) between the risers (2), along different portions of the wave configuration in operation being filled with materials of different density. Thereby there is achieved at least one light portion (5) of the configuration having a desired positive net buoyancy, and a heavy portion (6 resp. 7) on each side of the light portion (5) having a desired positive submerged weight.

Abstract: The invention is a system used for production of petroleum effluents situated at great water depths. The system includes an intermediate floating station situated below the surface at a depth selected according to the pressure of the effluent at the outlet of wellheads situated on the station, production risers communicating with the well to be worked, an anchor including production risers, a pump situated on the floating station which transfers the effluent to a processing or destination site, a transfer which transfers the effluent between the floating station, the water bottom and a final platform or a processing plant, and an energy source providing necessary energy to the various equipments installed on the floating station.

Abstract: A centralizing device is provided for a riser of an offshore well platform having an opening through which the riser passes from the platform to a subsea wellhead. The riser has generally planar fins extending radially outward from its outer diameter. The centralizing device has a frame which is mounted to the platform about the riser. A plurality of centralizing rollers are mounted to the frame and are radially extensible relative to the riser. The centralizing rollers bear against the riser and retain it laterally. A plurality of torsional rollers are mounted to the frame and are extensible towards the fins. The torsional rollers bear against the fins and retain the riser torsionally.

Abstract: A drilling unit comprises a floating drilling rig, a subsea wellhead, and a riser connecting the subsea drilling rig with the subsea wellhead. A floatation collar encircles the riser so as to reduce deck load on the floating drilling rig. The floatation collar comprises a hollow fabric body filled with gas. The floatation collar has a longitudinal axis and is formed from a sidewall body having a longitudinally extending slit extending through the sidewall body. The slit enables the floatation collar to be transversely mounted onto the marine riser.

Abstract: There are disclosed two embodiments of a subsea drilling, completion and/or workover apparatus which includes a spar buoy having a well therethrough, and a riser which extends through the well in the buoy for connection to the subsea wellhead during the drilling and/or completion process. A buoyancy tank is disposed about the riser within the buoy well to support the riser, and the upper end of the tank is fee to move vertically with respect to the well deck so that it will not be placed in compression despite anticipated rise and fall of the buoyancy tank.

Abstract: An apparatus for rapid venting of the compressed air and deballasting of a buoyant air tank in a positively buoyant riser system in the event of a premature drive off or a riser section parting is shown. The rapid venting of the compressed air ensures that the riser section cannot rapidly ascend to the surface and damage the drilling rig positioned above. In a first embodiment, the buoyancy tank or housing includes a vertical channel positioned on its exterior. A cover plate is placed over the vertical channel and sealed in place by a frangible weld. A tether line attaches to the cover plate and extends to an anchor point on the BOP stack below. In the event of a catastrophic parting of the riser, as the riser sections and attached buoyancy tank or housings begin ascending, the tether line is drawn tight. Further ascension of the buoyancy tank or housings, causes the frangible weld joints to break and peel back the cover plate, exposing the vertical channels.

Abstract: A system for offshore production of oil or gas, comprising a surface vessel having a means for maintaining a desired position and orientation, a bottom installation at the seabed for at least two production wells, and risers for connecting the bottom installation to the vessel. The vessel is provided with drilling equipment for wells at the seabed and with process equipment for produced oil or gas. The bottom installation comprises a template having its foundation at the seabed and being provided with a manifold unit and is designed with at least two well head sections adapted for installing associated Christmas trees. A drill string is adapted to extend from the drilling equipment on the vessel to an operation module at the bottom installation, and a product riser is adapted to connect the operation module to the process equipment on the vessel.

Abstract: An underwater installation for use in offshore drilling of and production from, respectively, oil and/or gas wells at deep and moderate deep water comprises an intermediate station in the form of a buoyancy based hollow body (16) tension strut anchored at the seabed (10) and located at a depth substantially closer to the surface of the sea than the seabed (10). At least one hydrocarbon conveying pipeline extends between the buoyancy body (16) and seabed depth, for the transfer of hydrocarbons from the reservoir to said buoyancy body (16). At least one casing extension pipe string (18a-18h) constitutes the tension leg/strut anchoring the buoyancy body (16). The invention also relates to a method for the building of an underwater installation.

Abstract: An apparatus for rapid venting of the compressed air and deballasting of a buoyant air tank in a positively buoyant riser system in the event of a premature drive off or a riser section parting is shown. The rapid venting of the compressed air ensures that the riser section cannot rapidly ascend to the surface and damage the drilling rig positioned above. In a first embodiment, the buoyancy tank or housing includes a vertical channel positioned on its exterior. A cover plate is placed over the vertical channel and sealed in place by a frangible weld. A tether line attaches to the cover plate and extends to an anchor point on the BOP stack below. In the event of a catastrophic parting of the riser, as the riser sections and attached buoyancy tank or housings begin ascending, the tether line is drawn tight. Further ascension of the buoyancy tank or housings, causes the frangible weld joints to break and peel back the cover plate, exposing the vertical channels.

Abstract: A riser guide and support mechanism for a floating vessel, and particularly a spar type structure, where the buoyancy can stem extends nearly the entire length of the floating vessel. A riser centralizing element is provided on the riser near the lower end of the buoyancy guide stem. Riser bend limiting elements are positioned on the riser so as to extend above and below the riser centralizing element. Since the buoyancy cans and buoyancy can stem are not required to rotate relative to the stem guides on the floating vessel, the stem guides can be formed from pipe sections that provide a much larger bearing area than is customary.

Abstract: A dual phase riser flotation system contains a number of passive phase buoyancy modules of syntactic foam contained within an outer skin, and a number of active phase buoyancy modules which are similar to air canisters in that they may be inflated or deflated as required to provide levels of buoyancy. The passive phase buoyancy modules may contain tubes filled with air, a compressed gas such as nitrogen, or evacuated to provide additional buoyancy. Charge and discharge valves connect gas flow lines to a manifold system serving the active phase buoyancy modules.

Abstract: A subsea wellhead connector has an upper body that abuts the rim of a wellhead member. A hydraulic wellhead connector is carried by the upper body and extends over the wellhead member. The hydraulic wellhead connector carries dogs for moving into an engaged position with a profile on the exterior of the wellhead member. The mating or complementary stepped profile at the top or rim of the wellhead housing is designed to engage at three surfaces. The first surface is the flat surface at the inner diameter. The second surface is the tapered surface at the step. The third surface is the flat surface on the rim from the tapered surface to the outer diameter of the rim. The profiles are dimensioned with bias toward initial contact at the outer diameter flat on the rim of the well housing, second contact is at the inner diameter flat on the rim of the well housing, and the third contact is at the tapered step.

Abstract: Apparatus for use in the completion and workover of a subsea well adapted for coil tubing intervention comprises a surface tree having an upper end on which a coil tubing injection unit may be mounted, a tension joint adapted to be connected to the upper end of a lower riser section extending to a subsea tree and to be suspended from a tensioning system at the surface to enable the lower riser section to be maintained in tension, an upper riser section for connection at its upper end to the surface tree and at its lower end to the tension joint, and a surface joint mounted on and surrounding the riser section in position to extend through the spider at the floor of an offshore rig.

Abstract: The present invention relates to an apparatus and methods for coupling objects that are displaced from one another. In particular, the present invention relates to an apparatus and methods for providing a connection member, for coupling objects that are displaced from one another, that is able to adapt to changing operating conditions. The connection member is a composite tubular that responds to pressure changes such that when the internal pressure of the composite tubular is changed, the length of the tubular proportionally changes, thereby enabling the composite tubular to do useful work.

Abstract: A riser arrangement increases the stability and/or decreases sensitivity to vortex induced vibration of risers of a riser system including steel tubular lines, SCRIBS and flexible hose risers leading to a floating storage/production vessel. A cross-link is placed between two or more steel tubular lines in order to enhance the stability of the riser system. Devices are coupled to the steel tubular lines for increasing their tension in order to increase the natural frequency of vibration in order to reduce sensitivity to vortex induced vibration.

Abstract: A tensioning device is provided for applying tension to a riser from a surface deck of an offshore oil or gas well. The tensioning device is used with a riser of the type having threads formed on an exterior surface thereof. A tension ring of the tensioning device is formed from first and second ring halves that are clamped together about the riser. The first and second halves have inner threads for engaging the threads of the riser. A clearance exists between the first and second ring halves when the ring halves are clamped together about the riser to allow the first and second ring halves to be tightened against the exterior surface of the riser so that the tension ring is securely fastened to the riser. Fastening means are used for clamping the first and second ring halves together about the riser. Tensioning members that couple at one end to the tension ring and at the other end to the surface deck are used to apply tension to the riser from the surface deck.

Abstract: A variable-buoyancy marine riser and a method for providing and adjusting the buoyancy for such a riser. The riser is comprised of a main riser conduit on which a plurality of cans are affixed. A slurry of buoyant material, e.g. small, hollow spheres, is pumped into the cans to displace the seawater therein and give buoyancy to the riser. When it is desired to reduce the buoyancy of the riser, the spheres are removed by merely opening the cans and allowing the surrounding seawater to displace the spheres from the cans.