Abstract: An arrangement on a floating device for overhauling offshore hydrocarbon wells comprises a drill floor for conducting the overhaul, where the drill floor is provided with an opening. A vertically movable working deck can be inserted into the opening, and is provided with an attachment for a riser which extends from a well to the working deck. The working deck is suspended in the floating device by riser tensioners in order to maintain approximately constant tension in the riser during vertical movement of the floating device.

Abstract: A monolithic isolation stress joint is disclosed having a first conduit element, a first insulating joint assembly, and a stress joint connected to the first conduit element through the first insulating joint assembly. The stress joint is formed of a material which has advantageous elastic flexure characteristics but which is electrochemically active with respect to the first conduit element from which it is electrically isolated by the first insulating joint assembly. A second conduit element is connected to the stress joint through a second insulating joint assembly, the second conduit element being formed of a material which is electrochemically active with respect to the stress joint and which is electrically isolated therefrom with the second insulating joint.

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: Method of, and apparatus for, sinking bore holes, in particular exploratory and extraction bore holes, in the sea bed (40). The material from the sea bed is loosened with the aid of a rotating drill head (10) which is arranged at the bottom end of a drill string (5) which is suitable for transmitting a torque. The top end of the drill string is mounted on a floating platform (1), it being the case that the drill string (5) comprises at least two telescopically interengaging drill-string parts (6, 7) which, during a vertical movement of the platform, induced for example by the sea swell, execute a movement relative to one another, with the result that the drill head (10) rests with an essentially constant force on the surface which is to be cleared away.

Abstract: An attachment extends between an outer sleeve and an inner riser pipe where the pipe penetrates the keel of a platform. In one version, the attachment is a conically-shaped with a small diameter ring that engages the riser pipe and a large diameter ring that engages the outer sleeve. This attachment has elements that are very flexible in bending but relatively stiff and strong in axial load. Other versions include flat rings where lateral load is taken directly into tension and compression in the beams, allowing for relatively high lateral load transfer. Both the conically-shaped attachment and the flat ring have a number of variations that provide low bending stiffness but high axial stiffness of the elements. Depending on whether resistance to axial loads, lateral loads, or resistance to combination of both loads is desired, the attachment and the flat ring may be used alone or in combination.

Abstract: The present invention discloses the use of fluid passages for structures in fluid environments such as offshore platform risers or spars to reduce and/or control vortex-induced vibrations and drag. The present invention also describes the use of fluid passages to protect a moored marine vessel by reducing and/or controlling low frequency drift oscillations due to random waves, and low frequency wind induced resonant oscillations.

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: Initially, a set of locking lugs lock an inner mandrel is locked in position with respect to an outer mandrel. Unlocking the travel joint is accomplished by applying a constant vertical or downward force on the tubing string. That vertical force is transmitted through the tubing string to the outer mandrel, which causes hydraulic pressure with a hydraulic chamber to increase. When the hydraulic pressure exceeds a pressure threshold, a pressure sensitive valve opens, and the hydraulic fluid gradually flows into a reserve hydraulic chamber, allowing the outer mandrel to move with respect to the inner mandrel. A viscosity independent flow restrictor limits the transfer of hydraulic fluid to a preset flow rate. After sufficient hydraulic fluid has been received into the reserve chamber, the outer mandrel aligns with the locking lugs, which then move from the locked position to the unlocked position. The travel joint then releases, allowing the outer mandrel to telescope inward and outward.

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: The present invention relates to an arrangement in a floating drilling and intervention vessel, for controlling a heave compensated drill floor 7 suspended in drill floor compensator cylinders 10. Below the compensated drill floor 7 there is installed a tidal structure (3) suspended in tidal cylinders 2 or wires 25. By adjusting the tidal cylinders 2 or the wires 25 in step with the tide 17 it is achieved that the drill floor compensator cylinders 10 can operate around their middle position regardless of the tide lifting or lowering the vessel 16.

Abstract: The invention is directed to a tensioner/slip-joint module for providing a conduit from a floating vessel at the surface of the ocean to the blowout preventer stack, or production tree, which is connected to the wellhead at the sea floor. The tensioner/slip-joint module compensates for vessel motion induced by wave action and heave and maintains a variable tension to the riser string alleviating the potential for compression and thus buckling or failure of the riser string. The tensioner/slip-joint module of the present invention preferably includes at least one mandrel having at least one hang-off donut; at least one upper flexjoint swivel assembly, at least one radially ported manifold, at least one tensioning cylinder, and at least one slip-joint assembly combined in a single unit.

Abstract: A floating rig or structure for drilling in the floor of an ocean using a rotatable tubular includes a seal housing having a rotatable seal connected above a portion of a marine riser fixed to the floor of the ocean. The seal rotating with the rotating tubular allows the riser and seal housing to maintain a predetermined pressure in the system that is desirable in underbalanced drilling, gas-liquid mud systems and pressurized mud handling systems. The seal is contemplated to be either an active seal or a passive seal. A flexible conduit or hose is used to compensate for relative movement of the seal housing and the floating structure because the floating structure moves independent of the seal housing. A method for use of the system is also disclosed.

Abstract: The present invention relates to a riser-tensioner for exerting a tensile force from a drilling vessel or drilling platform upon a riser, comprising a riser ring which is for fastening attachably to the top end of the riser, and one or more cables extending by way of cable pulleys from said vessel or platform to said riser ring, in which said cable pulleys are under such influence or tensioning means that a tensioning force can be applied to the cable, the riser ring being provided with riser ring sheaves and the cables being guided in an outgoing reeving from the vessel or the platform to said riser ring sheaves, and being guided back by way of said riser ring sheaves in a return reeving to said vessel or platform.

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 swivel assembly for installation at a well for subsea production of oil or gas and adapted to be connected to a production vessel at the sea surface. The swivel assembly comprises a main fluid swivel having at least two paths and an electric/hydraulic auxiliary swivel for signal communication and power transfer. The fluid swivel is provided with a rotatable swivel housing at the top of a stationary christmas tree, preferably comprising a small number of valves, such as a production master valve and an annulus master valve. The paths are through-running vertically in the central core member of the fluid swivel so as to make possible well intervention from the upper side of the fluid swivel.

Abstract: A ship type floating oil production system for access to subsea wells through installation of surface wellheads on a ship type surface vessel on the sea comprises a cylindrical turret moored to a seabed is located within a moon pool formed in the ship type surface vessel such that the ship type surface vessel is freely rotatable about the cylindrical turret. A plurality of riser pipes have a rigid structure and extend downward to subsea wells through the cylindrical turret, and each riser pipe is provided at its top portion with a surface wellhead including valves of the riser pipe. Accordingly, workover operations can be facilitated as needed by running workover tools through the surface wellhead of the corresponding riser pipe through use of a work-over-rig installed on the ship type surface vessel.

Abstract: A computer controlled heave compensation wireline logging winch system and method of use that compensates for the effects of wave motion on floating installations performing wireline logging measurements. A wireline winch and wireline cable with a logging measurement tool attached is installed on a floating installation. Vessel vertical movement is measured and is physically compensated for by a change in speed of the wireline cable so that the logging data is obtained at a controlled speed. Any error in this physical compensation is detected by a depth measurement system and is used to adjust the true depth at which the logging tool measurements are being recorded.

Abstract: Subsea well arrangement for offshore production of oil or gas, comprising a wellhead, a christmas tree mounted on the wellhead and at least one riser for connection with a production vessel at the sea surface. At the top of the christmas tree there is provided a swivel device communicating with the christmas tree, and the swivel device is provided with preferably laterally directed connecting members for risers or hoses and for an umbilical or control cable.

Abstract: Subsea unit for offshore production of oil or gas, comprising one or more wellheads with associated christmas trees provided on or at a bottom frame (template). On or at the template there is mounted a swivel device, having fluid connection to the christmas tree or trees and being provided with connection members for risers and an umbilical or control cable from a production vessel at the sea surface.

Abstract: A pressurized slip joint for a marine intervention riser decouples the flowhead assembly in the moon pool of a vessel from the riser string, enabling safe changeover of equipment during workover operations. One part of the slip joint assembly is coupled to the flowhead assembly through a flexible joint assembly. A second part of the slip joint assembly supports the riser string and is coupled to the tensioning mechanism. The first part may be inserted into the second part and locked in place during workover operations except when equipment changeover is taking place. When changeover is being carried out, the first and second parts are unlocked, so that the flowhead assembly does not move relative to the vessel. In the locked position, a metal-to-metal high pressure seal, with a secondary and tertiary seal controls the pressure in the riser. In the unlocked position, a hydraulically operated dynamic low pressure seal is used.

Abstract: An intervention riser for an oil or gas well, which forms a connection between the well head and a floating surface vessel, is sufficiently flexible to accommodate the relative vertical movement between and the well head and a floating surface vessel, is attached to a compensating deck on the vessel which is free to move vertically relative to the vessel, and has winching means having a winch line attached to the riser such that the winching means may pull upon the riser. The compensating deck comprises a deck surface supported on at least one vertically arranged gantry support. The riser system comprises a lower riser section which extends substantially vertically and is essentially rigid, being maintained under tension, and a flexible upper riser section to accommodate movements in the surface vessel.

Abstract: A slide joint for a riser between a well and a floating petroleum installation such as an oil platform includes an outer pipe and an inner pipe which are adapted to move telescopically relative to one another to compensate for changes in the distance between the sea bed and the platform. The inner pipe is connected to a piston, which piston is responsive to actuation by hydraulic pressure in order to provide tractive force on the riser. The outer diameter of the inner pipe is adapted to the diameter of the outer pipe so as to form an annulus between the pipes. The piston is fixedly connected to the inner pipe at or near the downward oriented end thereof, said annulus above the piston being subjected to hydraulic pressure. Below the piston is provided a protective sleeve, which is slidably disposed within the outer pipe.

Abstract: A wellbore motion control apparatus for controlling the motion of a tubular wellbore string (in one aspect with an additional item and/or apparatus connected thereto) in a wellbore extending from a surface down into the earth has been invented which has, in one aspect, a central mandrel connected to the tubular wellbore string, a housing with a hollow interior and fluid therein, at least one fluid passage apparatus disposable in the hollow interior and having a fluid flow channel extending therethrough, and the at least one fluid passage apparatus secured to the central mandrel, the housing surrounding the central mandrel, the at least one fluid passage apparatus disposed for movement in a chamber defined by an inner surface of the housing and an outer surface of the central mandrel, the at least one fluid passage apparatus positioned within the chamber so that fluid therein is flowable therethrough permitting movement of the fluid passage apparatus within the chamber and thereby controlling movement of the m

Abstract: A wellbore motion control apparatus for controlling the motion of a tubular wellbore string in a wellbore extending from a surface down into the earth and methods for using it. Such an apparatus, in one aspect, has a housing with a top end, a bottom end, and a hollow interior having an interior volume with fluid therein. There is at least one fluid passage apparatus having a top end and a bottom end and disposable in the hollow interior of the housing, the at least one fluid passage apparatus having a fluid flow channel extending therethrough from the top end to the bottom end.

Abstract: A centralizing device is provided for a riser of an offshore well platform having a frame that defines an opening through which the riser passes from the platform to a subsea wellhead. The centralizing device has a centralizing ring with an inner diameter greater than the outer diameter of the riser so that the riser can be passed longitudinally therethrough. The centralizing ring is positioned within the opening of the frame. Adjustable mounting means are used for mounting the centralizing ring to the frame at different positions within the opening. A roller assembly of the centralizing device is carried upon the riser as the riser is lowered through the centralizing ring. The roller assembly is configured to engage the centralizing ring as the riser is lowered through the centralizing ring so that the centralizing ring stops further carriage of the roller assembly by the riser.

Abstract: A travel joint provides economical manufacture, installation, service, and operation thereof. The travel joint substantially reduces the number of parts potentially exposed to corrosive fluid, eliminates cavities wherein such corrosive fluid may become trapped, and substantially reduces the number of dynamic and static seals required for its operation. Additionally, a torque transmitting member is utilized to prevent torquing through threaded service breaks in the travel joint. In a preferred embodiment, a travel joint has a tubular upper case, a torque collar rotationally and axially coupled to the upper case, a tubular mandrel axially slidably received in the upper case and torque collar, and rotationally coupled to the torque collar, and an adapter which axially and radially inwardly retains the torque collar.

Abstract: An offshore fluid transfer system (10) is provided, of the type that includes a riser (32) having an upper end (34) connected through a universal joint (36) to a turret (22) on a vessel and having a lower end (36) anchored by catenary chains (40), and that also includes hoses (70, 71) extending from a base (50, 58) on the seafloor to the turret on the vessel, which avoids the need for a complicated hose structure to pass fluid across the universal joint. A fluid coupling (73) near the bottom of the turret, which is widely spaced from the universal joint, connects to a hose that extends from the fluid coupling in a sinuous path down to the seafloor base. The long length of hose, enables it to bend when the vessel drifts, to avoid excessive hose tension or riser contact during such vessel drift. A riser connector (102) can be operated to disconnect the riser from the turret so the riser can sink. The fluid coupling can include a fluid connector (100) which can separately disconnect the hose from the turret.

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: A telescopic joint for an upper end of an offshore drilling riser is installed and controlled remotely. The telescopic joint has inner and outer telescoping barrels. A mandrel is located on the lower end of the outer barrel, the mandrel landing within a support ring which is supported by constant tension cables extending from the vessel. Control fluid passages are located in the mandrel for registering with control fluid passages in the support ring. Permanent control fluid lines extend between various points of the outer barrel and the mandrel. Control fluid hoses connect the support ring to the vessel. Fluid communication is achieved once the telescopic joint is oriented and landed in the support ring.

Abstract: A deep water offshore apparatus for use in oil drilling and production in which an upper buoyant hull of prismatic shape is provided with a passage longitudinally extending through the hull in which risers run down to the sea floor, the bottom of the hull being located at a selected depth dependent upon the wind, wave, and current environment at the well site, which significantly reduces the wave forces acting on the bottom of the hull, a frame structure connected to the hull bottom and extending downwardly and comprising a plurality of vertically arranged bays defined by vertically spaced horizontal water entrapment plates and providing open windows around the periphery of the frame structure, the windows providing transparency to ocean currents and to wave motion in a horizontal direction to reduce drag, the vertical space between the plates corresponding to the width of the bay window, the frame structure being below significant wave action whereby wave action thereat does not contribute to heave motion of

Abstract: An apparatus for tensioning a riser that extends from a floating platform to a subsea wellhead has hydraulic cylinders. The hydraulic cylinders attach between the platform and the riser in a cluster with the axis of the riser substantially parallel with the axes of the hydraulic cylinders. A guide sleeve within the cluster transfers bending moments of the riser to the platform.

Abstract: An offshore production system of the type that includes a TLP (tension leg platform) (12) and a derrick vessel (14) which moves to the TLP platform (16) whenever the derrick is required. The vessel carries fastener assemblies (131) that rigidly fix the vessel to the platform so they move vertically and horizontally as a single unit, which avoids any need to separately anchor the vessel and which facilitates operation of the derrick in more adverse weather. The vessel preferably has thruster equipment (88) which not only allows it to self-propel itself to the platform, but which also allows the vessel to propel itself and the platform sidewardly, to avoid drift of the platform during drilling. The vessel includes a vessel deck (70) which lies above the platform and a pair of vessel sides (72, 74) with pontoons (76, 78), that lie on opposite sides of the platform.

Abstract: A support system for supporting an underwater work platform includes a work platform submerged in a body of water and a support structure supported by the body of water above the work platform. The work platform is supported by a plurality of cables connected between the support structure and the work platform. Motions of the support structure in the body of water are sensed, and the length of the cables is adjusted in response to the sensed motions of the support structure so that the work platform can be maintained stationary even when the support structure is subjected to wave forces and currents.

Abstract: A method of providing a cathodic protection to an installed pile is disclosed in which a plurality of anodes are provided on a tendon foundation guide assembly which is attached to a lowering unit and lowered to the pile. The tendon foundation guide assembly is attached to the installed pile and at least one of the anodes is electrically connected to the pile. The tendon foundation guide assembly is then separated from the lowering unit. In another aspect of the invention, a tendon foundation guide assembly is disclosed for deployment upon the top of an installed pile for cathodically protecting the pile and a tendon receptacle inside the pile.

Abstract: Basically the system consists of a supporting structure (1) lying in an opening in floating vessel (9) to which a group of risers (3) is connected running from sea bottom to sea surface, linking undersea oil wells to their respective production trees (5) which lie on floating vessel (9), said supporting structure (1) being provided with ball joints that enable a group of risers (3) to articulate in relation to supporting structure (1), and slide blocks to enable said supporting structure to be connected/articulated to floating vessel (9).

Abstract: A system for turning a swivel aboard a vessel for oil extraction at sea includes a stationary swivel part connected to a rotary drilling rig on the vessel and one or more rotating parts connected to the vessel. The rotating swivel parts are connected to a torsionally rigid vertical frame structure via a drive mechanism which transmits rotary motion between the vessel and the swivel without angular displacement or significant reactive forces in the frame structure. The vertical frame structure includes four walls where one of the walls forms a gate for the insertion and removal of an entire swivel or parts of a swivel. The frame structure is attached to an overhead frame that extends across the diameter of the rotary drilling rig and is secured to the hull of the vessel.

Abstract: A passive tensioner is described for accommodating the tensile loading between a floating oil production platform and a riser. The tensioner includes a stack of strut elements, each of which has a plurality of struts of an elastomeric material individually configured to respond to a compressive load by buckling in a predetermined direction, means for constraining the stack during such buckling in a direction generally orthogonal to the direction of the compressive load and means for translating the tensile loading because of ocean wave, current or other liquid action on the platform into a compressive load and applying the same to the stack.

Abstract: A flexible riser extends from a wellhead on a seabed to a pipe system on a turret on a floating structure, such as a drilling or production vessel for recovery of oil and gas, through a guide pipe in the turret. The riser is connected with a rigid pipe which extends from a lower edge of the turret through the guide pipe in the turret and to the pipe system on the deck of the structure. The rigid pipe is fitted at an angle to the vertical, which angle essentially corresponds to the natural angle of the riser.

Abstract: A tensioning ring and riser assembly for use in oil well platform riser tensioning apparatus. The cylindrical riser has male threads formed on the exterior surface. The annular tensioning ring has female threads formed on the interior adapted to loosely thread onto the male threads. The tensioning ring is adapted to be tensioned in a first direction relative to the riser. The female threads have a leading face lying at a shallow angle to the assembly centerline in the first direction and a trailing face lying approximately perpendicular to the assembly centerline. The male threads have a complementary configuration. When the tensioning ring is tensioned in the first direction, the shallow angled faces are brought into tangential pressure contact so that hoop stress is uniformly distributed and minimized in both riser and tensioning ring with the shear load between them distributed over the wall thickness of both parts.

Abstract: A method of extending the working range of a main platform installation for oil deposits at sea involves:(1) positioning a temporary floating station at a location distance from the main platform installation and near to an oil deposit having small individual production capacity;(2) connecting the floating station with at least one well head of said oil deposit;(3) bringing up multi-component effluents from the at least one well head and pumping the effluents to the main platform installation;(4) when production of the effluents from said deposit ends, removing the floating station; and then(5) repositioning the floating station at at least one other oil deposit located at a distant location from said main platform installation to work the at least one other deposit. Also a facility for carrying out this method as described.

Abstract: A mooring system for a seagoing vessel, such as an oil tanker, employs a submerged buoy and a fluid swivel joint mounted in the vessel. The buoy is submerged to a depth sufficient enough to allow the moored vessel to drift over the buoy and other mooring elements without colliding with the same. A motor drive assembly is provided for a rotating shaft in the fluid swivel joint which maintains the shaft in the same position relative to the buoy, regardless of environmental induced changes in the heading of the moored vessel. This insures that one or more flexible hoses connected between the shaft and the mooring will not be twisted if the vessel begins to rotate about the vertical axis of the mooring. Positioning the fluid swivel joint within the vessel provides easy access to the joint for maintenance or repair and shields the joint from the seawater's detrimental effects.

Abstract: A method of extending the working range of a main platform installation for oil deposits at sea involves:(1) positioning a temporary floating station at a location distance from the main platform installation and near to an oil deposit having small individual production capacity;(2) connecting the floating station with at least one well head of said oil deposit;(3) bringing up multi-component effluents from the at least one well head and pumping the effluents to the main platform installation;(4) when production of the effluents from said deposit ends, removing the floating station; and then(5) repositioning the floating station at at least one other oil deposit located at a distant location from said main platform installation to work the at least one other deposit. Also a facility for carrying out this method as described.

Abstract: A semiactive heave compensation system for marine vessels, especially floating offshore drilling rigs, is described. The system can be installed in its entirety or can be used to modify existing passive systems by including heave and compensating sensors a microprocessor and a responsive operator to act upon the compensation elements of the system.

Abstract: A heave compensating support system is disclosed for positioning a subsea work package. The present invention provides a subsurface buoy with a lift line connected to the subsea work package and a compensating lift line having a catenary loop below its connection to the subsurface buoy on one end and connected to a surface vessel on the other end, whereby the heave compensating support system elements cooperate to establish a natural frequency for the suspended subsea work package which materially differs from the average wave frequency acting upon the surface vessel.

Abstract: The improved structure of the present invention is provided to utilize the drilling riser tension ring and rig tensioning to tension a completion riser. A tension sleeve is provide which is secured to the upper end of the completion riser and is designed to have a diameter sufficiently small to allow it to pass through the spider in the rotary table. An adapter tension ring is also provided which is secured to the drilling riser tension ring and has a design allowing the tension sleeve to pass therethrough and be secured therein so that raising the sleeve may raise the adapter tension ring and tension exerted on the drilling riser tension ring or the adapter tension ring may be utilized in tensioning the completion riser.

Abstract: A riser tensioner system 10 includes a pair of supports 14, 16 affixed to an offshore platform in spaced apart relation to one another. A shaft 24 extends between the supports 14, 16 and is pivotally coupled thereto by an elastomeric bearing 26. A central support 22 is pivotally coupled to the shaft 24 at about the midpoint between the supports 14, 16 and fixedly coupled to coil springs 30 or elastomeric springs 100 coaxially arranged about the shaft 24 and extending between the central support 22 and each of the supports 14, 16. The central support 22 is also coupled to a riser 12 so that relative movement between the offshore platform and the riser 12 causes the central support 22 to pivot on the shaft 24 and wind or unwind the coil springs 30 or elastomeric springs 100 for relative upward and downward movement thereof. A pretensioner mechanism 42 increases the force exerted by the springs 30 or elastomeric springs 100 to increase the upward force applied to the riser 12.

Abstract: A method for movement-compensating a riser pipe (6) running between a mobile offshore structure (7, 8) and a wellhead (2) on the sea-bed (1), employs a sliding joint (13, 15) in the form of a telescopic device (9) which is volume and pressure balanced. This balancing makes it possible to use the sliding joint under the extreme conditions of pressure which may be experienced in production riser pipes, which the advantage that the production systems may be fitted fixedly to the mobile offshore structure. The method also combines the sliding joint (13, 15) with a hydraulic cylinder (27) which maintains a movement-compensated tension in the riser pipe (6). Several examples of slidng joints (13, 15) with movement-compensated tension cylinders (27, 38, 43) are shown.

Abstract: A system for transferring fluids from a piping system which is firmly connected with a ship's hull (2) to a turning device (5), and vice versa, in which the turning device is rotatably connected with said hull. The turning device has a through hole (7) coaxially with its axis of rotation, through which a drill string, a rigid riser, or the like may be run by the aid of a derrick (16). Furthermore, turning device is arranged for anchoring to the sea floor and connection with at least one flexible riser being connected with respective devices which are firmly connected with the sea floor, and with hoses which are connected with the piping system in the hull.

Abstract: A method is described for conducting well operations from a floating platform that may be moved to various locations above subterranean formations. Marine risers that have been previously connected to the platform flex sufficiently to allow this movement. The mobility of the platform allows well drilling, completion, producing, and workover activities to be conducted simultaneously through the risers attached to the platform. The mobility of the platform also allows new wells to be drilled at more preferable locations than those that would be available from a fixed bottom supported well template.

Abstract: A motion compensation system is provided for use on a drilling vessel that is subject to heaving due to wave action, and wherein a motion compensator associated with a derrick supports a drill string that extends from the vessel downwardly through the seabed and into a drilled hole in the sub-sea formation, the system including a first encoder for sensing vertical motion of the vessel, due to sea heaving, and for producing an electrical signal that varies in response to such sensing, a device on the vessel for producing hydraulic fluid displacement corresponding to variations of the signal, and an hydraulic fluid responsive manipulator in the form of an actuator or actuators carried by the derrick for lifting and lowering the compensator in correspondence to such hydraulic fluid displacement, thereby to maintain the drill string substantially motionless, vertically.