Abstract: The present invention relates to an arrangement in connection with the drilling of oil wells, especially with coil tubing, and more specifically an arrangement comprising heave compensation by such drilling, comprising a first frame-like structure (3) which in relation to a floating vessel (1A) is mounted for allowing movement at least in the vertical direction in relation to said vessel, as well as devices for providing compensating power between said first frame stucture (3) and said vessel (1A), and in order to provide an improved heave compensation system it is according to the present invention suggested that said arrangement further comprising a second frame-like structure (1) arranged stationary on the deck (1AA) of the vessel (1A), said first compensated frame-like structure (3) and said second frame-like structure (1) being assembled by means of a further system (4) allowing compensation of said relative movement between the vessel (1A) and said compensated structure (3), i.e.

Abstract: A drilling and/or production riser includes on at least part of the length thereof, a stiffener suited to withstand strains induced by the stresses transmitted by the marine environment, those induced by said supporting and guide device, and the strains due to the weight of the loads supported by said stiffener. System intended for production of petroleum effluents from a production site, such as one or more production wells, to a floater having at least one assembly allowing transfer of the effluents from at least one of the production wells to the floater. The assembly includes a production riser equipped on at least part of the length thereof with a float and with at least one stiffener situated above the float and suited to withstand strains induced by the stresses transmitted by the marine environment, those induced by said supporting and guide device and the strains due to the weight of the loads supported by said stiffener.

Abstract: A dual bore riser system is described which includes a conventional monobore riser (12) for production access and an independent coil tubing (14) disposed in parallel with the monobore riser (12) for providing annular access. The monobore riser includes discrete A joints of tubing, casing or drill pipe and the coil tubing riser may be any suitable size but is normally between 23/8" and 27/8" outside diameter. The standard monobore riser (12) and coil tubing riser (14) is fed from a coiled tubing reel (78), which is conventional, via a sheave (80) and straightening rollers into the well with the tubing riser. The coiled tubing is clamped to the tubing riser by clamps (16) at intervals along its length corresponding to a joint every 30 ft. The upper end of the landing spool adaptor (28) receives the tubing (14) and also contains a termination for the coiled tubing which is typically a swage device (32). The 5".times.

Abstract: A segmented ring forms a set of latches for a tendon top connector on a floating platform. The latches reside in a housing and have either a groove or thread profile on an upper internal surface. The grooves interface with a mating groove profile on the tendon. The latches rotationally pivot backward and forward from the outer portion of the bottom surface. When the latches are forward, the profile in the internal surface engages the mating profile of the tendon top joint. When the latches are swung out, these profiles clear and permit the top joint to pass through the connector. Retraction of the latches is provided by application of force on the inside surface of an annular extension on the outer portion of the latches. This force can be provided by a variety of actuators. This top connector allows for passive dynamic engagement of the connector to the tendon top joint. When the latches are permitted to move inward, contact is made with the mating profile on the tendon top joint.

Abstract: There is disclosed an assembly including a protective sleeve spaced about an intermediate pipe of a riser which is adapted to extend through an opening in the bottom of a vertical compartment of a offshore rig for use in drilling or completing a subsea well, with a ball shaped portion on the upper end of the sleeve is closely received by ball shaped surfaces of the upper portion of the riser pipe, while a ball shaped part on the lower portion of the riser pipe is so received within the lower end of the sleeve to permit them to swivel as well as to move vertically with respect to one another.

Abstract: A drilling, production, test, and oil storage caisson for use in deep water offshore well operations. Separate low pressure and high pressure drilling risers are independently supported on buoyancy modules. Multiple drilling and production risers are left in the water and connected to the drilling rig and well(s) as needed to prevent the need for the raising and lowering of different risers during the various steps involved in beginning and completing wells. Surface and lower BOP stacks are utilized. Means for controlling the accelerations and velocity of the drilling riser buoyancy modules in the event of riser failure is provided. A subsea tree with dual master valves allows for production directly through a vertical production riser, flowline, to the production manifold on the caisson. A twisted tubing production riser is formed from three strings of tubing that are used for the flowline, annulus, and conduit for control lines.

Abstract: A controlled-pressure multi-cylinder riser tensioner has a plurality of preferably six control-cylinder units (1) with proximal ends (2) attached pivotally to a bottom surface of an operational floor (3) and distal ends (5) attached pivotally to a riser-tensioner ring (6). Pressure lines (20, 38) in communication with opposite ends of the control cylinders lead to sources of pressure (46, 47, 48, 52, 53, 62, 63) that are separately controlled. Stroke length of the control-cylinder units is typically 50 feet. Projection of the control-cylinder units downwardly into a moon pool (9) avoids their obstruction of work space on an operational floor (3) of a vessel (4). Positioning pneumatic and hydraulic machinery (10) below deck with tubing leading to the control cylinders lowers center of gravity for marine stability. An over-capacity for tensioning the marine riser with a portion of the control cylinders inactive or incapacitated increases reliability.

Abstract: An end of a composite cylinder is formed about an end connection assembly having two longitudinally arranged pieces having a contour which prevents the withdrawal of the end connection assembly from the cylinder. The two pieces of the end connection assembly are relatively forced apart and a snap ring having a certain rest diameter is reduced in diameter and inserted into the end connection assembly to a position between the pieces. The snap ring then assumes its rest diameter positioned between the pieces, forcing them to maintain intimate contact with the inner surface of the cylinder, thus removing any residual gap from the assembly process and/or preloading the interface between the end of the composite cylinder and the end assembly prior to application of an axial load.

Abstract: The invention relates to a guide arrangement 1 for a riser assembly 10 including a length of a second riser tube 6 running from a well head 2 to a surface vessel 6. First buoys 8 are provided which permit the evacuation and refilling of water to adjust the buoyancy effect and comprise a system to admit a controlled amount air or water and which are connected to the lower end of the riser assembly 10 by a first line 14 via a pulley 16 such that as the first buoys are raised the riser assembly 10 is pulled downwards towards the well head. Second buoys are provided to form a rigid frame work for the guide arrangement 1 when air has replaced the water contained therein. Support buoys 22 are connected to the first and second riser tubes 4, 8 by air line tubes 13 which enable air to be removed from and added to the support buoys 22 to adjust the amount of buoyancy they provide.

Abstract: An end of a composite cylinder is formed about a multipiece end assembly having a contour which prevents the withdrawal of the end assembly from the cylinder. The pieces of the end assembly are relatively forced apart and a spacer is positioned between the parts to maintain the pieces in intimate contact with the inner surface of the cylinder thus preloading the end prior to application of an axial load or removing any residual gap from the manufacturing process. The cylinder may have end assemblies at both ends and to which may be coupled external connectors such as flange members, for construction of a marine riser.

Abstract: A riser tensioning device that utilizes parallel air cans. A stem having an inner diameter larger than the outer diameter of the riser is positioned around the riser and is fastened in position at the wellhead of the riser on the offshore structure. A yoke attached to the stem supports a number of sleeves around the stem. Each sleeve receives a variable buoyancy air can. The sleeves and air cans are provided with a retainer that retains the air cans in the sleeves and transfers the vertical loads of the air cans to the sleeve. The retainer is also designed to allow the air cans to be selectively removed from their individual sleeves without the need to pull the entire riser assembly.

Abstract: A protective sleeve protects a riser that extends between a subsea wellhead and a floating vessel. The protective sleeve has less resistance to bending than the riser so as to allow the riser to bend normally due to normal movement of the vessel. The stiffness of the protective sleeve augments the stiffness of the riser only if the acceptable level of bending is exceeded. The protective sleeve is made up of at least three segments that are articulated together to facilitate bending.

Abstract: A tube assembly for servicing a well head injects an inner continuous coil tubing into an outer continuous coil tubing which can be connected at one end to a well head of an oil or gas reservoir. The inner coiled tubing can be connected to a tool string for servicing the well.

Abstract: A parasite mooring system is disclosed for restraining a compliant platform with respect to an auxiliary vessel. The parasite mooring system includes a parasite mooring line, a platform termination securing the parasite mooring line to the compliant platform; and a grip securing the parasite mooring line to a mooring line of the auxiliary vessel passing beyond the compliant platform. Another aspect of the present invention is a method for conducting offshore well operations in which a semisubmersible vessel is brought adjacent a compliant platform such that at least one mooring line of the semisubmersible vessel extends past the compliant platform and a parasite mooring line from the compliant platform is connected to the mooring line of the semisubmersible vessel.

Abstract: A compression element having a deflectable elastomeric member is disclosed. The compression element exhibits a decreasing axial spring rate in response to axial movement and compression of the deflectable member. The compression element may be used alone or in combination with other compression elements in riser tensioner systems to maintain a substantially constant upward tensioning force on a riser as it moves axially relative to a floating platform.

Abstract: A marine riser system which effectively combines rigid (e.g. steel catenary risers) with flexible flowlines. Basically, the steel catenary risers, which are merely the end portion of submerged rigid flowlines, are curved upward through the water in a gentle catenary path to a large, submerged buoy, which, in turn, is moored to the bottom by tension leg tether lines at a depth below the turbulence zone of the water. Flexible flowlines are fluidly connected to the steel catenary risers at the buoy and extend upward through the turbulence zone to the surface.

Abstract: A continuous bend flexible/rigid riser system is provided for coupling a subsea location to an offshore platform or vessel. The riser system comprises a first rigid pipe section coupled at its upper end to the platform. A plurality of intermediate pipe sections are mutually coupled end to end, and are coupled in series with the first rigid pipe section by means of a plurality of flexible couplings. The lower end of the last in the series of intermediate pipe sections is coupled to the subsea location. The flexible/rigid riser system reduces bending stresses transmitted along the riser by allowing angular displacement of the pipe sections with respect to one another.

Abstract: A connector employs a segmented nut and a seal. The connector includes a housing with a bore having a bowl in it. A shaft extends through the bore, the shaft having exterior threads. Segments are carried on the bowl and move between a upper retracted position to an engaged position. A drive system slides the segments down and rotates them until threads from the segments align with the shaft threads. Each segment has a resilient seal which also has a portion of a thread for sealing against the threads of the shaft. An actuator will move the seals from an outboard position which occurs during rotation to a sealing position after rotation.

Abstract: A mechanical device for centralizing a subsea riser in an opening in a floating drilling vessel. The centralizing device includes at least three arms that are pivotally connected at one end to the vessel and pivotally connected at the other end to a rotating collar with the riser extruding through the collar.

Abstract: A riser section for an oil or other fossil fuel floating platform is described having a high strength-to-weight ratio. The riser section includes a composite tubular shell for conveying the drilling mud, production oil, etc. and resisting its radial pressure. Such section also includes, though, a plurality of rods which extend along its length and act as tensile load carrying members.

Abstract: The interruptive mobile production (IMP) system comprises a floating semisubmersible structure with equipment and facilities for hydrocarbon production in association with a small tension leg wellhead platform (TLWP) having direct vertical access. The small TLWP has an upper deck positioned above the surface of the water with wellhead equipment thereon and has risers generally vertically connecting subsea wells to the upper deck.Lateral bending restraints of the risers and tendons are preferably located at about the same horizontal level as the lower pontoon section. The semisubmersible structure can be conveniently disconnected from its moorings and from the wellhead platform for demobilizing to another location while the TLWP remains tethered in place.

Abstract: A tension leg platform for supporting an oil rig above a seabed includes a deck, a buoyant hull and a single tubular tether. The tether has a lower end penetrating into the seabed and an upper end that is secured to the hull to hold the hull down against its own buoyancy. The deck is secured to the hull and adapted to support an oil rig. Multiple casing strings extend through the tether from the deck to the seabed. Supplemental buoyancy, tanks can be provided between the hull and the tether or within the tether itself.

Abstract: There is disclosed an apparatus for use in drilling an offshore well wherein the upper end of a riser is intermittently supported from a floating vessel to permit the lower ends of additional pipe sections to be connected thereto and then lowered through the table for connection at its lower end to an underwater wellhead. The riser is supported from the vessel in such a manner as to absorb the load of the riser as an additional section is landed on its upper end, and then carry the load of the riser as the vessel tilts or rolls without imposing undue bending loads on the riser.

Abstract: A preinstalled, adjustable conductor guide for offshore platforms. A conductor guide is provided with apertures spaced around its circumference. A rectangular tube is rigidly attached to the conductor guide at each aperture such that the tube extends upwardly from the conductor guide at an angle. The tube is provided with a plurality of offset slotted holes along its length on opposing sides. A slide having a plurality of offset holes along its length is received in the tube and movable between a first retracted position and a second inserted position. A bolt, received through the holes in the tube and slide, and nut are used to retain the slide in either the first or second position.

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 riser adapted to be immersed at a deep water level and including a main tube or an extension tube and peripheral lines. The riser includes at least two of an internal lining of an extension tube, a float only on the upper portion of the extension tube, and/or an extension tube and/or at least one of the peripheral lines having a weight less than that of an equivalent steel tube and/or of an equivalent steel line.

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 number of riser tensioner systems which use passive energy storage devices, such as springs, are disclosed. The geometrical construction of these systems, along with the selection of proper spring rates for the individual springs, produces systems that have a total spring rate which varies in proportion to the stroke of the riser. Thus, the tensioning force exerted by the systems on the riser remains substantially constant throughout the range of motion of the riser.

Abstract: A Heave-Restrained Platform and Drilling System (HRP/DS) comprises a floating structure having a central buoyance means, at least three out-rigger columns, and a hybrid mooring system in which a spread (lateral) mooring system functions with an array of tensioned production risers (serving as a vertical tension leg) to keep the structure generally over a specified seabed location. The central buoyancy means has supports for upper terminations of a plurality of well production risers. Each riser is comprised of plural concentric tubular structural and pressure containment elements connecting a hydrocarbon well on the sea floor with a pressure containment means located on the floating structure.

Abstract: A method is provided for reducing the force required to move a pipe through a J-tube attached to an offshore platform by coating the pipe with hydrophilic polymer and then moving the pipe through the J-tube, or by introducing a solution of hydrophilic polymer and water into the J-tube and then moving the pipe through the J-tube.

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: This invention pertains to a method of installing well conductors in such a way that the load upon the platform is significantly reduced thereby also eliminating the need for additional framing members. In accordance with this method, an end region of a well conductor is plugged which, if the conductor has a diameter-to-wall thickness ratio of about thirty to one (30:1), will cause the conductor to achieve nearly neutral buoyancy. By selectively adjusting the buoyancy of the conductor, such as by flooding or de-ballasting, additional conductor lengths may be added without imposing an unduly large load upon the platform. In this fashion, a smaller crane will be able to lower the conductor string without the need for a much larger derrick crane, which may then be more efficiently used solely to upend and stab the elongated conductors through the platform.

Abstract: A riser system includes inflatable buoyancy bladders and a near surface disconnect so that a drilling vessel can rapidly disconnect from the riser leaving the riser in a freestanding buoyant position.

Abstract: Built-up towers for offshore wells, production platforms and for microwave communications antennae, for example, are formed of triangular base members which may be made up of equilateral triangles which are arranged vertically spaced from each other and with their base legs laterally and vertically spaced, respectively, and so that the centroids of the triangles formed by said base members are aligned along a common longitudinal axis of the tower. Each of the triangular base members is connected to an adjacent base member by lateral braces which extend between the apices or nodes of each triangle to the adjacent apices or nodes of the adjacent base member.

Abstract: A hydraulic control umbilical is disclosed for supporting a plurality of hydraulic control lines along a riser between a surface facility and a subsea completion. The umbilical provides a skin encircling the riser substantially its entire length with means for supporting the skin about the riser and means for supporting the hydraulic control lines within the skin. A method for deploying and retrieving the hydraulic control umbilical is also disclosed.

Abstract: An offshore oil production and mooring system comprises a subsea well head production system connected to a subsea base located on the sea bed. A subsea restraining buoy is located at a position below the sea surface but above the sea bed. The buoy is pivottally connected by a flexible lower support line to the subsea base and by a flexible upper support line to a buoyant riser endpiece adapted for connection to a loading vessel. The endpiece is located in its rest position at a position below the sea surface but above the sea bed and is anchorable to the sea bed. A flexible production riser rises from a subsea connector to the production system to the subsea restraining buoy and is supported by the lower support line. The riser then passes over the buoy and so to the riser endpiece, this section of the riser being supported by the upper support line.

Abstract: An independent modular structure for providing lateral support for the well conductors of an offshore well platform and a method for designing and using such structure are disclosed. The modular structure can be inserted into a void in the jacket of the well platform. The vertical spacing between adjacent support points on the modular structure is determined by the lateral support requirements of the well conductors. Accordingly, the design of the platform jacket may be optimized without consideration of the lateral support requirements of the well conductors.

Abstract: An offshore subsea well includes a wellhead to which is connected an elongated somewhat flexible riser extending to the sea surface. The riser pipe is unstayed and is buoyed at least partially by a buoyancy member connected to the riser between the sea surface and the wellhead. Flow control valves and well access components are disposed at the upper end of the riser pipe and extend only a few feet above the sea surface during a normal or calm sea condition. A production fluid flowline returns to the sea floor alongisde the riser for extension to a central platform for the reservoir. The well support system provides for a low cost surface disposed Christmas tree arrangement which does not require a fixed support platform. The buoyancy member is preferably an annular can which is connected to an upper end of an elastically bendable section of the riser and which supports a tower for a work platform and hazards to navigation aids.

Abstract: A floating/tensioned production system for use in deepwater drilling and production operations generally combining a relatively small tension leg platform with a semisubmersible platform. The semisubmersible platform is provided with a working deck supported above the water surface so that an air gap exists between the working deck and the water surface. The tension leg platform provides a heave-restrained production deck for near-surface wellhead equipment. The production deck is supported above the drill site but beneath the water surface by buoyancy members and held in place by one or more tethers. Most other drilling and production equipment is located on the semisubmersible working deck. A caisson, surrounding the production deck, is used to provide a substantially dry working area. In one embodiment, the caisson is retractably attached to the production deck.

Abstract: A system for offshore operations include a column 1 extending above sea level from the seabed, which is connected by a bridge 2 to a semisubmersible offshore oil production platform 3. The connection of the bridge 2 to the platform 3 is achieved by an improved joint arrangement which permits relative rotation about both substantially vertical and horizontal axes to reduce loads transmitted to the column. The column 1 is connected by a universal joint arrangement 4 to a base on the seabed. The joint 4 has radially outwardly distributed joint surfaces which provides an axial passageway through the joint for risers. The joint arrangement includes a first main joint and a second normally unloaded ball joint which takes up the column load in the event of failure of the first joint.

Abstract: A resilient unit able to accomodate a large movement comprises a stack of elastomeric bearing units arranged to be loaded in series and to deform primarily in shear. Preferably a plurality of the stacks are provided in a nested configuration and interconnected in series to enable even greater movements to be accommodated.The resilient unit is particularly suitable for use on an offshore platform to accommodate movement between the platform and a riser pipe while also maintaining a tension loading in the riser pipe.

Abstract: A tensioner unit (12) comprising an inner cylinder (22), filled partially with hydraulic fluid, with a piston (26) and piston rod (28) reciprocal therein (sometimes referred to as a hydraulic cylinder) surrounded by a cylindrical chamber (40) (sometimes referred to as an accumulator) for hydraulic fluid and gas. The gas in accumulator (40) is pressurized to maintain the hydraulic fluid under pressure against the piston (26) placing the piston rod (28) under tension to provide the necessary tension force on a marine riser (14) and to compensate for the rise and fall of a floating platform. This is a self-contained integral unit with one end of the piston rod (28) connected to the riser (14), and the other end connected to a frame (16) supported on a platform of a TLP. A plurality of such tensioner units (12) on this frame (16) and connected to said riser (14) form a complete riser tensioner (10) without external accumulators.

Abstract: The present invention provides a service buoy for performing direct wireline maintenance of a subsea well. The buoy is maintained in position over the well by a rigid riser kept under tension and which allows for the well re-entry. The primary buoyant body of the buoy is maintained permanently submerged and a truss structure presenting the minimum surface area to the action of wind and waves extends above the sea level to support a small deck from which the wireline work can be performed. The centers of gravity and buoyancy for the buoy are in close proximity so as to minimize lateral surge and sway motions of the installed buoy.

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.

Abstract: In offshore waters an all-steel, flexible marine riser assembly may be used to transport production fluid from a submerged wellhead to a floating production facility.The marine riser assembly consists of an array of flexible steel flowline bundles which form a cantenary shape as they bend upward from the marine bottom to the production facility.

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 li

Abstract: A method and apparatus is set forth in the present invention for supporting the weight of a marine riser by use of a passive tensioning system which utilizes a buoyant member located upon the upper end of the riser. The member has a vertical slot defined through its side such that the riser may access the member from a lateral direction. Such lateral access of the riser to the member allows these buoyant members to be changed from beneath the riser when maintenance and/or inspection is required on a particular member.Since the riser need only to move laterally to access any member, and the riser may be temporarily supported at the surface by other means, the lower end of the riser does not need to be disconnected from subsea equipment when maintenance and/or inspection operations are required on a buoyant member. Well operations do not need to be interrupted, therefore, during buoyant member maintenance operations.

Abstract: A long strut between a sea-platform and the ocean bed needs to have its weight supported. Otherwise, much of its strength is used merely in supporting itself. The strut disclosed is made in sections, joined typically by screw threads. The joints need to be inspected periodically. The hollow sections of the strut have their buoyancy disposed internally, yet with the joints exposed internally for inspection by a probe that passes down inside along the length of the strut. The vulnerable joint area is made accessible to the probe. When the joint area includes welds, they too are vulnerable and need to be inspected; the fact that the buoyancy forces also have to be fed into the strut at the joint areas makes for even greater difficulty in providing access for the probe to all the places that need to be inspected. This access is provided in the various manners as shown.

Abstract: A riser string for a subsea well uses the outer conduit or air can members to support the weight of the riser string. The outer conduits have flanges on their ends which are bolted together. The outer conduits have ports to admit sea water, and a gas injection system to displace some of the sea water for providing buoyancy. Mounting plates are located at each end of the outer conduits. Inner conduits for conveying well and production fluids are mounted between these mounting plates. The mounting plates are intrinsically curved in vertical cross-section, such that when the conduit flanges are bolted together, the mounting plates flatten to provide a compressive force across the faces. Metal seals are located in the holes provided in the mounting plates for the inner conduits. The inner conduits are supported along their lengths by one or more lateral supports.

Abstract: A flotation riser having a series of annular chambers with a riser string extending in free-standing relation through said chambers, means for supplying gas to the chambers to control buoyancy, means to supply gas to a plurality of the lowermost chambers to provide an emergency supply of deballasting gas, and means for remotely releasing said supply of gas into the chambers above to render the flotation riser free-standing to permit release from the floating platform during emergencies. A method of storing emergency deballasting gas and for emergency deballasting of the chambers to render the flotation riser freee-standing including the steps of supplying gas to the lowermost chambers, retaining the gas in said lowermost chambers, and remotely releasing the gas and conducting it to higher chamber to deballast such chambers sufficient so that said flotation riser is free-standing.