Abstract: A connector for connecting sections of drilling riser pipe wherein a first riser contains a pin assembly with an external first grooved profile and a second riser contains a housing assembly. An internal split pivoting latch segment assembly carried by the housing assembly contains a second grooved profile adapted to mate to the first grooved profile and a split actuation ring movably carried by the housing assembly forces the second grooved profile of the latch segment assembly into engagement with the first grooved profile of the pin assembly. A plurality of retraction links engage an upper edge of the latch segment assembly to disengage the second grooved profile of the latch segment assembly from the first grooved profile of the pin assembly if the risers are to be disconnected.

Abstract: Systems and methods for well intervention include a lower riser package (LRP), and an emergency disconnect package (EDP). The LRP includes a tree connector, a connector and seal stab adapter (CSSA), and a LRP body; the tree connector has a profile for mating to the CSSA. The CSSA has at least one seal stab assembly for fluidly connecting with a subsea tree. The body of the LRP includes one or more sealing elements that are capable of sealing upon command, an integral annulus with an annulus isolation valve, an upper hub profile compatible with the EDP, and a lower flange profile that mates with the CSSA. The EDP includes a quick disconnect connector, at least one annulus isolation valve, and one or more sealing elements that are capable of sealing upon command. In some embodiments, an internal tie-back tool connects to the EDP via an EDP internal tie-back profile.

Abstract: A tensioner assembly for moveably carrying a conductor that communicates from a wellhead to a piece of well access equipment on a rig. The tensioner assembly includes a support frame, at least one hydraulic cylinder connected to the support frame, and at least one primary accumulator in fluid communication with the hydraulic cylinder.

Abstract: A subsea riser disconnect assembly 10 may be actuated from a drilling rig DR by axial movement of an upper riser 35 relative to a lower riser 28, for disconnecting the upper riser 35 from the lower riser 28. A subsea riser valve assembly 20 may be actuated from the drilling rig DR by axial movement of the upper riser 35 relative to the lower riser 28, for sealing an interior portion of the lower riser 28 and well bore WB below the subsea riser valve assembly 20. A drill pipe disconnect 30 may be actuated from a drilling rig DR, either onshore or offshore, for disconnecting an upper portion of drill pipe 236 from a lower portion of drill pipe 240. The drill pipe disconnect 30 may be actuatable by hydraulic and/or mechanical forces applied to the drill pipe disconnect 30 from the drilling rig DR. The drill pipe disconnect 30 may be compatible for use with or without the subsea riser disconnect assembly 10 and/or the subsea riser valve assembly 20.

Abstract: A method for servicing a component of a riser system, such as a flexible joint is disclosed. The riser system may be supported in a support apparatus such that the flexible joint and an adjoining section of riser are detached to allow for inspection, servicing, repair, and/or replacement of the flexible joint or various subcomponents thereof. An apparatus is also disclosed for supporting the flexible joint during servicing.

Abstract: Methods for deploying a subsea blowout preventer stack system comprising a lower marine riser package, a blowout preventer stack with a first ram blowout preventer, and an additional blowout preventer package releasably coupled to the blowout preventer stack and comprising a second ram blowout preventer. The subsea blowout preventer stack assembly can be deployed by coupling a drilling riser to the lower marine riser package that is releasably connected to the blowout preventer stack. The lower marine riser package and blowout preventer stack are then toward a subsea wellhead and then landed on the additional blowout preventer package that is coupled to the subsea wellhead.

Abstract: A method for preparing to move a floating structure away from a wellbore drilled below the bottom of a body of water includes filling a riser extending from the bottom of the body of water to the floating structure with water. The water in the riser is displaced to a selected first depth below the water surface. The riser is sealed at a second selected depth shallower than the first selected depth. The portion of the riser above the second selected depth is withdrawn onto the floating structure.

Abstract: A heave compensation system to enable the transfer of tubulars between a floating platform and a snubbing jack. The heave compensation system includes a first end connected to the floating platform and a second end in connection with a traveling slip assembly of the snubbing jack, the heave compensation system is operable between a disengaged position and an engaged position. When the heave compensation system is in the disengaged position the traveling slip assembly moves separate and independent from the movement of the floating platform, and when the heave compensation system is in the engaged position the traveling slip assembly is locked in a constant position relative to the floating platform.

Abstract: A method and device for use in the replacing of liquid in a riser (12) of the kind used in the recovery of petroleum offshore, wherein the riser (12) forms a connection between a wellhead (4) on or above the sea floor (6) and a drilling vessel (1), and wherein a body (30), which is arranged to keep the liquids separate, is displaced longitudinally of the riser (12).

Abstract: A riser connector connects the upper portion of a riser (12) having a latching enlargement (32) to a receptacle (14) on a vessel (16), so the riser upper end (22) can connect to a fluid coupling (42) leading to a conduit (40) on the vessel. A double-click mechanism (88), with parts on the enlargement and on the receptacle, turns a load ring on the enlargement to latch the enlargement in place when it is lifted to an upper position and lowered to a latched position, and releases it by again lifting and lowering. A cable coupling (24) is temporarily mounted on the top of the riser to enable the riser to be lifted by a cable (26), the cable coupling being later removed to connect the riser upper end to the fluid coupling on the vessel.

Abstract: The invention is directed to a tensioner for providing linear and angular movement of a drilling or production facility relative to a conduit or riser secured to the tensioner and to the wellhead in offshore operations. The tensioner 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 of the present invention preferably includes at least one top load plate that facilitates easy and quick installation and removal of the tensioner from the rig floor of the vessel or platform. The tensioner also facilitates the placement of at least one piece of equipment disposed within the area formed by the tensioning cylinders. The tensioner may also include one or more pieces of equipment, e.g., a rotary table, integrally formed with the tensioner to further increase the ease and speed of installation and removal of the tensioner from the rig floor.

Abstract: An offshore riser system has riser joints, each having a pin and a box. The pin has an external grooved profile that is engaged by a locking element carried by the box of another riser joint. An actuating ring engages with the locking element to move it into the locked position. A retractable spider supports the string of riser while the new joint is being made up. A makeup tool on the riser deploying floor moves the ring relative to the locking element, causing the locking element to move to the locked position.

Abstract: An offshore riser system has riser joints, each having a pin and a box. The pin has an external grooved profile that is engaged by a locking element carried by the box of another riser joint. An actuating ring engages with the locking element to move it into the locked position. A retractable spider supports the string of riser while the new joint is being made up. A makeup tool on the riser deploying floor moves the ring relative to the locking element, causing the locking element to move to the locked position.

Abstract: A system is disclosed for retrieving a tubular element extending into a subsea well provided with a wellhead, the tubular element being provided with a hanger suspending the tubular element at the wellhead, the hanger having a larger outer diameter than the tubular element. The system comprises a conduit assembly having a passage providing fluid communication between the wellhead and an offshore platform located above the well, the conduit assembly having at least an upper part of internal diameter allowing the tubular element to pass therethrough. The system further includes disconnection means for disconnecting the hanger from the tubular element, and retrieval means for retrieving the tubular element through the conduit assembly to the offshore platform.

Abstract: A riser assembly for offshore drilling has an inner conduit suspended within an outer riser. A seal assembly seals an annular space between the inner conduit and the riser at the lower end of the inner conduit. The seal assembly has a pressure area that is independent of the inner conduit, so that any forces acting on the assembly due to pressure in the annulus below the seal assembly pass through the assembly to the riser and not to the inner conduit.

Abstract: A protective element for a riser segment, including an elongated buffer body, at least one foot connected with the buffer body, the at least one foot being provided with an engagement part arranged to engage on a main pipe of a riser segment, the distance between the engagement part of the foot and the buffer body being such that in a mounted condition the part of the buffer body located farthest from the main pipe is located farther from the main pipe than auxiliary pipe elements arranged on the main pipe.

Abstract: The invention relates to flexible risers for transfer of hydrocarbons between a sea bed installation and a vessel (10) floating at the sea surface. The riser (18) is provided with means (20) for protecting the riser (18) from impacts. The protection means (20) covers at least the upper part of the riser (18) and is retractable to an inactive position. When in operation, the riser protection means (20) is either suspended from the vessel (10) or from a submerged turret buoy, forming part of a mooring system for the vessel (10).

Abstract: A floating offshore platform, of the type having a buoyancy can disposed within a support structure, includes a can guide assembly that has at least two compliant compression pads that are configured and arranged to provide a non-linear load-versus-deflection characteristic in response to impact loads generated by the impact of the can against the guide assembly. At least one of the compression pads is substantially stiffer (less compliant) than the other pad. The pads are arranged so that the relatively soft pad absorbs the impact load before the relatively stiff pad is engaged. In one embodiment, first, second, and third compression pads are arranged vertically, the upper and lower pads being softer (more compliant) than the middle pad. In another embodiment, a first, relatively soft, compression pad coaxially surrounds a second, relatively stiff compression pad.

Abstract: A method of preparing and operating a subsea well (23), comprising the steps of: locating a drill-through subsea tree (24) on a subsea wellhead; sealingly connecting a high pressure drilling riser (22) between the tree and a drilling platform at the sea surface; mounting a blow out preventer (16) at the top of the riser (22); drilling the well through the drilling riser and the subsea tree; and establishing a production connection between the tree (24) and a production collection facility at the sea surface through a production riser (52) which is separate from the drilling riser (22).

Abstract: Method intended for automatic control of an underwater pipe for connecting the lower end of the pipe to a wellhead, wherein the following stages are carried out: Stage 1: determining a mathematical model expressing the position of the lower end of the pipe as a function of the position of the upper end of the pipe, Stage 2: determining a reference path leading to the wellhead, Stage 3: from the mathematical model determined in stage 1, determining control laws allowing to control the path of the lower end of the pipe, Stage 4: applying determined motions to the upper end of the pipe so that the position of the lower end is as close as possible to the reference path determined in stage 2.

Abstract: A buoyancy can for supporting an offshore oil and gas riser includes an axial bore through which the riser extends coaxially, and a radio-axial slot extending through a side of the can and into the axial bore. A pair of spaced-apart support features are disposed coaxially on the riser, and the can includes a pair of corresponding sockets in the axial bore thereof. The sockets are adapted to receive and vertically support respective ones of the support features in a complementary, axial engagement. The can is placed in the water and moved laterally relative to a fully assembled, vertically supported riser such that the riser passes through the radio-axial slot of the can and into the axial bore thereof without the need for disassembly of the upper portion of the riser. The relative vertical positions of the can and riser are then adjusted such that the support features engage and seat within respective ones of their complementary sockets.

Abstract: A subsea riser disconnect assembly 10 may be actuated from a drilling rig DR by axial movement of an upper riser 35 relative to a lower riser 28, for disconnecting the upper riser 35 from the lower riser 28. A subsea riser valve assembly 20 may be actuated from the drilling rig DR by axial movement of the upper riser 35 relative to the lower riser 28, for sealing an interior portion of the lower riser 28 and well bore WB below the subsea riser valve assembly 20. A drill pipe disconnect 30 may be actuated from a drilling rig DR, either onshore or offshore, for disconnecting an upper portion of drill pipe 236 from a lower portion of drill pipe 240. The drill pipe disconnect 30 may be actuatable by hydraulic and/or mechanical forces applied to the drill pipe disconnect 30 from the drilling rig DR. The drill pipe disconnect 30 may be compatible for use with or without the subsea riser disconnect assembly 10 and/or the subsea riser valve assembly 20.

Abstract: A bottom-to-surface connection installation for an undersea pipe. The installation comprises a vertical riser having its bottom end connected to an undersea pipe on the sea bed, and having a float at its top end, and a pipe connecting a floating support at the top end of the vertical riser. The connection between the riser bottom end and the undersea pipe is via an anchor system having a base on the sea bed. The base holds and guides junction elements between the bottom end of the riser and the end of the lower end of the undersea pipe. The junction elements comprise a rigid pipe element presenting an angled bend and a pipe coupling element which are fixed to a moving support of the base. The junction elements are fixed to the moving support and are free to move only in translation in a single longitudinal direction.

Abstract: A cylinder-stem assembly to floating platform, gap controlling interface guide. A longitudinal wear strip and mating guide are positioned at an angle relative to a tangent to the nominally round exterior cylinder of the cylinder. Cylinder guides may be provided at more than a single elevation. The corners of the contacting surfaces of the wear strips may be rounded to reduce the risk of galling and to avoid any obvious point or line loading. During assembly, the cylinder-stem assembly is rotated after insertion into its slot in the floating platform. The rotation centers the cylinder and also may be used to control the magnitude of the gap or an interference fit.

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

Abstract: A system is disclosed for retrieving a tubular element extending into a subsea well provided with a wellhead, the tubular element being provided with a hanger suspending the tubular element at the wellhead, the hanger having a larger outer diameter than the tubular element. The system comprises a conduit assembly having a passage providing fluid communication between the wellhead and an offshore platform located above the well, the conduit assembly having at least an upper part of internal diameter allowing the tubular element to pass therethrough. The system further includes disconnection means for disconnecting the hanger from the tubular element, and retrieval means for retrieving the tubular element through the conduit assembly to the offshore platform.

Abstract: This invention provides a production riser system that enables fluid communication in a deepwater drilling environment through the use of a variable buoyancy device supporting both a hybrid riser tower and an steel catenary riser (SCR) system. Fluid communication is enabled between a surface production facility or unloading buoy and local and remote subsea (or remote non-subsea) production and export systems.

Abstract: This invention relates to a marine riser tower (112, 114) for use in the production of hydrocarbons from offshore wells. The riser tower (112, 114) includes a plurality of fluid conduits, which may comprise production flow lines (P), gas-lift lines (G), water injection lines (NV) and/or umbilicals (U). The conduits are supported in a single structure, and at least one of said conduits is provided with its own insulation within said structure.

Abstract: To maintain a riser under tension, the riser can be connected to a gripper (5, 12) which is connected to vertical toothed racks (4) that are in constant engagement with gear wheels (22) which are driven with constant torque, preferably by hydraulic motors (9) at constant pressure. An apparatus is also described for putting the riser under tension. The apparatus includes vertical guides (7) in a derrick, toothed racks (4) in the vertical guides (7), a gripper (5, 12) designed for interaction with a riser connected to the racks (4), and drive units (9) arranged in the derrick for drive-actuation of the racks (4) in the vertical guides (7).

Abstract: A system for establishing a fluid communication between a floating-body and a wellhead is provided. The system comprises a means for fluidly connecting the floating-body and the wellhead that defines a major axis essentially extending from about the floating-body to about the wellhead. The system further comprises a means for absorbing and releasing energy in response to the heave and surge of the floating-body that flexes in a direction essentially parallel to the major axis. An apparatus is also provided for establishing a fluid connection between a floating-body and a wellhead that is fixed to the seafloor. The apparatus comprises a riser pipe and a series of pre-formed curves in the riser pipe that defines a substantially linear axis between the floating-body and the wellhead.

Abstract: A guide for a buoyancy can on a floating offshore platform. The platform includes at least one support structure adjacent the buoyancy can. The guide comprises at least one compression pad supported by the support structure and adjacent the exterior surface of the buoyancy can. Lateral movement of the buoyancy can toward the support structure compresses the compression pad so as to absorb the force generated by the buoyancy can movement, and so as to protect the buoyancy can and components of the floating offshore platform from damage.

Abstract: 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 is disclosed. 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 is also disclosed.

Abstract: The present invention is a wellhead system for use in completing at least two well bores from within a single conductor housing. The wellhead system comprises at least one wellhead housing which is supported on the conductor housing and which comprises a top portion that is adapted to be connected to a lower portion of a wellhead component, a casing hanger which is supported within the wellhead housing and from which a casing string is suspended, and a connector for securing the wellhead component to the wellhead housing. In accordance with the present invention, the connector is selected from the group consisting of a latch ring and a segmented clamp assembly.

Abstract: A method of drilling an offshore underwater well comprising the steps of installing a riser conduit so that it is substantially vertically supported at a production deck. The riser conduit deviates progressively further from the vertical with increasing sea depth, so that its end can be anchored at the seabed by a skid either at an oblique angle so that drilling into the seabed can be carried out at the oblique angle, or horizontally, so that the riser conduit can extend some considerable distance across the seabed before drilling is carried out.

Abstract: A frame and system for adding buoyancy to a riser used in connection with floating platforms is provided which, in some example embodiments, includes a stem attached to multiple supports which include flanges arranged to take impact and abrasion loads off an internal buoyancy module. An air management system is also provided.

Abstract: A method and apparatus for connecting riser between a floating vessel and a subsea structure that reduces the size of the air tanks used and thereby allow closer positioning of the well slots and overall reduction in size of the floating vessel is disclosed. The apparatus includes an inverted hydraulically actuated connector positioned on the subsea structure and oriented to receive and sealingly attach to a complementary end connection member on the lower end of the riser string.

Abstract: A floating platform system supports one or more decks (14) above the water surface for accommodating equipment to process oil, gas and water recovered from a subsea hydrocarbon formation. The platform is secured to the seabed by one or more tendoms (17). A central column (12) of the platform includes a moonpool (19) extending axially through the central column (12). The moonpool (19) is open at the lower and upper ends thereof. Riser lateral restraint members (32) are supported within the moonpool (19) for laterally restraining risers (16) disposed in the moonpool (19) and minimizing riser spacing and riser deflection.

Abstract: A subsea riser disconnect assembly 10 may be actuated from a drilling rig DR by axial movement of an upper riser 35 relative to a lower riser 28, for disconnecting the upper riser 35 from the lower riser 28. A subsea riser valve assembly 20 may be actuated from the drilling rig DR by axial movement of the upper riser 35 relative to the lower riser 28, for sealing an interior portion of the lower riser 28 and well bore WB below the subsea riser valve assembly 20. A drill pipe disconnect 30 may be actuated from a drilling rig DR, either onshore or offshore, for disconnecting an upper portion of drill pipe 236 from a lower portion of drill pipe 240. The drill pipe disconnect 30 may be actuatable by hydraulic and/or mechanical forces applied to the drill pipe disconnect 30 from the drilling rig DR. The drill pipe disconnect 30 may be compatible for use with or without the subsea riser disconnect assembly 10 and/or the subsea riser valve assembly 20.

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 tieback connector includes 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 composed 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 riser connector is provided for connecting a riser to a wellhead assembly having a bore therethrough. The connector includes a housing having a first and a second end. The first end of the housing has an opening and is adapted for mounting to the wellhead assembly with the opening in communication with the bore of the wellhead assembly. The second end has a first opening connectable to the riser having a diameter at least the same as the inner diameter of the riser, and a second opening, having a diameter at least substantially the same as the diameter of the bore of the wellhead assembly. The housing further includes a first conduit connecting the opening in the first end of the housing to the first opening in the second end of the housing, and a second conduit connecting the opening in the first end of the housing to the second opening in the second end of the housing. In use, first well operations are conducted through the riser in the conventional manner.

Abstract: A device in connection with a riser for the transport of oil and/or gas, possibly including water, from a transport system, transport pipe (5) or similar on the sea bed to a platform or similar. The solution is characterized in that, in order to use a riser (1) for the transport of oil and/or gas from a small field with low oil/gas production where a transport pipe (5) with a small diameter is used, a flexible pipe (4) with generally the same internal diameter as the transport pipe (5) is arranged inside the riser (1). At its upper and lower ends, the riser (1) is provided with a coupling (6, 7), which forms a seal between the transport pipe (5) and the flexible pipe (4) and also forms a seal at the ends of the riser so that it is closed.

Abstract: A dual riser assembly for use with an offshore multi-activity drilling assembly to conduct drilling operations from a deck above the surface of a body of water into the bed of the body of water utilizing two risers, a first and a second, which extend from a location above the surface of a body of water to a common location adjacent to the bed of the body of water. Each riser terminates, at a distal end, into a dual riser assembly, allowing for selective open internal communication between each of the two risers and a single wellhole.

Abstract: A riser connector is provided for connecting a riser to a wellhead assembly having a bore therethrough. The connector includes a housing having a first and a second end. The first end of the housing has an opening and is adapted for mounting to the wellhead assembly with the opening in communication with the bore of the wellhead assembly. The second end has a first opening connectable to the riser having a diameter at least the same as the inner diameter of the riser, and a second opening, having a diameter at least substantially the same as the diameter of the bore of the wellhead assembly. The housing further includes a first conduit connecting the opening in the first end of the housing to the first opening in the second end of the housing, and a second conduit connecting the opening in the first end of the housing to the second opening in the second end of the housing. In use, first well operations are conducted through the riser in the conventional manner.

Abstract: A method for a dynamic shut-in of a subsea mudlift drilling system. The method comprises detecting a kick, isolating a wellbore, and adjusting a subsea mudlift pump and a surface mud pump to provide a selected wellbore pressure. Selected well parameters are measured and used to calculate a kick intensity. The invention is also a method for a dynamic shut-in of a subsea mudlift drilling system including detecting a kick and isolating a wellbore. A first inlet pressure of a subsea mudlift pump and a first drill pipe pressure are measured. A rate of the subsea mudlift pump and a rate of a surface mud pump are adjusted to pre-kick circulation rates. A second inlet pressure of the subsea mudlift pump and a second drill pipe pressure are recorded. The measured values are used to calculate a kick intensity.

Abstract: A universal catenary riser support that can be designed to accommodate all riser pipe diameters typically considered for production of offshore hydrocarbons and allows the catenary riser to exit from the vessel at any azimuth angle and at a wide range of angles from the vertical. The support structure at the keel of the offshore structure is provided with a receptacle to receive a curved riser segment. The curved riser segment is adapted to be received in the receptacle. The curved riser is also adapted to receive a vertical riser section through the offshore structure. Relative motions between the catenary riser and the offshore structure are accommodated by a tapered section of riser or flexible joint attached to the curved riser section. A removable plug may be provided in the curved riser section to prevent water from entering the catenary riser during installation in the offshore structure.

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: 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: A deep ocean drilling system is disclosed for drilling offshore wells in extremely deep water using smaller and more economical drilling vessels. The system utilizes a reduced diameter drilling riser that reduces the size and cost of conventional floating drilling unit. The reduced diameter drilling riser is detached from the blowout preventer stack and repositioned and attached to a mud return assembly. Large diameter casing is lowered into the wellbore outside of the reduced diameter riser. Thereafter, the reduced diameter drilling riser is released from the mud return assembly and repositioned over and reconnected to the blowout preventer stack.

Abstract: A riser tube tower for stabilizing riser tubes extending from respective wellheads associated with a seabed frame on the seabed to a platform, preferably a tension leg platform, at the sea surface. The riser tube tower includes vertical wires connecting the platform with the seabed frame. Horizontally disposed guide plates are fixed in position at one or more levels of the tower. Vertically movable shuttle plates are located in the vertical spaces over, between, and under the guide plates. The vertical wires and riser tubes pass through spaced apertures in the guide plates and the shuttle plates. The apertures in the shuttle plates are aligned with respective apertures in the guide plates. Bushings are disposed in the apertures of the guide plates and the shuttle plates for protecting the guide plates and shuttle plates from the riser tubes and wires, and for reducing friction therebetween. Elevator devices move the shuttle plates vertically above, below, or between the guide plates.