Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
  • E21B17/01—Risers
  • E21B17/012—Risers with buoyancy elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B22/00—Buoys
  • B63B22/02—Buoys specially adapted for mooring a vessel
  • B63B22/021—Buoys specially adapted for mooring a vessel and for transferring fluids, e.g. liquids
  • B63B22/025—Buoys specially adapted for mooring a vessel and for transferring fluids, e.g. liquids and comprising a restoring force in the mooring connection provided by means of weight, float or spring devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
  • B63B35/44—Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices
  • B63B35/4406—Articulated towers, i.e. substantially floating structures comprising a slender tower-like hull anchored relative to the marine bed by means of a single articulation, e.g. using an articulated bearing

Definitions

• the present invention relates to a marine riser tower, of the type used in the transport of hydrocarbon fluids (gas and/or oil) from offshore wells.
• the riser tower typically includes a number of conduits for the transport of fluids.
• apparatus for buoyancy tensioning of offshore deepwater structures It finds particular application in tensioning a slender, vertical or near-vertical, bottom- anchored, submarine structure, such as a riser or a bundle of risers (which may, or may not, include a structural member) or an umbilical.
• Tensioning is the act of ensuring that a marine structure doesn't experience excursions from its nominal upright position that would fall outside the acceptable limits, even in extreme environmental conditions, the said limits being possibly defined with reference to the occurring current profile and sea state. There should always be sufficient tension to ensure stability, no matter the weight of the structure and the weight of the pipelines/risers hanging off the structure.
• the structure may form part of the so-called hybrid riser, having an upper portions (“jumpers”) made of flexible conduit and suitable for deep and ultra-deep water field development.
• US-A-6082391 (Stolt/Doris) proposes a particular Hybrid Riser Tower
• HRT Hybrid Riser Tower
• Buoyancy tensioning conventionally requires a large hollow buoyancy tank including a number of compartments, which, when filled with air or specific gas as nitrogen and submerged, provides the required tensioning force to the top of the riser tower.
• manufacture of such a large tank is expensive.
• a buoyancy device for tensioning an elongate vertical (or quasi vertical) subsea structure at a point below the sea surface, anchored at its bottom, wherein said device comprises as its main buoyancy elements a plurality of hollow elongate objects, and further comprises at least one auxiliary buoyancy element, said at least one auxiliary buoyancy element substantially comprising a solid buoyant material.
• Vertical or quasi vertical is to be taken to mean that the structure is of the vertical tower type of riser structures (as opposed to catenary or other curved form of structure), particularly taking into regard its length. It is not to be interpreted as a structure that must be literally vertical, and in reality, it very rarely will be, due to the actions of sea currents and other forces.
• Said hollow elongate objects may be cylindrical. They may comprise sections of pipe, capped at both ends.
• Said hollow elongate objects may be arranged evenly and vertically around a central core, such that they are parallel with the buoyancy device's vertical axis.
• Said buoyancy device may comprise a supporting structure to support said hollow elongate objects around said core.
• Said plurality of hollow elongate objects preferably should be floodable.
• Said at least one solid buoyancy element may comprise a foam element.
• Said solid buoyancy element should preferably provide sufficient uplift to keep the buoyancy device afloat when all of said hollow elongate objects are flooded.
• Said plurality of hollow elongate objects may be arranged around the periphery of said solid buoyancy element.
• Said elongate subsea structure may comprise one or more rigid conduits.
• Said conduits may be arranged around a structural core. Alternatively some conduits may be located inside a tubular core. Alternatively the tubular core may be used as a conduit, which may be the sole conduit, or the structure may comprise further conduits arranged therearound.
• an elongate subsea structure having anchoring means at its bottom and a buoyancy device for tensioning said elongate subsea structure attached at, or near its top
• said buoyancy device comprises as its main buoyancy elements a plurality of hollow elongate objects, and further comprises at least one auxiliary buoyancy element, said at least one auxiliary buoyancy element substantially comprising a solid buoyant material.
• Said buoyancy device may include any of the variations described with reference to the first aspect of the invention above.
• Said elongate subsea structure may comprise one or more rigid conduits arranged around a structural core.
• some conduits may be located inside a tubular core.
• the tubular core may be used as a conduit, which may be the sole conduit, or the structure may comprise further conduits arranged therearound.
• Fig. 1 shows a known type of riser structure in an offshore oil production system
• Figs. 2a to 2i show the buoyancy tank according to an embodiment of the invention in different stages of fabrication
• Figs. 3a to 3c show in closer detail the top and bottom of the buoyancy tank of Fig. 2 with one, six and twelve buoyancy tubes attached;
• Fig. 4 shows the buoyancy tank of Fig. 2 in cross section.
• Vertical riser towers are provided at 112 and 114, for conveying production fluids to the surface, and for conveying lifting gas, injection water, gas and treatment chemicals such as methanol from the surface to the seabed.
• the foot of each riser, 112, 114, is connected to a number of well heads/injection sites 100 to 108 by horizontal pipelines 116 etc.
• Further pipelines 118, 120 may link to other well sites at a remote part of the seabed.
• the top of each riser tower is supported by a buoy
• a floating production unit (FPU) 128 is moored by means not shown, or otherwise held in place at the surface.
• FPU 128 provides production facilities, storage and accommodation for the fluids from and to the wells 100 to 108.
• FPU 128 is connected to the risers by flexible flow lines 132 etc arranged in a catenary configuration, for the transfer of fluids between the FPU and the seabed, via riser towers 112 and 114.
• Individual pipelines may be required not only for hydrocarbons produced from the seabed wells, but also for various auxiliary fluids, which assist in the production and/or maintenance of the seabed installation.
• a number of pipes carrying either the same or a number of different types of fluid are grouped in "bundles", and the riser towers 112, and 114 in this embodiment comprise each one a bundle of conduits for production fluids, lifting gas, water and gas injection, oil and gas export, and treatment chemicals, e.g. methanol. All the component conduits of each bundle are arranged around a central core, and are often held in place relative to each other (in the two lateral dimensions, longitudinal movement not being prevented) by guide frames attached to the central core.
• FIGs 2a to 2i show the buoyancy device according to an embodiment of the invention in different stages of fabrication.
• Figures 3a to 3c also show in closer detail the top and bottom of the buoyancy device according to an embodiment of the invention with one, six and all buoyancy tubes attached.
• Figure 4 shows the buoyancy device in cross section (with only one buoyancy tube shown for clarity).
• the buoyancy device comprises a central core 200, with top and bottom flanges 210 which support the main tube supports 220. Extensions 220a are then added to the main tube supports 220, so as to provide a plurality of insets 230 for the placing therein of the buoyancy tubes 240.
• Buoyancy foam (syntactic foam) 250 is placed around the core 200. Around this are placed the buoyancy tubes 240 such that they are held in place by main supports 220, such that their top and bottom rest in the insets 230.
• One of said buoyancy tubes 240 is shown in Figure 2f with closed ends shown in close-up.
• Figures 2g-2i show the buoyancy tank with 1 , 6 and all12 buoyancy tubes 240 attached.
• Each buoyancy tube 240 is closed and hollow and therefore produces uplift when submerged.
• the combined uplift from all the buoyancy tubes (and buoyancy foam, if present) is sufficient for tensioning a riser tower structure.
• each buoyancy tube 240 should be made floodable, for ballasting purposes.
• the buoyancy foam 250 results in, in one embodiment, sufficient uplift to keep the entire buoyancy device afloat, even when all buoyancy tubes 240 are flooded/ballasted. Therefore, it is not possible to accidentally lose this buoyancy device to the bottom of the sea.
• each pipe is a separate buoyancy tank
• overall buoyancy is also more controllable than with a conventional buoyancy tank, as flooding/ballasting may be done selectively, to only one or a portion of the buoyancy tubes 240. Therefore, it may be possible (assuming less foam than in the embodiment described in the previous paragraph), to balance forces resultant from the empty buoyancy tubes 240, buoyancy foam 250, and the weight of the device including ballasted tubes, so to make the device neutrally buoyant (or near so), making it easier to manoeuvre.
• the buoyancy device is suitable for any type of essentially vertical riser tower structure, including those that comprise a single riser conduit or a bundle of riser conduits, and those that have a central core, or not. Any central core, where present, may additionally act as a riser conduit, and in such a case, may comprise the whole riser structure, having no other conduits.
• the buoyancy device may be rigidly connected to the top of the riser structure, or connected via a mechanical articulation (such as a double pivot joint, or universal joint with two degrees of freedom), or flexible joint, or tether.
• buoyancy tube arrangement depicted is simply for illustration and may be varied, including provision of less or more than the twelve buoyancy tubes shown.
• buoyancy foam (or other material) may take different forms to that shown.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Ocean & Marine Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Combustion & Propulsion (AREA)
• Chemical & Material Sciences (AREA)
• Geology (AREA)
• Mining & Mineral Resources (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Architecture (AREA)
• Civil Engineering (AREA)
• Structural Engineering (AREA)
• Fluid Mechanics (AREA)
• Environmental & Geological Engineering (AREA)
• Physics & Mathematics (AREA)
• Earth Drilling (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=40139548

Family Applications (1)

Country Status (7)

Families Citing this family (6)

Family Cites Families (11)

• 2008
  • 2008-11-07 GB GBGB0820395.2A patent/GB0820395D0/en not_active Ceased
• 2009
  • 2009-10-06 CN CN2009801401162A patent/CN102202963A/zh active Pending
  • 2009-10-06 AU AU2009302018A patent/AU2009302018A1/en not_active Abandoned
  • 2009-10-06 EP EP09774936A patent/EP2334545A2/en not_active Withdrawn
  • 2009-10-06 BR BRPI0920575A patent/BRPI0920575A2/pt not_active IP Right Cessation
  • 2009-10-06 WO PCT/IB2009/055204 patent/WO2010041229A2/en not_active Ceased
  • 2009-10-06 US US12/998,313 patent/US20110253027A1/en not_active Abandoned

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events