Classifications

• • 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
  • B63B35/4413—Floating drilling platforms, e.g. carrying water-oil separating devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B1/00—Hydrodynamic or hydrostatic features of hulls or of hydrofoils
  • B63B1/02—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement
  • B63B1/10—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement with multiple hulls
  • B63B1/107—Semi-submersibles; Small waterline area multiple hull vessels and the like, e.g. SWATH
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B75/00—Building or assembling floating offshore structures, e.g. semi-submersible platforms, SPAR platforms or wind turbine platforms

Definitions

• This invention relates to a simplified floating production system for an undersea oil well, and in particular to a system which seeks to minimise the amount of equipment on the sea bed.
• the invention also relates to a semisubmersible vessel for use with such a system.
• pipes from the undersea wells extend straight up to a fixed platform on the surface, with the well heads on the main deck.
• a floating production vessel is moored alongside to reduce the size, and hence the cost, of the platform. Nonetheless, the cost of such a fixed platform is high.
• the legs must be of rounded cross-section in view of the action of waves and currents on the structure.
• the legs and the elongate bottom connecting structures are of cylindrical cross-section which means that complicated connecting sections are required at the bottom corners of the vessel if the required rigidity is to be obtained.
• the present invention also aims -to provide a floating production system wherein the amount of subsea equipment is minimised and wherein relatively rigid pipes can be " used not only for flow lines but for risers and other purposes.
• Figure 1 shows a perspective view of a floating production system in accordance with the present invention
• Figure 2 shows a lateral elevation of the system shown in Figure 1 ;
• Figures 4 to 8 show the stages of installation of the system of Figures 1 to 3;
• Figure 9- shows the structure of one embodiment of the semi- submersible vessel of the invention.
• Figure 12 is a partial view of an undersea cable for the export of electricity from the vessel
• FIG. 13 shows diagrammatically how part of the vessel of Figure 9 is assembled
• the wellheads 10 each comprise simply a master valve and an annulus valve.
• the risers 12 curve tangentially from the buoy 18 down to the seabed and then along the seabed to the
• the buoy 18 comprises a number of buoyancy tanks 26 and is anchored to the seabed by four anchor chains 20 which hold it against any substantial movement.
• the tanks can be filled or emptied to adjust the depth of the buoy.
• catenary steel pipes 12 are used for conveying oil or gas. Some- of them will be used for choke and kill lines. The installation of the system is illustrated in Figures 4 to 8.
• a steel riser 12 is conveyed to the • site and laid in position by a pipelaying barge 34, anchored adjacent the buoy 18 which at this stage is on the surface.
• the upper end of the riser is then transferred to a crane 32 and lifted into position on the buoy 18 as shown in Figure 5.
• the upper end of the riser is secured to the buoy.
• a flexible riser 22, with one end connected to the crane 32, is then secured by that end to the buoy 18. Its other end (the lower end as shown in Figure 6) is connected by a cable 36 to the barge 24.
• This end is then winched by a derrick 30 to be connected up at 31 to the required processing facilities on the barge.
• the adjacent ends of the flexible riser 26 and the steel riser 12 are then connected on the buoy 18.
• the barge according to the invention has a square base 58 from which the four upright legs 60 project upwards to support the deck 62.
• the legs 60 each have a cross section made up of four boxes welded together, imparting considerable strength and rigidity.
• the base 58 is made up of pairs of boxes welded together side by side and the deck is constructed from a single layer of boxes.
• the deck is provided with conventional equipment for a semi-submersible vessel of this type, including a deck crane 52, accommodation 54, a helicoptor landing pad 56 and winches 63.
• FIG 10 there is shown a semi- submersible barge the upper part of which is similar in shape to that shown in Figure 9 and which has an upper deck 70 which can be equipped in the same way as that of Figure 9. The equipment need not therefore be described again.
• the upper deck is supported on four piers or legs 71 which project upwardly from a subsea housing 73.
• the housing 73 is largely hollow to provide the required buoyancy, and houses buoyancy tanks and oil or liquefied gas storage tanks 75. The latter can be reached via hatches 74 giving access throuh the piers 71.
• a delivery and pump ⁇ ing system 76 is also provided at the bottom ends of the tanks. It is further envisaged in accordance with the invention that two or more semi-submersible barges, such as those shown in Figure 9 and 10, may be secured together, for example by bolting or welding, to form larger platforms.
• Figure 11 shows schematically an on—board gas-fired generating system which may be provided on the vessels of Figures 10 and 11. Gas from the risers is fed via a riser balcony toa processing plant 81 which renders the gas suitable for combustion.
• the gas is then fed to a gas turbine 80 which drives an electrical generator 86 via a reduction gear system 84.
• the generator ' 86 supplies to main power board 88 of the vessel which supplies the power requirements of the vessel such as heating, lighting, pumps etc.
• Power can also be exported to the shore via a submarine cable such as that 5 illustrated in part in Figure 12.
• This comprises an insulated cable 98 with a protective sheath 99 of helically wound wire made from, or coated with, a suitably non-corroding alloy.
• the platform could for example be triangular and supported by three legs rather than four.
• the base will norm ⁇ ally also be triangular in plan view.
• the shape of the boxes can also be adapted so that simple butt welds will 0 still give continuous walls without the need for complicated connecting sections.
• one of four legs 60 support ⁇ ing the platform 62 is made up of steel boxes 50 welded together in layers of four.
• the platform 62 and base 104 are also square so that simple abutting connections can be made between the leg, the platform and the base to form continuous flat structural surfaces without the need for complicated connecting structures as in the cylindrical- columned vessels of the prior art.
• each of the boxes 15 has one open vertical side the edges of which abut, and are welded to a vertical side of an adjacent box. There is thus prod ⁇ uced a simple structure having high rigidity, and in part ⁇ icular having a strong central connection up the middle of the leg.
• the base 104 is made up of rectangular boxes 102, butt- welded together in much the same way as the boxes 50 making up the leg.
• the insides of the boxes may define separate compart ⁇ ments or continuous shafts or passages, depending on whether the boxes have one, two or three open sides. These shafts, passages and compartments can be used for access, ducting, pipes, cables, accommodation or storage as desired.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• Ocean & Marine Engineering (AREA)
• Architecture (AREA)
• Structural Engineering (AREA)
• Civil Engineering (AREA)
• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Earth Drilling (AREA)

Applications Claiming Priority (4)

Publications (1)

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ID=26292815

Family Applications (1)

Country Status (6)

Cited By (3)

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• 1988
  • 1988-10-03 BR BR888807228A patent/BR8807228A/pt unknown
  • 1988-10-03 JP JP63507889A patent/JPH02501561A/ja active Pending
  • 1988-10-03 WO PCT/GB1988/000816 patent/WO1989002848A1/en not_active Application Discontinuation
  • 1988-10-03 AU AU24855/88A patent/AU2485588A/en not_active Abandoned
  • 1988-10-03 EP EP88908308A patent/EP0335928A1/de not_active Withdrawn
• 1989
  • 1989-06-01 FI FI892687A patent/FI892687A0/fi not_active IP Right Cessation

Non-Patent Citations (1)

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