EP0122273A1 - Structure flottante semi-submersible - Google Patents

Structure flottante semi-submersible

Info

Publication number
EP0122273A1
EP0122273A1 EP83903230A EP83903230A EP0122273A1 EP 0122273 A1 EP0122273 A1 EP 0122273A1 EP 83903230 A EP83903230 A EP 83903230A EP 83903230 A EP83903230 A EP 83903230A EP 0122273 A1 EP0122273 A1 EP 0122273A1
Authority
EP
European Patent Office
Prior art keywords
platform
legs
semi
floating
submersible
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP83903230A
Other languages
German (de)
English (en)
Inventor
Einar Kjelland-Fosterud
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
KVAENER ENGINEERING AS
Kvaerner Oil and Gas AS
Original Assignee
KVAENER ENGINEERING AS
Kvaerner Engineering AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by KVAENER ENGINEERING AS, Kvaerner Engineering AS filed Critical KVAENER ENGINEERING AS
Publication of EP0122273A1 publication Critical patent/EP0122273A1/fr
Withdrawn legal-status Critical Current

Links

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
    • B63B1/04—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement with single hull
    • B63B2001/044—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement with single hull with a small waterline area compared to total displacement, e.g. of semi-submersible type
    • 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
    • B63B2035/442—Spar-type semi-submersible structures, i.e. shaped as single slender, e.g. substantially cylindrical or trussed vertical bodies

Definitions

  • the invention relates to a floating, semi-submersible structure of steel and/or concrete, comprising at least three mutually connected legs which are spaced a distance of at least twice the largest cross-sectional dimension of the legs and adapted to contain ballast at their lower ends to increase the stability of the structure.
  • a semi-submersible vessel would under such conditions move somewhat less than half the movements of an ordinary ship's hull.
  • Semi-submersible vessels in principle consist of one or more submerged pontoons plus a number of legs or columns which penetrate the water surface and support a deck or a superstructure above the water. The improvement of the characteristics with respect to vertical movement or heave is achieved by balancing the cross-sectional area of the columns against the volume and shape of the pontoons, as will be explained:
  • the first floating production platform which has been built is the Tension Leg Platform for Hutton. In this plat-
  • OMPI iVty 1PO form the hull is shaped as a semi-submersible vessel to reduce the forces acting on the tension legs which tie the platform at a fixed distance from the sea bed.
  • the platform substantially moves on a spherical surface with its centre in the anchorage on the bottom.
  • the weight of the equipped deck of the Hutton platform is 17.000 ton, and the tension in the legs totals 13.600 ton in calm sea.
  • the supporting structure must withstand the variations in tension in a seaway, also in case one tension leg should break.
  • the supporting structure weighs around 30.000 ton.
  • the total displacement is thus about 60.000 ton, and the weight of the anchorages amounts to another 8.000 ton.
  • Shell Spar which is installed on the Brent field. This is a narrow, deep concrete cylinder having a smaller diameter close to the surface of the sea than lower down.
  • the cylinder is anchored in a conventional manner. It is designed as a storage and loading structure with only small deck weight. The structure is kept upright by means of
  • Shell Semi-Spar This is a semi- submersible platform having a tuned volume ratio between the columns and a cylindrical pontoon. Ballast in six legs con ⁇ tribute to the stability. These legs will be lowered after the platform has been towed into position. Before this is done, the structure has a very small draught and can be con ⁇ structed at shallow water yards. Since the pontoon is positioned at a relatively large depth, the heave motion is limited to approximately 1/3 of the wave height. For this reason the platform can probably be used in recovering oil in the North Sea, but not for gas production, which places heavier demands on the riser system.
  • a further design is the articulated tower.
  • This structure is kept in an upright position by buoyancy elements and ballast, and the tower is secured to the seabed by an universal joint.
  • the amount of ballast is chosen so that the joint is hardly stressed in calm sea.
  • the structure can thus be regarded as a floating platform which is anchored in the joint.
  • Articulated towers are built as loading towers or flare stacks. If designed as a production unit, they are made from concrete or a combination of concrete and steel, or as a shell or framework structure.
  • the dimensions can be optimized as for semi-submersible platforms so as to reduce the loads imposed on the universal joint.
  • a disadvantage is that the joint is difficult to repair because of its size and position.
  • An articulated tower platform for 38.000 ton pay- load and 300 m water depth will have a steel weight of
  • the main purpose of the invention is to develop a floating structure in which the riser system is subjected to significantly smaller loads than in previously known structures of floating production platforms, thus making deep water production of both oil and gas possible.
  • Another object is to avoid the complicated,, heavy and costly tension leg systems used in tension leg platform designs, to avoid the depth limit and the vulnerable joint of the articulated tower and to avoid the risk of capsizing after damages because of the poor stability of conventional semi-submersible platforms.
  • the draught of the structure in operation is at least twice the maximum wave height in the waters for which the structure is designed. In the North Sea the maximum wave height is 32 m, and hence the platform shall have a draught of at least 64 m. However, it is preferred to make the draught at least 128 m, and a large platform can have a draught of approximately 200 m.
  • the invention can also be regarded as a combination of a semi-submersible vessel (which is stable because of the spreading of the waterplane area over a large area and the positioning of ballast at a substantial distance from the vertical centre axis) and a deep cylinder of the Spar type. No indication of such a combination can be seen to have been suggested or constructed.
  • the structure is shaped as a floating tower, it will be possible to provide bearings or anchorages supporting the riser or to protect it by passing it through a column
  • the riser From this level and down to the sea bed the riser will not be subjected to wave forces. Additionally, the current in these depths usually flows at less than half the speed of the surface current.
  • the free length of the riser is reduced by a length corresponding to the draught of the platform, and also this fact contributes to a reduction of the forces on the riser. Since the wave forces have a resulting force attacking near the surface, the wave induced rotations of the platform will be centered close to the maximum draught. Thereby, the waves will induce only small horizontal motions of the free length of the riser, * and small changes in angle between the riser and the platform.
  • the volume of the lower part of the structure may be increased, thereby providing an effect similar to the pontoons. This may upset the balance required by the semi- submersible theory between the volumes of the columns and the horizontally enlarged parts or pontoons, and hence increase the heave amplitudes. To restore the required balance it may be useful to streamline the volumes of the horizontally enlarged parts so that less water is set in motion.
  • the platform can be constructed in several ways.
  • a pre ⁇ ferred alternative is to build the supporting or main struc ⁇ ture and the deck separately and to connect these parts at an inshore deep water site on.the route to the site at which the platform is to be used.
  • the main structure can be built as a conventional steel jacket platform, launched, upended and lowered by filling
  • O PI e/ty. . 1PO with water until only a few meters of at least one leg pene ⁇ trates the water surface.
  • it can be built like a condeep, the lower part being built in a dry dock, floated out, and lowered progressively into the water by water filling while the legs are built.
  • a third method is to build the large cylindrical legs separately and connect these with the bracing while floating horizontally.
  • the fully equipped deck can be self buoyant or carried on a barge. After placing the deck over the main structure, water will be pumped out of the main structure, which then lifts the deck clear of the water or the barge. The com ⁇ pleted platform can then be towed to its destination.
  • the main structure can be towed out horizontally and upended near its final operating site.
  • Equipment in the form of modules can then be lifted on board as for a jacket.
  • a platform according to the invention is diagrammatically shown in the drawing.
  • the platform constitutes a floating structure of steel and/or concrete consisting of legs or columns 1 having horizontal and possibly diagonal bracings 2 and 3, respectively.
  • the platform may be terminated at a large draught by one or more pontoons 4.
  • the geometry of the pontoons can be tuned to the crosssectional area of the legs in the same manner as for other semi-submersible vessels.
  • the upper part 5 of the legs is filled with air to a depth providing an adequate buoyancy.
  • a part of the platform can be shaped as a tube 6 between the deck and a point well below the surface. This tube can be used for pro ⁇ tecting the riser 7 from wave forces.
  • riser guides and an arrangement for accommodating angular motions between the riser and the platform, if desired, can be mounted within the platform structure.
  • the platform will usually depend on fixed ballast 8 to be stable. If an oil storage volume is required, the lower part of the columns and the pontoons will be kept full of oil 9 and water 10 in varying ratios. Trim-
  • O PI ⁇ S-VATl ming tanks 11 in the legs are used for compensation of weight changes. These tanks will be filled with gas/oil or air/ water in controlled ratios. If required, the volume of the trimming tanks can be used as oil separators to save the weight of deck mounted separators.
  • the platform is anchored with anchor lines 12. If the fairleads for these anchor lines are mounted far down on the legs, the anchor lines may be significantly shortened com ⁇ pared with a mounting of the fairleads higher up. Also the dynamic forces in the anchor lines will be reduced, and the horizontal motions for the riser will be smaller. On the other hand the heel angles induced by current, wind and wavedrift will increase. If required, this heel may be offset by asymmetrical filling of the trimming tanks or the storage volume.
  • the platform cannot capsize even if one of the legs should lose its buoyancy totally.
  • the security can be increased using known methods such as dividing the buoyancy elements by watertight partitions, giving extra attention to collision zones, and designing the deck with sufficient buoyancy to keep it floating even if the main structure should lose a major part of its buoyancy.

Landscapes

  • Engineering & Computer Science (AREA)
  • Architecture (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • Ocean & Marine Engineering (AREA)
  • Earth Drilling (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)

Abstract

Une structure flottante, semi-submersible, de haute mer, comprend au moins trois jambes reliées entre elles, qui sont espacées d'une distance au moins égale à deux fois la dimension de la section la plus grande des jambes et qui sont adaptées pour contenir un lest à leurs extrémités inférieures pour améliorer la stabilité de la structure, comme cela se fait généralement pour les navires semi-submersibles. Cependant, la structure selon la présente invention possède un tirant d'eau qui est égal à au moins deux fois la hauteur maximum des vagues des eaux pour lesquelles la structure a été conçue.
EP83903230A 1982-10-20 1983-10-19 Structure flottante semi-submersible Withdrawn EP0122273A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO823489 1982-10-20
NO823489A NO823489L (no) 1982-10-20 1982-10-20 Flytende offshore-plattform.

Publications (1)

Publication Number Publication Date
EP0122273A1 true EP0122273A1 (fr) 1984-10-24

Family

ID=19886767

Family Applications (1)

Application Number Title Priority Date Filing Date
EP83903230A Withdrawn EP0122273A1 (fr) 1982-10-20 1983-10-19 Structure flottante semi-submersible

Country Status (3)

Country Link
EP (1) EP0122273A1 (fr)
NO (1) NO823489L (fr)
WO (1) WO1984001554A1 (fr)

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1250491A (fr) * 1984-10-22 1989-02-28 Jacek S. Pawlowski Installation de forage semi-submersible a flotteurs cylindriques annulaires
NO177897C (no) * 1993-08-05 1996-02-20 Kvaerner As Flyter
FR2737179B1 (fr) * 1995-07-26 1997-10-17 Technip Geoproduction Plate-forme d'exploitation petroliere en mer
GB2306137A (en) * 1995-10-10 1997-04-30 Mp Seaways Ss Ltd Storage of Liquid Hydrocarbons
GB2321036A (en) * 1995-10-10 1998-07-15 Mp Seaways Ss Ltd Storage of liquid hydrocarbons
ID21673A (id) * 1996-12-31 1999-07-08 Shell Internationale Res Maatc Anjungan tiang dengan alur vertikal
US6273018B1 (en) * 1997-08-22 2001-08-14 Graham Frederick Gottsche Buoyant substructure for offshore platform
US6190089B1 (en) * 1998-05-01 2001-02-20 Mindoc, Llc Deep draft semi-submersible offshore structure
BR9912257A (pt) * 1998-07-10 2001-10-16 Fmc Corp Método para produzir e executar operações de intervenção seletivamente em uma pluralidade de poços submarinos e sistema de produção submarina para uma pluralidade de poços submarinos
US6935810B2 (en) 2003-06-11 2005-08-30 Deepwater Technologies, Inc. Semi-submersible multicolumn floating offshore platform
US20180044872A1 (en) * 2015-03-09 2018-02-15 Noble Drilling Services Inc. Jackup drilling unit having material storage in jacking legs

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1511153A (en) * 1922-11-07 1924-10-07 Edward R Armstrong Sea station
US3327668A (en) * 1966-02-04 1967-06-27 Mobil Oil Corp Marine structure
US3837309A (en) * 1971-06-17 1974-09-24 Offshore Technology Corp Stably buoyed floating offshore device
JPS50147401A (fr) * 1974-05-16 1975-11-26
NO145686L (fr) * 1974-06-03
NO141466C (no) * 1975-11-07 1980-03-19 Akers Mek Verksted As Anordning ved midler for forankring av en produksjonsplattform eller lignende
US4168673A (en) * 1976-01-26 1979-09-25 Preussag Aktiengessellschaft Floating island for extracting or processing gas

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8401554A1 *

Also Published As

Publication number Publication date
WO1984001554A1 (fr) 1984-04-26
NO823489L (no) 1984-04-24

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Legal Events

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PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 19840625

AK Designated contracting states

Designated state(s): FR GB

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 19860109

RIN1 Information on inventor provided before grant (corrected)

Inventor name: KJELLAND-FOSTERUD, EINAR