GB2186527A - Platform topsides removal vessel - Google Patents

Abstract

A mono-hull vessel in two parts, bow and stern, adapted for uplifting an offshore production platform topsides as a single unit, transporting same under its own power and either discharging the topside unit at a quayside or launching the topsides at a deepwater abandonment location. The topside is carried by box girder beams 3 which are fitted with skidding systems on the bases for movement over the vessel deck and a separate skidding system on top of the beams for moving the topside unit along the beams. The vessel acts as an integrated mono-hull for transportation and as separate units for topsides uplifting, loading and discharging. In its integrated form the full seagoing capability of the vessel is maintained. <IMAGE>

Description

SPECIFICATIONS Platform topsides removal vessel This invention relates to a vessel for carrying outthe removal of an offshore oil or gas production platform topsides as a single unit.

The installation and removal of large offshore structures is currently carried out with large capacityfloating cranes in conjunction with othersupportcraftsuch as supply boats, barges and anchor handling tugs.

Existing limits of lifting capacities are approximately 6,000 tonnes although this capacity is expected to increase to about 8,000 tonnes within the next five years.

Platform topsides are currently assembled in modular forms, with modules weighing from a few tones up to 6,000tonnes. The total topside weight can be in excess of 25,000tonnes. The dis-assembly of the platform topsides is currently anticipated to be exceedingly expensive and requiring extensive use of large capacity cranes.

This invention provides the concept for utilising a mono-hull vessel for the removal of a platform topsides as a single unit without the use of high capacity craneage.

The invention comprises of a purpose built vessel or a modified tanker adapted to the concept of uplifting a platform topsides as a single unit, transporting same under its own power and either discharging the topsides unit at a quayside or launching the topsides at a deepwater abandonment location.

Specific embodiment of the invention will now be described byway of example with reference to the accompanying drawings in which Drawing 60820/01 shows the general arrangement of the platform topside removal vessel; Drawing 60820/02 illustrates the removal of a platform topsides; Drawing 60820/03 shows the vessel discharging the topside unit at a quayside; and Drawing 60820/04 shows the vessel launching the topsides unit into a deepwater abandonment area.

Outline specification for platform topside removal vessel Vessel See drawing 60820/01 for general arrangement.

Basic Vessel 250,000 tonne capacity vessel. Either built to order or a converted tanker.

Detachable Bow Section Capable of carrying approximately 50,000 tonnes This bow section contains the following: - Dedicated anchoring/mooring system - Dedicated ballasting/de-ballasting system.

- Hydraulic Skid TrackSystem on deck - Landing and securing system for mating with skid beams - Hydraulic locking system to mate with stern section - Dedicated power supplies to run systems outlined above and life support and safety systems.

- Bow capable of being submerged.

Stern Section Capable of carrying approximately 200,000tonnes - Dedicated anchoring/mooring system - Dedicated ballasting/de-ballasting system - Hydraulic Skid Track System on deck - Dedicated power supplies to run systems outlines above and life support and safety systems.

- Motive power and accommodation - Stern helideck Skid Beams Approximately 200 metres long and - Capable of spanning 100 metres and builtto carrythe weight of platform topsides to be removed.

- Skidding system for sliding beam along tanker deck skidding system.

- Separate skidding system for sliding platform topsides along skid beam - Rocker beam for launching platform topside into deepwater - Locking system for securing platform topsides to beams and beams to vessel - Landing and securing system for connection to bow section.

Outlineprocedure for jacket topside removal Referring to drawing 60820/02 the removal of a platform topside in a single unit is accomplished in five basic stages.

Stage one is that the vessel is brought to the location of the platform to be removed and moored in a cross anchorfashion at a safe distance away from the platform.

In reasonable weather conditions the bow section is unlatched and under tug is moored a safe distance from the platform on the opposite side to the stern section.

Stage two commences with a good weather forecast and satisfactory sea conditions when both the sections ofthe vessel are moved adjacent to the platform and ballasted to the designated levels.

Stagethree is the launch forward of the skid beamsfrom the stern section, underthe structure to be removed and connecting on to the bow section where they are made fast by the landing and locking system.

The beams are guided into position by winch wires from the bow section of the vessel. Once locked on the vessel is de-ballasted to take thefull weight of the platform topsides. A section is then cut out of the jacket legs by explosive charges to release the topside unit. The length of section to be removed will vary dependent on the structure and sea conditions designed for.

Stage four is the sideways movement ofthe vessel by means of its anchoring system to carry thetopsides clear of the jacket structure.

Stage five is the re-assembly ofthe vessel ready for a sea voyage. This is carried out by the skidding systems with positional control by the anchor systems. Once the vessel sections are mated together and moved a safe distance away from the jacketstructure sea fastening is completed, the anchors are uplifted and the vessel made ready for sea tow.

Throughout the entire operation standby tugs are in attendance although not shown in the drawings.

Outline procedure for discharge of platform topside ata quayside Referring to the drawing number 60820/03 the discharge of a platform topside onshore is achieved in six stages.

The first stage is the voyage from the platform location back to a nominated port capable of accepting the vessel.

Stage two is carried out in sheltered water probably moored alongside a quay or at anchor in a safe anchorage. The platform topside unit together with the skid beams is moved aftto enablethe bowsectionto be disconnected.

Stage three takes place once the load is sufficiently aft and is the unlatching of the bow section and its removal by tugs from the stern section of the vessel .

Stage four is the docking of the stern section end on to a quayside. The ballast of the vessel being adjusted to enable the skid beams to line up with prepared foundations onshore.

Stage five is when, with good weather conditions forecast, the skid beams are moved forward onto prepared runway areas onshore. The vessel trim is adjusted to keep to the correct level. The hydraulic skidway is assisted by onshore winches that act both as directional guides and to give pulling powerto assist the skidding system.

Stage six starts once the skid beams are fully extended from the stern section of the vessel and is the final skidding of the platform topside unit relative to the skid beams so that it can socket into prepared foundations. The skid beams are then released from the structure and pulled back onboard the vessel.

Through the operation tugs are on standby to ensurethevessel remains in the correct position atalltimes.

Outline procedure fordisposalofplatform topside ata deep water abandonment location Referring to drawing number 60820/04the disposal of a platform topside unit in a deepwaterabandonment area is carried out in four stages.

The first stage is the voyage to the designated abandonment area which would be accomplished at an economic cruising speed for a 250,000 tonne capacity vessel. This speed is approximately 12 knots.

Stage two starts on arrival at location and in good sea conditions with a continuing good weather forecast.

The vessel is ballasted down by the bows ready for a launch situation after sea fastenings have been released.

Stage three begins once the vessel is properly trimmed down, the skid beams are then moved forward to where the rocker arm fulcrum is at the bow of the vessel.

Stage four is when the platform topside unit is skidded forward on to the rocker arm, pastthe balance point and so the topside is launched into the sea.

Once the topside unit has gone the rocker arm can be winched backto position and the skid beams moved aftforthe return voyage.

Duringthe launch ofthetopside unit notugsare required.

Claims (14)

1. Avessel comprising a mono-hull in two separate sections, fore and aft, capable of separating and joinging together at sea underfull load, together with box girder beams on deck, which can carry a platform topsides as a single unit. The beams skid backwards, forwards, sideways and span the full width of an offshore platform between the two parts of the hull to uplift and carry the full load of the platform topsides off from a jacket structure by ballasting/deballasting operations.

2. The vessel as claimed in claim 1 hasthe abilityto remove an offshore platform topside in a single unit and transport it under the vessels own power.

3. The vessel as claimed in claim 1 has the ability to unload the platform topside unit in a single unit ata suitable onshore location by skidding the unit off ofthevessel by using the skid system on the base of the box girder beams to move the beams on to dry land and then to movethetopsides along and offthe boxgirder beams by the skid system on top of the box girder beams.

4. The vessel as claimed in claim 1 has the ability to anchor both sections ofthe hull at an offshore location as joined or separate units.

5. The vessel as claimed in claim 1 has the abilityto discharge the topsides in deepwater by ballasting down the bowofthevessel,skidding the beams over the bow and skidding thetopsides along the box girders on to a rocker arm fulcrum, past the balance point and so into the sea.

6. The vessel as claimed in any preceding claim has onboard accommodation for personnel and workshop facilities to carry out the activities claimed as an independent vessel except for anchor handling activities.

7. The vessel as claimed in claim 1 has the ability to skid the box girders from the stern section ofthe vessel under a platform topsides and land and lockthem onto the bow section ofthevessel. Both parts ofthe vessel are ballasted down.

8. The vessel as claimed in claim 1 takes the load ofthetopsides by controlled and synchronised deballasting of both vessel sections with the carried load being monitored by load cells underthe box girders.

9. The vessel as claimed in claim 1 severs the legs holding the topsides by explosive cutting out of a section of each leg.

10. A vessel substantially as described by the specification and drawings submitted with patent application number 8600306.

11. Avessel as claimed in claim 10 can be usedforthe installation of a platform topside as a single unit.

12. Avessel as claimed in claim 10 can be usedforthe raising of platform topsides to allowadditional jacket sections to be inserted.

13. Avessel as claimed in claim 10 can be usedforthetransportation and installation of shore based process/production plants.

14. Avessel as claimed in claim 10 can be usedforthe load-out and installation of jacket structures.

NOTES FOR DRAWINGS Numeric index to drawings 1A to 7F 1 indicates Hydraulic Locking System 2 indicates HydraulicSkidway 3 indicates Skid Beams NOTES TO ACCOMPANY THE DRAWINGS Drawing reference Notes Fig 1 A and 1 B Basic Vessel having a detachable bow section with a hydraulic locking system.

Page 1 and 2 of 23 Deck is builtto carry a hydraulic skidway capable of carrying 200 metre long skid beams loaded with a platform topside.

Fig 1 C and 1 D Box Girder Skid Beams. Approximately 9 metres deep, 200 metres long, capable Page3 and 4 of 23 ofspanning 100 metres underfull load.

Fig 1 E and 1 F Landing and Locking System for mating skid beams to bow section. Rocker arms Page 5 and 6 of 23 in-built into skid beams for launching topside into deepwater.

Bow designed to take rocker arm launch situation.

Fig 2A Stage 1. Bow and stern sections of vessel cross anchored in proximity of Page 7 of 23 platform.

Fig 2B Stage 2. Bow and stern sections warped towards platform under control of Page 8 of 23 anchors. Vessel ballasted to maximum draft.

Fig 2C Stage 3. Box girder skid beam jacked from stern to bow section and locked on to Page 9 of 23 structure. Vessel deballasted to take full topside weighs Fig 2D Stage 4. Vessel and topside section moved sideways on anchors tp avoid jacket Page 10 of 23 structure.

Fig 2E Stage 5. Bow and stern sections of vessel skidded together and latched ready for Page 11 of 23 voyage to disposal location.

Fig 3A Stage 1. Platform Removal Vessel carries the platform topside to a nominated Pagel2of2 port.

Fig 3B Stage 2. In sheltered waters the platform topside and the box girder skid beams Page 13 of 2 are skidded aft to clearthe bow section.

Fig 3C Stage 3. The bow section of the platform removal vessel is removed.

Page 14of2 Fig 3D Stage 4. The stern section of the vessel is docked against a deepwaterquayside.

Page 1 5 of 2 Fig 3E Stage 5. The platform topside and the box girder skid beams are both skidded Page 16 of 2 forward to locate topside unit over prepared foundations.

Fig 3F Stage 6. Platform topside is lowered onto prepared foundations and the skid Page 17 of 2 beams brought back to the removal vessel.

Fig 4A Stage 1. Removal Vessel plus load travels under own power to topside Page 18 of 2 abandonment location.

Fig 4B Stage2. At abandonment location the platform removal vessel is ballasted Page 19 of 2 down atthe bows.

Fig 4C Stage 3. The platform topside on the bow girder skid beams are both skidded Page 20 of 2 forward.

Fig 4D Stage 4. The platform topside is skidded forward on the box girder skid beamsto Page 21 of2 where the rocker arm is activated and the topside is launched into the sea.