WO2014076293A1

WO2014076293A1 - Vessel for carrying a platform

Info

Publication number: WO2014076293A1
Application number: PCT/EP2013/074145
Authority: WO
Inventors: Kartin Hentze; Kári PETERSEN
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-11-19
Filing date: 2013-11-19
Publication date: 2014-05-22
Anticipated expiration: 2015-05-19
Also published as: DK177714B1

Abstract

The invention relates to a vessel for carrying an oil platform, where the vessel comprises two elongate hulls arranged with a space between them and where support elements for supporting an oil platform are arranged on the vessel, where the support elements comprises carrying beams movably arranged on the vessel, said carrying beams being configured to extend under an oil platform in such a way that said carrying beams being supported at both ends; said vessel comprising means for moving said carrying beams, in relation to the rest of the vessel, in an essentially horizontal direction parallel to a longitudinal direction of said carrying beams.

Description

TITLE

Vessel for carrying a platform FIELD OF THE INVENTION

The invention relates to the area of oil platforms located at sea and in particular relates to the process of removal of a platform from its service location after end of service.

BACKGROUND OF THE INVENTION

Oil exploitation at sea is a widespread activity and incorporates a number of different types of exploitation equipment for drilling and recovering the oil and/or gas. Common for these are that they are to be maintained in position over a preferred location on the seabed, where the drilling into the seabed and into the deeper located oil and gas containing formations. A number of the equipment are fixed onto carrying structure supported onto the seabed, whereas other equipment are floating and may be moved when a particular drilling has been accomplished.

The present invention in particular relates to the type of drilling equipment with a fixed location onto supporting structures on the seabed. After a certain time of service the platform may become due to removal. This may be due to wear and tear, technology updating or simply the lack of exploitation opportunities on the location. In case the platform must be removed from the site, this may be done in a number of ways, which will be explained further in the following.

The first and mostly used way of removing a platform is simply taking the platform apart, in larger and smaller chunks and transporting these away on vessels adapted for carrying such scrap material. Major problems related with this method is the lengthiness of the process, the possible spill of polluting material in the sea, and further the often dangerous working conditions on sea, which besides being a health and safety issue further increases the lengthiness of the process.

Another known way of removing a platform is by removing the entire platform on a single vessel after having detached the platform from the supporting structure. A number of such vessels are known and will be explained further in the following. The present invention is related to improvements with such vessel for removing entire oil drilling and exploitation platforms. From US 5829919 a vessel adapted for carrying and transporting a

superstructure, e.g. a platform, appears, where jack-up like arrangements are located to engage with the platform at the edge area of this.

From US 3078680 a vessel for carrying and removal of a rig appears. The vessel requires that the rig has been provided with outwardly protruding engagement brackets for engaging with the lifting equipment on the vessel.

Common for the previously known vessels for carrying a platform is the lack of a sufficiently stable construction to carry out the carrying and transporting operation in a sufficiently reliable and safe manner.

SUMMARY OF THE INVENTION

The objective of the invention is to provide a vessel for carrying a platform, where the vessel may be able to perform this carrying and transporting in a more reliable manner than previously known vessels.

According to the invention this objective is achieved through a vessel for carrying an oil platform, where the vessel comprises two elongate hulls arranged with a space between them and where support elements for supporting an oil platform are arranged on the vessel, where the support elements comprises carrying beams movably arranged on the vessel, said carrying beams being configured to extend under an oil platform in such a way that said carrying beams being supported at both ends; said vessel comprising means for moving said carrying beams, in relation to the rest of the vessel, in an essentially horizontal direction parallel to a longitudinal direction of said carrying beams. By having support beams that extend over the entire width of the platform and support the underside of this, a reliable support has been achieved and hence an increased reliability and safety is the result. The contribution to the increased safety also comes from the fact that the beams extending between the two hulls will stabilize the whole construction and may even provide a possibility for reducing the rigidity of the single hull and thereby saving material in the hull construction.

In a preferred embodiment the vessel comprises carrying beams extending in a direction transversal to the elongate hulls. Hereby at least two beams are foreseen, however the number may be higher, such as 3, 4 or 5.

Preferably the vessel further comprises carrying beams extending essentially parallel to the elongate hulls, i.e. in the longitudinal direction of the vessel. In one embodiment the longitudinal beams are supported on the transversal beams. Hereby at least two longitudinal beams are foreseen, however the number may be higher, such as 3, 4 or 5. In a particular embodiment case the vessel comprises a single transversally extending beam to support one end of the longitudinally extending beams. The longitudinally extending beams may at their support on the carrying deck be horizontally movable to take an angular position slightly varying from the direction parallel with the hulls.

In a preferred embodiment the two hulls are connected with a carrying deck carrying the longitudinally and the transversally extending carrying beams of the vessel. Hereby the carrying deck is preferably supported on hydraulic jacks or lifting devices located on the hulls of the vessel.

In one embodiment the transversally extending carrying beams are distributed between the two hulls, preferably evenly distributed between the two hulls. In a further embodiment the transversally arranged carrying beams comprises two beam parts that are mutually connectable and separable. Preferably the vessel comprises a carrying deck supported on the hulls and where the carrying beams and their respective supports are located on the carrying deck. In this respect the carrying deck is preferably supported on the hulls by means of jack up devices, preferably hydraulic jack up devices, adapted for lowering and raising the carrying platform or parts thereof.

In a preferred embodiment the longitudinal beams are adapted to be positioned above transversal beams and where the longitudinal beams at their free end area comprises carrying elements for carrying the transversal beams during their displacement. Preferably the carrying elements on the longitudinal beams are claw like arrangements adapted to engagement with the transversal beams at the lower side of these.

Advantageously the way the transversal and/or the longitudinal beams and their supports are adapted to be moved individually in a direction perpendicular to the displacement direction of the beams. Hereby the accommodation of various types and dimensions of platform support may be facilitated without changing the functionality of the vessel construction. A wider leg or support of a platform/offshore structure may be accommodated by sliding the supports and the beams away from each other to allow a free passage of the beams when displacing these to the carrying position. The supports may be slidable along rails or grooves in the deck.

The invention further relates to a method for removing and carrying a platform from an operational site, by use of a vessel according to the invention.

According to the invention the method comprises positioning the carrying beams to leave the area between the hulls freely accessible, positioning the vessel to accommodate the platform between the hulls, positioning the carrying beams under the platform to be supported at both ends and detaching the platform from its supporting structure.

Hereby a reliable and relatively quick removal of a platform may be achieved. The successive decomposition of the platform may take place under more controlled circumstances when brought to shore.

In a particular advantageous embodiment the following steps are carried out in displacement and positioning of the beams:

the longitudinal beams are displaced to a receiving position for a transversal beam;

the transversal carrying beam is displaced from a first side towards a second side of the vessel and engaging with the longitudinal beams in order to let these partly carry the weight of the beam;

the transversal beam is received at the second side of the vessel;

the longitudinal beams are displaced to a receiving position for a next

transversal beam; and

the steps of displacement and receiving of the transversal beams and successive displacement of the longitudinal beam to a new receiving position is repeated for the number of transversal beams available.

The invention finally relates to a use of a vessel according to the invention for carrying an oil platform.

The invention will be explained in more detail with reference to the

accompanying drawing, wherein:

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a vessel according to the invention in a first top view;

FIG. 2 shows a vessel according to the invention in a second top view:

FIG. 3 shows a vessel according to the invention in a third top view; FIG. 4 shows a vessel according to the invention in a fourth top view;

FIG. 5 shows a vessel according to the invention in a side view;

FIG. 6 shows in more detail a side view of the engagement between two beams; FIG. 7 shows a vessel according to the invention in a front view;

FIG. 8 shows a vessel according to the invention in an aft view; and

FIG. 9 shows the support structure for a carrying beam in more detail.

DESCRIPTION OF A PREFERRED EMBODIMENT

From FIG. 1 and FIG. 2 the vessel according to the invention appears in a first and a second top view, and further from FIG. 7 and FIG. 8 in front and aft views, where the construction of the vessel with two hulls 1,2 or pontoons and a connection deck 3 between the two hulls is visible. The deck 3 carries the bridge 4 and possibly other parts of the vessel. The hulls comprise a front end 5 and a rear end 6, where the connecting deck is located closer to the front end. Above the hulls a carrying platform 7 is provided and supported on the hulls by means of hydraulic jack devices 8-13 and 14-19. The carrying platform 7 carries the carrying beams 20-22 and 23-25 that are arranged to be movable between a receiving position, FIG. 1, for the vessel and a carrying position, FIG. 4, for the vessel. In the receiving position for the vessel the carrying beams are displaced to a position where the area between the two hulls is open and ready for accommodation a platform. This will be explained in more detailed below with reference to FIG. 2 and FIG. 3. From FIG. 7 and FIG. 8 it appears that the connecting deck structure 3 is located lower than the carrying platform 7 and the bridge 4 is located on this connecting deck structure.

It appears from FIG. 1 that the carrying beams are arranged in two directions, one set of beams 20-22 being arranged to extend parallel to the longitudinal direction of the hulls and one set of beams 23-25 being arranged to extend transversal to the longitudinal direction of the hulls 1,2. In a carrying position for the vessel the carrying beams extend under the platform to be carried and support the underside of this. The two sets of beams 20-22,23-25 are arranged to constitute a common carrying structure, where one of the sets, the transversal set 23-25, is provided to support the other set, the longitudinal set 20-22, of beams. The interaction between the two sets of beams will allow the use of beams with a reduced rigidity and hence lower weight, which in particular is relevant when the beams are displaced into a receiving position for the vessel, where the one set of beams will be carried at one hull, and thereby will exercise a significant torque on the hull. The beams will due to their weight bend downwards, and to reduce the bending a fixed support structure may be provided to support the beams when displaced to the receiving position for the vessel. By decreasing the weight the torque impact on the hull is reduced.

Advantageously the transverse displaceable carrying beams are distributed between the two hulls to avoid the combined torque impact of all beams on one hull. The other set of beams extending in the longitudinal direction of the hulls and being carried on the carrying platform between the hulls will not exercise such torque on the hulls as a consequence of movement of these into the receiving position for the vessel. When the longitudinally arranged beams are displaced into the supporting positions, the beams will at one end be supported on the deck 7 and at the other end on a transversally arranged beam below the level of the longitudinally arranged beams.

The displacement of the carrying beams preferably takes place using a hydraulic engine. The beams and the hydraulic engine will preferably comprise a rack and pinion type power transmission which will be sufficient for displacing the carrying beams from their carrying position, which they normally will take during the transport to the platform position, to the receiving position, which they will take when preparing for accommodating the platform in the space between the hulls, and further back to the carrying position, when preparing for the carrying operation. The vertical position of the vessel in relation to the platform to be removed will be variable through the vertical positioning of the vessel itself in the sea. This may take place by lowering the entire vessel through ballast tanks that are filled with water and raising the vessel again after completing the positioning of the carrying beams, by emptying the ballast tanks. Additionally the carrying platform 7 may be lowered and raised by means of the hydraulic jack arrangements 8-13, 14-19 supporting this on the hulls 1,2. This is clearly visible from FIG. 5. From FIG. 9 a detailed view of a carrying beam support appears. The support of the carrying beams on the carrying platform and the deck in the receiving position for the vessel comprises a relatively wide contact face or two separated contact areas, which then may have a reduced contact area with the beam. The support will typically be constituted by sliding blocks 26 or bearing

arrangements. When in the carrying position for the vessel a reduced contact area at each end of the carrying beam will be sufficient for the stable positioning of the carrying beams. In order to allow the accommodation of different dimensions of supports of the offshore constructions/oil platforms/rigs the carrying beam support may be movable or slidable in a direction perpendicular to the displacing direction of the beams. The block 26 may in this context be provided with a engagement construction 27 securing the block in relation to the deck 7. It appears that the longitudinal beams in the present design comprise two support blocks 26 at their ends supported on the carrying deck. In order to enable an even weight distribution in the vessel with or without the load of a platform, ballast tanks or provided throughout the vessel and separated in the longitudinal direction of the hulls. The exact degree of filling and emptying of the ballast tanks will depend on several factors, where the most influential ones are the weight distribution in the vessel itself and the weight of the load to be carried.

The removal operation will be described in more detail in the following.

Upon arrival at the platform or superstructure to be removed, the carrying beams are displaced from the transport position to the receiving position for the vessel. The transversal beams are free hanging from the support blocks 26 and the additional support 29 provided on the side of the carrying platform 7. The vessel is lowered to the appropriate level relative to the platform to be removed, allowing the displacement of the carrying beams under the platform to the transport position and locking these in this position. Following this the vessel is again raised to support the platform and finally the detachment of the platform or superstructure from its support may take place. Having detached the platform from its support, the platform may be transported to a desired location for its further or final decommissioning procedure.

As depicted in FIG. 2, FIG. 3, FIG. 5 and FIG. 6 the displacement of the carrying beams to their carrying position follows a particular scheme, where the longitudinal beams are displaced to a position where engagement claws 28 at the ends of the first longitudinal beams are ready to engage with the first transversal beam when this is displaced transversally. Hereby the longitudinal beams with their claws will carry the transversal beam 23 during displacement and hence only a limited free and unsupported length of the transversal beam will protrude from a claw 28 and allow the transversal beam to engage with the support elements on the other side of the carrying deck. After this process the

longitudinal beams are displaced to a position where they are ready to engage with the second transversal beam 24. The longitudinal beams will be supported on the first transversal beam and hence only have a limited free and

unsupported length themselves. This will significantly limit the bending of the beams and allow the displacement of the second beam in a similar manner as explained with the first transversal beam. After completing the displacement of the second transversal beam, the third and further transversal beams are displaced in a similar manner with a support from the longitudinal beams now supported on the previous transversal beam.

Obviously other engagement means than a claw 28 may be used, as the principle only prescribes a support or carrying of the transversal beam by a number of superior located longitudinal beams.

Claims

A vessel for carrying an oil platform, where the vessel comprises two elongate hulls arranged with a space between them and where support elements for supporting an oil platform are arranged on the vessel, where the support elements comprises carrying beams movably arranged on the vessel, said carrying beams being configured to extend under an oil platform in such a way that said carrying beams being supported at both ends; said vessel comprising means for moving said carrying beams, in relation to the rest of the vessel, in an essentially horizontal direction parallel to a longitudinal direction of said carrying beams.

A vessel according to claim 1, where the vessel comprises carrying beams extending in a direction essentially transversal to the elongate hulls.

A vessel according to claim 1 or 2, where the vessel further comprises carrying beams extending essentially parallel to the elongate hulls.

A vessel according to claim 3, where the vessel further comprises a transversally extending beam to support one end of the longitudinally extending beams.

A vessel according to any of the preceding claims, where the two hulls are connected with a carrying deck deck carrying the longitudinally extending and/or the transversally extending carrying beams of the vessel.

6. A vessel according to claim 5, where the carrying deck comprises deck parts extending over the hulls and supporting the transversal carrying beams in a receiving position for the vessel.

7. A vessel according to claim 5 and 6, where the carrying deck(s) are supported by hydraulic lifts or jacks, either as a common deck structure or as individual deck parts.

8. A vessel according to any of the preceding claims, where the transversally extending carrying beams are distributed between the two hulls, preferably evenly distributed between the two hulls.

9. A vessel according to any of the preceding claims, where the transversally arranged carrying beams comprises two beam parts that are mutually connectable and separable.

10. A vessel according to any of the preceding claims, where longitudinal beams are adapted to be positioned above transversal beams and where the longitudinal beams at their free end area comprises carrying elements for carrying the transversal beams during their displacement.

11. A vessel according to claim 10, where the carrying elements on the

longitudinal beams are claw like arrangements adapted to engagement with the transversal beams at the lower side of these.

12. A vessel according to any the preceding claims, where the transversal and/or the longitudinal beams and their supports are adapted to be moved individually in a direction perpendicular to the displacement direction of the beams.

13. A method for removing a platform from its location using a vessel

according to claim 1, where the carrying beams are positioned to leave the area between the hulls freely accessible, where the vessel is positioned to accommodate the platform between the hulls, where the carrying beams are positioned under the platform to be supported at both ends and where the platform is detached from its supporting structure.

14. A method according to claim 13, further comprising lowering the position of the vessel before positioning the vessel to accommodate the platform.

15. A method according to claim 13 or 14, further comprising raising the position of the vessel after having positioned the carrying beams in their carrying positions.

16. A method according to any of the preceding claims, comprising the

following steps: where longitudinal beams are displaced to a receiving position for a transversal beam;

where the transversal carrying beam is displaced from a first side towards a second side of the vessel and engaging with the longitudinal beams in order to let these carry partly the weight of the beam;

where the transversal beam is received at the second side of the vessel;

where the longitudinal beams are displaced to a receiving position for a next transversal beam; and where the steps of displacement and receiving of the transversal beams and successive displacement of the longitudinal beam to a new receiving position is repeated for the number of transversal beams available.

17. Use of a vessel according to any of the claims 1 - 12 for carrying an oil platform.