Field of the invention
[0001] The present invention relates to a method and system for removing a part of a platform
at sea, the platform resting on a seabed.
[0002] Methods for removing such platforms are known in the field of the art. It is widely
known that platforms at sea, for instance in the oil and gas industry, have a certain
life span, after which they are to be decommissioned and removed. This removal process
often is a costly, complicated and sometimes dangerous operation. There is a general
need in the field of the art for cost-effective, simple, and safe methods for removing
such platforms.
Prior art
[0003] US2003/0108392 discloses a system for removing decks from offshore structures. A drawback of this
system is that it requires two barges, which is expensive and cumbersome during transport.
[0004] GB2165188 discloses a method for installing and removing an upper part of a platform (called
deck module) at sea from a leg assembly of the platform.
[0005] A disadvantage of the system of
GB2165188 is that it comprises a support frame 20 (comprising of girders 51) which is integral
with the deck module itself, see Figure 2 and page 1, lines 78-80 of
GB2165188. The support frame 20 is essential to the system, and hence the system of
GB2165188 can only by used for removing deck modules having such a support frame 20. Since
most existing platforms do not have such a support frame 20, the value of the system
of
GB2165188 is limited in practice.
[0006] A disadvantage of the system of
GB2165188 is further that it requires barges which extend to a substantial height above the
water surface, in order to remove the deck module from the leg assembly. This is due
to the fact that for safety reasons, the deck module is located at a substantial height
above the water line, and consequently the support structure 20 is also located at
a substantial height above the water line.
[0007] WO98/24980 discloses a system for lifting a sea-going structure. One drawback of this system
is that it requires two vessels, which is expensive and cumbersome during transport.
Another drawback of this system is that it is difficult to unload the sea-going structure
from the vessels once it is lifted with the vessels.
Object of the invention
[0008] It is an object of the invention to provide an alternative method and device for
removing an upper part of a platform which rests on a seabed.
[0009] It is an object of the present invention to provide a method and device suffering
less from at least one of the drawbacks mentioned above.
[0010] It is an object of the invention to provide a simple, cost-effective and reliable
method and device for removing an upper part of a platform which rests on a seabed.
[0011] At least one of the objects is achieved in a method of removing an upper part of
a platform which rests on a seabed and which extends above the waterline, the platform
comprising legs which extend upwards from the seabed, the method comprising the subsequent
steps of:
- providing a vessel comprising a single hull, the hull defining a contour of the vessel
when viewed from above;
- providing a support structure which is configured to rest on the vessel, the support
structure comprising one or more beams, the one or more beams having connection ends
that are constructed to extend outside the contour of the hull on opposite sides of
the vessel, the connection ends configured to be connected to the legs of the platform;
- positioning the vessel between the legs of the platform;
- connecting the connection ends to the legs of the platform;
- disconnecting the upper part of the platform from the lower part;
- lifting the upper part of the platform from the lower part by the vessel via the support
structure;
- moving the vessel and the upper part of the platform away from the lower part of the
platform.
[0012] The method is simple because the support structure is connected directly to the upper
part of the platform. The connection may be effected by welding the support structure
to the platform. Other types of connections such as bolting or using special coupling
members are also possible.
[0013] The method can be dedicated to removing platforms, and thus can be made free of any
requirements or equipment relating to installing such a platform. This further specialization
allows a simplification of the system, in contrast with complex systems of the
prior art.
[0014] The method may also be used to remove the lower part of the platform or to remove
the entire platform at once.
[0015] Generally, the support structure is not fixed to the vessel prior to the moving of
the vessel to a position at the platform. Once the vessel is in position, the support
structure is handed over to the platform in order to eliminate movement of the barge
caused by waves and or wind. This can be achieved for instance by laying the support
structure into supports connected to the piles before the vessel arrived, or by means
of winch wires lowered from the platform deck. The vessel is then ballasted down so
that the support beams come free of the barge and can be welded to the platform legs
without interference from movement of the vessel during the welding.
[0016] After connection of the support beams, the vessel is positioned and de-ballasted
until the barge deck makes contact again with the support beams. The vessel is de-ballasted
to an extent that the barge presses onto the support beams and thereby movement of
the barge is minimized. Then the support beams are welded to the vessel deck.
[0017] The moment of contact between the vessel and the support beams is critical. Measures
may be taken in order to minimize the impact between the structures. For instance
shock absorbers may be used. Alternatively a hydraulic system may be used, that can
pull the vessel towards the support beam.
[0018] Generally, positioning the vessel between the legs of the platform is performed prior
to connecting the connection ends to the legs of the platform. In this case, it is
the vessel which has an important function in positioning the support beams. However,
it is also possible that the beams of the support structure are connected to the legs
of the platform when the vessel is not present. The vessel may pre-position the support
beams and be removed during the connecting of the connection ends to the legs. Alternatively,
the vessel may not be involved at all in the connecting of the beams to the legs of
the platform. In this case, the support beams may be positioned by a crane on the
platform itself and the vessel is positioned between the legs of the vessel only after
the support structure is connected to the legs.
[0019] Generally, the support structure rests on the deck of the vessel and extends substantially
horizontally.
[0020] The hull of the vessel will generally be elongate and can also be referred to as
a mono-hull.
[0021] In an advantageous embodiment, the support structure comprises a hydraulic system
for raising the one or more beams including the platform relative to the vessel, the
method comprising raising the upper part of the platform relative to the vessel by
the hydraulic system while at the same time deballasting the vessel. In this way,
the duration of the time period in which the upper part and the lower part of the
platform are so close together that they are at risk of collision stays relatively
short. In an aspect of the invention, the method comprises:
- positioning the one or more beams of the support structure in a target position wherein
the connection ends engage the legs;
- supporting the one or more beams in their target positions by the platform via provisional
or preliminary support means on the platform such that possible motions of the support
vessel under influence of waves and wind do not affect or disturb the connecting of
the one or more beams to the legs;
- connecting the one ore more beams to the legs. Advantageously, the connecting of the
support structure to the legs can take place without hindrance from movement of the
vessel.
[0022] The provisional or preliminary support means may be a ridge, collar or other projection
on the legs of the platform on which the support structure is placed and comes to
rest. In an advantageous embodiment, the method comprises:
- positioning the one or more beams of the support structure in a target position wherein
the connection ends engage the legs;
- supporting the one or more beams in their target positions by the platform via provisional
or preliminary support means on the platform;
- disconnecting the support structure from the vessel such that possible motions of
the support vessel under influence of waves and wind do not affect or disturb the
connecting of the one or more beams to the legs;
- connecting the one ore more beams to the legs;
- reconnecting the support structure to the vessel prior to the lifting of the upper
part of the platform from the lower part of the platform.
When the vessel is disconnected from the support structure, the connecting operation
can be performed under relatively quiet circumstances. To this end, the vessel may
be ballasted to a deeper draft or a hydraulic lift system may be operated to lower
the support structure relative to the deck of the vessel, thereby gradually transferring
the weight of the beams to the legs of the platform.
In one aspect of the invention the support structure comprises one or more rails or
skid tracks which rest on the vessel, wherein the beams of the support structure are
movably arranged on the one or more rails or skid tracks via wheels or skid means,
the method comprising rolling or skidding the one or more beams relative to the vessel
for unloading the upper part of the platform from the vessel.
This method allows very heavy platforms to be unloaded fro the vessel with relative
ease.
In another aspect, the method comprises removing the upper part of the platform from
the vessel by
- positioning one or more support carriages on the deck of the vessel,
- disconnecting the one or more beams from either the vessel deck or the platform
- lifting the upper part of the platform optionally including one or more beams from
the deck
- unloading the combination of support carriage, beams and upper part of the platform
from the vessel.
[0023] Via the support carriages, the upper part of the platform is simply rolled off the
vessel.
[0024] The present invention further relates to a system for removing an upper part of a
platform which rests on a seabed and which extends above the waterline, the platform
comprising legs which extend upwards from the seabed, the system comprising:
- a vessel comprising a single hull, the hull defining a contour of the vessel when
viewed from above;
- a support structure which is configured to rest on the vessel, the support structure
comprising one or more beams, the one or more beams having connection ends that are
constructed to extend outside the contour of the hull on opposite sides of the vessel,
the connection ends configured to be connected to the legs of the platform.
[0025] The present invention also relates to a support structure for use in the method of
claim 1 or for use in the system of claim 10.
[0026] The present invention further relates to a vessel for use in the method of claim
1 or for use in the system of claim 10.
[0027] The present invention further relates to a docking station for unloading the platform
from the vessel, the docking station comprising a bay for the vessel and support members
positioned around the bay, the support members being configured to support the support
beams of the support structure, thereby allowing the unloading method of:
- positioning the vessel with the upper part of the platform in the docking station,
- ballasting the vessel such that the vessel moves downward and the support beams engage
the support members, thereby shifting the weight of the upper part of the platform
from the vessel to the docking station via the one or more support beams;
- removing the vessel from the docking station.
Brief description of the Figures
[0028]
Figure 1 shows a platform removal system according to the prior art;
Figure 2 shows an isometric view of an embodiment of the invention;
Figure 3 shows a front view of a platform removal system of the invention supporting
an upper part of the platform;
Figure 4 shows a side view of a platform removal system of the invention carrying
an upper part of the platform;
Figures 5a-5g show different steps in a platform removal method according to the invention;
and
Figure 6 shows an isometric view of an alternative embodiment of the invention.
Detailed description of the Figures
[0029] Figures 1 a and 1 b show the system of
GB2165188 and discloses a vessel 70. The platform (or jacket structure) is built with a specific
future removal method in mind. To this end, the deck module 16 of the platform is
provided with a horizontal beam 51. Further, support members 76a are provided at the
underside of the beam 51 via which the deck module 16 is removably supported by the
leg construction of the platform via support points 24a. This combination of features
allows the removal vessel 70 to move between the legs of the jacket. Lifting means
56 are provided which engage with outwardly projecting ends of the beams 51. The deck
module 16 is subsequently lifted integrally from the support positions 24a.
[0030] As mentioned, the method and system of
GB2165188 can only be used for platforms which are specifically designed and constructed to
be removed with this system. If the platform does not have a beam 51 with outwardly
projecting ends or if the platform does not have support points 24 which allow a disconnection
of the deck module from the jacket legs, the system of
GB2165188 does not work or works only at high costs. See page 1, lines 78-80 of
GB2165188 which disclose that the support frame is integral with the deck module. Since most
existing platforms do not have such a support frame, the value of the system of
GB2165188 is limited in practice.
[0031] A further disadvantage of the system of
GB2165188 is that the deck module including the beams 51 generally is located at a substantial
distance above the mean sea level water line in order to stay clear of storm waves.
This distance is generally a design requirement for safety purposes of platforms.
In that case, the lifting means 56 also need to be provided high above the water line,
which is complicated and disadvantageous.
[0032] In particular the strut assemblies 50 shown in Figures 1 a and 1 b may need a substantial
length in order to reach the girders 51. Figures 2, 3 and 4 show an embodiment of
the platform removal system according to the invention. A vessel or barge 2 is provided
having skid means 33 on the deck 46. The barge 2 is substantially elongate and the
skid means 33 extend in the longitudinal direction of the barge 2. The skid means
33 may be rails or tracks or simply a path defined on deck 46. Alternatively or additionally,
deck supports 33 may be provided.
[0033] The jacket structure or platform 1 which is to be removed rests on the seabed (not
shown) on legs 5. The platform 1 comprises a top module or deck module 6 which is
located above the water line 8. The barge 2 has a width 62 which is smaller than the
distance 64 between two legs 5 of the platform 1, allowing the barge 2 to be positioned
between the legs 5 of the platform 1.
[0034] The removal system further comprises a support structure 30 comprising one or more
beams 31. The beams 31 have ends 32 which are connected to the legs 5 of the platform.
The beams 31 are configured to rest on the skid means 33 and are supported in such
a way that they can move relative to the barge 2 by sliding or rolling.
[0035] The vertical distance between the beam 31 and the underside 44 of the deck module
6 may be substantial. The beam 31 may be located substantially below a nominal wave
height, whereas the deck 42 and in particular the underside 44 of the deck module
6 is located at a substantial height above the nominal wave height Hs. This feature
allows the platform removal system to be relatively low.
[0036] In figure 3 a front view of the removal system is shown, the barge 2 carrying the
upper part of the platform. The beams 31 are connected to the legs 5 at connection
points 32. Figure 4 shows the system from the side. The skid means 33 may extend beyond
the hull of the barge 2 for easy roll-off or skid-off of the support structure 3 with
the upper part of the platform from the barge 2.
[0037] Figure 5a shows a first step in a method for removing the upper part 11 of a platform
1. Hang-off provisions or support members 4 are connected to the legs 5. The support
members 4 may be steel beams or collars which are welded to the legs 5 of the platform
1. This step may be executed prior to the arrival of the barge 2.
[0038] Figure 5b shows a next step wherein the barge 2 arrives with the beams 31 supported
on the deck 46. The beams 31 may be uncoupled from the barge 2. The barge 2 is positioned
such that the beams 31 come to rest on the support members 4. Subsequently, the barge
2 is ballasted by filling ballast compartments in order to lower the barge 2 relative
to the beams 31. The beams 31 come loose from the barge 2 and are now fully supported
by the support members 4. The beams 31 can now be fixed to the legs 5.
[0039] It is also possible that the beams 31 are lifted relative to the barge 2and placed
on support members 4. In an alternative variant, the barge 2 may not be present during
installation of the beams 31 on the support members 4. In this case, a crane vessel
installs the beams 31, or the beams may be installed by the workers on the platform
1 itself, without the use of an additional vessel.
[0040] In figure 5c, it is shown that in a next step the ends 32 of the beams 31 are connected
to the legs 5 of the platform 1. Welding is a suitable way of making the connection.
[0041] Figure 5d shows that in a next step, the barge 2 is positioned such that the beams
31 engage the skid means 33 on the deck 46. Generally, the barge 2 will be deballasted
by emptying the ballast compartments 7. However, it is also possible that connection
means extend upwards from the deck 46 of the barge 2 and form a connection between
the deck 46 and the beams 31.
[0042] Figure 5e shows that in a next step, the legs 5 of the platform are cut, such that
the platform 1 is divided in an upper part 11 and a lower part 12. Although the drawing
shows that the legs are cut above the water line, alternatively this can be done beneath
the water line.
[0043] Figure 5f shows how in a next step, the barge 22 lifts the upper part 11 from the
lower part 12 via the beams 31. This may be performed by further deballasting the
barge 2. In order to accelerate this step, a further hydraulic lifting system 34 may
be provided on deck 46, which may be operated simultaneously with the deballasting.
The hydraulic lifting system 34 is configured to move the beams 31 upward relative
to the deck and to lower the beams 31 relative to the deck 46.
[0044] Figure 5g shows a situation in which the upper part 2 is completely removed and the
lower part 12 remains behind. The lower part 12 may be removed separately.
[0045] Figure 6 shows an alternative embodiment, in which carriages 80 are used to unload
the upper part 11 of the platform from the barge 2. The upper part may be positioned
on the carriages directly after removal from the lower part of the platform, but it
is also possible that the upper part is placed on the carriages when the barge arrives
at the unloading location. Hydraulic lifting means 34 may be present for lifting the
upper part 11 from the deck 46 and onto the carriages 80. The present invention relates
to the following clauses:
- 1. Method of removing an upper part of a platform which rests on a seabed and which
extends above the waterline, the platform comprising legs which extend upwards from
the seabed, the method comprising the subsequent steps of:
- providing a vessel comprising a single hull, the hull defining a contour of the vessel
when viewed from above;
- providing a support structure which is configured to rest on the vessel, the support
structure comprising one or more beams, the one or more beams having connection ends
that are constructed to extend outside the contour of the hull on opposite sides of
the vessel, the connection ends configured to be connected to the legs of the platform;
- positioning the vessel between the legs of the platform;
- connecting the connection ends to the legs of the platform;
- disconnecting the upper part of the platform from the lower part;
- lifting the upper part of the platform from the lower part by the vessel via the support
structure;
- moving the vessel and the upper part of the platform away from the lower part of the
platform.
- 2. Method of clause 1, the vessel further comprising a ballast system for varying
the draft of the vessel, the method comprising:
- ballasting the vessel to a deep draft when positioned between the legs of the vessel
- lifting the upper part of the platform by deballasting the vessel.
- 3. The method of clause 1, wherein the support structure comprises a hydraulic system
for raising the one or more beams including the platform relative to the vessel, the
method comprising raising the upper part of the platform relative to the vessel by
the hydraulic system, optionally while at the same time deballasting the vessel.
- 4. The method of clause 1, comprising pre-assembling the support structure prior to
the removal operation in order to fit the support structure to the size and shape
of the platform which is to be removed.
- 5. Method of clause 1, comprising:
- positioning the one or more beams of the support structure in a target position wherein
the connection ends engage the legs;
- supporting the one or more beams in their target positions by the platform via provisional
or preliminary support means on the platform such that possible motions of the support
vessel under influence of waves and wind do not affect or disturb the connecting of
the one or more beams to the legs;
- connecting the one ore more beams to the legs.
- 6. Method of clause 1, comprising:
- positioning the one or more beams of the support structure in a target position wherein
the connection ends engage the legs;
- supporting the one or more beams in their target positions by the platform via provisional
or preliminary support means on the platform;
- disconnecting the support structure from the vessel such that possible motions of
the support vessel under influence of waves and wind do not affect or disturb the
connecting of the one or more beams to the legs;;
- connecting the one ore more beams to the legs;
- reconnecting the support structure to the vessel prior to the lifting of the upper
part of the platform from the lower part of the platform.
- 7. Method of clause 1, wherein the beams are releasably arranged on the vessel such
that the upper part of the platform and the support structure connected to it can
be unloaded from the vessel by moving the beams relative to the vessel, the method
comprising:
- moving the combination of the vessel and the upper part of the platform to a target
location, and
- unloading the upper part of the platform from the vessel by moving the beams and the
upper part away from the vessel.
- 8. The method of clause 1, comprising unloading the upper part of the platform from
the vessel by moving the one or more beams including the upper part of the support
structure substantially horizontally relative to the vessel.
- 9. The method of clause 3, wherein the support structure comprises one or more rails
or skid tracks which rest on the vessel, wherein the beams of the support structure
are movably arranged on the one or more rails or skid tracks via wheels or skid means,
the method comprising rolling or skidding the one or more beams relative to the vessel
for unloading the upper part of the platform from the vessel.
- 10. The method of clause 1, comprising removing the upper part of the platform from
the vessel by
- positioning one or more support carriages on the deck of the vessel,
- disconnecting the one or more beams from either the vessel deck or the platform
- lifting the upper part of the platform optionally including one or more beams from
the deck
- unloading the combination of support carriage, beams and upper part of the platform
from the vessel.
- 11. The method of clause 1, comprising unloading the upper part of the platform by
moving the support structure and the upper part of the platform in a longitudinal
direction of the vessel.
- 12. The method of clause 1, comprising unloading the upper part of the platform by
moving the upper part of the platform in a transversal direction of the vessel.
- 13. The method of clause 1, comprising unloading the upper part of the platform by
providing a docking station comprising a bay for the vessel and supports member positioned
around the bay , the support members being configured to support the support beams
of the support structure, the method comprising:
- positioning the vessel with the upper part of the platform in the docking station,
- ballasting the vessel such that the vessel moves downward and the support beams engage
the support members, thereby shifting the weight of the upper part of the platform
from the vessel to the docking station;
- removing the vessel from the docking station.
- 14. A system for removing an upper part of a platform which rests on a seabed and which
extends above the waterline, the platform comprising legs which extend upwards from
the seabed, the system comprising:
- a vessel comprising a single hull, the hull defining a contour of the vessel when
viewed from above;
- a support structure which rests on the vessel, the support structure comprising one
or more beams, the one or more beams having connection ends that extend outside the
contour of the hull on opposite sides of the vessel, the connection ends configured
to be connected to the legs of the platform.
- 15. The system of clause 14, the vessel further comprising a ballast system for varying
the draft of the vessel.
- 16. The system of clause 14, wherein the one or more beams are movable in a substantially
horizontal direction relative to the vessel.
- 17. The system of clause 14, wherein the support structure comprises a hydraulic system
which rests on the vessel and is configured to raise the one or more beams including
the platform relative to the vessel.
- 18. The system of clause 14, wherein the support structure comprises one or more beams
having connection ends which project substantially horizontally away from the vessel,
a central part of the beam resting on the vessel, such that the connection ends meet
the legs of the platform for connection with the legs when the vessel is positioned
between the legs of the upper part for the platform.
- 19. The system of clause 14, wherein the connection ends of the support structure
extend on opposite sides of the vessel, one end of a first beam being configured to
be connected to a first leg of the platform, and the opposite end of the first beam
being configured to be connected to a second leg of the platform.
- 20. The system of clause 14, wherein the one or more beams are releasably arranged
on the vessel such that the one or more beams are unloadable at a target location
from the vessel together with the upper part of the platform.
- 21. The system of clause 14, wherein the support structure comprises one or more rails
or skid tracks which rest on the vessel, wherein the beams of the support structure
are movably arranged on the one or more rails or skid tracks via wheels or skid means,
such that the one or more beams may be rolled or skidded in a substantially horizontal
direction relative to the vessel for unloading the one or more beams and the upper
part of the platform from the vessel.
- 22. The system of clause 14, wherein the support structure comprises one or more support
carriages which rest on the deck of the vessel, the support carriages configured to
carry the beams including the upper part of the platform, the support carriages further
configured to move substantially horizontally relative to the deck for unloading the
upper part of the platform from the vessel.
- 23. The system of clause 14, wherein the support structure comprises one or more rails
or skid tracks which rest on the vessel, and wherein the rails or skid tracks extend
in a longitudinal direction of the vessel.
- 24. The system of clause 14, further comprising provisional or preliminary support
means constructed to support the one or more support beams in a target position on
the platform such that possible motions of the support vessel under influence of waves
and wind do not affect or disturb the connecting of the one or more beams to the legs.
- 25. A support structure for use in the method of clause 1 or for use in the system
of clause 14.
- 26. A vessel for use in the method of clause 1 or for use in the system of clause
13.
- 27. A docking station for unloading the platform from the vessel, the docking station
comprising a bay for the vessel and support members positioned around the bay, the
support members being configured to support the support beams of the support structure,
thereby allowing the unloading method of:
- positioning the vessel with the upper part of the platform in the docking station,
- ballasting the vessel such that the vessel moves downward and the support beams engage
the support members, thereby shifting the weight of the upper part of the platform
from the vessel to the docking station via the one or more support beams;
- removing the vessel from the docking station.
[0046] It will be obvious to a person skilled in the art that numerous changes in the details
and the arrangement of the parts may be varied over considerable range without departing
from the spirit of the invention and the scope of the claims.
1. Method of removing an upper part of a platform which rests on a seabed and which extends
above the waterline, the platform comprising legs which extend upwards from the seabed,
the method comprising the subsequent steps of:
- providing a vessel comprising a single hull, the hull defining a contour of the
vessel when viewed from above;
- providing a support structure which is configured to rest on the vessel, the support
structure comprising one or more beams, the one or more beams having connection ends
that are constructed to extend outside the contour of the hull on opposite sides of
the vessel, the connection ends configured to be connected to the legs of the platform;
- positioning the vessel between the legs of the platform;
- connecting the connection ends to the legs of the platform;
- disconnecting the upper part of the platform from the lower part;
- lifting the upper part of the platform from the lower part by the vessel via the
support structure;
- moving the vessel and the upper part of the platform away from the lower part of
the platform.
2. Method of claim 1, the vessel further comprising a ballast system for varying the
draft of the vessel, the method comprising:
- ballasting the vessel to a deep draft when positioned between the legs of the vessel
- lifting the upper part of the platform by deballasting the vessel.
3. The method of claim 1 or 2, wherein the support structure comprises a hydraulic system
for raising the one or more beams including the platform relative to the vessel, the
method comprising raising the upper part of the platform relative to the vessel by
the hydraulic system, optionally while at the same time deballasting the vessel.
4. Method of any of claims 1-3, comprising:
- positioning the one or more beams of the support structure in a target position
wherein the connection ends engage the legs;
- supporting the one or more beams in their target positions by the platform via provisional
or preliminary support means on the platform;
- disconnecting the support structure from the vessel such that possible motions of
the support vessel under influence of waves and wind do not affect or disturb the
connecting of the one or more beams to the legs;;
- connecting the one ore more beams to the legs;
- reconnecting the support structure to the vessel prior to the lifting of the upper
part of the platform from the lower part of the platform.
5. Method of any of claims 1-4, wherein the beams are releasably arranged on the vessel
such that the upper part of the platform and the support structure connected to it
can be unloaded from the vessel by moving the beams relative to the vessel, the method
comprising:
- moving the combination of the vessel and the upper part of the platform to a target
location, and
- unloading the upper part of the platform from the vessel by moving the beams and
the upper part away from the vessel, and/or comprising unloading the upper part of
the platform from the vessel by moving the one or more beams including the upper part
of the support structure substantially horizontally relative to the vessel, and/or
wherein the support structure comprises one or more rails or skid tracks which rest
on the vessel, wherein the beams of the support structure are movably arranged on
the one or more rails or skid tracks via wheels or skid means, the method comprising
rolling or skidding the one or more beams relative to the vessel for unloading the
upper part of the platform from the vessel.
6. The method of any of claims 1-5, comprising removing the upper part of the platform
from the vessel by
- positioning one or more support carriages on the deck of the vessel,
- disconnecting the one or more beams from either the vessel deck or the platform
- lifting the upper part of the platform optionally including one or more beams from
the deck
- unloading the combination of support carriage, beams and upper part of the platform
from the vessel.
7. The method of any of claims 1-6, comprising unloading the upper part of the platform
by moving the support structure and the upper part of the platform in a longitudinal
direction of the vessel, and/or comprising unloading the upper part of the platform
by moving the upper part of the platform in a transversal direction of the vessel.
8. A system for removing an upper part of a platform which rests on a seabed and which
extends above the waterline, the platform comprising legs which extend upwards from
the seabed, the system comprising:
- a vessel comprising a single hull, the hull defining a contour of the vessel when
viewed from above;
- a support structure which rests on the vessel, the support structure comprising
one or more beams, the one or more beams having connection ends that extend outside
the contour of the hull on opposite sides of the vessel, the connection ends configured
to be connected to the legs of the platform.
9. The system of claim 8, wherein the one or more beams are movable in a substantially
horizontal direction relative to the vessel, and/or wherein the support structure
comprises a hydraulic system which rests on the vessel and is configured to raise
the one or more beams including the platform relative to the vessel.
10. The system of claim 8 or 9, wherein the support structure comprises one or more beams
having connection ends which project substantially horizontally away from the vessel,
a central part of the beam resting on the vessel, such that the connection ends meet
the legs of the platform for connection with the legs when the vessel is positioned
between the legs of the upper part for the platform, and/or wherein the connection
ends of the support structure extend on opposite sides of the vessel, one end of a
first beam being configured to be connected to a first leg of the platform, and the
opposite end of the first beam being configured to be connected to a second leg of
the platform, and/or
wherein the one or more beams are releasably arranged on the vessel such that the
one or more beams are unloadable at a target location from the vessel together with
the upper part of the platform.
11. The system of any of claims 8-10, wherein the support structure comprises one or more
rails or skid tracks which rest on the vessel, wherein the beams of the support structure
are movably arranged on the one or more rails or skid tracks via wheels or skid means,
such that the one or more beams may be rolled or skidded in a substantially horizontal
direction relative to the vessel for unloading the one or more beams and the upper
part of the platform from the vessel, and/or wherein the support structure comprises
one or more support carriages which rest on the deck of the vessel, the support carriages
configured to carry the beams including the upper part of the platform, the support
carriages further configured to move substantially horizontally relative to the deck
for unloading the upper part of the platform from the vessel, and/or
wherein the support structure comprises one or more rails or skid tracks which rest
on the vessel, and wherein the rails or skid tracks extend in a longitudinal direction
of the vessel.
12. The system of any of claims 8-11, further comprising provisional or preliminary support
means constructed to support the one or more support beams in a target position on
the platform such that possible motions of the support vessel under influence of waves
and wind do not affect or disturb the connecting of the one or more beams to the legs.
13. A support structure for use in the method of claim 1 or for use in the system of claim
8.
14. A vessel for use in the method of claim 1 or for use in the system of claim 8.
15. A docking station for unloading the platform from the vessel, the docking station
comprising a bay for the vessel and support members positioned around the bay, the
support members being configured to support the support beams of the support structure,
thereby allowing the unloading method of:
- positioning the vessel with the upper part of the platform in the docking station,
- ballasting the vessel such that the vessel moves downward and the support beams
engage the support members, thereby shifting the weight of the upper part of the platform
from the vessel to the docking station via the one or more support beams;
- removing the vessel from the docking station.