U.S. patent application number 12/325417 was filed with the patent office on 2009-06-11 for removal of platforms at sea.
This patent application is currently assigned to HEEREMA MARINE CONTRACTORS NEDERLAND B.V.. Invention is credited to Jan-Willem Ouwehand.
Application Number | 20090148241 12/325417 |
Document ID | / |
Family ID | 40482001 |
Filed Date | 2009-06-11 |
United States Patent
Application |
20090148241 |
Kind Code |
A1 |
Ouwehand; Jan-Willem |
June 11, 2009 |
REMOVAL OF PLATFORMS AT SEA
Abstract
The present invention relates tot 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. The present
invention further relates to a system for carrying out the
method.
Inventors: |
Ouwehand; Jan-Willem;
(Katwijk, NL) |
Correspondence
Address: |
HOFFMANN & BARON, LLP
6900 JERICHO TURNPIKE
SYOSSET
NY
11791
US
|
Assignee: |
HEEREMA MARINE CONTRACTORS
NEDERLAND B.V.
Leiden
NL
|
Family ID: |
40482001 |
Appl. No.: |
12/325417 |
Filed: |
December 1, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61012570 |
Dec 10, 2007 |
|
|
|
Current U.S.
Class: |
405/195.1 ;
114/263 |
Current CPC
Class: |
E02B 17/00 20130101;
B63B 35/003 20130101; E02B 2017/0052 20130101; E02B 2017/0047
20130101 |
Class at
Publication: |
405/195.1 ;
114/263 |
International
Class: |
E02D 29/09 20060101
E02D029/09 |
Claims
1. 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; and moving the vessel
and the upper part of the platform away from the lower part of the
platform.
2. The 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; and lifting the upper part of the platform by
deballasting the vessel.
3. The method of claim 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 claim 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. The method of claim 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; and connecting the one ore more beams to the legs.
6. The method of claim 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; and 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. The method of claim 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 claim 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 claim 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 claim 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; and unloading the combination of support carriage,
beams and upper part of the platform from the vessel.
11. The method of claim 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 claim 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 claim 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; and 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; and 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 claim 14, the vessel further comprising a ballast
system for varying the draft of the vessel.
16. The system of claim 14, wherein the one or more beams are
movable in a substantially horizontal direction relative to the
vessel.
17. The system of claim 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 claim 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 claim 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 claim 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 claim 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 claim 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 claim 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 claim 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 claim 1.
26. A support structure for use in the system of claim 14.
27. A vessel for use in the method of claim 1.
28. A vessel for use in the system of claim 13.
29. 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; and removing the
vessel from the docking station.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/102,570, filed Dec. 10, 2007, the contents of
which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a method and system for
removing a part of a platform at sea, the platform resting on a
seabed.
[0003] Methods for removing such platforms are known in the field
of the art.
[0004] 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
[0005] 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.
[0006] 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.
[0007] 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 FIG. 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.
[0008] 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.
[0009] 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.
OBJECTS OF THE INVENTION
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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:
[0014] providing a vessel comprising a single hull, the hull
defining a contour of the vessel when viewed from above;
[0015] 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 connection ends
configured to be connected to the legs of the platform;
[0016] positioning the vessel between the legs of the platform;
[0017] connecting the connection ends to the legs of the
platform;
[0018] disconnecting the upper part of the platform from the lower
part;
[0019] lifting the upper part of the platform from the lower part
by the vessel via the support structure;
[0020] moving the vessel and the upper part of the platform away
from the lower part of the platform.
[0021] 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.
[0022] 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.
[0023] The method may also be used to remove the lower part of the
platform or to remove the entire platform at once.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] Generally, the support structure rests on the deck of the
vessel and extends substantially horizontally.
[0029] The hull of the vessel will generally be elongate and can
also be referred to as a mono-hull.
[0030] 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.
[0031] In an aspect of the invention, the method comprises:
[0032] positioning the one or more beams of the support structure
in a target position wherein the connection ends engage the
legs;
[0033] 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;
[0034] connecting the one ore more beams to the legs.
[0035] Advantageously, the connecting of the support structure to
the legs can take place without hindrance from movement of the
vessel.
[0036] 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.
[0037] In an advantageous embodiment, the method comprises:
[0038] positioning the one or more beams of the support structure
in a target position wherein the connection ends engage the
legs;
[0039] supporting the one or more beams in their target positions
by the platform via provisional or preliminary support means on the
platform;
[0040] 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;
[0041] connecting the one ore more beams to the legs;
[0042] 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.
[0043] 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.
[0044] 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.
[0045] This method allows very heavy platforms to be unloaded fro
the vessel with relative ease.
[0046] In another aspect, the method comprises removing the upper
part of the platform from the vessel by
[0047] positioning one or more support carriages on the deck of the
vessel,
[0048] disconnecting the one or more beams from either the vessel
deck or the platform
[0049] lifting the upper part of the platform optionally including
one or more beams from the deck
[0050] unloading the combination of support carriage, beams and
upper part of the platform from the vessel.
[0051] Via the support carriages, the upper part of the platform is
simply rolled off the vessel.
[0052] 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:
[0053] a vessel comprising a single hull, the hull defining a
contour of the vessel when viewed from above;
[0054] 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.
[0055] The present invention also relates to a support structure
(i) for use in the method of the present invention 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; and moving the vessel and the upper part of the
platform away from the lower part of the platform; or (ii) for use
in the system of the present invention 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; and 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.
[0056] The present invention further relates to a vessel (i) for
use in the method of the present invention 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; and moving the vessel and the upper part of the
platform away from the lower part of the platform; or (ii) for use
in the system of the present invention 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; and 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.
[0057] 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:
[0058] positioning the vessel with the upper part of the platform
in the docking station,
[0059] 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;
[0060] removing the vessel from the docking station.
BRIEF DESCRIPTION OF THE FIGURES
[0061] FIG. 1 shows a platform removal system according to the
prior art;
[0062] FIG. 2 shows an isometric view of an embodiment of the
invention;
[0063] FIG. 3 shows a front view of a platform removal system of
the invention supporting an upper part of the platform;
[0064] FIG. 4 shows a side view of a platform removal system of the
invention carrying an upper part of the platform;
[0065] FIGS. 5a-5g show different steps in a platform removal
method according to the invention; and
[0066] FIG. 6 shows an isometric view of an alternative embodiment
of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0067] FIGS. 1a and 1b show the system of GB2165188 and disclose 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.
[0068] 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.
[0069] 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.
[0070] In particular the strut assemblies 50 shown in FIGS. 1a and
1b may need a substantial length in order to reach the girders
51.
[0071] FIGS. 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.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] In FIG. 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.
[0076] FIG. 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.
[0077] FIG. 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.
[0078] FIG. 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.
[0079] 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.
[0080] It is also possible that the beams 31 are lifted relative to
the barge 2 and 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.
[0081] In FIG. 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.
[0082] FIG. 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.
[0083] FIG. 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.
[0084] FIG. 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.
[0085] FIG. 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.
[0086] FIG. 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.
[0087] 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.
* * * * *