U.S. patent application number 11/632307 was filed with the patent office on 2008-04-17 for method and device for connecting a riser to a target structure.
Invention is credited to Ion Coppens, Robert Paul Hovinga, Robert Reinder Narold, Peter Salome.
Application Number | 20080089745 11/632307 |
Document ID | / |
Family ID | 34972041 |
Filed Date | 2008-04-17 |
United States Patent
Application |
20080089745 |
Kind Code |
A1 |
Salome; Peter ; et
al. |
April 17, 2008 |
Method And Device For Connecting A Riser To A Target Structure
Abstract
The present invention relates to a method for connecting a free
end of an at least partially submerged riser to a target structure,
the method comprising: (a) connecting the riser by the free end
thereof to a riser support assembly; (b) positioning the target
structure near the riser support assembly; (c) connecting a lifting
assembly, with the free end (24) of the riser; (d) moving the riser
by the free end thereof from the riser support assembly toward the
target structure by the lifting assembly; and (e) connecting the
riser with the target structure. The present invention also relates
to a riser support assembly for connecting a riser by a free end
thereof with a target structure.
Inventors: |
Salome; Peter; (Boskoop,
NL) ; Narold; Robert Reinder; (Hoofddorp, NL)
; Hovinga; Robert Paul; (Av 'S Gravenzande, NL) ;
Coppens; Ion; (Oegsigeesi, NL) |
Correspondence
Address: |
BROWDY AND NEIMARK, P.L.L.C.;624 NINTH STREET, NW
SUITE 300
WASHINGTON
DC
20001-5303
US
|
Family ID: |
34972041 |
Appl. No.: |
11/632307 |
Filed: |
July 8, 2005 |
PCT Filed: |
July 8, 2005 |
PCT NO: |
PCT/NL05/00493 |
371 Date: |
January 12, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60586871 |
Jul 12, 2004 |
|
|
|
Current U.S.
Class: |
405/224.2 |
Current CPC
Class: |
E21B 19/004 20130101;
E21B 17/012 20130101 |
Class at
Publication: |
405/224.2 |
International
Class: |
E21B 17/01 20060101
E21B017/01 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 18, 2004 |
US |
60619015 |
Claims
1. A method for connecting a free end of an at least partially
submerged riser to a target structure, the method comprising: (a)
connecting the riser by the free end thereof to a riser support
assembly; (b) positioning the target structure near the riser
support assembly; (c) connecting a lifting assembly with the free
end (24) of the riser; (d) moving the riser by the free end thereof
from the riser support assembly toward the target structure by the
lifting assembly; and (e) connecting the riser with the target
structure.
2. The method of claim 1, wherein the target structure and the
riser support assembly are maintained in their respective positions
independently from one another.
3. The method of claim 1 or 2, wherein the target structure
comprises the lifting assembly.
4. The method of claim 1, wherein the riser support assembly is
anchored to the seabed by a first anchoring device.
5. The method of claim 4, wherein the target structure is anchored
to the seabed by a second anchoring device which is an independent
device from the first anchoring device.
6. The method of claim 1, wherein the riser support assembly is
directly connected to the first anchoring device throughout steps
(a), (b), (c), (d) and (e).
7. The method of claim 1, wherein during step (b) the target
structure and the riser support assembly are connected by a
connecting means.
8. The method of claim 7, wherein during step (b) the target
structure and the riser support assembly are moved towards one
another by reducing a length of the connection means.
9. The method of claim 1, wherein the riser support assembly is
positioned at a predetermined depth under the water surface when
the riser is suspended from the riser support assembly.
10. The method of claim 9, wherein the riser support assembly is
positioned at a depth at which the riser support assembly is
substantially free from influences from wind and waves at the water
surface.
11. The method of claim 1, wherein in step (b) the target structure
is at least temporarily positioned substantially above the riser
support assembly.
12. The method of claim 1, comprising a further step (f) of
removing the riser support assembly.
13. The method of claim 1, wherein prior to step (a) the riser is
suspended by the free end thereof from a pipe-laying vessel and in
step (a), the riser is transferred from the pipe-laying vessel to
the riser support assembly.
14. The method of claim 13, wherein in step (a) the riser support
assembly is moved towards the pipe-laying vessel, for transferring
the riser from the pipe-laying vessel to the riser support
assembly.
15. The method of claim 1, wherein the target structure is chosen
from a group of floating structures, comprising: a TLP, a Spar, a
Semi-submersible, an FPSO, an FPDSO, an FPWSO, a storage barge, an
FSO, an FSU.
16. The method of claim 1, wherein the riser is chosen from a group
of risers, comprising: a steel catenary riser, a lazy wave riser
with buoyancy elements, a steep wave riser, and a flexible
riser.
17. The method of claim 1, wherein the riser is manufactured from a
material, chosen from a group of materials, comprising: steel,
titanium, a synthetic material, and a composite of a metal and a
synthetic material.
18. The method of claim 1, wherein the riser comprises flexible
pipe sections.
19. The method of claim 1, wherein at least two risers are
connected to the target structure.
20. The method of claim 19, wherein in step (a) at least two risers
are connected to a single riser support assembly.
21. The method of claim 19 or 20, wherein a first riser support
assembly and a second riser support assembly are provided, and
wherein the first riser support assembly and second riser support
assembly are connected by a mooring connecting means for
maintaining a predetermined distance between the first and second
riser support assembly.
22. The method of claim 21, wherein the mooring connecting means
are selected from a group of mooring connecting means, comprising:
a flexible mooring connecting means and a rigid mooring connecting
means.
23. The method of claim 1, wherein the lifting assembly is chosen
from a group of lifting assemblies, comprising: a pull-in device
with chain jacks, a winch, a crane and a drill tower.
24. The method of claim 1, wherein the target structure is anchored
to the seabed using a second anchoring device.
25. The method of claim 1, wherein the lifting assembly is
connected to the riser by a remotely operated device.
26. A riser support assembly for connecting a riser by a free end
thereof with a target structure, the riser support assembly
comprising: a buoyancy device for providing a predetermined
buoyancy to the riser support assembly; a suspending device
configured for suspending the riser by the free end thereof from
the riser support assembly; a first anchoring device for anchoring
the riser support assembly to the seabed.
27. The riser support assembly of claim 26, wherein the suspending
device is constructed for allowing an upwards movement of the riser
relative to the riser support assembly.
28. The riser support assembly of claim 26 or 27, wherein the riser
support assembly comprises a recess configured for receiving the
riser therein.
29. The riser support assembly according to claim 28, wherein the
recess is a channel which, in use, extends substantially through
the buoyancy device, preferably in a substantially vertical
direction.
30. The riser support assembly according to claim 26, wherein the
riser support assembly has a substantially elongated form.
31. The riser support assembly according to claim 30, wherein the
substantially elongated form extends in a substantially horizontal
direction.
32. The riser support assembly according to claim 26, wherein the
buoyancy device comprises a first buoyancy means and a second
buoyancy means, wherein the first and second buoyancy means are
connected with one another by means of a bridging body.
33. The riser support assembly according to claim 26, wherein the
bridging body comprises the suspending device.
34. The riser support assembly according to claim 26, wherein the
suspending device is configured for suspending a number of risers
therefrom.
35. The riser support assembly according to claim 26, wherein the
first anchoring device comprises an mooring line and an anchoring
means, the anchoring means being chosen from a group of anchoring
means, comprising: a piled foundation, a suction pile and a gravity
foundation.
36. The riser support assembly according to claim 35, wherein the
anchoring means are configured for bearing a substantially upwardly
directed force which is exerted on the anchoring means by the
mooring line.
37. The riser support assembly according to claim 26, wherein the
first anchoring device comprises a mooring line, the mooring line
being chosen from a group of mooring lines, comprising: a tendon, a
polyester line, a steel wire and a chain.
38. The riser support assembly according to claim 26, having at
least one riser suspended therefrom.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method and device for
connecting a riser to a target structure. Risers are widely applied
in the offshore industry in oil and/or gas fields at sea. An oil
and/or gas well is located at a seabed level. The product, e.g. oil
and/or gas, is produced by the well and is transported to a
structure at the water level. From the structure, the product is
transported further on, for instance by means of another pipeline
to a shore. The product may also be temporarily stored in a storage
facility close to, or on the structure. In order to transport the
product to the structure, the well is connected to the structure by
a pipeline for conveying the product to the structure.
[0002] During the installation of oil and/or gas field, a pipeline
is laid connecting the well with the structure located at the water
surface. Such a pipeline usually has a first part which rests on
the seabed, and a second part which rises from the seabed towards
the structure at the water level. The second part of the pipeline
is known in the field of the art as a "riser".
[0003] Typically, the riser follows a curved trajectory from the
seabed towards the riser support assembly. At the seabed level, the
riser has a substantially horizontal orientation. Near the riser
support assembly, the riser may have a substantially vertical
orientation.
DESCRIPTION OF THE PRIOR ART
[0004] In a known method of installation of a riser, a transfer of
a product riser and a transfer of a number of anchor lines from a
first, temporary buoy to a second, permanent buoy are combined. The
product riser is produced and installed by a pipe-laying vessel,
located at the water surface. The first buoy is anchored to the
seabed by at least a first and a second anchor line. The product
riser connected by a free end thereof to the first buoy. The riser
may stay in this position for a considerable period of time, until
a second, permanent mooring buoy is put in place.
[0005] When the second buoy is ready, it is positioned in a desired
position, close to the first buoy. The first and the second buoy
are connected to one another via a member which can take up tension
forces. A tug boat is provided for pulling the second buoy away
from the first buoy. Then, the anchor lines are detached one by one
from the first buoy and connected to the second buoy. During the
time period in which at least one of the anchor lines is detached,
the combination of the first and second buoy is no longer anchored
in a stable and secure way, and is in risk of drifting away from
the desired location. The tug boat is provided for keeping the
buoys in place.
[0006] Subsequently, the second anchor line is transferred from the
first buoy to the second buoy. During this operation, the tug boat
also keeps the first and second buoy in place en prevents drifting
away of the first and second buoy.
[0007] Then, the product riser is transferred from the first buoy
to the second buoy. This is performed by using a cable which is
connected to a winch on the second buoy. The free end of the cable
is connected to a free end of the product riser. When the product
riser is detached from the first buoy, the cable is pulled by the
winch, transferring the product riser from the first buoy to the
second buoy.
[0008] A drawback of the above mentioned method is that it is a
complicated procedure, requiring a tug boat
[0009] Further, the combination of transferring the anchor lines
and the product riser at the same time provides the drawback that
the first buoy is no longer anchored to the seabed at the end of
the operation and is to be moved away by the tug boat. A reverse
operation of transferring the product riser back to the first buoy
cannot be performed without re-anchoring the first buoy back to the
seabed.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a method
and device for connecting a riser to a target structure which is
substantially free of the above mentioned drawbacks.
[0011] It is a further object of the invention to provide a method
and device for connecting a riser to a target structure, which is
relatively fast, reliable and simple to perform.
[0012] It is in particular an object of the present invention to
provide a method and device of connecting a riser to a target
structure, wherein a free end of the riser can temporarily be
positioned in a predetermined way during a time period in which the
target structure is not yet present and connected to the target
structure when the target structure is present at its desired
position.
[0013] Thereto the method according to the invention comprises the
steps of: [0014] (a) connecting the riser by the free end thereof
to a riser support assembly; [0015] (b) positioning the target
structure near the riser support assembly; [0016] (c) connecting a
lifting assembly with the free end of the riser; [0017] (d) moving
the riser by the free end thereof from the riser support assembly
toward the target structure by the lifting assembly; and [0018] (e)
connecting the riser with the target structure.
[0019] With the method according to the invention, risers can be
installed when the target structure is not yet present at the time
of installation of the riser itself.
[0020] The word "riser" may refer to a production, injection,
communication and/or control riser for conveying oil and/or gas or
another product. A production or injection riser is constructed to
convey a product, such as oil or gas or water or any fluid, from
the seabed to the target structure or vice versa from the target
structure to the well. The word riser may also refer to a
communication and/or control riser. A communication and/or control
riser is constructed to transmit signals from the target structure
to devices on the seabed, such as for instance the wells, or
controllable valves. Also, signals may be transmitted by the riser
from the oil well and/or other devices on the seabed to the target
structure, for controlling the devices on the seabed.
[0021] Other types of risers also exist, for instance risers that
are used to convey water from the target structure toward the
seabed, for injection of the water in the well. Other types of
riser are well control risers.
[0022] The words "target structure" are to be interpreted broadly
and can indicate a wide range of structures, floating or resting on
the seabed. A number of non-limiting examples of target structures
are provided hereinafter.
[0023] The words "lifting assembly" are to be understood as to
indicate a wide range of lifting assemblies. The lifting assembly
may be a crane or a winch or a drilling tower, or another device.
The lifting assembly may be positioned on the target structure or
on a separate vessel or structure.
[0024] The riser support assembly indicates any construction
configured for supporting a riser by a free end thereof. The riser
support assembly preferably comprises a buoyancy device for
providing a required buoyancy for supporting the riser.
[0025] Preferably, the target structure and the riser support
assembly are maintained in their respective positions independently
from one another.
[0026] In this way the riser support assembly and the target
structure may be accurately positioned with respect to one
another.
[0027] Preferably, the target structure comprises the lifting
assembly. This provides the advantage of obviating the need for
providing a separate vessel with a lifting assembly. The moving of
the riser can be conducted from the target structure itself, which
is simple and reliable.
[0028] Preferably, the riser support assembly is anchored to the
seabed by a first anchoring device.
[0029] The anchoring device advantageously keeps the riser support
assembly in a fixed position.
[0030] Preferably, the target structure is anchored to the seabed
by a second anchoring device which is an independent device from
the first anchoring device. In this way, advantageously the step of
transferring the anchoring device of the riser support assembly to
the target structure can be left out of the procedure.
[0031] Preferably, the riser support assembly is directly connected
to the first anchoring device throughout steps (a), (b), (c), (d)
and (e). This provides the advantage of having a simple and
reliable positioning of the riser support assembly throughout steps
(a), (b), (c), (d) and (e).
[0032] Preferably, during step (b) the target structure and the
riser support assembly are connected by a connecting means. With
the connecting means, a horizontal distance between the riser
support assembly and the target structure can be reduced, providing
easier transfer of the riser.
Preferably, the target structure and the riser support assembly are
not connected to one another.
[0033] Preferably, during step (b) the target structure and the
riser support assembly are moved towards one another by reducing
the length of the connection means. Also, the length of the mooring
lines of the target structure can be adjusted, thereby moving the
target structure toward the riser support assembly. This may be a
substantial horizontal movement. Advantageously, the target
structure and the riser support assembly can be positioned very
close to one another, facilitating the transferal of the riser from
the target support assembly to the target structure.
[0034] Preferably, the riser support assembly is positioned at a
predetermined depth under the water surface when the riser is
suspended from the riser support assembly. This facilitates an
eventual positioning of the riser support assembly close to the
target structure.
[0035] Preferably, the riser support assembly is positioned at a
depth at which the riser support assembly is substantially free
from influences from wind and waves at the water surface. This
provides the advantage of a stable support for the riser with
relative low dynamic forces exerted on the riser support assembly
and the riser.
[0036] Preferably, in step (b) the target structure is at least
temporarily positioned substantially above the riser support
assembly. This provides the advantage that the riser can be moved
from the riser support assembly to the target structure in a
substantially vertical direction. This enables a simple lift
operation by the lifting assembly.
[0037] Preferably, the depth at which the riser support assembly is
positioned is greater than the draught of the target structure.
This enables the positioning of the riser support assembly under
the target structure.
[0038] Preferably, the method according to the invention comprises
a further step (f) of removing the riser support assembly.
Advantageously, the riser support assembly may be reused at another
location.
[0039] Preferably, prior to step (a) the riser is suspended by the
free end thereof from a pipe-laying vessel and in step (a) the
riser is transferred from the pipe-laying vessel to the riser
support assembly. This enables the pipe-laying vessel to start
another operation elsewhere, and obviates the need for the
pipe-laying vessel to wait for a substantial amount of time for
late arrival of the target structure.
[0040] Preferably, in step (a) the riser support assembly is moved
towards the pipe-laying vessel, for transferring the riser from the
pipe-laying vessel to the riser support assembly.
[0041] Preferably, the target structure is chosen from a group of
floating structures, comprising: a TLP, a Spar, a Semi-submersible,
an FPSO, an FPDSO, an FPWSO, a storage barge, an FSO, an FSU. For
these structures and other structures, the method according to the
invention provides a reliable way of connecting the riser to the
target structure.
[0042] Different riser configurations exist to provide a reliable
connection between the pipeline on the seabed and the target
structure. Preferably, the riser comprises rigid sections.
Alternatively the riser comprises only flexible pipe sections. The
riser can also be of a hybrid type comprising rigid sections and
flexible sections.
[0043] Preferably, in step (a) at least two risers are connected to
a single riser support assembly. This provides the advantage of
needing only a limited number of riser support assemblies, in some
cases only one.
[0044] Preferably, a first riser support assembly and a second
riser support assembly are provided, wherein the first riser
support assembly and second riser support assembly are connected by
a mooring connecting means for maintaining a predetermined distance
between the first and second riser support assembly.
[0045] This embodiment advantageously prevents damage to the riser
support assemblies. The mooring connecting means may be a wire or a
line, a cable or a rigid bar, or another connecting means known in
the art.
[0046] Alternatively, the riser support assemblies may be
positioned at a sufficient large distance from one another. The
riser support assemblies may comprise fenders to prevent damage at
contact between the riser support assemblies.
[0047] Alternatively, two or more riser support assemblies are
integrated into to a large riser support assembly. A large riser
support assembly can support a number of risers, thereby further
simplifying the construction.
[0048] Preferably, the lifting assembly is chosen from a group of
lifting assemblies, comprising: a pull-in device with chain jacks,
a winch, a crane and a drill tower. These lifting assemblies have a
lifting power that is sufficient to move the riser from the riser
support assembly to the target structure.
[0049] Preferably, the target structure is anchored to the seabed
using a second anchoring device. This provides the advantage of a
secure anchoring of the target structure, while obviating the need
for detaching the first anchoring device from the riser support
assembly.
[0050] Preferably, the lifting assembly is connected to the riser
by a remotely operated vehicle (ROV) The lifting assembly comprises
a lifting means such as a cable or a wire or another lifting means
known in the art. The ROV will assist to connect underwater the
lifting means and the riser with the advantage of diverless
operations.
[0051] The invention also relates to a riser support assembly for
connecting a riser by a free end thereof with a target structure,
the riser support assembly comprising: [0052] a buoyancy device for
providing a predetermined buoyancy to the riser support assembly;
[0053] a suspending device configured for suspending the riser by
the free end thereof from the riser support assembly; [0054] a
first anchoring device for anchoring the riser support assembly to
the seabed.
[0055] With the riser support assembly, a riser can be connected to
a target structure in a reliable and simple way.
[0056] Preferably, the riser support assembly is constructed for
allowing an upwards movement of the riser relative to the riser
support assembly. In this way the lifting assembly can lift the
riser from the riser support assembly without hindrance, for
instance when the riser support assembly is positioned
substantially underneath the target structure.
[0057] Preferably the riser support assembly comprises a recess
configured for receiving the riser therein. Advantageously, the
riser is positioned in the recess, thereby exerting a downwards
pulling force on the riser support assembly substantially on the
center of the riser support assembly, when viewed from above. The
riser support assembly will subsequently stay in a stable
orientation.
[0058] Preferably, the recess is a channel which, in use, extends
substantially through the buoyancy device, preferably in a
substantially vertical direction. This provides the advantage that
the free end of the riser will extend on the upper side of the
riser support assembly, allowing easy access to the riser from
above, for instance for connecting a connecting means thereto.
[0059] Preferably, the riser support assembly has a substantially
elongated form.
[0060] Preferably, the substantially elongated form extends in a
substantially horizontal direction. In this way, space is created
for suspending more than one riser from the riser support
assembly.
[0061] Preferably, the buoyancy device comprises a first buoyancy
means and a second buoyancy means, wherein the first and second
buoyancy means are connected with one another by means of a
bridging body. This provides the further advantage of enabling a
configuration of a large riser support assembly.
[0062] Preferably, the bridging body comprises the suspending
device. An integration of the bridging body and the suspending
device provides the advantage of a simple design and ease of
construction.
[0063] Preferably, the suspending device is configured for
suspending a number of risers therefrom. This provides the
advantage that less riser support assemblies will need to be
installed when a relatively large number of risers is present.
[0064] Often, a number of oil and/or gas wells are located in a
same oil and/or gas field at relatively close distances with
respect to one another. In that case, a number of riser may rise
from the wells and be suspended from a single riser support
assembly.
[0065] Preferably, the first anchoring device comprises a mooring
line and an anchoring means, the anchoring means being chosen from
a group of anchoring means, comprising: a piled foundation, a
suction pile and a gravity foundation. These anchoring means have
shown to be reliable for these purposes.
[0066] Preferably, the anchoring means are configured for bearing a
substantially upwardly directed force which is exerted on the
anchoring means by the mooring line. On the first anchoring means
an upwards force may be exerted by the buoyancy device. Therefore,
the anchoring means preferably allows for an upwardly directed
force.
[0067] Preferably, the first anchoring device comprises a mooring
line, the mooring line being chosen from a group of mooring lines,
comprising: a tendon, a polyester line, a steel wire and a chain.
These mooring lines have shown to be reliable.
[0068] The word tendon indicates a rigid and stiff pipe, used for
vertical mooring and high loads. Preferably the tendon comprises
pipe section which are screwed to one another. These tendons
technology is well known and has been used to moor Tension Leg
Platforms (TLP) to the seabed.
[0069] The claims and advantages will be more readily appreciated
as the same becomes better understood by reference to the following
detailed description and considered in connection with the
accompanying drawings in which like reference symbols designate
like parts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0070] Hereinafter the present invention will be illustrated in
more detail by a drawing. Herein shows:
[0071] FIG. 1 a schematic perspective view of a typical
configuration of a target structure;
[0072] FIG. 2 a schematic top view of a typical configuration of
the target structure;
[0073] FIG. 3 shows a schematic top view of the target structure in
a production field;
[0074] FIG. 4 shows a schematic top view of an existing method to
pre-lay the mooring lines and risers of the target structure to the
seabed;
[0075] FIG. 5 shows a schematic side view of a pipe-laying vessel
approaching a riser support assembly;
[0076] FIG. 6 shows a schematic side view of the riser support
assembly in a vertical position;
[0077] FIG. 7 shows a schematic side view of the riser connected to
the riser support assembly;
[0078] FIG. 8 shows a schematic side view of a part of the riser
support assembly;
[0079] FIG. 9 shows a schematic top view of a part of the riser
support assembly;
[0080] FIGS. 10a and 10b show an alternative embodiment of the
riser support assembly;
[0081] FIG. 11 shows another alternative embodiment of the riser
support assembly;
[0082] FIGS. 12 and 13 show a side view of an installation of the
riser onto a riser support assembly;
[0083] FIG. 14 shows a side view of the riser 6 suspended from the
riser support assembly;
[0084] FIGS. 15 and 16 show a side view of the riser 6 with
buoyancy elements;
[0085] FIG. 17. shows a top view of a number of pre-installed
risers;
[0086] FIG. 18 shows a top view of the target structure in the
vicinity of the buoyancy devices;
[0087] FIG. 19 shows a side view of the target structure which is
moved toward a buoyancy device;
[0088] FIGS. 20 shows a side view of an alternative embodiment of
moving the buoyancy device and the target structure towards one
another;
[0089] FIG. 21 shows a side view of a movement of the riser support
assembly after the riser is lifted off the riser support
assembly;
[0090] FIG. 22 shows a side view of a pull-in device for pulling
the riser towards a target structure;
[0091] FIGS. 23a, 23b, 23c show a chain jacking device for pulling
the riser towards the target structure; and
[0092] FIGS. 24, 25 show schematic views of the pull-in device,
movably positioned onboard a target structure.
[0093] FIG. 1 a schematic perspective view of a typical
configuration of a target structure 2 in use. A number of risers
6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j and 6k are suspended from
the target structure 2. For ease of reference, a riser is referred
to as riser 6. The target structure 2 is anchored to the seabed by
an anchoring device 8, comprising a number of mooring lines 8a, 8b,
8c; 8d, 8e, 8f, 8g, 8h, 8i, 8j, 8k, 8l. For ease of reference, a
mooring line is referred to as mooring line 8. The target structure
2 may typically be a floating production facility, such as a
Tension leg Platform (TLP), a Spar, a Semi-submersible, a Floating
Production Storage and Offloading Facility (FPSO), a Floating
Production Drilling Storage and Offloading Facility (FPDSO), a
Floating Production well Workover Storage and Offloading Facility
(FPWSO), a storage barge, a Floating Storage and Offloading
Facility (FSO), or a Floating Storage Unit (FSU).
[0094] The riser 6 may be manufactured from well-known construction
materials such as steel or titanium. Preferably, the riser 6 is a
Steel Catenary Riser (SCR). The riser 6 may also be manufactured
from a synthetic material, or a composite material. It is also
possible that the riser is a flexible riser. The riser 6 may also
be a hybrid curved riser comprising rigid sections and flexible
sections (not shown).
[0095] FIG. 2 shows a schematic top view of the target structure 2.
The risers 6a, 6b, 6c, . . . 6q are connected to the target
structure 2 on different sides of the target structure 2.
[0096] FIG. 3 shows a schematic top view of the target structure 2
in a production field. Pipelines 9 extend between the wells 10a,
10b, 10c, 10d, 10e, 10f, 10g, 10h and the target structure 2. The
wells produce a product such as oil and/or gas. The product from
the wells 10a . . . 10h is conveyed through the pipeline in the
direction of the target structure 2. Some pipelines 9 are not
directly connected to the target structure, but are connected to
another pipeline 9 at a junction 11, from which junction 11 the
product is further conveyed by another pipeline 9. The part of the
pipeline which rises from the seabed to the target structure is the
riser 6, which is not separately indicated in this figure. Other
lines extend on the seabed, such as water injection lines and
umbilicals. These are not indicated by a reference sign.
[0097] FIG. 4 shows a schematic top view of an existing method to
pre-lay the mooring lines 8 and risers 6 of the target structure 2
to the seabed. In this phase, the target structure 2 is not
present. The mooring lines 8a, 8b, 8c, . . . 8l are connected on
one end thereof to a respective anchoring point 12a, 12b, 12c, . .
. 12l. The mooring lines are then laid on the seabed to rest for a
predetermined period of time.
[0098] In the same way, the risers 6a, . . . , 6f are laid on the
sea bed, possibly connected on one end thereof with a respective
well.
[0099] Then, the target structure 2 is positioned in its desired
position. The mooring lines 8a, . . . , 8l are picked up from the
seabed by an installation vessel (not shown). The mooring lines 8a,
. . . , 8l are then connected at their free end to the target
structure 2.
[0100] In the same way, the risers 6a, 6f are picked up from the
seabed and connected on a respective free end 24a, . . . , 24f
thereof to the target structure 2.
[0101] Turning to FIG. 5, a side view of a pipe-laying vessel 16
approaching a riser support assembly 20 is shown. The pipeline or
riser 6 is suspended from the pipe-laying vessel 16. In this
configuration, the pipeline or riser 6 is laid in J-lay mode,
wherein the free end 24 of the pipeline or riser 6 extends in a
substantially vertical direction near the pipe-laying vessel 16.
Instead of a J-lay vessel, other type of lay vessels can be used to
install the risers, such as S-lay or reel-lay vessels. The
pipe-laying vessel 16 moves in the direction indicated by arrow 26.
The pipeline 6 is formed on the pipe-laying vessel 16 by joining
abutting pipe sections (not shown) with the pipeline 6. The
pipeline 6 comes to rest on the seabed 18.
[0102] The riser support assembly 20 comprises a buoyancy device 28
and an anchoring device 29. The anchoring device 29 comprises a
mooring line 14 and an anchoring means 30, the mooring line 14
being connected with a first end to the buoyancy device 28 and with
a second end to the anchoring means 30, anchored in the seabed at
an anchoring point 12. An indicating buoy 32 is connected with a
line to the riser support assembly 20 and floats at the water
surface 34, for indicating the position of the riser support
assembly 20.
[0103] The anchoring means 30 may be a piled foundation, a suction
pile, a gravity foundation. Preferably, the anchoring means 30 is
configured to resist a substantially upwardly directed vertical
force exerted on it by the mooring line 14.
[0104] The mooring line 14 can be a tendon, a light weight line
such as a polyester line, a steel wire or a chain.
[0105] The buoyancy device 28 may be completely under the water
surface 34 or partially above the water surface 34 when there is no
riser 6 suspended from the riser support assembly 20. When the
riser 6 is suspended from the riser support assembly 20, the
buoyancy device 28 will be under the water surface 34 at a depth 41
where there is no influence from wind and/or waves.
[0106] When the riser 6 is connected to the riser support assembly
20, the mooring line 14 may extend along a substantially straight
line or may extend along a catenary line.
[0107] FIG. 6 shows a riser support assembly 20 having a buoyancy
device 28 which is positioned partially submerged and partially
above the water surface 34.
[0108] FIG. 7 shows the riser 6 connected to the riser support
assembly 20. The buoyancy device 28 is positioned at a
predetermined depth under the water surface 34.
[0109] FIGS. 8 and 9 show schematic views from the side and from
the top of a part of the riser support assembly 20. The buoyancy
device 28 has a substantially cylindrical form. Other forms of the
buoyancy device 28, such as box-like, are also possible. A mooring
line 14 is attached to the buoyancy device 28 at a bottom side
thereof. A recess 36 extends through the buoyancy device 28 to form
a channel 37 in a substantial vertical direction through the
buoyancy device 28. A person skilled in the art will readily
appreciate that if the riser 6 is not positioned substantially
vertically but in an inclined orientation, the buoyancy device 28
can adopt the orientation of the riser 6 and the channel 37 will
have an inclined orientation.
[0110] The riser 6 has at the free end 24 thereof a lifting
connector 40 for connecting the riser 6 to a lifting assembly (not
shown), in order to lift the riser 6 from the buoyancy device 28.
Further, at the free end 24 of the riser 6 a first collar 42 is
provided for suspending the riser 6 from the buoyancy device 28. A
second collar 44 is provided to hang the riser 6 from the target
structure (not shown).
[0111] The riser support buoy 28 has a suspending device 31 for
suspending the riser 6 therefrom. The suspending device comprises a
contact area 33, wherein the collar 42 engages the buoyancy device
28.
[0112] FIGS. 10a and 10b show an alternative embodiment of the
riser support assembly 20. The buoyancy device 28 has an elongated
form and extends in a substantially horizontal orientation. Two
mooring lines 14a, 14b are connected on a first end thereof to
respective ends of the riser support assembly 20. The mooring lines
14a, 14b are connected on a second end thereof to anchoring means
30a, 30b. Other forms of the buoyancy device are also possible.
[0113] A number of risers 6a, 6b, 6c, 6d, 6e are suspended from the
riser support assembly 20. Each riser has at the free end 24
thereof a suspending device 46 in the form of a hook 46a, 46b, 46c,
46e for suspending the respective risers 6 from the buoyancy device
28. A person skilled in the art will appreciate that many other
embodiments such a suspending device 46 are possible, without
departing from the scope of the invention.
[0114] FIG. 11 shows another alternative embodiment of the riser
support assembly 20. In this embodiment, two buoyancy means 28a,
28b are provided which are connected by a bridging body 48. The
bridging body 48 is configured to suspend the risers 6a, . . . 6g
therefrom. The bridging body 48 may be a rigid bar.
[0115] Turning to FIGS. 12 and 13, the installation of the riser 6
onto a riser support assembly 20 is shown. When the riser 6 has
reached the required length, it is to be transferred to the riser
support assembly 20. In FIG. 12, the riser support assembly 20 is
pulled toward the pipe-laying vessel 16 by a line 50. The buoyancy
device 28 is moved in close proximity with the pipe-laying vessel
16. This may be performed using a winch (not shown) on board the
pipe-laying vessel 16 or by using an assisting tug boat (not
shown). Then, the riser 6 is transferred from the pipe-laying
vessel 16 to the riser support assembly 20 and is suspended from
the buoyancy device 28.
[0116] FIG. 14 shows the riser 6 suspended from the riser support
assembly 20. In this position, the riser 6 may rest in a suspended
position for a period of time. In some cases, this period of time
may last for a number of months. The riser support assembly 20
should preferably be in a submerged position at a depth well below
the water surface 34, at which depth the riser support assembly 20
experiences no wind and smaller wave induced forces that it would
experience when in the water surface 34.
[0117] FIGS. 15 and 16 show a riser 6 with a number of buoyancy
elements 52a, 52b, 52c, 52d, 52e attached thereto, for providing
buoyancy to the riser 6. In FIG. 15, the riser 6 has a lazy wave
configuration, to reduce fatigue of the riser at the touch down
point and to reduce riser weight.
[0118] In FIG. 16, the buoyancy elements 52a, 52b, 52c, 52d, 52e
are attached to the part of the riser 6 which extends from the
seabed 18 towards the buoyancy device 28 to reduce riser weight and
the size of the buoy 28.
[0119] FIG. 17. shows a top view of a number of pre-installed
risers 6a, 6b, 6c, and 6d, suspended from riser support assemblies
20a, 20b, 20c, 20d. A connecting element 54 is provided between the
buoyancy device 28b and the buoyancy device 28c, for keeping the
buoyancy device 28b and the buoyancy device 28c at a desired
distance from one another. In this way, contact between the
buoyancy devices 28b, 28c in a current flow, can be avoided, which
could result in damage. Connecting elements 54 may also be provided
between the other buoyancy devices 28.
[0120] Alternatively, in order to prevent contact between the
buoyancy devices 28, a sufficient large distance between the
buoyancy devices may also be provided. Also fenders on the buoyancy
devices 28 may be provided in order to avoid damage during contact.
Another possibility of avoiding damage to the buoyancy devices 28
is to integrate a number of buoyancy devices into a single large
buoyancy device 28.
[0121] FIG. 18 shows the target structure 2 in the vicinity of the
buoyancy devices. The target structure 2 is moored to the seabed
after arrival in the field. In order to reduce installation time of
the target structure, use can be made of pre-installed mooring
lines 8. These mooring lines 8 can for instance be pre-installed
and laid on the seabed, as is shown in FIG. 4. The mooring lines 8
can also be connected to buoyancy devices 28 (not shown) allowing
pre-installation of the mooring lines prior to arrival of the
target structure 2.
[0122] The anchoring means 30a, 30b, 30c . . . 30h are positioned
on the other side of the target structure as the respective
corresponding buoyancy devices 28a, . . . 28h.
[0123] The risers 6a, 6b, 6c, . . . 6h extend in different
directions, and are connected to the target structure 2 on
different sides thereof.
[0124] Mooring connecting means 54 connect buoyancy devices 28a,
with 28e, 28b with 28c, 28d with 28h, and 28g with 28f. Other ways
of connecting the buoyancy devices 28a . . . 28h with one another
are also possible.
[0125] FIG. 19 shows a target structure 2 which is moved toward a
buoyancy device 28. The target structure 2 is anchored to the
seabed by mooring lines 8a,8b, shown and designated in a first
position as 8a1 and 8b1. In order to move the target structure 2
towards the buoyancy device 28, the mooring line 8b is winched to
shorten the length thereof. Consequently, the target structure 2
will move in the direction of arrow 56, toward the buoyancy device
28. The mooring lines 8a,8b will adopt respective second positions
8a2, 8b2. In an alternative embodiment, a tug boat is used to move
the target structure toward the buoyancy device 28.
[0126] When the target structure 2 is in the desired position, the
riser 6 can be transferred to the target structure.
[0127] If a number of risers 6 are to be connected to the target
structure 2, the target structure may be moved from one desired
position to the next one, picking up a riser 6 in each position.
After the risers 6 are connected to the target structure 2, the
target structure 2 is moved to its final position.
[0128] FIG. 20 shows an alternative embodiment of moving the
buoyancy device 28 and the target structure 2 towards one another.
In FIG. 20, the buoyancy device 28 is winched towards the target
structure 2 by a winching device 58 located on the target structure
2. A guiding assembly 60 is provided for guiding a connection line
62 between the winching device 58 and the buoyancy device 28, in
order to ensure a correct positioning of the buoyancy device 28
relative to the target structure 2.
[0129] FIG. 21 shows a movement of the riser support assembly 20
after the riser 6 is lifted off the riser support assembly 20 and
transferred to the target structure 2. The buoyancy device 28 will
move with respect to the anchoring point 12, until it reaches its
equilibrium position vertically above the anchoring point 12.
[0130] The buoyancy device 28 can be left in this position,
allowing a reverse operation of transferring the riser 6 from the
target structure 2 onto the riser support assembly 20.
Alternatively the riser support assembly 20 may be removed and
reused in another location. The riser support assemblies 20 may be
disconnected from the anchoring means 30 by a remote operated
vehicle (ROV, not shown), known in the art. Partial flooding of the
buoyancy device 28 may be performed prior to disconnecting from the
buoyancy device 28. The ROV may also be used to assist in
connecting the connection line 62 to the buoyancy device 28.
[0131] In an alternative embodiment, the riser 6 is lifted off the
riser support assembly 20 by a support vessel (not shown) and moved
towards the target structure 2 by the support vessel. The support
vessel requires a high capacity winch to lift the heavy riser
(possibly weighing in the order of 2000-6000 kiloNewton).
[0132] FIG. 22 shows a pull-in device 63 for pulling the riser 6
towards a target structure 2. In this embodiment, the pull-in
device 63 is a drilling tower 64. The pull-in device 63 may also be
a crane or a jacking device (not shown).
[0133] FIG. 23 shows a chain jacking device 66 for pulling the
riser 6 towards the target structure 2. The chain jacking device 66
comprises lift cylinders 68a and 68b, a fixed latch 70, a
travelling latch 72 and a traveling cross-arm 74. Chain jacking
devices are known in the art.
[0134] FIGS. 24 and 25 show a configuration of a pull-in device 63,
movably positioned onboard a target structure 2, on rails 76a, 76b,
such as skidding rails.
[0135] A number of risers 6 are positioned on the side 83 of the
target structure 2. Hydraulic rams 78a, 78b are provided for moving
the pull-in device in the directions of arrows relative to the
target structure A pulling rig skid base 81 is provided for
skidding on the skidding rails 78a, 78b. In this way, a single
pull-in device 63 can be used to sequentially pull in a number of
risers 6a, 6b, 6c towards the target structure 2.
[0136] 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.
* * * * *