GB2536998A

GB2536998A - Deck for offshore rig

Info

Publication number: GB2536998A
Application number: GB1600615.7A
Authority: GB
Inventors: Claxton Dannie
Original assignee: Claxton Engineering Services Ltd
Current assignee: Claxton Engineering Services Ltd
Priority date: 2015-01-13
Filing date: 2016-01-13
Publication date: 2016-10-05
Also published as: GB201500518D0; GB201600615D0

Abstract

A deck assembly for an offshore rig (2, Fig 1) comprises an auxiliary platform (20, Fig. 5) that provides, in use, an upper surface for receiving equipment. A number of elongate struts 32a, 32b are connectable at their first ends to the platform and at their second ends to a part of said rig such that, in use, the platform is suspended below a part of said rig. An aperture 48 for receiving a riser through it extends through the platform. A safety shroud 52 is attached at a first end to the platform so that the shroud extends fully around the hole. The secondary platform may comprise three separate sections, which may be connected with hinges. The platform may be deployed in a first, extended position and stowed in a second, folded, configuration. The shroud may be telescopic. A method of deploying such an assembly is also disclosed.

Description

Deck for Offshore Rig

BACKGROUND

a. Field of the Invention

The present invention relates to a deck for an offshore platform or rig, and more specifically relates to a deck for a jack-up rig for use during the decommissioning of offshore wells, and to a method of deploying such a deck.

b. Related Art The decommissioning of oil and gas wells involves the completion of a number of operations. These operations are often collectively referred to as plugging and abandonment (P&A) operations, and include the removal of the wellhead and the plugging of the casing. The operations involve equipment to cut casings and pull tubing, as well as lift and handle assemblies such as a well head and Christmas tree.

These operations are typically carried out from a rig such as a jack-up rig. The jack-up rig may be positioned next to the well and each of the operations required to abandon that well can then be undertaken. Once a first well has been decommissioned, the jack-up rig is then moved to a second well and the process is repeated.

The time and cost of decommissioning a well is significant. For example, the cost of using a jack-up rig for a day can be of the order of £100,000, and the time required at a single well can be around 400 hours. It would, therefore, be desirable to decrease the length of time that the rig is required at each well site to complete the decommissioning.

It is, therefore, an object of the present invention to provide a means by which the -2 -duration of time taken to complete P&A operations can be decreased.

SUMMARY OF THE INVENTION

In a first aspect of the present invention there is provided a deck assembly for an offshore rig comprising: a platform having a substantially flat support surface that provides, in use, an upper surface for receiving equipment; a plurality of elongate struts, each strut having a first end and a second end, and each strut being connectable at its first end to the platform and connectable at its second end to a part of said rig, such that, in use, the struts suspend the platform below a part of said rig; an aperture extending through the platform, the aperture being sized to receive a riser therethrough; and a shroud attached at a first end to the platform so that the shroud extends fully around the periphery of the aperture, and the shroud extending in a direction away from the support surface of the platform such that the shroud prevents access to the aperture from the support surface.

Preferably the shroud is a cylindrical shroud. The shroud may, however, have any other shape, for example being a box-like shroud formed with straight sides.

It is envisaged that the deck assembly of the present invention will be provided on an offshore rig, such as a jack-up rig. During decommissioning of an offshore well, the deck assembly can be deployed so that the platform is suspended from a part of the rig above the well. Equipment modules for use in decommissioning operations can then be placed onto the support surface of the platform to allow some of the operations to be carried out on the deck assembly in parallel to operations that are being carried out on the main rig. With some operations able to be carried out simultaneously, the total length of time that the rig is required at the well site can, therefore, be reduced. -3 -

In preferred embodiments the platform comprises three sections, a central section and two side sections, each of the sections including a part of the support surface of the platform. In these embodiments each side section is hingedly connected to a respective opposing edge of the central section. The hinged connection is such that in a first, deployed position the sections are in a linear arrangement such that the support surface of each of the sections is contiguous. The sections may then be moved into a second, stowed position in which the side sections are rotated about the hinge with respect to the central section such that the support surface of each of the side sections faces the support surface of the central section. This second, stowed position creates a platform with a footprint having a reduced area so that the platform can be stowed on the rig.

In some embodiments of the invention the shroud is a telescopic shroud.

Accordingly, the shroud comprises a plurality of sections, for example either cylindrical or box-section, that are arranged telescopically. A first section having the smallest cross-sectional area of the sections forms the first end of the shroud and is connected to the support surface of the platform. In use, when the shroud is deployed, the sections are slid with respect to each other so that the shroud extends in a direction away from the support surface. The second end of the shroud formed by the section having the largest cross-sectional area of the sections preferably includes means for connecting the second end of the shroud to a part of the rig above the platform.

The shroud of the present invention forms a cylindrical protective wall that fully surrounds the aperture in the platform and any riser that may extend through the aperture in use. The shroud prevents objects falling through the aperture from the platform, and additionally prevents workers or equipment on the platform coming into contact with the riser.

The deck assembly may comprise access means, which will typically be in the form of a staircase or ladder, connected between the platform and a part of the rig. -4 -

The staircase or ladder provides a means of access for personnel to the platform from the rig.

The platform may include means for securing equipment to the support surface so 5 that the equipment does not move with respect to the support surface. These securing means are arranged so that equipment may be quickly and easily secured to and removed from the platform.

The platform preferably includes a slot for receiving a part of a J-tool. The J-tool may be used to lift and lower the platform into the required position from the rig.

The J-tool slot may be included in a part of a side wall of the aperture.

In some embodiments the struts are removeably attached to the platform. In this way, when the deck assembly is stored on the rig the struts are not connected to the platform. In use, once the platform has been located in the required deployed position, for example by means of the J-tool, the first end of each of the struts is then attached to the platform. The second end of each of the struts may be permanently attached to a part of the rig. Alternatively, the second end of each of the struts may be detachable from the rig so that the struts may be stored on the rig in a suitable location when the deck assembly is not in use.

In some embodiments the first end of each of the struts may be pivotally attached to the platform. The struts or the platform may include means for preventing rotation of the strut with respect to the platform when the deck assembly is fully deployed to prevent movement of the platform with respect to the supporting rig.

Primarily for the protection of the workers on the deck assembly, the platform preferably includes railings, a perimeter wall or fencing that extends completely around the full perimeter of the support surface.

In a second aspect of the invention there is provided a method of deploying a deck assembly on an offshore rig, the deck assembly comprising a plurality of support -5 -struts, a shroud and a platform having a through hole, and the method comprising: attaching the platform to a deployment tool; using the deployment tool to lower the platform such that the platform is suspended below a part of the rig; connecting support struts between the platform and a part of the rig, the struts arranged to secure the platform in a fixed position relative to the rig; detaching the deployment tool so that the platform is suspended from the rig by the struts; and installing the shroud around the through hole so that a wall of the shroud 10 extends upwards from an upper surface of the platform and prevents access to the through hole from the upper surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a side view showing a jack-up rig located near an offshore well and a deck assembly according to a preferred embodiment of the present invention which is illustrated in a stowed position on the jack-up rig; Figure 2 is a plan view from above of the jack-up rig and well of Figure 1; Figure 3 is a side view of a part of the jack-up rig and well of Figure 1, the view orientation being at 90' to the view depicted in Figure 1; Figure 4 is a detailed view of a part of Figure 1; Figure 5 is a side view of the jack-up rig and well of Figure 1, showing a platform of the deck assembly in a partially deployed position; -6 -Figure 6 is a plan view from above of the jack-up rig, well, and platform of Figure 5; Figure 7 is a side view of a part of the jack-up rig, well and platform of Figure 5 showing in particular the location of the platform with respect to the well, the view orientation being at 90' to the view depicted in Figure 1; Figure 8 is a side view of the jack-up rig and well of Figure 5, showing the platform of the deck assembly in a partially deployed position suspended by a J-tool; Figure 9 is a side view of the jack-up rig, well and platform of Figure 8, showing struts of the deck assembly in a partially connected position; Figure 10 is a side view of the jack-up rig, well and platform of Figure 9, showing the struts of the deck assembly in a fully connected position such that the platform is now suspended from the rig by the struts, and with the J-tool withdrawn from the platform; Figure 11 is a detailed view of the platform and struts of Figure 10, showing in particular the connection of the struts to the platform and a part of the rig; Figure 12 is a view of the platform and struts of Figure 11 and, additionally, illustrates a shroud of the deck assembly in a partially deployed position; Figure 13 is a view of the platform, struts and shroud of Figure 12 with the shroud in a fully deployed position; Figure 14 is a side view of the deck assembly of Figure 13 illustrating the locating of equipment modules on the platform; Figure 15 is a plan view of above of the deck assembly illustrating its -7 -dimensions and position relative to the rig; Figure 16 is a perspective view of the deck assembly of Figure 14 suspended from and supported by a part of the rig, and shows a set of steps providing access between the rig and the platform; Figure 17 is a perspective view of the deck assembly of Figure 16 with the rig removed for clarity; and Figures 18a and 18b show preferred dimensions, in mm, of the platform and struts of the deck assembly of the present invention.

DETAILED DESCRIPTION

Figures 1 to 4 show a jack-up rig 2 on which is mounted a deck assembly 4 according to the present invention. The jack-up rig 2 includes three open truss legs 6 made of tubular steel sections that support a drilling deck 8. Once the jack-up rig 2 has been located next to an offshore well 10, the legs 6 are secured, at their lower end 12, to the sea bed or mudline 14 and the drilling deck 8 is raised to the correct height with respect to the well 10.

In a cantilever jack-up rig 2, a derrick 16 on the jack-up rig 2 is secured to an arm or deck 18 that may be extended outwards from the drilling deck 8 to enable the derrick 16 to be positioned over the well 10.

In a stowed arrangement the deck assembly 4 of the present invention is preferably located beneath the derrick 16. As shown most clearly in Figure 3, a platform 20 of the deck assembly 4 is located below the cantilever arm or deck 18 on which the derrick 16 is supported.

The platform 20 of the deck assembly 4 is moved from its stowed position and deployed by means of a deployment tool 22. In this example the deployment tool -8 - 22 is a J-slot running tool or a J-tool 22. A first end of the J-tool 22 includes a projection that is received in a slot formed in the platform 20 to enable the J-tool 22 to be connected to the platform 20. The J-tool 22 is also operatively connected to the derrick 16. This allows the platform 20 to be raised and lowered with respect to the derrick 16 by the J-tool 22.

Once the jack-up rig 4 has been located adjacent the required offshore well 10, as depicted in Figure 1, the cantilever arm 18 is extended outward over a part of the well 10, as illustrated in Figure 5. The J-tool 22 is then operated to lower the platform 20 away from the cantilever arm 18 in a direction towards the well 10.

During this stage of the deployment the platform 20 is suspended by the J-tool 22 at a distance above the well 10, as shown most clearly in Figure 7.

In preferred embodiments, and as shown most clearly in Figures 16 and 17b, the platform 20 of the deck assembly 4 comprises a structural framework 24 made of tubular sections and a support surface 26 that extends over the framework 24 and provides, in use, an upper surface of the platform 20. The platform 20, and in particular the support surface 26, has a generally rectangular shape. However, it will be appreciated that in other embodiments the platform 20 may be of any desired shape.

In the illustrated example the support surface 26 of the platform 20 has dimensions 12 m by 26 m. A depth of the framework 24, i.e. a distance between 25 the upper support surface 26 and an opposing lower surface of the framework 24, is preferably about 1 m.

Returning now to Figures 7 to 9, the platform 20 comprises three sections 28, 30 that are hingedly connected. Each of the sections 28, 30 comprises a part of the structural framework 24 and a part of the support surface 26 of the platform 20. In this example, the platform 20 includes two side sections 30a, 30b and a central section 28. Each side section 30a, 30b is hingedly or pivotally connected to a -9 -respective opposing side edge of the central section 28. In this way, each of the two side sections 30a, 30b can be rotated about the hinge connection with respect to the central section 28 to enable the platform 20 to be moved between a stowed configuration, shown in Figure 7, and a deployed configuration, shown in Figure 9.

In the stowed configuration the side sections 30a, 30b are positioned such that the support surface 26 of each of the side sections 30a, 30b faces the support surface 26 of the central section 28. In other words, the side sections 30a, 30b are folded inwards on top of the central section 28. This decreases the area of the footprint of the platform 20 when the platform 20 is stowed on the rig 2. In the deployed configuration the side sections 30a, 30b are positioned such that they extend outwardly from the central section 28 and the support surfaces 26 of the central section 28 and side sections 30a, 30b are continuous. Movement of the side sections 30a, 30b between the stowed and deployed configurations is preferably achieved by means of hydraulic actuators.

The platform 20 preferably includes means for locking or latching the platform 20 in the deployed configuration, and may also include means for locking or latching the platform 20 in the stowed configuration.

Having a platform 20 divided into three sections 28, 30 as described above enables the dimensions of the deployed platform 20 to be greater that the dimensions of the cantilever arm 18 of the rig 2. In particular, the side sections 30a, 30b of the platform 20 may extend out beyond the sides of the cantilever arm 18 and this enables equipment to be lowered directly onto the support surface 26 of the platform 20 from the rig 2, as described further below.

Once the platform 20 has been deployed, support struts 32 are then connected between the platform 20 and the rig 2, as illustrated in Figures 9 and 10. A deck assembly 4 will typically include four struts 32 extending between the platform 20 and a part of the rig 2.

Each support strut 32 includes a primary member 34 and a secondary member 36. The primary member 34 is an elongate tube or rod that extends between the support surface 26 of the platform 20 and the rig 2. A first end 38 of the primary member 34 is connected to the support surface 26 and a second end 40 of the primary member 34 is connected to the rig 2, as shown most clearly in Figures 11 and 17. Typically the second end 40 of the primary member 34 will be secured to a part of the cantilever arm 18 of the rig 2 below the derrick 16.

The secondary member 36 comprises an elongate tube or rod that extends 10 between the support surface 26 of the platform 20 and the primary strut member 34. A first end 42 of the secondary member 36 is connected to the support surface 26 and a second end 44 of the secondary member 36 is attached to the primary member 34 about midway along the length of the primary member 34. The length of the secondary member 36 will, therefore, typically be shorter than the length of the primary member 34. In a preferred embodiment each primary strut member 34 has a length of about 11.5 m and each secondary strut member 36 has a length of about 6 m.

The connections to the platform 20 and to the rig 2 at the first and second ends 38, 20 40, 42, 44 respectively of each of the primary and secondary strut members 34, 36 may be pivotal connections.

In some embodiments of the invention the second end 40 of each of the primary members 34 may be permanently secured to the rig 2. During deployment of the 25 deck assembly 4 the first end 38 of the primary member 34 is then lowered and attached to the platform 20 once the platform is in the correct location.

In embodiments in which the platform 20 comprises a central section 28 and two side sections 30 the struts 32 are preferably arranged such that, for a first pair of struts 32a, the first end 38 of the primary member 34 is connected to the central section 28 and the first end 42 of the secondary member 36 is connected to a first one of the side sections 30a, and for a second pair of struts 32b, the first end 38 of the primary member 34 is connected to the central section 28 and the first end 42 of the secondary member 36 is connected to a second one of the side sections 30b. This is shown most clearly in Figure 17.

In a preferred embodiment the second end 40 of each of the primary members 34 is pivotally secured to the cantilever arm 18 of the rig 2. The first end 38 of each of the primary members 34 is then lowered towards the platform 20 and secured to the central section 28 of the support surface 26. A mechanism may be provided to lock the first end 38 of each of the primary members 34 to the platform 20. Each of the secondary members 36 is then installed to extend between a side section 30 of the support surface 26 and a respective primary member 34.

Once the struts 32 have been securely connected between the platform 20 and the rig 2, the deployment tool 22 may be disconnected from the platform 20 and 15 withdrawn. The platform 22 is then solely suspended and supported by the struts 32.

The platform 20 preferably includes a hand rail or guard fence 46 that extends completely or substantially completely around the periphery of the support surface 26. In some embodiments the hand rail 46 may be permanently attached to the support surface 26; however, typically the hand rail 46 will be installed on the support surface 26 after deployment of the platform 20.

The platform 20 includes an aperture or through hole 48 most clearly shown in Figure 17. The aperture 48 is centrally located in the support surface 26 of the platform 20 and extends through the support surface 26 and the underlying framework 24. In this example the aperture 48 is rectangular; however, in other embodiments the aperture may be of any suitable shape. The aperture 48 is sized to receive a riser 50 therethrough. In particular, the aperture 48 is positioned to enable a riser 50 from the rig 2 to be extended through the aperture 48 to the well 10.

The deck assembly 4 further comprises a protective shroud 52 that surrounds the aperture 48 and extends between the support surface 26 of the platform 20 and the rig 2 above.

In preferred embodiments the shroud 52 comprises a first portion 54 and a second portion 56. The first portion 54 comprises a tubular section 54 of the shroud 52 that extends upwards from the support surface 26 of the platform 20 in a direction toward the rig 2. A first end 58 of the tubular section 54 is attached to the support surface 26 of the platform 20 around the aperture 48. A wall 60 of the tubular section 54 extends upwards surrounding the part of the riser 50 that extends between the rig 2 and the platform 20. This first portion 54 of the shroud 52, therefore, provides a barrier between the surrounding support surface 26 of the platform 20 and the aperture 48 and riser 50.

A second end 62 of the tubular section 54 of the shroud 52 attaches to the second portion 56 of the shroud 52. The second portion 56 of the shroud 52 is connected to the cantilever arm 18 of the rig 2 and is located below or towards the bottom of the cantilever arm 18. The second portion 56 of the shroud 52 extends generally radially outwardly from around the second end 62 of the tubular section 54 of the shroud 52. This second portion 56 of the shroud 52 provides a barrier above the platform 20 to protect workers and equipment on the platform 20 from objects that may fall from the cantilever arm 18 of the rig 2. Any such objects may be funnelled by the second portion 56 of the shroud 52 into the tubular section 54 and through the aperture 48, thereby avoiding the platform 20.

As illustrated in Figures 12 and 13, the tubular section 54 of the shroud 52 may be telescopic. Accordingly, this portion 54 of the shroud 52 comprises a plurality of concentric, tubular segments 64. The segment 64a having the smallest diameter or cross-sectional area is connected to the support surface 26 of the platform 20 and forms the first end 48 of the tubular section 54 of the shroud 52. During installation of the shroud 52, the segments 64 are slid with respect to each other so that the tubular shroud 54 increases in length. The segment 64b having the largest diameter or cross-sectional area forms the second end 62 of the tubular shroud 54 and may be attached to a second portion 56 of the shroud 52 or to a part of the rig 2.

Once the deck assembly 4 has been fully deployed, power and communications lines may be run between the rig 2 and the platform 20. Additionally, access means 66, for example a set of steps 66, are installed to permit access for personnel to the platform 20 from the rig 2.

Equipment can be lowered onto the support surface 26 of the platform 20 from the rig 2 by cranes, as illustrated in Figures 14 and 16. In particular, the side sections 30 of the platform 20 extend the dimensions of the platform 20 out beyond the sides 68 of the cantilever arm 18, as shown most clearly in Figure 15, so that the support surface 26 of these sections 30 may be easily accessed by rig cranes.

A range of different equipment may be placed onto the platform 20 to enable workers to perform a variety of tasks associated with the decommissioning of a well independently, or 'offline', from the activities being undertaken on the rig deck 8. This equipment may include modules 70 associated with wireline, cementing, tube pulling or riser racking operations. Additional equipment, such as cranes 72, may be installed on the platform 20 to enable the lifting and handling of components such as well heads and Christmas trees.

An advantage of the deck assembly 4 of the present invention is that it is entirely self contained so that no significant modifications are required to existing rigs to enable the installation of a deck assembly 4.

The deck assembly 4 of the present invention allows the division of well plugging and abandonment tasks into 'off-line' and 'rig-based' phases, i.e. a portion of the tasks may be completed using equipment installed on the platform 20 (off-line'), while the remaining tasks are completed using rig-based equipment. The deck-based and rig-based operations may be completed simultaneously, and these simultaneous operations (SIMOPs), therefore, reduce the length of time that the rig 2 is required on site at a particular well 10.

Furthermore, the operation of simultaneous off-line and rig-based phases introduces the flexibility to take tasks off-line in the event of technical difficulties, enabling operations to continue on the rig and maintaining rig floor productivity.

The present invention, therefore, provides a means by which the duration of time taken to complete plugging and abandonment operations can be decreased. In particular, the present invention provides a deck for a jack-up rig for use during the decommissioning of offshore wells, enabling some of the decommissioning tasks to be completed on the deck, 'off-line' from the rig-based operations.

Claims

CLAIMS1. A deck assembly for an offshore rig comprising: a platform having a substantially flat support surface that provides, in use, an upper surface for receiving equipment; a plurality of elongate struts, each strut having a first end and a second end, and each strut being connectable at its first end to the platform and connectable at its second end to a part of said rig, such that, in use, the struts suspend the platform below a part of said rig; an aperture extending through the platform, the aperture being sized to receive a riser therethrough; and a shroud attached at a first end to the platform so that the shroud extends fully around the periphery of the aperture, and the shroud extending in a direction away from the support surface of the platform such that the shroud prevents access to the aperture from the support surface.
2. A deck assembly as claimed in Claim 1, wherein the platform comprises three sections, each of the sections including a part of the support surface of the platform.
3. A deck assembly as claimed in Claim 2 in which the three sections include a central section and two side sections, each side section being hingedly connected to a respective opposing edge of the central section.
4. A deck assembly as claimed in Claim 3, wherein the hinged connections are such that in a first, deployed position the sections are in a linear arrangement such that the support surface of each of the sections is contiguous.
5. A deck assembly as claimed in Claim 4, wherein the platform comprises means for locking the platform in the deployed position.
6. A deck assembly as claimed in Claim 4 or Claim 5, wherein the hinged connections are configured such that the sections are movable into a second, stowed position in which the side sections are rotated about each hinge with respect to the central section such that the support surface of each of the side sections faces the support surface of the central section.
7. A deck assembly as claimed in Claim 6, wherein the platform comprises means for locking the platform in the stowed position.
8. A deck assembly as claimed in any preceding claim, wherein the shroud is a telescopic shroud and comprises a plurality of sections that are arranged telescopically.
9. A deck assembly as claimed in Claim 8, wherein a first section of the shroud having the smallest cross-sectional area of the sections forms the first end of the shroud and is connected to the support surface of the platform.
10. A deck assembly as claimed in Claim 9, wherein a second end of the shroud formed by a section having the largest cross-sectional area of the sections includes means for connecting the second end of the shroud to a part of the rig above the platform.
11. A deck assembly as claimed in any preceding claim, further comprising access means in the form of a staircase or ladder connectable between the platform and a part of the rig.
12. A deck assembly as claimed in any preceding claim, wherein the platform includes means for securing equipment to the support surface so that the equipment does not move with respect to the support surface.
13. A deck assembly as claimed in any preceding claim, wherein the platform includes a slot for receiving a part of a J-tool.
14. A deck assembly as claimed in any preceding claim, wherein the struts are removeably attached to the platform.
15. A deck assembly as claimed in any preceding claim, wherein an end of each of the struts is pivotally attached to the platform.
16. A deck assembly as claimed in Claim 15, wherein the deck assembly comprises means for preventing rotation of each of the struts with respect to the platform when the deck assembly is fully deployed to prevent movement of the platform with respect to the supporting rig.
17. A deck assembly as claimed in any preceding claim, wherein the platform comprises structural framework and the support surface extends over said framework.
18. A method of deploying a deck assembly on an offshore rig, the deck assembly comprising a plurality of support struts, a shroud and a platform having a through hole, and the method comprising: attaching the platform to a deployment tool; - using the deployment tool to lower the platform such that the platform is suspended below a part of the rig; - connecting support struts between the platform and a part of the rig, the struts arranged to secure the platform in a fixed position relative to the rig; - detaching the deployment tool so that the platform is suspended from the rig by the struts; and installing the shroud around the through hole so that a wall of the shroud extends upwards from an upper surface of the platform and prevents access to the through hole from the upper surface.
19. A method of deploying a deck assembly as claimed in Claim 18, wherein the shroud comprises a plurality of sections that are arranged telescopically, and the method comprises sliding the segments with respect to each other so that the tubular shroud increases in length.
20. A deck assembly for an offshore rig substantially as herein described with reference to or as shown in the accompanying drawings.
21. A method of deploying a deck assembly on an offshore rig substantially as herein described with reference to the accompanying drawings.