GB2522063A

GB2522063A - Drill String Stabiliser Assembly

Info

Publication number: GB2522063A
Application number: GB1400553.2A
Authority: GB
Inventors: Simon Vincent; John Whitaker; Peter Richards
Original assignee: Fugro Seacore Ltd
Current assignee: Fugro Seacore Ltd
Priority date: 2014-01-14
Filing date: 2014-01-14
Publication date: 2015-07-15
Also published as: GB201400553D0

Abstract

A stabiliser assembly 2, comprising a central support assembly 4 connected to the drill string, a plurality of stabilisers 50 arranged around said support 6, said stabiliser 50 remains non-rotating when the drill string is rotating and each stabiliser 50 comprising a stabiliser member 52 mounted on a support assembly 60, which may comprise a pivotally mounted upper 62 and lower arm 68, said assembly being moveable between extended and retracted positions, by moving downwards and inwards from extended into the retracted position and may be held by a stop 32 in a partially extended position.

Description

DRILL STRING STABILISER ASSEMBLY

The present invention relates to a stabiliser assembly for a drill string.

The stabiliser assembly of the present invention finds particular use in drilling bores for piles and the like, in which a downhole portion of the bore is greater in diameter than the surface opening of the bore.

Off shore installations, in particular wind turbines, are being installed at the sea bed in ever deeper water. One particular arrangement finding increasing use for offshore wind turbines is a monopile installed in a bore in the sea bed. In many cases, the monopile has a non-uniform diameter and, in particular has a subterranean portion that is larger in diameter than the portion at and above the sea bed. The installation of the monopile requires a bore to be drilled below the sea bed and a pile installed having a diameter greater than that of the pile extending above the sea bed to the surface of the water.

Drill bit assemblies for forming an underground bore with an underground portion of enlarged diameter are known in the art. The technique for forming such enlarged diameter portions of the bore is known as under reaming. Drill bit assemblies with under reamers are known in the art and are used commercially. The drill bit assembly is supported on the end of a drill string. During the drilling operation, as the drill bit proceeds into the formation being bored, it is necessary to stabilise the drill string, for example to hold the string centrally within the bore and prevent the drill string from moving or whipping.

Stabiliser assemblies are known for stabilising a drill string when drilling a subterranean well having a constant diameter. Examples of such stabiliser assemblies are described and shown in US 4,491,187 and US 4,407,377.

However, such stabiliser assemblies are not suitable for stabilising a drill string in a pile having a diameter that differs at different horizons within the

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bores, such as the piles required to be formed for installing offshore wind turbines, as discussed above.

Accordingly, there is a need for an improved stabiliser assembly for a drill string. In particular there is a need for a stabiliser assembly that can accommodate variations in the diameter of the pile and can function to stabilise the drill string to which it is attached in portions of the pile of different diameter. It would also be an advantage if the stabiliser assembly could be arranged to facilitate recovery of the assembly from the pile in the event of a failure, such as a failure of the power supply to the stabiliser.

An improved stabiliser assembly is now provided. The stabiliser assembly comprises a plurality of stabiliser members for contacting the wall of the bore within which the assembly is located. The stabiliser members are moveable between a retracted position and an extended position.

Advantageously, the stabiliser members are biased into the retracted position.

There is also provided a stabiliser assembly comprising a plurality of stabiliser members, as mentioned above, and in which the action of recovering the assembly vertically upwards within the bore urges the stabiliser members into the retracted position.

The aforementioned principles of construction of the stabiliser assembly allow for the assembly to be recovered from the bore in the event of a component failure or failure of power supply to the assembly. This is particularly important when recovering the assembly from a region of the pile that is of greater diameter than the diameter of a region closer to the surface.

In a first aspect, the present invention provides a stabiliser assembly for use in stabilising a drill string in a downhole location within a pile during a drilling operation, the assembly comprising: a central support assembly having a connector for connecting to the drill string; a plurality of stabilisers arranged around the central support assembly and rotatable with respect to the central support assembly, each stabiliser comprising: a stabiliser member for bearing against the wall of the pile, the stabiliser member being moveable between an extended position and a retracted position; and a moveable support assembly connecting the stabiliser member to the central support assembly and supporting the stabiliser member between the retracted and extended positions; the moveable support assembly arranged to move the stabiliser member from the extended position downwards and inwards towards the central support assembly to the retracted position.

The stabiliser assembly of the present invention has a normal operating position when in use and connected to a drill string to be stabilised. The terms upwards', downwards', upper' and lower' are used with reference to the assembly when in this normal operating position. The terms inner', outer', inwards' and outwards' are used herein with reference to a position or movement of the moveable components relative to the central support assembly.

With the stabiliser members in the retracted position, the stabiliser assembly has a first outer diameter. With the stabiliser members in the extended position, the stabiliser assembly has a second outer diameter, with the second outer diameter being greater than the first outer diameter. By allowing each stabiliser member to be moved between the retracted position, the outer diameter of the assembly may be varied, thereby accommodating variations in the diameter of the pile in the region of the stabiliser assembly and allowing the stabiliser members to being kept in contact with the wall of the pile.

As noted above, each stabiliser member moves in a path from the extended position to the retracted position that is downwards and inwards towards the central support assembly. In this way, the weight of the stabiliser members and the moveable support assemblies serves to urge the stabiliser members into the retracted position. This arrangement assists in returning the assembly to the retracted position, which is of particular advantage when recovering the assembly from the bore. In addition, the action of recovering the assembly upwards within the bore from a region of larger diameter into a region of the pile with a relatively smaller diameter also urges the stabiliser members into the retracted position. In particular, as the stabiliser members are brought into contact with the wall of the pile as the diameter of the pile reduces, the stabiliser members are forced downwards and inwards, into the retracted position. This is particularly advantageous when recovering the assembly in the event of a component or power failure.

The stabiliser assembly of the present invention comprises a central support assembly. The central support assembly comprises means for connecting the stabiliser assembly to a drill string to be stabilised. Suitable connection means are known in the art. In a preferred embodiment, the central support assembly comprises a generally cylindrical support housing arranged to be oriented substantially vertically when the assembly is in use.

The stabiliser assembly further comprises a plurality of stabilisers, arranged around the central support assembly. The stabilisers are arranged to be moveable relative to the central support assembly. In particular, the stabilisers are moveable between the retracted and extended positions, as described above. Further, the stabilisers are rotatable relative to the central support assembly. In this way, with the central support assembly connected

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in the drill string and the stabilisers in an extended position bearing against the inner wall of the pile, the central support assembly can rotate with the drill string while keeping the stabilisers stationary.

Each stabiliser comprises a stabiliser member. The stabiliser members are preferably arranged equidistantly around the central support assembly.

Any suitable number of sabiliser members may be provided. In one preferred embodiment, three stabiliser members are provided around the central support assembly, most preferably arranged a 1200 intervals around the central support assembly.

The stabiliser members may be of any suitable form to contact the wall of the bore and hold the stabiliser assembly and the drill string centrally within the bore. In one preferred embodiment, each stabiliser member comprises an arcuate member, in particular in the form of a curved plate or ski having a major outer surface for contacting the inner wall of the pile.

Each stabiliser further comprises a moveable support assembly for supporting each slabiliser member and moving the member between the retracted and extended positions. The moveable support assembly of each stabiliser is rotatably mounted to the central support assembly. Further, the support assembly moves the respective stabiliser member from the extended position in a motion that is downwards and inwards relative to the central support assembly into the retracted position. Movement of the stabiliser member from the retracted position towards the extended position preferably follows that opposite motion, that is upwards and outwards away from the central support assembly.

Each moveable support assembly supports the respective stabiliser member throughout its movement and when in position, for example in the retracted position, the extended position or held in a position therebetween.

In one embodiment, each moveable support assembly comprises one or more arms, the or each arm pivotally connected at an outer end to the respective stabiliser member and pivotally connected at an inner end to the central support assembly. In one preferred arrangement, the central support assembly comprises a collar to which the inner ends of the arms are pivotally connected. The collar is rotatably mounted relative to the central support assembly. In a preferred embodiment, each moveable support assembly comprises an upper arm and a lower arm, more preferably with the inner ends of the upper and lower arms pivotally connected to respective upper and lower collars, both collars being rotatably mounted to the central support assembly.

The or each arm of the moveable support assembly may be moved by any suitable means or arrangement, so as to move the respective stabiliser member between the retracted and extended positions. In a preferred embodiment, the central support assembly comprises a moveable collar. The moveable collar is moveable vertically up and down the central support assembly and is keyed to the central support assembly so as to be rotatable therewith.

Each moveable support assembly preferably comprises a connecting arm pivotally and rotatably connected at an inner end to the moveable collar and pivotally connected to an arm of the moveable support assembly, preferably between the inner and outer ends of the arm. In this way, movement of the moveable collar in a vertical direction moves each stabiliser member between the retracted and extended positions. Preferably, the inner ends of the connecting arms are pivotally mounted to a collar moveable with but rotatable with respect to the moveable collar. Preferably, the moveable collar and the connecting arm are disposed below the arm of the moveable support assembly.

In one preferred embodiment, the assembly comprises an upper collar, a lower collar and a moveable collar located therebetween, each of the upper and lower collars being rotatable relative to the central support assembly and the moveable collar being rotatable with the central support assembly and moveable vertically with respect to the central support assembly. Each moveable support assembly comprises an upper arm, having an outer end pivotally connected to the respective stabiliser member and an inner end pivotally connected to the upper collar, a lower arm having an outer end pivotally connected to the respective stabiliser member and an inner end pivotally connected to the lower collar, and a connecting arm pivotally connected at an outer end to the upper arm and pivotally connected at an inner end to the moveable collar.

Any suitable means may be employed to move the moveable collar.

Preferably, the collar is moved byway of hydraulic rams.

As indicated above, the stabiliser members may be held in the retracted position, in the extended position or in a position therebetween, that is a partially extended position. Any suitable means may be employed to control the position of the moveable support assemblies, to thereby control the position of the stabiliser members. In one embodiment, the movement of the moveable support assemblies and the stabiliser members is limited by a stop, preferably a stop provided in the central support assembly. In the preferred embodiment in which the central support assembly comprises a moveable collar, as described above, the stop is preferably provided in the central support assembly to limit the movement of the moveable collar. This is particularly advantageous when the collar is being moved by means of hydraulic rams, as the rams can be retracted or extended against the action of the stop, avoiding the need to hold the ram in a partially extended state. The length of the stop may be changed, to vary the position into which the

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stabilisers may be extended. Removal of the stop allows the assembly to be moved into the fully extended position.

In a further aspect, the present invention provides a drill string comprising a stabiliser assembly as hereinbefore described.

A further aspect of the present invention provides a method of forming a subterranean bore comprising deploying in a pile a stabiliser assembly or a drill string as hereinbefore described.

Embodiments of the present invention will now be described, by way of example only, having reference to the accompanying drawings, in which: Figure 1 is a side view of a stabiliser assembly according to one embodiment of the present invention in the retracted condition; Figure 1A is a detail view of the portion of Figure 1 marked 1A; Figure 2 is a plan view of the stabiliser assembly of Figure 1; Figure 3 is side view of the stabiliser assembly of Figure 1 in a partially extended condition; Figure 3A is a detail view of the portion of Figure 3 marked 3A; Figure 4 is a plan view of the stabiliser assembly of Figure 3; Figure 5 is side view of the stabiliser assembly of Figure 1 in a fully extended condition; Figure 5A is a detail view of the portion of Figure 5 marked SA; Figure 6 is a plan view of the stabiliser assembly of Figure 5; and Figure 7 is a schematic view of a stabiliser assembly of the present invention in a drill string at a downhole location within a pile extending into a subterranean bore.

Referring to Figure 1, there is shown a stabiliser assembly according to one embodiment of the present invention. The stabiliser assembly, generally indicated as 2, is shown in the retracted condition.

The stabiliser assembly 2 is shown in Figures 1, 3 and 5 in the orientation in which the assembly is employed in a downhole location during a drilling operation.

The stabiliser assembly 2 comprises a central support assembly 4 having a generally cylindrical support column 6 with connections 8 and 10 at its upper and lower ends for connecting to a drill string (not shown for clarity).

In use, the central support assembly 4 rotates with the drill string.

An upper collar 20 extends around an upper end portion of the support column 6 and a lower collar 22 extends around a lower end portion of the support column 6. Each of the upper and lower collars 20, 22 are free to rotate relative to the support column 6 of the central support assembly 4 and are provided with bearing pads (not shown for clarity) to contact the support column 6 to facilitate relative rotation.

A moveable collar 24 extends around the support column 6 and is located to rotate with the support column 6 and for vertical movement up and down the support column between the upper and lower collars 20, 22.

Hydraulic rams 26 are fixed at an upper end to respective pivot mounts 28 extending from the support column 6 immediately below the upper collar 20. The rams 26 are fixed at their lower ends to respective pivot mounts 30 on a lower portion of the moveable collar 24. In operation, the hydraulic rams 26 are used to raise and lower the moveable collar 24 up and down the central column 6.

Stops 32 extend downwards from a flange 33 on the support column 6.

The length of stops 32 is selected according to the partially extended position to be adopted by the assembly, as described hereinafter. Removal of the stops 32 allows the assembly to adopt the fully extended position, as also described hereinafter. The stops 32 are shown in more detail in Figures 1A and 3A and the arrangement without stops 32 is shown in Figure 5A.

The stabiliser assembly further comprises a plurality of stabilisers 50.

In use, the stabilisers 50 are free to rotate relative to the support column 6 of the central support assembly 4 by reason of the upper and lower collars 20, 22. The stabilisers 50 comprise stabiliser members in the form of curved plates or skis 52. In the embodiment shown, the stabiliser assembly 2 comprises three stabilisers 50 arranged equidistantly around the central support assembly 4, as shown in Figure 2.

Each stabiliser 50 further comprises a moveable support assembly 60.

Each moveable support assembly 60 comprises upper arms 62 pivotally connected at their outer ends to mounts 64 on the inner side of the respective ski 52 and pivotally connected at their inner ends to mounts 66 on the upper collar 20. Similarly, each moveable support assembly 60 also comprises lower arms 68 pivotally connected at their outer ends to mounts 70 on the inner side of the respective ski 52 and pivotally connected at their inner ends to mounts 72 on the lower collar 22.

Connecting arms 74 extend from pivot mounts 76 on the upper arms 62 to pivot mounts 78 on a further collar 79 extending around the lower portion of the moveable collar 24. The collar 79 is mounted so as to rotate relative to the moveable collar 24, allowing the moveable collar 24 to rotate together with the support column 6 with the stabilisers 50 remaining stationary, but is keyed to the moveable collar 24 so as to move vertically therewith up and down the support column 6 under the action of the rams 26.

Cross braces 80 extend between the upper arms 62 and between the lower arms 68, to provide rigidity to the moveable support assemblies 60.

In use, operation of the hydraulic rams 26 to raise the moveable collar 24 moves the collar 79 and the moveable support assemblies 60 so as to move the skis 52 upwards and outwards from the retracted position shown in Figures 1 and 2. With stops 32 in place, movement of the moveable support assemblies 60 and the skis 52 is limited by the upper end of the moveable collar 24 contacting the lower end of the stops 32, as shown in Figure 3A.

With movement limited in this manner, the assembly adopts the partially extended position shown in Figures 3 and 4. With the stops 32 shortened or removed, further upwards movement of the moveable collar 24 is possible.

With the stops 32 removed, the stabiliser assembly 2 can adopt the fully extended position shown in Figures 5 and 6, with the moveable collar 24 contacting the lower surface of the upper collar 20, as shown in Figure 5A.

To move the assembly into the retracted position, the hydraulic rams 26 are extended.

Referring to Figure 7, the stabiliser assembly 2 is shown in position in a drill string 100 within a subterranean bore 102 formed in the sea bed 104.

The drill string 100 is rotatable as indicated by the arrows in Figure 7, in conventional manner, to conduct a drilling operation. In use, a drill bit (not shown for clarity) is mounted to the lower end of the drill string 100 for rotation therewith, again in known manner.

The bore 102 has an opening 106 at the ssea bed 104. A pile 110 extends from the surface 112 of the water downwards into the bore 102. The pile has a first portion 114 having a first diameter Dl and a second portion 116 below the first and having a diameter D2, larger than the diameter Dl. As shown in Figure 7, the second portion 116 of the pile 110 extends downwards from the opening 106 of the bore.

The stabiliser assembly 2 is shown in Figure 7 in the extended condition of Figures 5 and 6 located within the second, wider portion 116 of the pile 110. In this position, the skis 52 of the stabilisers 50 are in contact with and bear against the inner surface of the pile 100, maintaining the drill string 100 in a central posiliori wilhin the pile 100. As described above, Ihe stabilisers 50 remain stationary when in contact with the pile 100, while the central support assembly rotates with the drill string 100.

When the stabiliser assembly 2 is located in the narrower first portion 114 of the pile, the stabilisers 50 are retracted from the position shown in Figure 7, to allow the assembly to be accommodated in the narrower portion of the pile 100.

With the stabiliser assembly 2 in the normal operating position shown in the figures, the weight of the stabilisers 50, the moveable support assemblies 60 and the moveable collar 24 is such as to urge the assembly into the retracted position shown in Figures 1 and 2, under the action of gravity.

In the event of an attempt to recover the stabiliser assembly upwards within the bore, for example from the position shown in Figure 7, with the assembly in the extended condition, the skis 52 are forced against the inner wall of the pile 100 as the assembly is drawn upwards out of the second portion 116 of the pile, the action of which also urges the assembly into the retracted position shown in Figures 1 and 2. In this way, in the event of a failure, for example of the hydraulic fluid to the rams 26, the weight of the aforementioned components of the stabiliser assembly and the action of recovering the assembly upwards within the bore causes the assembly to retract, thereby facilitating recovering to the surface and out of the pile.

Claims

CLAIMS1. A stabiliser assembly for use in stabilising a drill string in a downhole location within a pile during a drilling operation, the assembly comprising: a central support assembly having a connector for connecting to the drill string; a plurality of stabilisers arranged around the central support assembly and rotatable with respect to the central support assembly, each stabiliser comprising: a stabiliser member for bearing against the inner wall of the pile, the stabiliser member being moveable between an extended position and a retracted position; and a moveable support assembly connecting the stabiliser member to the central support assembly and supporting the stabiliser member between the retracted and extended positions; the moveable support assembly arranged to move the stabiliser member from the extended position downwards and inwards towards the central support assembly to the retracted position.
2. The stabiliser assembly according to claim 1, wherein the stabiliser members are arranged equidistantly around the central support assembly.
3. The stabiliser assembly according to any preceding claim, comprising three stabilisers.
4. The stabiliser assembly according to any preceding claim, wherein each stabiliser member comprises an arcuate member having a major outer surface for contacting the inner wall of the pile.
5. The stabiliser assembly according to any preceding claim, wherein each moveable support assembly comprises an arm pivotally connected at an outer end to the respective stabiliser member and pivotally connected at an inner end to the central support assembly.
6. The stabiliser assembly according to claim 5, wherein the inner end of each arm is pivotally connected to a collar rotatably mounted to the central support assembly.
7. The stabiliser assembly according to either of claims 5 or 6, wherein each moveable support assembly comprises an upper arm and a lower arm, each of the upper and lower arms pivotally connected at an outer end to the respective stabiliser member and pivotally connected at an inner end to the central support assembly.
8. The stabiliser assembly according to claim 7, wherein the inner end of the upper arm is pivotally connected to an upper collar rotatably mounted to the central support assembly and the inner end of the lower arm is pivotally connected to a lower collar rotatably mounted to the central support assembly.
9. The stabiliser assembly according to any of claims 5 to 8, further comprising a moveable collar, the moveable collar being rotatable with the central support assembly and moveable up and down relative to the central support assembly, movement of the collar up and down the central support assembly moving the stabiliser members between the retracted and extended positions.
10. The stabiliser assembly according to claim 9, wherein each moveable support assembly comprises a connecting arm pivotally and rotatably connected at an inner end to the moveable collar and pivotally connected at an outer end to an arm of the moveable support assembly.
11. The stabiliser assembly according to claim 10, wherein the connecting arm is pivotally connected at its outer end to the arm between the inner and outer ends of the arm.
12. The stabiliser assembly according to either of claims 10 or 11, wherein the connecting arm is pivotally connected at its inner end to a collar, the collar being moveable with the moveable collar and rotatable with respect to the moveable collar.
13. The stabiliser assembly according to any of claims 9 to 12, wherein the moveable collar is disposed below an arm of the moveable support assembly.
14. The stabiliser assembly according to any of claims 9 to 13, wherein the moveable collar is moved by at least one hydraulic ram extending between the moveable collar and the central support assembly.
15. The stabiliser assembly according to any preceding claim, wherein movement of the stabilisers between the retracted and extended position is limited by a stop, whereby the stop determines a partially extended position of the stabilisers.
16. A stabiliser assembly substantially as bereinbefore described having reference to any of Figures 1 to 7.
17. A drill string comprising a stabiliser assembly according to any preceding claim.
18. The use of a stabiliser assembly according to any of claims 1 to 16 or a drill string according to claim 17 in forming a subterranean bore.
19. A method of forming a subterranean bore comprising deploying a stabiliser assembly according to any of claims 1 to 16 or a drill string according to claim 17 in a pile.
20. The method according to claim 19, wherein the pile has a first portion having a first internal diameter and a second portion below the first portion having a second diameter, the second diameter being greater than the first diameter.
21. A method of forming a subterranean bore substantially as hereinbefore described having reference to any of Figures 1 to 7.