WELLHEAD RETRIEVAL TOOL AND METHOD OF RETRIEVING A WELLHEAD

Description

TECHNOLOGICAL FIELD

The present disclosure relates to a wellhead retrieval tool, and a method of retrieving a wellhead, particular a subsea wellhead.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of UK patent application No. 2405879.4, entitled “WELLHEAD RETRIEVAL TOOL AND METHOD OF RETRIEVING A WELLHEAD,” filed Apr. 26, 2024, which is hereby incorporated by reference in its entirety for all purposes.

BACKGROUND

An offshore wellbore typically comprises a tubular conductor casing which is embedded in the seabed around the top of the wellbore, and a tubular conductor housing which is mounted on top of the conductor casing to extended generally vertically upwardly of the seabed. A tubular wellhead is mounted in the conductor housing and locked thereto typically by means of a locking ring which is provided on the radially outwardly facing surface of the wellhead, and which expands radially outwarding to engage with a locking formation provided on the radially inwardly facing surface of the conductor housing.

The wellhead is provided with a main passage in which is landed at least one casing hanger from which one or more casings may be suspended, each casing extending down into the wellbore. A pack-off is also provided to provide a substantially fluid tight seal between the wellhead and the casing hanger.

When decommissioning such an offshore wellbore, for example because the wellbore has reached the end of its production life, it is necessary to remove all the wellhead components at the seabed and all the casings to a specified depth below the ocean floor before the wellbore can be plugged. As part of this process, it is known to run a pack-off recovery tool into the wellbore and to operate the tool to unlock the pack-off, and then to pull the tool to recover the pack-off. Typically, a casing cutting tool is then run into the wellbore and operated to cut the casing at the required depth. The cutting tool is then retrieved and a casing hanger recovery tool is run into the wellbore, and engaged with the casing hanger from which the casing is suspended. The casing hanger recovery tool, together with the casing hanger and the top section of casing, may then be pulled from the wellbore.

Once all the casing hangers and top sections of casing have been removed, the wellhead is retrieved by first running a tool to unlock the wellhead from the conductor casing, and then running another tool to lift the wellhead from the conductor housing.

The present application relates to an improved tool suitable for use in retrieving the wellhead from the conductor casing of an offshore well.

SUMMARY

According to a first aspect of the disclosure we provide a wellhead retrieval tool comprising a body having a first portion and a second portion, the first portion carrying a release actuator assembly which is adapted to engage with a wellhead release mechanism of a housing and which is operable to actuate the wellhead release mechanism to release a wellhead from the housing, the second portion carrying a locking mechanism which is operable to engage with a wellhead to lock the wellhead to the wellhead retrieval tool.

In one embodiment, the first portion of the tool body is generally tubular and has an open end which is configured to facilitate the positioning of the first portion of the tool body around the housing.

In one embodiment, the first portion of the tool body is provided with a frusto-conical portion which is configured such that the diameter of space enclosed by the first portion of the tool body decreases from the open end towards the second portion of the tool body.

In one embodiment, the body of the tool is tubular and has a main passage which extends through the first and second portions of the tool body, a first portion of the main passage being located within the first portion of the body and a second portion of the main passage being located within the second portion of the body. In one embodiment, tool further comprises an end cap which is provided on the second portion of the tool body to at least partially close the second end of the main passage.

In one embodiment, the tool is provided with a connector which is mounted on the end of the tool body adjacent the second portion of the tool body. The connector may be configured to provide means of mounting the tool on an end of a tubular landing string. The connector may be mounted on the end cap, where provided. The release actuator assembly may comprise a release actuator which is mounted on the exterior of the first portion of the tool body, and a plurality of actuating elements which are spaced circumferentially around the first portion of the tool body and which are movable by the release actuator into the space enclosed by the first portion of the tool body.

In one embodiment, the actuating elements are movable by the release actuator from a retracted position to an extended position, the portion of each actuating element which extends into the space enclosed by the first portion of the tool body increasing as the actuating elements move from the retracted position to the extended position.

In one embodiment, the release actuator comprises a ring which extends around the first portion of the tool body. The ring may be rotatable relative to the tool body and configured such that rotation of the ring in a first direction moves the actuating elements from the retracted position to the extended position, and rotation of the ring in a second direction moves the actuating elements from the extended position to the retracted position. Alternatively, the ring may be compressible to alter the internal diameter thereof, and configured such that compression of the ring to decrease its internal diameter moves the actuating elements from the retracted position to the extended position.

Each actuating element may be connected to the ring by means of a connection which comprises a spring, the connection being configured such that the ring can be rotated/compressed without any movement of the actuating element providing the rotational/compressive force applied to the ring is sufficiently large to overcome the biasing force of the spring.

In one embodiment, the release actuator assembly is hydraulically operable and comprises a plurality of pistons each of which is mounted in a cylinder and connected to one of the actuating elements. In this case, the release actuator assembly may comprise a main hydraulic fluid conduit which is fluidly connected to each of the cylinders. Also in this case, each actuating element may be connected to the piston by a spring.

In one embodiment, the locking mechanism comprises a locking actuator which is mounted on the second portion of the tool body, and a plurality of locking elements which are spaced circumferentially around the second portion of the tool body and which are movable by the locking actuator between a retracted position and an extended position.

In one embodiment, the locking elements are movable by the locking actuator from the retracted position to the extended position, the proportion of each locking element which extends into the second portion of the main passage increasing as the locking elements move from the retracted position to the extended position.

In another embodiment, the locking actuator is movable to move the locking elements radially outwardly of the second portion of the tool body.

According to a second aspect of the disclosure we provide a wellhead system comprising a tool according to the first aspect of the disclosure, a wellhead assembly comprising a housing mounted at an end of a wellbore, a wellhead mounted in the housing, the tool being mounted on the wellhead assembly with the first portion of the tool around the housing and the second portion of the tool engaging with the wellhead.

In one embodiment, the first portion of the body of the tool is tubular, the housing being located in the space enclosed by the first portion of the main passage.

In one embodiment, the second portion of the body is located in the wellhead.

In another embodiment, the body of the tool is tubular and has a main passage which extends through the first and second portions of the tool body, a first portion of the main passage being located within the first portion of the body and a second portion of the main passage being located within the second portion of the body, housing being located in the first portion of the main passage and the wellhead being located in the second portion of the main passage.

In one embodiment, the system further comprises a tubular landing string which is secured to the second portion of the tool body.

The housing may have a tubular body which encloses a generally cylindrical space, the wellhead extending into the generally cylindrical space.

In one embodiment, the wellhead is provided with a wellhead locking element which is movable to lock the wellhead in the housing. In this case, the wellhead locking element may comprise a split ring which is located around the wellhead and in the generally cylindrical space, and which, when in a lock position engages with a radially inwardly extending locking formation of the housing and a radially outward extending locking formation of the wellhead to prevent removal of the wellhead from the housing.

The housing may be provided with a wellhead release mechanism which comprises a plurality of wellhead release elements which are spaced circumferentially around the body of the housing and which are movable radially inwardly of the body of the housing to engage with the locking element of the wellhead and move the locking element into a release position in which the wellhead can be removed from the housing.

In one embodiment, the release actuator assembly comprises a release actuator which is mounted on exterior of the first portion of the tool body, and a plurality of actuating elements which are spaced circumferentially around the first portion of the tool body and which are movable by the release actuator into the space enclosed by the first portion of the tool body into an extended position in which each one of the actuating elements engages with one of the wellhead release elements and exerts a radially inwardly directed force on the wellhead release element.

The tool locking mechanism may comprise a locking actuator which is mounted on the second portion of the tool body, and a plurality of locking elements which are spaced circumferentially around the second portion of the tool body. In one embodiment, the locking elements are movable by the locking actuator into the second portion of the main passage to engage with a locking formation provided on a radially outward facing surface of the wellhead.

In an alternative embodiment of the disclosure, the locking elements are movable by the locking actuator radially outwardly of the second portion of the tool body to engage with a locking formation provided on a radially inward facing surface of the wellhead.

According to a third aspect of the disclosure we provide a method of retrieving a wellhead mounted in a housing at an end of a wellbore, the wellhead being locked to the housing by means of a locking mechanism, the method comprising mounted a tool according to the first aspect of the disclosure on a string or wire, lowering the string/wire towards the wellhead so that the first portion of the tool engages with the housing and the second portion of the tool engages with an end of the wellhead, operating the release actuator assembly to actuate the locking mechanism of the housing and to unlock the wellhead from the housing, operating the locking mechanism to lock the wellhead to the second portion of the tool, and lifting the string/wire and tool with the wellhead secured thereto to remove the wellhead from the housing.

The release mechanism may be operated before the locking mechanism, or vice versa, or both may be operated simultaneously.

The method may comprise using an ROV or a torque tool to actuate the locking mechanism and the release mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics will become clear from the following description of illustrative embodiments, given as non-restrictive examples, with reference to the attached drawings, in which

FIG. 1 is a perspective view of a wellhead retrieval tool according to the first aspect of the disclosure,

FIG. 2 is a perspective view of the release actuator assembly of the tool illustrated in FIG. 1,

FIGS. 3a and 3b show longitudinal cross-sections through the radially extending and axially extending pins of the release actuator assembly illustrated in FIG. 2,

FIG. 4 is a cut-away perspective view of an alternative configuration of release actuator assembly suitable for use in the tool illustrated in FIG. 1,

FIG. 5 is an enlarged illustration of the portion labelled X in FIG. 4,

FIG. 6 is an illustration of a longitudinal cross-section through the second portion of the tool illustrated in FIG. 1,

FIG. 7a is an enlarged illustration of the portion labelled Y in FIG. 6,

FIG. 7b is an illustration of a cross-section along the line labelled C in FIG. 7a,

FIG. 7c is an enlarged illustration of the portion labelled Z in FIG. 6,

FIG. 8 is an illustration of a wellhead system including an alternative embodiment of wellhead retrieval tool according to the first aspect of the disclosure,

FIG. 9 is an enlarged illustration of the portion of the wellhead retrieval tool labelled Z in FIG. 8,

FIG. 10 is an illustration of a longitudinal cross-section through a wellhead system comprising a further alternative embodiment of wellhead retrieval tool according to the first aspect of the disclosure,

FIG. 11a is a schematic illustration of an alternative configuration of release actuator assembly suitable for use in the tools illustrated in FIGS. 1, 8 and 10, with the actuating elements in the retracted configuration,

FIG. 11b is a schematic illustration of the release actuator assembly illustrated in FIG. 11a with the actuating elements in the extended configuration, and

FIG. 11c is a schematic illustration of the release actuator assembly illustrated in FIG. 11a showing its configuration if the actuator is actuated but the actuating elements are stuck in the retracted configuration.

DETAILED DESCRIPTION

The following description may use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, “upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the disclosed tool and method. The terms are used for the reader's convenience only and shall not be limiting.

Referring now to FIGS. 1-3b, there is shown a wellhead retrieval tool 10 comprising a body 12 having a first portion 12a and a second portion 12b, the first portion 12a carrying a release actuator assembly 14 which is adapted to engage with a locking mechanism of a housing and which is operable to actuate the locking mechanism to release a wellhead from the housing, the second portion 12b carrying a locking mechanism 16 which is operable to engage with a wellhead to lock the wellhead to the wellhead retrieval tool 10. The tool body 12 has a longitudinal axis A.

Whilst the first portion of the tool body 12a could be integral with the second portion 12b, in this embodiment, the first portion 12a is separate to the second portion 12b, and the two portions are joined together by a plurality of fasteners.

The body 12 of the tool 10 is tubular and has a main passage 18 which extends through the first and second portions of the tool body 12a, 12b along the longitudinal axis A, a first portion 18a of the main passage 18 being located within the first portion of the tool body 12a and a second portion 18b of the main passage 18 being located within the second portion of the body 12b. The first portion of the tool body 12a forms an open end of the tool body 12, and therefore the main passage 18 has a first open end which is enclosed by the first portion of the tool body 12a. In this embodiment, the second end of the main passage 18 is at least partially closed by an end cap 20 which is mounted on the second portion of the tool body 12b. Whilst in this embodiment, the end cap is a separate part to the second portion of the tool body 12b, it should be appreciated that it could equally be integral with the second portion of the tool body 12b.

The tool 10 is also provided with a connector 22 which is mounted on the end of the tool body 12 adjacent the second portion of the tool body 12b. The connector 22 is configured to provide means of mounting the tool on an end of a tubular landing string, and in this embodiment, is mounted on the end cap 20. Any conventional configuration of connector for connecting a tool to a landing string known to a person of skill in the art may be used. The landing string could be any configuration of tube or pipe including a drill string.

In an alternative embodiment, the connector 22 is configured to by connected to a wireline, so that the tool 10 may be run to the wellhead when suspended from a wire line.

In this embodiment, the first portion of the tool body 12a has a frusto-conical end portion 13a, and a connecting portion 13b. The end portion 13a is configured such that the diameter of the first portion of the main passage 18a decreases from the first end of the main passage 18 towards the second portion of the main passage 18b. The purpose of this will be described in more detail below in relation to FIG. 8.

The connecting portion 13b in the embodiment illustrated in FIG. 1 encloses a generally cylindrical portion of the first portion of the main passage 18a and is connected to the second portion of the tool body 12b. The release actuator assembly 14 is located between the end portion 13a and the connecting portion 13b. In this embodiment, the release actuator assembly 14 is mounted on the connecting portion 13b via a release actuator assembly support part 15 which comprises an annular plate which extends radially outwardly of the connecting portion 13b.

The release actuator assembly 14 is illustrated in more detail in FIG. 2 and comprises a release actuator 24 which is mounted on exterior of the first portion of the tool body 12a, and a plurality of actuating elements 26 which are spaced circumferentially around the first portion of the tool body and which are movable by the release actuator 24 between a retracted position and an extended position, the portion of each actuating element 26 which extends into the first portion of the main passage 18a increasing as the actuating elements 26 move from the retracted position to the extended position.

In this example, the release actuator 24 comprises a ring which extends around the first portion of the tool body 12a. In this embodiment, the ring 24 is rotatable relative to the tool body 12 and is configured such that rotation of the ring in a first direction moves the actuating elements 26 from the retracted position to the extended position, and rotation of the ring in a second direction moves the actuating elements 26 from the extended position to the retracted position. In this embodiment, the ring 24 rotates about the longitudinal axis A of the tool body 12.

The ring 24 is supported on a ring support 38 which in this embodiment is an annular plate which secured to the release actuator support part 15 by means of a plurality of connecting rods 17 so that the ring support 38 is spaced from and generally parallel to the release actuator support part 15.

In this embodiment, the actuating elements 26 are each supported by a pair of actuating element supports 35 which are connected to and extend between the ring support 38 and the frusto-conical end portion 13a of the first portion of the tool body 12a. Each actuating element support 35 comprises a window 35a which receives an edge portion of the associated actuating element 26, and a bearing surface 35b which supports the actuating element 26, the actuating element 26 sliding along the bearing surfaces 35b as it moves between its retracted and extended positions.

In this embodiment, the tool 10 is provided with bearings 40 which engage with the ring 24 to restrict transverse movement thereof relative to the tool body 12, but which facilitate easy rotation of the ring 24 around the tool body 12. The bearings 40 may, as in this example, comprise a plurality of rollers which are spaced around the tool body and which engage with the radially inward facing surface of the ring 24. The rollers could, however, equally engage with the radially outwardly facing surface of the ring 24. Alternatively, some rollers could engage with the radially inward facing surface and some with the radially outward facing surface of the ring 24.

In this embodiment, the bearings 40 are mounted on the ring support 38, but they could equally be mounted on the first portion of the tool body 12a.

In this embodiment, the ring 24 is connected to each actuating element 26 by means of a camming arrangement which converts the rotational movement of the ring 24 to a radial force on the actuating element 26. In this example the camming arrangement comprises a radially extending pin 28 one end of which is secured to the actuating element 26, and an axially extending pin 30, a first end of which is secured to the radially extending pin 28. It will be understood that each radially extending pin 28 has a longitudinal axis which extends generally parallel to a radius of the ring 24, whilst each axially extending pin 30 has a longitudinal axis which extends generally parallel to the axis of the ring 24 (the axis of the ring being the axis which extends through the centre of the ring perpendicular to the plane in which the ring lies).

A second end of the axially extending pin 30 is received in an elongate aperture 32 provided in a guide 34 which is mounted on the ring 24, the guide 34 extending radially outwardly of the ring 24. The elongate aperture 32 extends around part of the circumference of the ring 24, the separation between the elongate aperture 32 and the ring 24 increasing from a first end of the elongate aperture 32 to a second end thereof. Only the ring 24 and guide 34 are permitted to rotate relative to the tool body 12—the actuating elements 26, and hence the radially extending and axially extending pins 28, 30 are secured to the tool body 12 such that only radial movement relative tool body 12 is permitted.

The second end of the axially extending pin 30 is movable along the elongate aperture 32 in the guide 34 from the first end to the second end of the elongate aperture 32 as the ring 24 rotates, such movement causing radially inward or outward movement of the axially extending pin 30. The axially extending pin 30 acts on the radially extending pin 28, which in turn acts on the associated actuating element 26, and so this radial movement of the axially extending pin 30 causes radially inward or outward movement of the actuating element 26.

It should be appreciated that in this embodiment, instead of extending into an elongate aperture 32 in the guide 34, the second end of the axially extending pin 30 could travel along a similarly configured groove or channel in the guide 34.

To facilitate rotation of the ring 24 by an ROV, the tool 10 is operating with an release operating element, which in this embodiment comprises a handle 36 which is secured to the ring 24 and which extends radially outwardly thereof. The handle 36 may be provided with a suitable connector or engagement formation which is configured to engage with a corresponding connector or engagement formation provided on an ROV.

It may be necessary to use a hydraulically operated torque tool to achieve the torque required to rotate the ring 24, and, in this case, the handle 36 may be configured to engage with such a torque tool. The torque tool could be provided on an ROV.

Advantageously, each actuating element 26 is connected to the ring 24 by means of a connection which comprises a spring 42, the connection being configured such that the ring 24 can be rotated without any movement of the actuating element 26 providing the rotational force applied to the ring 24 is sufficiently large to overcome the biasing force of the spring 42. In this embodiment, to facilitate this, and end of the radially extending pin 28 is mounted in a radially extending support tube 44 which is secured to the actuating element 26. A compression spring 42 is provided in the support tube 44 between the radially outwardly facing surface of the actuating element 26 and the radially extending pin 28. This is illustrated in FIG. 3a.

An elongate radially extending aperture 46 is provided in the support tube 44, and the axially extending pin 30 extends through this aperture to connect to the radially extending pin 28.

FIG. 3a shows the pins 28, 30 and spring 42 in their normal configuration, with the axially extending pin 30 at the radially outward end of the radially extending aperture 46. The spring 42 may be compressed in this configuration, engagement of the axially extending pin 30 with the support tube 44 preventing any further expansion of the spring 42. When the actuating element 26 is free to move radially, the pins 28, 30 and spring 42 remain in this configuration and the entire assembly moves together as the ring 24 is rotated to move the actuating element 26.

If the actuating element 26 has become jammed and cannot move, if the ring 24 is rotated with sufficient force to overcome the biasing force of the spring, movement of the axially extending pin 30 along the elongate aperture 32 will further compress the spring to allow the axially extending pin 30 to move radially inwardly along the radially extending aperture 46 and to drive the radially extending pin 28 radially inwardly without any radial movement of the actuating element 26. This is illustrated in FIG. 3b.

An alternative embodiment of release actuator assembly 14′ is illustrated in FIGS. 4 & 5. This has similarities to the release actuator assembly 14 illustrated in FIGS. 2, 3a and 3b, and works in substantially the same way. As such, equivalent parts are labelled with the same reference numerals as used in FIGS. 1-3b. In this embodiment, however, the ring support 38 is connected to the frusto-conical end portion 13a of the tool body 12, and the actuating element supports 35 extend between the ring support 38 and an auxiliary ring support 47, the auxiliary ring support 47 being secured to the release actuator assembly support part 15 via connecting rods 27.

In this embodiment, the release actuator 24 also comprises a ring, but in this case, rather than being supported by a plurality of roller bearings 40, the release actuator 24 is supported on a shoulder provided in the radially outwardly facing surface of the ring support 38. Moreover, in this embodiment, no guide is mounted on the release actuator 24—instead the elongate aperture 32 which receives the second end of the axially extending pin 30 is provided in the release actuator ring 24 itself.

Moreover, in this embodiment, the actuating element supports 35 each comprise a plate or block having an aperture or through-bore through which the radially extending pin 28 extends, each radially extending pin 28 extending from the associated actuating element 26 on the radially inward side of the actuating element support 35 to the axially extending pin 30 located at the radially outward side of the actuating element support 35. Each actuating element 26 is supported on the ring support 38, the ring support 48 providing a bearing surface for reciprocating movement of the actuating elements 26 as they move between their extended and retracted positions.

Also in this embodiment, a spring 42 is provided to ensure that the ring 24 can be rotated without any movement of the actuating element 26 providing the rotational force applied to the ring 24 is sufficiently large to overcome the biasing force of the spring 42. The configuration of the radially extending pin 28 is, however, different to that illustrated in FIGS. 2, 3a and 3b. In this case, the radially extending pin 28 comprises a piston and cylinder arrangement. The first end of the axially extending pin 30 is secured to the cylinder 28a, and the cylinder 28a is supported in the aperture of the associated actuating element support 35. The piston 28 extends from the cylinder 28a, and is connected to the associated actuating element 26, in this embodiment, by means of a pin 28c. The spring 42 is located inside the cylinder 28a between the cylinder 28a and piston 28b, so that compression or extension of the spring 42 facilitates translational movement of the piston 28b relative to the cylinder 28a.

The release actuator assembly 14 is shown in FIGS. 4 and 5 with the actuating elements in their retracted configuration. As with the embodiment of release actuator assembly 14 illustrated in FIGS. 2, 3a and 3b, the actuating elements may be moved radially inwardly into their extended configuration by rotation the release actuator/ring 24 about the ring support 38. The second end of the axially extending pin 30 moves along the elongate aperture 32 in the guide 34 from the first end to the second end of the elongate aperture 32 as the ring 24 rotates, such movement causing radially inward movement of the axially extending pin 30. The axially extending pin 30 acts on the radially extending pin 28, which in turn acts on the associated actuating element 26, and so this radial movement of the axially extending pin 30 causes radially inward movement of the actuating elements 26.

If one of the actuating elements 26 cannot move radially inwardly, radially inward movement of the piston 28b is prevented, but compression of the spring 42 allows the cylinder 28a and axially extending pin 30 to move radially inwardly as the axially extending pin 30 moves along the elongate aperture 32.

The locking mechanism 16 of the wellhead retrieval tool 10 is illustrated in more detail in FIGS. 6, 7a, 7b and 7c and comprises a locking actuator 48 which is mounted on exterior of the second portion of the tool body 12b, and a plurality of locking elements 50 which are spaced circumferentially around the second portion of the tool body 12b and which are movable by the locking actuator 48 into the second portion of the main passage 18b.

The locking elements 50 each extend through one of a plurality of apertures which are spaced circumferentially around the second portion of the tool body 12b and which extend through to the second portion of the tool body 12b to connect the exterior of the tool body 12 with the second portion of the main passage 18b. The locking elements 50 are movable by the locking actuator 48 from a retracted position to an extended position, the portion of each locking element 50 which extends into the second portion of the main passage 18b increasing as the locking elements 50 move from the retracted position to the extended position.

In this embodiment, each locking element 50 is a locking dog.

In this embodiment, the locking actuator 48 comprises a locking ring which is mounted around the second portion of the tool body 12b for rotation about the longitudinal axis A of the tool 10. A radially outward end of each locking element 50 extends out of the tool body 12b and is secured to the locking ring 48 by means of a guide pin 51. Each guide pin 51 extends from the radially outward end of the associated locking element 50 into a circumferential slot 48a provided in the locking ring 48. The circumferential slot 48a is shaped such that rotation of the locking ring 48 causes radial movement of the locking elements 50 between their retracted and extended positions.

Referring now to FIGS. 8 & 9, there is shown a wellhead system 52 comprising a tool 10, a wellhead assembly comprising a housing 54 mounted at an end of a wellbore (not shown) and supported by a well template 56. The housing 54 has a tubular housing body 62 which encloses a generally cylindrical main housing passage 64. A wellhead 58 is mounted in the housing 54, with an uppermost end 58a thereof extending from the housing 54, and a lowermost end 58b thereof being located in the main housing passage 64. The wellhead 58 is tubular, and has a main passage 58c extending from its uppermost end 58a to its lowermost end 58b.

The tool 10 illustrated in FIGS. 8 and 9 include the release actuator assembly 14′ illustrated in FIGS. 4 and 5. It will be appreciated that it could equally comprise the release actuator assembly 14 illustrated in FIGS. 1-3b. Moreover, in this embodiment, the connecting portion 13b of the first portion 12a of the tool body 12 encloses a frusto-conical space.

The tool 10 is mounted on the wellhead assembly with the end portion 13a of the first portion of the tool body 12a around the housing 54 and the housing 54 is located in the first portion of the main passage 18a, and the second portion of the tool body 12b around the uppermost end 58a of the wellhead 58 and the wellhead 58 extending into the second portion of the main passage 18b.

The radially outwardly facing surface of the uppermost end of the wellhead 58 is provided with a tool locking engagement formation 60, which is configured to engage with the locking elements 50 to prevent the tool 10 from being separated from the wellhead. The tool locking engagement formation 60 may comprise a circumferential groove around the radially outwardly facing surface of the uppermost end 58a of the wellhead 58. In this example, the wellhead 58 is provided with a plurality of such grooves.

The wellhead 58 may thus be locked to the tool by the locking mechanism 16 illustrated in FIGS. 6, 7a, 7b and 7c, by operating the locking actuator 48 to move the locking elements 50 into their extending position in the second portion of the main passage 18b to engage with the tool locking engagement formation 60 of the wellhead 58, specifically in this so that an end of each locking element 50 becomes lodged in the or one of the grooves around the wellhead 58.

The wellhead 58 is also provided with a wellhead locking element 66 which is movable to lock the wellhead 58 in the housing 54 (best illustrated in FIG. 9). In this case, the wellhead locking element 66 comprises a split ring which is located around the lowermost portion 58b of the wellhead 58 in the main housing passage, and which, when in a locked position engages with a radially inwardly extending locking formation 68 of the housing 54 and a radially outward extending locking formation 70 of the wellhead 58 to prevent removal of the wellhead 58 from the housing 54.

The housing 54 is provided with a wellhead release mechanism which comprises a plurality of wellhead release elements 72 which are spaced circumferentially around the housing body 62. These are movable radially inwardly of the housing body 62 to engage with the wellhead locking element 66 and move the locking element 66 out of engagement with the housing locking formation 68 into a release position in which the wellhead 58 can be removed from the housing 54.

Specifically, in this embodiment, in which the wellhead locking element 66 is a split ring, when moved radially inwardly of the housing body 62, the wellhead release elements 72 exert a radially inwardly directed force on the split ring 66, which compresses it, and reduces its diameter. This pushes the split ring 66 out of engagement with the housing locking formation 68.

In this embodiment, the wellhead release elements 72 comprise a plurality of release pins.

The tool 10 is mounted on the wellhead so that each of the actuating elements 26 of the tool 10 are aligned with one of the wellhead release elements 72. As such, operation of the release actuator 24 to cause the actuating elements 26 to move radially inwardly of the tool body 12 into their extended position, causes the actuating elements 26 to engage with the wellhead release elements 72. The actuating elements 26 thus exert a radially inward force on the wellhead release elements 72 to push the split ring 66 out of engagement with the housing locking formation 70 and to release the wellhead 58.

The tool 10 may be used to retrieve a wellhead mounted in a housing 64 at an end of a wellbore as follows.

The tool 10 is mounted on a landing string as described above, and the landing string is lowered towards the wellhead 58 so that the first portion of the tool body 12a surrounds at least an uppermost end of the housing 54 and the second portion of the tool body 12b surrounds the uppermost end 58a of the wellhead 58. The frusto-conical end portion 13a of the tool body 12a assists in guiding the tool 10 onto the wellhead 58 and the housing 54.

Then, the release actuator assembly 14 is operated to actuate the wellhead release mechanism to unlock the wellhead 58 from the housing 54, and the locking mechanism 16 is operated to lock the wellhead 58 to the second portion 12b of the tool 12. The landing string and tool 10 with the wellhead 58 secured thereto is then lifted to remove the wellhead 58 from the housing 54.

The release actuator assembly 16 may be operated before the locking mechanism 14, or vice versa, or both may be operated simultaneously.

The method may comprise using an ROV to actuate one or both of the locking mechanism 14 and the release actuator assembly 16.

By virtue of the provision of the spring 42, if any of the actuating elements 26 of the release actuator assembly 14 become jammed, and unable to move to their extended position, or if any of the wellhead release elements 72 become jammed and unable to move radially inwardly of the housing 54, the compression of the spring 42 allows the release actuator 24 to rotate to actuate the other actuating elements 26/wellhead release elements 72 to move radially inwardly to release the wellhead 58.

An alternative embodiment of tool 10″ is illustrated in the wellhead system 52′ illustrated in FIG. 10. In this embodiment, rather than latching to the exterior surface of the wellhead 58, the second portion 12b′ of the tool body 12 is configured to latch to the interior surface of the wellhead 58. As such, rather than being mounted around the uppermost end 58a of the wellhead 58, the second portion 12b′ of the tool body 12 is located inside the main passage 58c of the wellhead 58.

This embodiment uses the same configuration of release actuator assembly 14′ as described above in relation to FIGS. 4 and 5, and the same reference numerals are used to designate the common parts. As such, it should be appreciated that the release actuator assembly 14′ of this embodiment operates in the same way as described above. It should also be appreciated that this embodiment of tool 10″ could equally be provided with the release actuator assembly 14 shown in FIGS. 1-3c. The differences lie in the configuration of the tool body 12′, in particular the second portion 12b′ and the associated locking mechanism 16′.

In this embodiment, the first portion 12a′ of the tool body 12′ comprises only the frusto-conical end portion 13a-a connecting portion is not provided. In this case, the connecting rods 27′ are significantly longer, and extend between the release actuator assembly 14′ (specifically in this embodiment from the auxiliary ring support 47) a connecting flange 74 which extends radially outwardly from a distal end of the second portion 12b′ of the tool body 12′. The second portion 12b′ of the tool body 12′ is tubular, having an exterior surface and an interior surface, and encloses a generally cylindrical passage which extends from the distal end towards the first portion 12a′ of the tool body 12′.

This embodiment of tool 10″ is not provided with an end cap, instead, it is mounted on a landing string 76 the lowermost end of which extends along the cylindrical passage of the second portion 12b′ of the tool body 12′. The second portion 12b′ of the tool body 12′ is supported on a landing shoulder 78 which extends radially outwardly of the landing string 76.

The tool 10″ is mounted on a wellhead assembly as illustrated in FIG. 10, with the first portion 12a′ of the tool body 12 mounted around the housing 54 and the release actuator assembly 14′ aligned with the wellhead release elements 72 exactly as previously described in relation to FIGS. 8 and 9. In this embodiment, however, the second portion 12b′ of the tool body 12′ is located inside the wellhead 58 with the connecting flange 74 supported on the edge of the uppermost end 58a of the wellhead 58 and extending radially outwardly of the wellhead 58 and the connecting rods 27′ arranged around and radially outwardly of the wellhead 58.

The tool 10″ additionally comprises a plurality of locking elements 50′ which are spaced circumferentially around the second portion 12b′ of the tool body 12′ and which are movable by a locking actuator 48′ radially outwardly of the second portion 12b′ of the tool body 12′. In this embodiment, each locking element 50′ is a locking dog. The locking actuator 48′ in this embodiment is a locking ring 48′ mounted around the landing string 76 and located between the landing string 76 and the interior surface of the second portion 12b′ of the tool body 12′ in line with the locking elements 50′.

The locking elements 50′ are all located in one of a plurality of apertures which are spaced circumferentially around the second portion 12b′ of the tool body 12, the apertures extending through to the second portion 12b′ of the tool body 12′ to connect the exterior surface with the interior surface of the second portion 12b. The locking elements 50′ are movable radially by the locking actuator 48′ between a retracted position to an extended position, the portion of each locking element 50′ which extends outwardly of the exterior surface of the second portion 12b of the tool body 12′ increasing as the locking elements 50′ move from the retracted position to the extended position.

The locking ring 48′ has a threaded radially inwardly facing surface which is engaged with a corresponding screw thread provided on the radially outward facing surface of the landing string 76. Rotation of the locking ring 48′ relative to the landing string 76 and second portion 12b′ of the tool body is prevented by means of an anti-rotation pin. As such, rotation of the landing string 76 within the second portion 12b′ of the tool body causes the locking ring 48′ to move along the radially outwardly facing surface of the landing string 76 parallel to the longitudinal axis A of the tool 10″.

The outer diameter of the locking ring 48′ increases from one end thereof to the other. The locking ring 48′ therefore has a thin end and a thick end. When the locking elements 50′ are in their retracted configuration, they are aligned with and engaged with the thin end of the locking ring 48′. Movement of the locking elements 50′ into their extended positions is therefore achieved by rotating the landing string 76 above the longitudinal axis A of the tool 10″ so that the thick end is aligned with the locking elements 50′ as illustrated in FIG. 10. The disclosure is not limited to the specific configurations described above. Various modifications may be made within the scope of the disclosure.

For example, the radially extending pins 28 of the release actuator assembly 14 may be omitted, and the axially extending pins 30 connected directly to the actuating elements 26.

Instead of being rotatable to move the actuating elements 26, the release actuator 24 may be compressible to alter the internal diameter thereof, and configured such that compression of the release actuator 24 to decrease its internal diameter moves the actuating elements from the retracted position to the extended position. In this case, the ring could be a split ring which has two free ends, the internal diameter of the ring being altered by changing the spacing between the free ends of the ring. This could be achieved using a threaded element such as a bolt which extends between correspondingly threaded apertures provided at the free ends of the ring. This would remove the need for the guide 34 and axially extending pin 30, as the ring could be arranged radially outwardly of the radially extending pins 28 to engage directly therewith. Equally, the actuating elements 26 and radially extending pins 28 could be omitted, and the ring arranged to act directly on the wellhead release elements 72.

Whilst in the examples described above, the release actuator assembly 14 may be configured to move the actuating elements 26 mechanically, by movement of the release actuator 24, in a further alternative embodiment, the release actuator assembly 14 may be configured to use hydraulic power to move the actuating elements 26. This may be achieved as illustrated in FIGS. 11a, 11b and 11c. In this embodiment, the release actuator 24 does not comprise a movable ring, and the axially extending pin 30, support tube 44 and radially extending aperture 46 are also omitted Instead, each radially extending pin 28 is provided in a cylinder 80 which is mounted on the actuating element support 35, and is in sealing engagement with the cylinder and to form a piston within the cylinder 80.

One end of the radially extending pin 28 is secured to the associated actuating element 26 via the spring 42 whilst the other end forms a variable volume chamber 82 within the cylinder 80. The cylinder 80 is provided with an inlet port 84 which is connected to a main hydraulic fluid conduit (not shown) mounted on or provided in the ring support 38 via a pipe, tube or other such conduit 86. The conduit 86 provides a passage for flow of hydraulic fluid between the main hydraulic fluid conduit and the variable volume chamber 82.

Advantageously, the conduit 86 of the cylinder 80 associated with each actuating element 26 is connected to the same main hydraulic fluid conduit. The main hydraulic fluid conduit may be mounted on the actuating element support 35, or elsewhere on the tool body 12, and is provided with an inlet port which is configured to be connected to a source of pressurised hydraulic fluid. Whilst the inlet port may be connected to a topside source of pressurised hydraulic fluid via a pipe or umbilical, advantageously, it is configured to be temporarily connected to a portable subsea source of hydraulic fluid, which may, for example, be provided on an ROV. In this case, advantageously, the inlet port is provided with a valve which is configured to close the inlet port when no source of hydraulic fluid is connected, and to open when a source of hydraulic fluid is connected to allow flow of hydraulic fluid into and out of the main hydraulic fluid conduit.

When pressurised hydraulic fluid is supplied to the main hydraulic fluid conduit, pressurised hydraulic fluid flows into the variable volume chamber 82 associated with each actuating element. The pressurised hydraulic fluid pushes the radially extending pin 28 in a radially inward direction, which thus increases the volume of the chamber 82 as illustrated in FIG. 11b. Each radially extending pin 28 pushes the associated actuating element 26 radially inwardly into its extended configuration, in which it acts on the associated wellhead release element 72 just as described above in relation to FIG. 9. If either the wellhead release element 72 or actuating element 26 is jammed and cannot move radially inwardly, the radially extending pin 26 will still move to increase the volume of the chamber 82, facilitated by compression of the spring 42, whilst the actuating element 26 remains in the retracted position. The spring 42 may thus prevent over-pressure in the variable volume chamber 82 which could cause damage to the cylinder 80 or the seal between the cylinder and the pin 28.

Whilst in the examples, the tool 10 is lowered onto the wellhead system 52 using a tubular landing string 60, it could equally be suspended from a wire or cable.

The housing 54 may comprise a conductor casing.

The disclosure is not limited by the embodiments described above; reference should be had to the appended claims.

PARTS LIST

• • 10—wellhead retrieval tool
  • 12—tool body
  • 12a—first portion of the tool body
  • 12b—second portion of the tool body
  • 13a—frusto-conical end portion
  • 13b—connecting portion
  • 14—release actuator assembly
  • 15—release actuator assembly support part
  • 16—locking mechanism
  • 18—main passage of the tool
  • 18a—first portion of the main passage
  • 18b—second portion of the main passage
  • 20—end cap
  • 24—release actuator
  • 26—actuating elements
  • 27—connecting rods
  • 28—radially extending pin
  • 28a—cylinder
  • 28b—piston
  • 28c—pin
  • 30—axially extending pin
  • 32—elongate aperture
  • 34—guide
  • 35—actuating element support
  • 35a—window
  • 35b—bearing surface
  • 36—handle
  • 38—ring support
  • 40—bearings
  • 42—spring
  • 44—support tube
  • 46—radially extending aperture
  • 47—auxiliary ring support
  • 48—locking actuator
  • 48a—slot
  • 50—locking elements
  • 51—guide pin
  • 52—wellhead system
  • 54—housing
  • 56—well template
  • 58—wellhead
  • 58a—uppermost end of the wellhead
  • 58b—lowermost end of the wellhead
  • 58c—main passage of the wellhead
  • 60—tool locking engagement formation
  • 62—
  • 64—
  • 66—wellhead locking element
  • 68—housing locking formation
  • 70—wellhead locking formation
  • 72—wellhead release element
  • 74—connecting flange
  • 76—landing string
  • 78—landing shoulder
  • 80—cylinder
  • 82—variable volume chamber
  • 84—inlet port
  • 86—conduit