Wellhead Retrieval Tool and Method of Retrieving a Wellhead

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

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.

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.

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.

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, there is shown a wellhead retrieval toolcomprising a bodyhaving a first portionand a second portion, the first portioncarrying a release actuator assemblywhich 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 portioncarrying a locking mechanismwhich is operable to engage with a wellhead to lock the wellhead to the wellhead retrieval tool. The tool bodyhas a longitudinal axis A.

Whilst the first portion of the tool bodycould be integral with the second portion, in this embodiment, the first portionis separate to the second portion, and the two portions are joined together by a plurality of fasteners.

The bodyof the toolis tubular and has a main passagewhich extends through the first and second portions of the tool body,along the longitudinal axis A, a first portionof the main passagebeing located within the first portion of the tool bodyand a second portionof the main passagebeing located within the second portion of the body. The first portion of the tool bodyforms an open end of the tool body, and therefore the main passagehas a first open end which is enclosed by the first portion of the tool body. In this embodiment, the second end of the main passageis at least partially closed by an end capwhich is mounted on the second portion of the tool body. Whilst in this embodiment, the end cap is a separate part to the second portion of the tool body, it should be appreciated that it could equally be integral with the second portion of the tool body

The toolis also provided with a connectorwhich is mounted on the end of the tool bodyadjacent the second portion of the tool body. The connectoris 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. 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 connectoris configured to by connected to a wireline, so that the toolmay be run to the wellhead when suspended from a wire line.

In this embodiment, the first portion of the tool bodyhas a frusto-conical end portion, and a connecting portion. The end portionis configured such that the diameter of the first portion of the main passagedecreases from the first end of the main passagetowards the second portion of the main passage. The purpose of this will be described in more detail below in relation to.

The connecting portionin the embodiment illustrated inencloses a generally cylindrical portion of the first portion of the main passageand is connected to the second portion of the tool body. The release actuator assemblyis located between the end portionand the connecting portion. In this embodiment, the release actuator assemblyis mounted on the connecting portionvia a release actuator assembly support partwhich comprises an annular plate which extends radially outwardly of the connecting portion

The release actuator assemblyis illustrated in more detail inand comprises a release actuatorwhich is mounted on exterior of the first portion of the tool body, and a plurality of actuating elementswhich are spaced circumferentially around the first portion of the tool body and which are movable by the release actuatorbetween a retracted position and an extended position, the portion of each actuating elementwhich extends into the first portion of the main passageincreasing as the actuating elementsmove from the retracted position to the extended position.

In this example, the release actuatorcomprises a ring which extends around the first portion of the tool body. In this embodiment, the ringis rotatable relative to the tool bodyand is configured such that rotation of the ring in a first direction moves the actuating elementsfrom the retracted position to the extended position, and rotation of the ring in a second direction moves the actuating elementsfrom the extended position to the retracted position. In this embodiment, the ringrotates about the longitudinal axis A of the tool body.

The ringis supported on a ring supportwhich in this embodiment is an annular plate which secured to the release actuator support partby means of a plurality of connecting rodsso that the ring supportis spaced from and generally parallel to the release actuator support part.

In this embodiment, the actuating elementsare each supported by a pair of actuating element supportswhich are connected to and extend between the ring supportand the frusto-conical end portionof the first portion of the tool body. Each actuating element supportcomprises a windowwhich receives an edge portion of the associated actuating element, and a bearing surfacewhich supports the actuating element, the actuating elementsliding along the bearing surfacesas it moves between its retracted and extended positions.

In this embodiment, the toolis provided with bearingswhich engage with the ringto restrict transverse movement thereof relative to the tool body, but which facilitate easy rotation of the ringaround the tool body. The bearingsmay, 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. The rollers could, however, equally engage with the radially outwardly facing surface of the ring. Alternatively, some rollers could engage with the radially inward facing surface and some with the radially outward facing surface of the ring.

In this embodiment, the bearingsare mounted on the ring support, but they could equally be mounted on the first portion of the tool body

In this embodiment, the ringis connected to each actuating elementby means of a camming arrangement which converts the rotational movement of the ringto a radial force on the actuating element. In this example the camming arrangement comprises a radially extending pinone end of which is secured to the actuating element, and an axially extending pin, a first end of which is secured to the radially extending pin. It will be understood that each radially extending pinhas a longitudinal axis which extends generally parallel to a radius of the ring, whilst each axially extending pinhas a longitudinal axis which extends generally parallel to the axis of the ring(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 pinis received in an elongate apertureprovided in a guidewhich is mounted on the ring, the guideextending radially outwardly of the ring. The elongate apertureextends around part of the circumference of the ring, the separation between the elongate apertureand the ringincreasing from a first end of the elongate apertureto a second end thereof. Only the ringand guideare permitted to rotate relative to the tool body—the actuating elements, and hence the radially extending and axially extending pins,are secured to the tool bodysuch that only radial movement relative tool bodyis permitted.

The second end of the axially extending pinis movable along the elongate aperturein the guidefrom the first end to the second end of the elongate apertureas the ringrotates, such movement causing radially inward or outward movement of the axially extending pin. The axially extending pinacts on the radially extending pin, which in turn acts on the associated actuating element, and so this radial movement of the axially extending pincauses radially inward or outward movement of the actuating element.