FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a method and a tool for enabling removal of tubing from a hydrocarbon well, which tubing is at its upper end provided with a tubing hanger mounted in a central passage of the wellhead.

Removing tubing from hydrocarbon well, in particular from subsea hydrocarbon wells is often necessary in plug and abandonment procedures, i.e. when sealing off a well at the end of its economic lifetime. To seal off the well, permanent plugs need to be provided in the wellbore, which requires tubing mounted in the wellbore to be removed first. This because the tubing is often provided with wires and control lines, extending along the outside of the tubing, which wires and lines may damage the integrity of the plugs over time. Thus, to enable reliable and permanent seals to be mounted in the wellbore, the tubing needs to be removed first. It is noted that tubing differs from well casing in that the latter is often cemented in place during the drilling of the bore hole. This casing can often remain in the borehole and may serve as a support for plugs mounted in the borehole.

The tubing can be, for example, a production tubing for the production of hydrocarbon fluid from a subterranean formation. Such production tubing is near its lower end generally sealed to the wellbore casing by a production packer.

Typically, hydrocarbon wells are provided with a wellhead, which wellhead has a central passage. The tubing is provided with a hanger at its upper end, which tubing hanger rests on a shoulder in the wellhead. The tubing hanger thus flares out in the radially outward direction to engage the shoulder provided in the well head. Thus, the outer diameter of the tubing hanger is a larger than the outer diameter of the tubing itself.

When the hydrocarbon well is in operation, the wellhead is at its upper end provided with a X-mas tree from which the produced fluids are transported to a storage device. Also, when the hydrocarbon well is a subsea hydrocarbon well, the wellhead may be provided with a BOP to enable a riser, supported from a vessel or jack up rig, to be connected to the wellhead.

Retrieval of the tubular element together with the hanger requires the X-mas tree and/or BOP to have a bore or passage with a diameter large enough for passing the tubing hanger.

Furthermore, if the tubular element has to be retrieved from a subsea well, often a riser is used, which extends from the wellhead up to a vessel or jack up ridge. Typically the riser, and at least part of the wellbore, are filled with wellbore fluid to provide counter pressure to prevent the hydrocarbon from escaping the well. Retrieval of the tubing with the tubing hanger through the riser requires the internal passage of the riser to be of relatively large diameter, which as a consequence holds a relatively large volume of drilling fluid.

Consequently the riser is heavy. The vessel or platform supporting the riser has to be suited to support the heavy riser and the drilling fluid held therein.

It is an object of the invention to provide an improved method and/or tool for enabling removal of tubing from a hydrocarbon well, which method and/or tool overcomes one or more of the aforementioned problems, and which preferably obviate the need for a relatively heavy riser and large vessel.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a method according to claim 1 , for enabling removal of tubing from a hydrocarbon well, which tubing is at its upper end provided with a tubing hanger mounted in a central passage of the wellhead..

According to the invention, a machining device is lowered into a central passage of the tubing hanger and machines away at least part of the tubing hanger, thus disconnecting the tubing from the tubing hanger and enlarging the central passage of the tubing hanger to a diameter wide enough for lifting the tubing out of the hydrocarbon well. Thus, the tubing hanger no longer forms an obstacle when removing the tubing from the hydrocarbon well. Thus the tubing can be removed through an opening or passage having a diameter larger than the outer diameter of the tubing, but smaller than the outer diameter of the tubing hanger. Furthermore, once the tubing has been disconnected from the tubing hanger and a passage is provided that has a diameter wide enough for lifting the tubing, including the control wires and control lines provided on the outside thereof, out of the hydrocarbon well, there is no need to remove and/or replace equipment, such as a BOP, X-mas tree or riser, mounted on the wellhead having an internal passage with a diameter smaller than the outer diameter of the tubing hanger but larger than the outer diameter in of the tubing. In other words: there is no need to provide equipment, such as a BOP, X-mas tree or riser, having a passage with an inside diameter large enough for passing through the tubing hanger when removing tubing form the well bore. Equipment with a smaller diameter passage, i.e. just large enough for passing through the tubing including the control wires and control lines provided on the outside thereof, will suffice. Thus the invention facilitates removal of tubing from a hydrocarbon well and reduces the time needed to plug and abandon a hydrocarbon well.

According to the invention, a method for enabling removal of tubing from a hydrocarbon well, which tubing is at its upper end provided with a tubing hanger mounted in a central passage of the wellhead, comprises the steps:

- lowering a machining device into a central passage of the tubing hanger and machining away at least part of the tubing hanger, thus disconnecting the tubing from the tubing hanger and enlarging the central passage of the tubing hanger to a diameter wide enough for lifting the tubing out of the hydrocarbon well; and

- lifting the disconnected tubing out of the hydrocarbon well.

Thus, according to the invention the tubing hanger is at least partially removed and disconnected form the tubing. Thus, the tubing hanger does no longer need to be removed with the tubing and no longer forms a hindrance.

Furthermore, the tubing can be lifted out of the well via equipment, such as a BOP, riser or X-mas tree, having an internal passage larger than the outer diameter of the tubing but smaller than the outer diameter of the tubing hanger that supported the tubing. It is noted that in particular with BOP's and risers a smaller internal passage comes with a large saving in weight and volume of the particular equipment. Because the tubing is removed without the tubing hanger, BOP's and risers having a large sized passage are no longer required, and a riser and/or BOP having a smaller sized passage can be used. Thus a significant saving in costs can be achieved.

It is furthermore noted with respect to X-mas trees that they often have a passage that is unfit for removing tubing, even without the tubing hanger. This because their internal passage has a diameter that is too small and/or is provided with valves that block passage of the tubing. Furthermore, X-mas trees are often too small to allow for their passage to be enlarged to a passage having a diameter wide enough for passing a tubing hanger.

However, since the invention allows the tubing to be removed via a relatively small passage, it is now in many cases possible to mill the passage in an X-mas tree up to the required size and/or remove the valves provided in the passage using a milling device, to provide the X- mas tree with a passage fit for removing the tubing. Thus, in such cases the X-mas tree does no longer need to be removed from the wellhead to allow for the tubing to be removed from the hydrocarbon well.

A further method according to the invention comprises the steps:

- engaging a top portion of the tubing at its inside and below the tubing hanger, preferably using a clamping device; and

- holding, optionally supporting, the tubing while the machining device is machining away at least part of the tubing hanger. In a method, a radially expandable clamping unit is provided for engaging the inside surfaces of the tubing to be lifted from the well. Such clamping devices are known form the prior art for clamping casing sections, for example to rotatably fix a Bottom Hole Assembly or for removing a packer from a well. A clamping device according to the invention differs form the known clamping devices in that it should be dimensioned to engage the tubing, and to enable lifting the tubing form the well. In an alternative embodiment, the tubing is engaged by drilling and/or cutting holes in the tubing and providing hooks for engaging the holes. In an embodiment, for example three radial extending drills are used to drill through tubing and subsequently function as hooks for engaging the tubing, more in particular to enable lifting the tubing from the well.

A further method according to the invention comprises the step:

- cutting the tubing downhole prior to engaging the top portion of the tubular string. For example, in a method the tubing is cut near or at its bottom end, i.e. near or at the production packer, so that after removal of the tubing hanger, substantially the entire production tubing can be lifted from the well. In an alternative method, the tubing is not cut near or at its bottom end, but is cut somewhere between its bottom end, and its top end, i.e. the end at the tubing hanger. This may be the case when the tubing has been fixed in the well at intermediate locations between the top of the well and the bottom well. In such a method the tubing is not lifted form the well in its entirety, but may be removed out of the well section by section. Also, a bottom section may remain in the well if this does not interfere with reliable sealing the well. In an alternative embodiment, the tubing does not need to be cut, for example because it is not fixed to the well or because it has already been cut free in a previous step.

In a further method according to the invention the hydrocarbon well is a subsea well, and the method further comprises the steps:

- providing a riser between the well head and a surface vessel or jack up rig, the riser having a central passage with a diameter larger than the external diameter of the tubing but smaller than the diameter of the central passage of the wellhead above the tubing hanger;

- optionally: lowering the machining device into the wellhead via the central passage of the riser; and

- lifting the disconnected tubing through the central passage of the riser to the vessel or jack up rig.

In a further method according to the invention, the diameter of the central passage of the riser is smaller than an external diameter of the tubing hanger.

A further method according to the invention comprises the step:

- mounting a BOP on the wellhead, the BOP having a bore connecting the well head to the riser string. Thus, in such an embodiment, the tubing is lifted from the well via the central passage of the well head, via the bore of the BOP and via the central passage of the riser. In a further method according to the invention, the bore has a diameter which is larger than the diameter of the central passage the riser string, preferably is substantially similar to the diameter central passage of the wellhead above the tubing hanger, the method further comprising the step:

- providing an adapter between the BOP and the riser string, the adapter having a conduit that connects the bore of the BOP with the central passage of the riser.

In such an method, the riser can be provided with an internal diameter large enough for removing the tubing, including the control wires and control lines provided on the outside thereof, but smaller than the external diameter of the tubing hanger, since the tubing hanger, or at least what remains of the tubing hanger, does not need to be removed from the well head. Thus, compared with current techniques, in which the tubing hanger is removed with the tubing, a comparatively small diameter riser can be used, even when the BOP does have a large diameter bore, i.e. a bore having a diameter large enough for removing the tubing hanger.

In a further method according to the invention, the bore of the BOP has a diameter which is smaller than the diameter of central passage of the wellhead above the tubing hanger, preferably is substantially similar to the diameter of the central passage of the riser string, the method further comprises the step:

- providing an adapter between the wellhead and the BOP, the adapter having a conduit that connects the bore of the BOP with the central passage of the wellhead.

In such an embodiment, the riser and BOP can be provided with an internal diameter large enough for removing the tubing, including the control wires and control lines provided on the outside thereof, but smaller than the external diameter of the tubing hanger, since the tubing hanger, or at least what remains of the tubing hanger, does not need to be removed from the well head. Thus, compared with current techniques, in which the tubing hanger is removed with the tubing, a comparatively small diameter BOP and riser can be used, even when the well head does have a large diameter central passage, i.e. a central passage having a diameter large enough for removing the tubing hanger.

A further method according to the invention comprises the step:

- shredding swarf generated by machining away the tubing hanger, or at least a part thereof, for example using a shredding device such as a plasma cutter provided in an adapter, and/or collecting swarf generated by machining away the tubing hanger, for example using a collecting device such as a magnet provided in the adapter. A further method according to the invention comprises the step:

- supporting the machining device using a tubular, for example a drilling string or coiled tubing, the tubular extending through the riser. In such an embodiment, preferably the tubing is used to lower the machining device through the riser, and preferably for lifting the machining device and the tubing after the tubing hanger has been partially removed by the machining tool.

A further method according to the invention comprises the step:

- rotating the tubular and using this rotational movement for driving the machining device, for example driving the machining device by rotating a drill string supporting the machining device. Thus, the machining device does not need to comprise a drive, such as an electric drive, which allows for a compact configuration of the machining device.

A further method according to the invention comprises the step:

- circulating drilling mud through the wellhead to drive the machining device and/or to remove swarf (cuttings) generated by the machining of the tubing hanger, the drilling mud flowing downward via an annulus between the tubular and the riser string and flowing upward through the tubular or vice versa. Preferably, the swarf is removed from the well head during the milling away of the tubing hanger, such that the cutting do not interfere with the milling process. Furthermore, the swarf is preferably removed from the well head prior to lifting the tubing form the well, thus reducing the chance that swarf may hamper the lifting process, for example gets stuck between the tubing and/or milling device on the one hand and the well head, BOP or riser on the other hand.

A further method according to the invention comprises the step:

- enlarging the diameter of a bore in a X-mas tree mounted on the wellhead to a diameter larger than the outer diameter of the tubing. In such an embodiment a machining tool, preferably the machining tool for machining at least part of the tubing hanger, is used for enlarging the diameter of the bore in the X-mas tree mounted on the wellhead. When the bore of the X-mas tree is in line with the well, the machining device can for example be lowered from the riser, through the bore in the X-mas tree and into the tubing hanger. In a method, the machining device is configured for machining away part of the X-mas tree and at least part of the tubing hanger separate, subsequent steps. In a method, the machining device is first lowered onto or into the bore of the x mas tree, is secured relative to the X- mas tree and subsequently is used to machine part of the X-mas tree to enlarge the bore. In an embodiment, the machining device is configured to machine the bore of the X-mas tree in an axial direction thereof, preferably in a single machining step.

In an alternative embodiment, the machining device is configured to machine the bore of the X-mas tree in a substantially radial direction, preferably in a single step. In an alternative embodiment, the machining of the X-mas tree is done in several subsequent steps, comprising machining a section of the bore in a radial direction, lowering the machining device further down the bore and again machining a section of the bore.

A further method according to the invention comprises the step:

- positioning a tubing hanger removal tool, the tool comprising the machining device adapted to machine away at least part of the tubing hanger, below the BOP, or at least below the shear rams of the BOP, prior to the machining away of the tubing hanger, and keeping the tool below the BOP, or at least below the shear rams of the BOP, during the machining away of the tubing hanger. In such an embodiment, the tool does not obstruct the working of the shear rams of the BOP. It is noted that BOP's are typically configured for shearing tubulars. Therefore, other bodies, such as a milling device, may prevent the BOP from functioning correctly, i.e. prevent the BOP from blocking the riser, in case of a blow out.

A further method according to the invention comprises the step: - after removal of the tubing, providing temporary abandonment caps in the wellhead and/or providing one or more plugs in the bore hole, preferably permanent plugs. Thus the well is plugged, preferably permanently plugged. The plugs may be provided by pouring concrete into the well and/or by mechanical devices being secured in the well or well head. Other techniques for providing a plug, known from the prior art, may also be used.

In a preferred embodiment according to the invention for removal of tubing from a subsea hydrocarbon well, which tubing is at its upper end provided with a tubing hanger, which tubing hanger is mounted in a central passage of a wellhead, comprises the steps:

- providing a riser between the well head and a surface vessel or jack up rig, the riser having a central passage;

- providing a tubing hanger removal tool, the tubing hanger removal tool comprising a machining device and a clamping device;

- lowering the tubing hanger removal tool into the wellhead via the central passage of the riser, and thus lowering the machining device into a central passage of the tubing hanger and the clamping device into the tubing below the tubing hanger;

- engaging a top portion of the tubing at its inside and below the tubing hanger using the clamping device; and

- machining away at least part of the tubing hanger, thus disconnecting the tubing from the tubing hanger and enlarging the central passage of the tubing hanger to a diameter wide enough for lifting the tubing out of the hydrocarbon well; and

- lifting the disconnected tubing out of the hydrocarbon well, through the central passage of the tubing hanger and through the central passage of the riser, to the vessel or jack up rig, wherein the central passage of the riser has a diameter larger than the external diameter of the tubing but smaller than the diameter of the central passage of the wellhead above the tubing hanger and smaller than an external diameter of the tubing hanger.

Thus, a method according to the invention allows for using a compact riser, i.e. a riser having an internal diameter smaller than an external diameter of the tubing hanger, when removing the tubing from a well. Also, the method according to the invention allows for using a BOP with an internal bore having a diameter smaller than an external diameter of the tubing hanger, when removing the tubing from a well.

The invention furthermore provides a tubing hanger removal tool for enabling removal of tubing from a hydrocarbon well, which tubing is at its upper end provided with a tubing hanger mounted in a central passage of a wellhead. According to the invention, the tubing hanger removal tool comprises a machining device adapted to be lowered into a central passage of the tubing hanger and to machine away at least part of the tubing hanger, thus disconnecting the tubing from the tubing hanger and enlarging the central passage of the tubing hanger to a diameter wide enough for lifting the tubing out of the hydrocarbon well, and to thus enable lifting the disconnected tubing out of the hydrocarbon well. In an embodiment, the tubing hanger removal tool further comprises a clamping device, for engaging the inside of the tubing at a top portion thereof, and for holding, optionally supporting, the tubing while the machining device is machining at least part of the tubing hanger. In an embodiment, the tubing hanger removal tool is adapted to be fully lowered into tubing, and the machining device is adapted to cut the tubing downhole and/or the tool comprises a cutting device adapted to cut the tubing downhole. Thus, if a lower section of the tubing is secured to the well, for example to the production packer and/or to the casing located in the well, the secured tubing section can be severed from the tubing section to be removed from the well. The tubing section that remains in the well later, or can be left in the well permanently.

In an embodiment, the tubing hanger removal tool is adapted to operate in a subsea hydrocarbon well, preferably is provided with a communication device that allows the tool to be operated from a vessel or a jack up. Preferably, the communication device provides information on the position of the machining device relative to the tubing hanger, to thus facilitate correctly positioning the machining device in the well head. In an alternative method, wherein the position of the well head is known. The machining device is lowered through a riser using a tubular string, and the length of the tubular string is registered and used to determine the position of the machining device relative to the well head, more in particular to the tubing hanger in the well head.

In an embodiment, the tubing hanger removal tool is adapted to be lowered into the wellhead via a central passage of a riser extending between the wellhead and a vessel or a jack up and/or via a bore of a BOP mounted on the well head, wherein preferably the central passage of the riser and/or the bore of the BOP have a diameter larger than the external diameter of the tubing but smaller than the diameter of the central passage of the wellhead. Thus, in such an embodiment, the riser can be provided with an internal diameter large enough for removing the tubing, including the control wires and control lines provided on the outside thereof, but smaller than the diameter of the central passage of the wellhead. In this context it is noted that typically the central passage of the well head is configured for passing the tubing hanger, to thus enable installing the tubing and the tubing hanger. However, the invention allows for the tubing hanger, or what remains of the tubing hanger after the severing the tubing in the well head form the tubing hanger, to remain in the well head. Therefore, the BOP and riser do not need to be dimensioned for removing the tubing hanger with the tubing. Thus, compared with current techniques, in which the tubing hanger is removed with the tubing, a comparatively small diameter BOP and/or small diameter riser can be used when removing the tubing from a well.

In an embodiment, the tubing hanger removal tool further comprises a coupling device, which coupling device is adapted to couple the tubing hanger removal tool to a tubing hanger removal tool support, preferably a tubular, for example a drilling string or coiled tubing, the tubular extending through the riser. In such an embodiment, the tubing can be used to lower the tubing hanger removal tool is supported by the tubing, and can be lowered through the riser, and can be lifted through the riser, using the tubing supporting the removal tool. This is in particular beneficial when for example a drilling rig is used for providing the tubing hanger removal tool, since a drilling rig is typically configured for lowering a string of tubulars into, and lifting a string of tubulars out of, a riser. Furthermore, in such a

configuration, the tubulars for supporting the tubing hanger removal tool can also be sued for lifting the tubing from the well, after the tubing in the well has been disconnected from the tubing hanger.

In a preferred embodiment, the tubing hanger removal tool is lifted together with the disconnected tubing form the well.

In an embodiment, the tubing hanger removal tool is configured to couple the disconnected tubing, i.e. the tubing in the well that has been disconnected from the tubing hanger, with the tool support, for example a string of drilling tubulars extending through a riser, said riser connecting the well with a surface vessel such as a jack up or drilling vessel, such that the disconnected tubing can be lifted through the riser to the vessel or jack up rig using tool support. Thus, in such an embodiment the tubing hanger removal tool is not only configured for machining away at least part of the tubing hanger, but also forms a coupling device for connecting the severed tubing with the tubing hanger removal tool support. In an

embodiment, the tubing hanger removal tool is provided with a clamping device configured for engaging the inside surface of the tubing located in the well, preferably prior to the tubing being severed from the tubing hanger, with a force sufficient to enable lifting the tubing from the well after at least part of the tubing hanger has been removed.

In an embodiment of the tubing hanger removal tool, preferably the machining device of the tubing hanger removal tool, is adapted to be coupled with a tubular tool support, and preferably to be driven via that tubular tool support by a drive located above the connecting tool, preferably located on a vessel or jack up.

In an embodiment, the tubing hanger removal tool is adapted to be rotatably supported by the tool support and/or the tubing hanger removal tool further comprises a clamping device for engaging the inside of the tubing supported by the tubing hanger at a top portion thereof, and for holding, optionally supporting, the tubing while the machining device is machining at least part of the tubing hanger, wherein the clamping device is rotatably connected to the tool.

In an embodiment, the tubing hanger removal tool is provided with a drive, for example an electric drive or a mud motor, for driving the machining device.

In an embodiment of the tubing hanger removal tool, the tubing hanger removal tool further comprises a clamping device for engaging the inside of the tubing supported by the tubing hanger at a top portion thereof, and for holding, optionally supporting, the tubing while the machining device is machining at least part of the tubing hanger, and the machining device has a cutting face that is rotatably mounted such that it can rotate relative to the clamping device and about the longitudinal axis of the tubing removal tool.

In an embodiment of the tubing hanger removal tool the machining device has a cutting face that is adapted for cutting in a direction parallel to a longitudinal axis of the tubing hanger removal tool, preferably in a downward direction. In an embodiment of the tubing hanger removal tool the machining device, in particular the cutting face of the machining device, has a fixed outer diameter which is larger than the outer diameter of the tubing but is smaller than the inner diameter of the bore of the BOP and/or the central passage of the riser. In such an embodiment, cutting face of the machining device can pass through the bore of the BOP and/or through the central passage of the riser, and is large enough for machining the tubing hanger such that the tubing, when cut from the tubing hanger, can be lifted through what remains of the tubing hanger and the BOP and/or the central passage of the riser.

In an alternative embodiment, the machining device, in particular the cutting face of the machining device, has a compact transport configuration and an extend machining configuration. In such an embodiment, the machining device for example has a cutting face composed out of multiple cutting face sections, which cutting face sections can be moved and/or hinged between an extended cutting position and a retracted transport position. It is submitted that other techniques, known from the prior art and suitable for transporting cutting faces through risers, can also be used for providing such a cutting face.

In an embodiment of the tubing hanger removal tool the machining device comprises two or more counter rotating cutting faces to at least partially cancel out the torque generated by the machining of the tubing hanging.

In an embodiment of the tubing hanger removal tool the tubing hanger removal tool is provided with one or more inner channels for guiding drilling mud from one end to an opposite end of the tubing hanger removal tool, which channels preferably have at one end openings adapted to be connected with a tubular supporting the tool. Thus, the drilling mud can be guide from the supporting tubulars towards and optionally through the machining device, for example to drive the machining device and/or for removing swarf during the cutting process. In an embodiment, the tubing hanger removal tool comprises a clamping device for engaging the inside of the tubing supported by the tubing hanger at a top portion thereof, which clamping device is configured to be manipulated, i.e. to be switched between an active position in which it engages the inside surface of the tubing and an inactive positon in which it does not engage the inside surface of the tubing, by the drilling mud, for example by pressure difference in the flow of drilling mud passing the tubing hanger removal tool.

In an embodiment, the tubing hanger removal tool comprises a clamping device, and the tool provides channels between a tubing section above the clamping device and a tubing section below the clamping device that allows drilling mud to flow between those sections. In such an embodiment a flow of drilling mud can pass the clamping device while the clamping device engages the inside surface of the tubing, i.e. the tubing to be removed from the well. Thus the clamping device can engage the inside of the tubing without obstructing the flow of drilling mud. It is noted that when the tubing hanger removal tool is used, drilling mud is not circulated in the riser and/or well for driving a drill bit. The drilling mud can be provided to a certain pressure in the well and thus prevent gasses or liquids to escape from the well. The drilling mud can be circulated through the riser and/or well for example to drive the machining device and/or to remove swarf during the machining process.

In an embodiment, the tubing hanger removal tool further comprises a shredder device for shredding cuttings generated by the machining device. The shredder device can be a mechanical shredder, preferably drive by the drive that also drives the machining device. In an alternative embodiment, the shredder can be a mechanical shredder.

In an embodiment, the tubing hanger removal tool is at its front end provided with a reaming device for enlarging the diameter of a bore in a X-mas tree mounted on the wellhead to a diameter larger than the outer diameter of the tubing.

In such an embodiment the reaming device is used to enlarge the diameter of the bore in the X-mas tree mounted on the wellhead. When the bore of the X-mas tree is in line with the well, the machining device can for example be lowered from the riser, through the bore in the X-mas tree and into the tubing hanger. In such an embodiment, the tubing hanger removal tool is configured to first machine away part of the X-mas tree, for example for machining away valves provided in the bore of the X-mas tree, and subsequently machine the tubing hanger, or at least a part thereof to an extend sufficient to sever the tubing hanging in the well from the tubing hanger. Thus, when the well head is provided with an X- mas tree having a bore too narrow for passing through the tubing to be removed from the well, it is not required to remove the X-mas tree. By reaming the bore and/or removing vlaves provided in the bore of the X-ams tree, the X-mas tree is adapted to allow for the tubing to be lifted form the well.

In an embodiment, the tubing hanger removal tool is at its front end provided with a reaming device for enlarging the diameter of the central passage of the tubing. Thus, the inside surface of the tubing can be provided with a clean and/or flat gripping surface for engagement by a clamping device, preferably for engagement by a clamping device of the tubing hanger removal tool. In an embodiment, the tubing hanger removal tool is dimensioned such that, at least during the machining of the tubing hanger, the tool is located below the BOP, or at least below the shear rams of the BOP. In such an embodiment, the tubing hanger removal tool does not obstruct the working of the shear rams of the BOP while machining the tubing hanger. It is noted that BOP's are typically configured for shearing tubulars. Therefore, other bodies, such as a machining device, may prevent the BOP from functioning correctly, i.e. prevent the BOP from blocking the riser, in case of a blow out.

In an embodiment, the tubing hanger removal tool is adapted to be mounted on a well head, or on an adapter mounted on a well head.

The invention furthermore provides a tubing removal assembly comprising a tubing hanger removal tool according to the invention, and an adapter, wherein the adapter is adapted to be mounted between a BOP and the wellhead, the bore of the BOP having a diameter smaller than the diameter of the central passage of the wellhead, or

is adapted to be mounted between a riser and a BOP, the central passage of the riser having a diameter smaller than the diameter of the bore of the BOP.

Providing an assembly comprising such an adapter, allows for using a riser and optionally for using a BOP having a comparatively small central passage and bore.

This is beneficial because a riser with a reduced central passage has a reduced internal volume and thus holds a smaller volume of drilling mud. Therefore, during use, i.e. when filled with drilling mud, a riser having a smaller central passage is easier to support.

Also, a BOP having a large bore typically has a larger weight and is more voluminous as a BOP having a smaller bore, This is even more the case since BOP's, for safety reasons, are over dimensioned. Also, the diameter of the central passage of a riser typically matches the bore of the BOP, and the bore of the BOP often matches the central passage of the well head. Since a heavier, more voluminous BOP is difficult to move, especially at great depths, it is beneficial when it is not required to replace a BOP already present on a wellhead with a smaller BOP to allow for a riser with a smaller central passage.

Also, when no BOP is provided on the well head, and presence of a BOP is required for safety reasons during the removal of the tubing form the well, it is beneficial when a more compact BOP can be used, and consequently a compact riser, by providing an adapter between the well head and the BOP.

Thus, providing an assembly comprising an adapter, or adapters, as set out above, allows for using a riser and optionally a BOP that match the outer diameter of the tubing to be lifted form the well. The riser no longer needs to match a wider diameter of a BOP already present on the well head, and when a BOP needs to be provided, the BOP does no longer need to match the wide passage of the well head.

When completing a well, the tubing is preferably lifted from the well to the surface via a riser, to thus prevent the tubing contaminating the seawater. Thus, the riser and optionally the BOP are provided by the vessel or jack up providing the tubing hanger removal tool. Any reduction in weight of the riser and/or BOP facilitates installation and support of the riser and/or BOP, and thus facilitates the over al process of removing the tubing from the well.

Preferably, the adapter is a separate component, to be mounted between the BOP and riser or between the BOP and wellhead prior to the tubing hanger removal tool to be lowered into the wellhead.

In a further embodiment, the adapter of the tubing removal assembly according to the invention comprises one or more of the following: a sealing device, for example comprising a hatch or valve, for temporarily sealing off the central passage of the wellhead, and thus sealing off the hydrocarbon well;

a sealing device, for example comprising a hatch or valve, for temporarily sealing off the bore of the BOP mounted on the well head and thus sealing off the hydrocarbon well; a positioning device, for example a mount, movable grips or a robot arm, for positioning the machining device relative to the tubing hanger;

a positioning device, for example a mount, movable grips or a robot arm, for stabilising the machining device while it is machining the tubing hanger;

a storage space for holding a temporary abandonment cap, and preferably mounting device for mounting the temporary abandonment cap in the well head;

a communication device for communicating with the machining device; and

a swarf collecting device for collecting swarf generated by machining away the tubing hanger, or at least a part thereof. Advantageous embodiments of the method according to the invention and the device and assembley according to the invention are disclosed in the subclaims and in the description, in which the invention is further illustrated and elucidated on the basis of a number of exemplary embodiments, of which some are shown in the schematic drawing. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 shows a side view in cross section of the top of a subsea hydro carbon well with tubing supported via tubing hanger in a well head mounted in a conductor wellhead;

Fig. 2 shows the removing of the tubing with the tubing hanger through a schematically indicated BOP having a wide bore;

Fig. 3 shows schematically a tubing hanger removal tool inserted in the wellhead and the tubing hanger via an BOP having a small sized bore, which BOP is mounted on the well head using an adapter, and which tubing hanger removal tool is supported by a tubular string;

Fig. 4 shows a machining device of the tool machining away part of the tubing hanger, while a clamping device of the tool engages an upper section of the tubing, thus supporting the tubing;

Fig. 5 shows the machining device in a retracted position, and the enlarged central passage of the tubing hanger;

Fig. 6 shows the lifting of the tubing out of the hydrocarbon well into the BOP and riser, using the tubing hanger removal tool. DETAILED DESCRIPTION

Fig. 1 shows a side view in cross section of the top of a hydro carbon well 1 with tubing 2 supported via tubing hanger 3 in a well head 4.

In the particular configuration shown, the wellhead 4 is mounted in a conductor wellhead 5 and is provided with a temporary abandonment cap 17.

The hydrocarbon well 1 depicted is a subsea hydrocarbon well, the well head 4 extending above the seafloor 6. In the configuration shown, the wellhead 4 further supports intermediate casing strings 7, 7', which casings strings are supported by casing hangers 8 in the wellhead. It is submitted herewith that a method according to the invention and a tool according to the invention may also be used in removing intermediate casing strings supported via casing hangers in a well head, in particular in a wellhead of a subsea hydrocarbon well. It is however noted that casing often remains in the well, as it can be used as a basis for securing the concrete plugs to seal off the well. Furthermore, a casing hanger removal tool would differ in dimensions from a tubing hanger removal tool according to the invention since the tubing is provided inside the casing, the casing and corresponding casing hangers thus having a central passage with an inside diameter larger than the outside diameter, and consequently than the inside diameter, of the tubing.

Fig. 2 depicts the removing of the tubing 2 with the tubing hanger 3 through a schematically indicated BOP 9 having a wide bore 10. Above the BOP there is provided a riser 1 1 , having a central passage 12, which riser connects the hydrocarbon well 1 with a surface vessel or platform, for example a jack up.

It is noted that it will often be necessary to provide a BOP on the wellhead during the main part of plug and abandonment activities, in particular when removing the tubing. This, because during this stage of the plug and abandonment process, the well has not yet been plugged, and therefore there is the potential risk of a blow-out.

To enable the tubing to be removed, currently BOP's are used with a large sized bore, i.e. a bore wired enough to allow the tubing with the tubing hanger to be lifted out of the well, through the BOP and through the riser provided above the BOP to a vessel or platform, such as a jack up rig, supporting the riser.

Fig. 3 shows the hydrocarbon well 1 , well head and tubing of fig. 1 , but now in combination with a, schematically depicted, tubing hanger removal tool 15 according to the invention shown. The tubing hanger removal tool 15 has been lowered into the wellhead 4 and into the tubing hanger 3 via a BOP 13 and a riser 1 1 1. The schematically depicted BOP 13 is a BOP with a small size bore 14, i.e. a bore having a diameter larger than the outer diameter of the tubing 2, but smaller than the outside diameter of the tubing hanger 3.

Furthermore, the riser 1 11 is a riser having a small sized central passage 112, i.e. a central passage having a diameter larger than the outer diameter of the tubing 2, but smaller than the outside diameter of the tubing hanger 3. In the particular embodiment shown, the central passage 1 12 of the riser 1 1 1 fits the bore 14 of the small sized BOP 13.

In the particular embodiment shown, the tubing removal tool 15 is part of a tubing removal assembly, the assembly comprising the tubing hanger removal tool 15, and an adapter 16. In the particular embodiment shown, the adapter 16 is mounted between the BOP and the wellhead, such that a BOP having a diameter smaller than the diameter of the central passage of the wellhead can be used in removing the tubing from the well.

Thus, a BOP that has been designed to be mounted on a wellhead having a smaller central passage can be used.

In an alternative embodiment, in addition to or instead of an adapter mounted between wellhead and BOP, an adapter can be provided between BOP and riser as well. The adapters enable to use a riser and BOP having a central passage and bore large enough for lifting the tubing out of the well, but not larger than that.

It is noted that in the embodiment shown, a simple adapter is provided, i.e. an adapter that is mainly configured for mounting a BOP on a wellhead and which does not comprise additional devices and or features. In a further embodiment, the adapter cnabe provided with for example monitoring equipment, for monitoring conditions inside the well head during the plug and abandonment procedure. Also, the adapter can for example be provided with excess ports, for example an excess port that allows for a small sized remotely operated vehicle (ROV) to enter the well head.

The exemplary embodiment of the tubing hanger removal tool 15 is configured for enabling removal of tubing, which tubing is at its upper end provided with a tubing hanger mounted in a wellhead, from a hydrocarbon well. The tubing hanger removal tool comprises a coupling device 19, a clamping device 20 and a tubing hanger machining device 21.

The coupling device 19 of the tubing hanger removal tool 15 is located at a first end of the tubing hanger removal tool. The coupling device 19 is adapted to couple the tubing hanger removal tool to a tubing hanger removal tool support 22, in the particular

embodiment shown a drilling string, i.e. a string of drilling tubulars.

The clamping device 20 is located at a second end of the tubing removal tool 15. The clamping device 20 is adapted for engaging the inside of the tubing 2 at a top portion thereof and for holding the tubing. It is noted that the clamping device 20 is located for engaging the tubing 2 at a section located below the tubing hanger 3. Thus it does not block obstruct removal of the tubing hanger.

In the particular embodiment shown, the tubing hanger removal tool is configured to connect the tubing 2 with the tool support 22. Furthermore, since the clamping device 20 is configured for supporting the tubing 2. the tubing hanger removal tool 15 thus enables the tool support 22 to be used for lifting the tubing 2 out of the well.

The tubing hanger machining device 21 is located between the coupling device 19 and the clamping device 20. The machining device 21 is adapted to be lowered into a central passage 23 of the tubing hanger 3 and to machine away at least part of the tubing hanger, which has been depicted in figs. 4 and 5, thus disconnecting the tubing 2 from the tubing hanger 3 and enlarging the central passage 23 of the tubing hanger 3 to a diameter wide enough for lifting the tubing 2 out of the hydrocarbon well 1 , and to thus enable lifting the disconnected tubing out of the hydrocarbon well. The latter has been depicted in Fig. 6.

In the particular embodiment shown, the tubing hanger removal tool 15 is provided with a machining device 21 for cutting away part of the tubing hanger 3. The machining device 21 has a cutting face that is rotatably mounted such that it can rotate relative to the clamping device and about a longitudinal axis of the tubing removal tool 1. Furthermore, the cutting face of the machining device faces forward, i.e. the machining device has a cutting face that is adapted for cutting in a direction parallel to the longitudinal axis of the tool, and thus parallel to the longitudinal axis of the tubing supported by the tubing hanger. When cutting away part of the tubing hanger, and possibly some of the tubing, the cutting face engages the tubing hanger from above and cuts to the bottom end of the tubing hanger in a downward direction. ln the particular embodiment shown, the cutting face of the machining device, has a fixed outer diameter which is larger than the outer diameter of the tubing but is smaller than the outer diameter of the tubing hanger. The outer diameter of the cutting face furthermore is smaller than the inner diameter of the bore of the BOP and/or the central passage of the riser, thus enabling the machining device to be transported via the riser and the BOP.

In an alternative embodiment, the machining device could be provided with many types of cutting blades or cutting teeth, for example with retractable cutting blades that allow for a compact configuration of the machining device when transported through the riser and are to be extended prior to the cutting of the tubing hanger to form the cutting face.

Fig. 4 shows the machining device 21 of the tool 15 machining away part of the tubing hanger 3, while the clamping device 20 of the tool 15 engages an upper section of the tubing 2, thus supporting the tubing. Fig. 5 shows the machining device 21 in a retracted position, and the enlarged central passage 23 of the tubing hanger 3.

Fig. 6 shows the lifting of the tubing 2 out of the hydrocarbon well 1 through the BOP 13 and riser 1 1 1 , using the drilling string 22 to lift the tubing hanger removal tool 15 and thus the tubing.

Thus, according to the invention the tubing, and the control lines provided on that tubing, can be removed from a hydro carbon well. It is noted that when performing plug and abandonment of wells from a vessel or jack up it will often be required to pull the tubing from the well. In particular if the tubing has control lines attached, especially in the deeper regions where one would want to set isolation plugs. The control lines may otherwise constitute leak paths when extending through plugs cemented in the wellbore.

Thus, the invention provides a tubing hanger removal tool to enable removal of tubing from a hydrocarbon well in an efficient way, more in particular a tool that enables lifting tubing out of a well through opening having an inner diameter smaller than the outer diameter of the tubing hanger. According to the invention, the tubing hanger is separated from the tubing hanger. Of the tubing hanger a central part is cut away to provide a passage for the tubing to be lifted from the well, the passage being large enough to pass there through the tubing and its control lines.

Thus, with a method according to the invention, part of the tubing hanger remains in the well head, and the tubing is lifted through the central, enlarged opening of the tubing hanger out of the well.

With a method according to the invention, a riser and BOP having an inner diameter smaller than the outer diameter of the tubing hanger can be used for lifting the tubing to a surface vessel or jack up. This allows for a light and compact riser and BOP, which are more easy to handle and install. Thus the tubing removal can dealt with in an efficient manner.

In a further preferred embodiment of the tubing hanger removal tool, the tool is furthermore configured for engaging and supporting the tubing, such that the tubing hanger removal tool can also be sued for lifting the tubing. Thus, with lifting the removal tool from the well, the top end of the tubing is lifted from the well as well.

The tubing hanger removal tool 15 according to the invention comprises a machining device 21 adapted to be lowered into a central passage 23 of the tubing hanger 3 and to machine away at least part of the tubing hanger, thus disconnecting the tubing 2 from the tubing hanger 3 and enlarging the central passage 23 of the tubing hanger 3 to a diameter wide enough for lifting the tubing out of the hydrocarbon well, and to thus enable lifting the disconnected tubing out of the hydrocarbon well.

The preferred embodiment of a tubing hanger removal tool 15 shown further comprises a clamping device 20, for engaging the inside of the tubing at a top portion thereof, and for holding, optionally supporting, the tubing 2 while the machining device is machining at least part of the tubing hanger. The clamping device thus secures the tubing hanger removal tool 15 in the tubing hanger 3, which may be beneficial to support torque forces generated by the milling of the tubing hanger. Thus, the machining device 21 can held in place during the removal of the central part of the tubing hanger 3.

In the preferred tubing hanger removal tool 15 shown, the clamping device 20 is configured to support the disconnected tubing 2 such that the disconnected tubing can be lifted through the tubing hanger 3 to the vessel or jack up rig using the tubing hanger removal tool support.

The tubing hanger removal tool 15 is lowered into, and lifted out of, the well head 4 using a tool support 22, in the embodiment shown a drilling string, i.e. a string of drilling tubulars. The tubing hanger removal tool 15 is connected to the drilling string 22 with a coupling device 19.

The tubing hanger removal tool is furthermore dimensioned such that, at least during the machining away of the tubing hanger, the tool is located below the BOP, or at least below the shear rams of the BOP. Thus, the in case of a blowout, the shear rams only need to cut through the drilling string supporting the tubing hanger removal tool, and not through tool. In this context it is noted that BOP's are typically designed for cutting tubulars, and may malfunction when trying to cut through other objects, such as the tubing hanger removal tool.

In a preferred embodiment according to the invention, the tubing is removed from the subsea hydrocarbon well 1 using the tubing hanger removal tool 15 shown. The method comprises the steps:

- providing the riser 1 1 between the well head 4 of the hydrocarbon well 1 and a surface vessel or jack up rig, the riser 1 1 1 having a central passage 12;

- providing the tubing hanger 15 removal tool, the tubing hanger removal tool 15 comprising the machining device 21 and the clamping device 20;

- lowering the tubing hanger removal tool 15 into the wellhead 4 via the central passage 12 of the riser 1 1 , and thus lowering the machining device 21 into a central passage 23 of the tubing hanger 3 and the clamping device 20 into the tubing 2 below the tubing hanger 3;

- engaging a top portion of the tubing 2 at its inside and below the tubing hanger 3 using the clamping device 20;

- machining away at least part of the tubing hanger 3, thus disconnecting the tubing from the tubing hanger and enlarging the central passage 23 of the tubing hanger 3 to a diameter wide enough for lifting the tubing 2 out of the hydrocarbon well 1 ; and

- lifting the disconnected tubing 2 out of the hydrocarbon well 1 , through the central passage 23 of the tubing hanger 3 and through the central passage 12 of the riser 1 1 , to the vessel or jack up rig,

wherein the central passage 12 of the riser 1 1 has a diameter larger than the external diameter of the tubing 2 but smaller than an external diameter of the tubing hanger 3.

In the particular embodiment shown, the tubing hanger removal tool 1 , more in particular its machining device 21 , is driven via the tubular removal tool support 22 by a drive located on the surface vessel or platform, for example a jack up, supporting the riser. In the particular embodiment shown, the clamping device rotation of the tool support 22 rotates the cutting face of the machining device.

In an embodiment, the tubular removal tool support rotates part of the toll comprising the machining device, and thus rotates the cutting face of the machining device about a longitudinal axis of the tubing hanger removal tool. In such an embodiment, the part of the tool comprising the clamping device is rotatable connected with the part of tool comprising the machining device to thus enable the clamping device to engage the tubing while the cutting face of the machining device is rotated. ln an alternative embodiment, the tubing removal tool is provided with a drive, for example an electric drive or a mud motor, for driving the machining device.

In a further embodiment, the tubing hanger removal tool is adapted to be fully lowered downhole, i.e. past the tubing hanger and into the tubing towards the bottom of the well, and the machining device is adapted to cut the tubing downhole prior to removing part of the tubing hanger. In an alternative embodiment, the tubing hanger removal tool comprises a further cutting device specifically adapted to cut the tubing downhole. In an embodiment, the tubing hanger removal tool is at its front end, i.e. the end of the tool facing a bottom of the well when the machining device is machining the tubing hanger, provided with a reaming device for enlarging the diameter of a bore in a X-mas tree mounted on the wellhead to a diameter larger than the outer diameter of the tubing, to thus enable the tubing to be lifted out of the well through the tubing hanger and subsequently through X- mas tree the riser.

Reference signs

01 hydro carbon well

02 tubing

03 tubing hanger

04 wellhead

05 conductor wellhead

06 seafloor

07 intermediate casing string

08 casing hanger

09 Blow Out Preventer (BOP), large

10 large sized bore of BOP

11 riser

12 central passage riser

13 BOP, small

14 small sized bore of BOP

15 tubing hanger removal tool

16 adapter

7 temporary abandonment cap 18 central passage tubing

19 coupling device

20 clamping device

21 machining device

22 tool support / drilling string

23 central passage tubing hanger

111 riser with small central passage

112 small sized central passage of riser