NL2014753B1

NL2014753B1 - Method and tool enabling removal of tubing from a hydrocarbon well.

Info

Publication number: NL2014753B1
Application number: NL2014753A
Authority: NL
Inventors: Roodenburg Joop; Bernardus Wijning Diederick
Original assignee: Itrec Bv
Priority date: 2015-05-01
Filing date: 2015-05-01
Publication date: 2017-01-25
Also published as: EP3307983A1; EP3307983B1; NL2014753A; WO2016178561A1

Abstract

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. The method involves lowering a machining device into a central passage of a tubing hanger and machining away at least part of that 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.

Description

Title: METHOD AND TOOL ENABLING REMOVAL OF TUBING FROM A HYDROCARBON WELL

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 a 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 overtime. 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 form 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 tool which 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 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, the method comprising the steps, according to claim 1.

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.

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.

Thus the invention facilitates removal of tubing form 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 tubular string while the machining device is machining at least part of the tubing hanger. A further method according to the invention comprises the step: - cutting the tubular string downhole prior to engaging the top portion of the tubular string.

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, 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 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.

In a further method according to the invention, the bore has a diameter which is larger than the diameter of 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. A further method according to the invention the bore 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. 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 tool using a tubular, for example a drilling string or coiled tubing, the tubular extending through the riser. A further method according to the invention comprises the step: - rotating the tubular and using this rotational movement for driving the machining device by rotating that drill string. 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. 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. A further method according to the invention comprises the step: - positioning the tool 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. 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

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 wherein the machining device is adapted to cut the tubing downhole and/or the tool comprises a cutting device adapted to cut the tubing downhole.

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.

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.

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 an embodiment, the tubing hanger removal tool is configured to couple the disconnected tubing with the tool support, such that the disconnected tubing can be lifted through to the vessel or jack up rig using tool support.

In an embodiment of the tubing hanger removal tool the machining device is adapted to be coupled with a tubular tool support, and 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 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 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 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 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 removal tool is provided with one or more inner channels for guiding drilling mud from one end to an opposite end of the tubing removal tool, which channels preferably have at one end openings adapted to be connected with a tubular supporting the 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 an embodiment, the tubing hanger removal tool further comprises a shredder device for shredding cuttings generated by the machining device.

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 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.

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 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.

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 tool; 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 tool 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 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 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 sued in removing intermediate casing strings supported via casing hangers in a well head, in particular in a wellhead of a subsea hydrocarbon well.

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 11, 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 111.

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 111 is a rise 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 112 of the riser 111 fits the bore 14 of the small sized BOP 13.

In the particular embodiment shown, the BOP 13 has been mounted on the well head 4 using an adapter 16.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.

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.

The exemplary embodiment of the tubing hanger removal tool 15 for enabling removal of tubing from a hydrocarbon well, which tubing is at its upper end provided with a tubing hanger mounted in a wellhead, 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 is located at a first end of the tubing hanger removal tool 15, and 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.

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. In the particular embodiment shown, the tubing hanger removal tool is furthermore configured to connect the tubing with the tool support 22 and the clamping device 20 is configured for supporting the tubing 2, the tool 15 thus enabling 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.

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 111, 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 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.

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 17 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

Claims

1. 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, the method comprising 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.

2. Method according to claim 1, further comprising 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 at least part of the tubing hanger.

3. Method according to claim 2, further comprising the step: - cutting the tubing downhole prior to engaging the top portion of the - tubing.

4. Method according to one or more of the preceding claims, wherein the hydrocarbon well is a subsea well, the method further comprising 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.

5. Method according to claim 4, wherein the diameter of the central passage of the riser is smaller than an external diameter of the tubing hanger.

6. Method according to claim 4 or 5, further comprising the step: - mounting a BOP on the wellhead, the BOP having a bore connecting the well head to the riser string.

7. Method according to claim 6, wherein the bore has a diameter which is larger than the diameter of the central passage the riser, preferably is substantially similar to the diameter of the central passage of the wellhead above the tubing hanger, the method further comprising the step: - providing an adapter between the BOP and the riser-, the adapter having a conduit that connects the bore of the BOP with the central passage of the riser.

8. Method according to claim 6, wherein the bore has a diameter which is smaller than the diameter of the central passage of the well head, preferably is substantially similar to the diameter of the central passage of the riser, the method further comprising 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.

9. Method according to one or more of the claims 4-8, further comprising 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.

10. Method according to one or more of the claims 4-9, further comprising the step: supporting the machining -device using a tubular, for example a drilling string or coiled tubing, the tubular extending through the riser.

11. Method according to claim 10, further comprising the step: - rotating the tubular and using this rotational movement for driving the machining device by rotating that drill string.

12. Method according to claim 10 or 11, further comprising the step: - circulating drilling mud through the wellhead to drive the machining device and/or to remove swarf generated by machining away the tubing hanger, the drilling mud flowing downward via an annulus between the tubular and the riser and flowing upward through the tubular or vice versa.

13. Method according to one or more of the preceding claims, further comprising 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.

14. Method according to one or more of the preceding claims, further comprising the step: - positioning the tool below a BOP, or at least below the shear rams of a 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.

15. Method according to one or more of the preceding claims, further comprising 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 of the well, preferably permanent plugs

16. 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, the tool comprising 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.

17. Tubing hanger removal tool according to claim 16, the tool further comprising 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.

18. Tubing hanger removal tool according to claim 16 or 17, wherein the tool is adapted to be fully lowered into tubing, and wherein the machining device is adapted to cut the tubing downhole and/or the tool comprises a cutting device adapted to cut the tubing downhole.

19. Tubing hanger removal tool according to one or more of the preceding claims 16-18, wherein 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.

20. Tubing hanger removal tool, according to one or more of the preceding claims 16-19, wherein the tool is adapted to be lowered into the wellhead via a central passage of a riser extending between the wellhead and a surface vessel or a jack up and/or via a bore of a BOP mounted on the wellhead, 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. -21. Tubing hanger removal tool according to claim 19 or 20, the 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.

22. Tubing hanger removal tool according to claim 21, wherein the tool is configured to couple the disconnected tubing with the tool support, such that the disconnected tubing can be lifted through to the vessel or jack up rig using the tubing removal tool support.

23. Tubing hanger removal tool according to claim 21 or 22, wherein the machining device is adapted to be coupled with a tubular tubing removal tool support, and to be driven via that tubular removal tool support by a drive located above the connecting tool, preferably located on a surface vessel or jack up.

24. Tubing hanger removal tool according to one or more of the claims 21-23, wherein the tool is adapted to be rotatably supported by the tool support and/or wherein the clamping device is rotatably connected to the tool.

25. Tubing hanger removal tool according to one or more of the preceding claims 16-24, wherein the tubing removal tool is provided with a drive, for example an electric drive or a mud motor, for driving the machining device.

26. Tubing hanger removal tool according to one or more of the preceding claims 16-25, wherein 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.

27. Tubing hanger removal tool according to one or more of the preceding claims 16-26, wherein the machining device has a cutting face that is adapted for cutting in a direction parallel to a longitudinal axis of the tool, preferably in a downward direction.

28. Tubing hanger removal tool according to one or more of the preceding claims 16-27, wherein 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.

29. Tubing hanger removal tool according to one or more of the preceding claims 16-28, wherein the machining device comprises two or more counter rotating cutting faces to at least partially cancel out the torque generated by the machining away of the tubing hanger.

30. Tubing hanger removal tool according to one or more of the preceding claims 16-29, wherein the tubing removal tool is provided with one or more inner channels for guiding drilling mud from one end to an opposite end of the tubing removal tool, which channels preferably have at one end one or more openings adapted to be connected with a tubular supporting the tubing removal tool.

31. Tubing hanger removal tool according to one or more of the preceding claims 16-30, wherein the tool comprises a clamping device according to claim17, and wherein 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.

32. Tubing hanger removal tool according to one or more of the preceding claims 16-31, wherein the tubing removal tool further comprises a shredder device for shredding cuttings generated by the machining device.

33. Tubing hanger removal tool according to one or more of the preceding claims 16-32, wherein the 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.

34. Tubing hanger removal tool according to one or more of the preceding claims 16-33, wherein the tool is at its front end provided with a reaming device for enlarging the diameter of the central passage of the tubing.

35. Tubing hanger removal tool according to one or more of the preceding claims 16-34, wherein the tool is 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.

36. Tubing hanger removal tool according to one or more of the preceding claims 16-35, wherein the tool is adapted to be mounted on a well head, or on an adapter mounted on a wellhead.

37. Tubing removal assembly comprising a tubing hanger removal tool according to one or more of the claims 16-36, 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

38. Tubing removal assembly according to claim37, wherein the adapter 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 tool; and A swarf collecting device for collecting swarf generated by machining away the tubing hanger, or at least a part thereof.