Wellhead tool

Abstract

A tool for use in a well system, the tool comprising: a stator and a rotor; the rotor being rotatably connected to the stator, the rotor being arranged to rotate around a main axis of rotation; the rotor comprising a main body and a surface, the surface facing the main axis of rotation, the surface being movable with respect to the main body of the rotor, and the surface being arranged to engage with a wall of the well system.

Description

[0001] Wellhead Tool

[0002] Field of the invention

[0003] The invention relates to tools for use in a well such as a hydrocarbon producing well, a CO2 injection well, a non-producing well, or a water injection well, and in particular to a tool for carrying out work on a wall of a wellhead or a wall of a Christmas tree.

[0004] Background

[0005] A hydrocarbon producing well comprises a plurality of elements with standardised dimensions and material properties. Fig. 1 illustrates the top of a wellhead. The wellhead typically extends above the seabed, while the rest of the well extends below the seabed into a hydrocarbon producing formation. The wellhead is usually below the water surface, but it may also be on dry land. The wellhead illustrated in Fig. 1 is an open wellhead, in that the top is not closed and any water or hydrocarbon products from the well would flow out due to the overpressure in the well. In practice, the well would not be open during normal operating conditions, but be attached to a so-called Christmas tree, which is an standardised assembly comprising a plurality of access channels, safety valves, emergency shutdown valves and release mechanisms. The Christmas (or X- mas) tree is placed on top of an H4 profile, which is the top area of the wellhead. The X-mas tree itself also has an H4 profile for attaching tubulars or other equipment. Fig. 1 illustrates the main pipe of the well 101 , and a set of 4 grooves 102 provided on the outside wall of the wellhead, whereby the 4 grooves are arranged above one another and are perpendicular to the main longitudinal axis of the wellhead. The datum 103 of the wellhead is the generally flat top edge. A VX-seal 104 is provided on the inside of the wellhead adjacent to the datum and forms a boundary of the inside wall 105. The VX seal will form a sealing connection to the X-mas tree and is one of the important parts of the wellbore because it is the primary seal for preventing leaks to the environment. The H4 profile on the X-mas tree has a similar profile with 4 grooves, a datum and seal.

[0006] Statement of invention

[0007] 38249088-1 According to a first aspect of the invention, there is provided a tool for use in a well system, the tool comprising: a stator and a rotor; the rotor being rotatably connected to the stator, the rotor being arranged to rotate around a main axis of rotation; the rotor comprising a main body and a surface, the surface facing the main axis of rotation, the surface being movable with respect to the main body of the rotor, and the surface being arranged to engage with a wall of the well system.

[0008] The stator may be arranged to be at least partially received within the wellhead. The stator may comprise a locking member for setting the wellhead tool against the internal wall of the wellhead. The locking member may be a hydraulic piston.

[0009] The stator may comprise an axle and the rotor may comprise a sleeve, and the sleeve may be arranged to rotate around the axle. The axle may define a channel, and the channel may comprise one or more hydraulic fluid conduits. The rotor may comprise a collar extending from the axle, the collar may comprise a driven gear, the stator may comprise a drive gear, and the driven gear may mesh the drive gear.

[0010] The rotor may be hydraulically driven by a hydraulic motor, wherein the hydraulic motor is provided at the stator. The stator and the rotor may each comprise a hydraulic connector for receiving at least one corresponding hydraulic control line.

[0011] The rotor may comprise a radial adjustment mechanism for adjusting the radial position of the surface, and the radial adjustment mechanism is optionally a hydraulic piston.

[0012] The rotor may comprise a vertical adjustment mechanism for adjusting the vertical position of the surface along the direction of said main axis of rotation.

[0013] The surface may comprise a grinding wheel. The grinding wheel may be received within a grinding carrier, and the grinding carrier may comprise one or more further wheels arranged adjacent the grinding wheel for setting the distance of the grinding wheel to said wall. The rotor may comprise a hydraulic motor arranged to rotate the grinding wheel.

[0014] 38249088-1 Optionally, the tool further comprising a datum polishing pad. The tool may further comprise a VX-seal polishing pad. The tool may further comprise a lifting sub, the lifting sub comprising an eye at an upper end for lifting the tool to the surface.

[0015] According to a second aspect of the invention, there is provided a method of treating a wall of a well system, the method comprising: setting a stator of a tool at a fixed position with respect to the well system; rotating a rotor with respect to the stator to position a surface of the rotor to a portion of the wall of the well system that is to be treated; driving the surface against the portion of the wall of the well system that is to be treated; moving the surface to treat said portion of the wall of the well system.

[0016] The step of setting may comprise actuating a hydraulic piston within the stator to expand against an internal wall of the well system.

[0017] The step of rotating may comprise driving a hydraulic motor to actuate a drive gear within the stator, wherein the drive gear meshes with a driven gear at the rotor.

[0018] The step of driving may comprise actuating a hydraulic piston.

[0019] The step of moving may comprise rotating the surface to treat the portion of the wall of the well system.

[0020] Additionally, a step may be provided of adjusting the vertical position of the surface along the direction of the main axis of rotation of the rotor.

[0021] Drawings

[0022] Some embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0023] Fig. 1 is a perspective view of a wellhead;

[0024] Fig. 2 is a vertical cross section through the wellhead with a wellhead tool attached to the wellhead;

[0025] Fig. 3 is a perspective view of the wellhead and wellhead tool from the top;

[0026] Fig. 4 is a perspective view of the wellhead and wellhead tool from underneath;

[0027] 38249088-1 Fig. 5 is a side view of the wellhead and wellhead tool;

[0028] Fig. 6 is a perspective view of the wellhead tool from underneath without the wellhead;

[0029] Fig. 7 is a perspective view of a detail of the tool from underneath;

[0030] Fig. 8 is a cross section of a detail of the stator;

[0031] Fig. 9 is a perspective view of a cross section of the tool;

[0032] Fig. 10 is a perspective view of the tool with see-through elements;

[0033] Fig. 11 is a vertical cross section of the tool;

[0034] Fig. 12 is a vertical cross section of the tool;

[0035] Fig. 13 is a perspective view of the tool; and Fig. 14 is a method diagram.

[0036] Specific description

[0037] A tool is provided which can be attached to a wellhead, more specifically to a top portion of the wellhead ending in an H4 profile, or to a Christmas tree H4 profile. The tool can be used for carrying out work on the outside wall of the wellhead, such as polishing or removing surface damage. The tool comprises two main parts: a stator and a rotor. The stator is arranged to be attached to the wellhead and will be static with respect to the wellhead during use. The rotor has a rotating connection to the stator and is arranged to rotate during use. The rotation of the rotor with respect to the stator can be continuous, or the rotor can operate in a fixed orientation with respect to the rotor for some time, before moving to a different rotational position. The rotor further comprises a surface that is movable with respect to the main body of the rotor. The surface may be a vibrating or rotating pad that can be pressed against an outside wall of the wellhead, for example for polishing an external wall of the wellhead, for removing dirt, or for removing surface damage on the external wall. Although rotation of the pad is described in more detail below, a vibrating action may be used alternatively. Different pads can be provided depending on the intended purpose. For example, a relatively soft pad can be used for removing dirt, or an abrasive pad can be used for removing a top layer of the external wall of the wellhead when the top layer is damaged. The pad may also be a rotating wheel with an abrasive surface. The rotating wheel may have a geometry to match a particular surface and can be suitable for grinding both flat, angled and grooved surfaces.

[0038] The stator is fixed with respect to the wellhead or X-mas tree and static during use. A fixed connection can be achieved in different ways. The stator can be fit to the outside

[0039] 38249088-1 of the wellbore, for example using a hydraulic clamp mechanism. The external stator can have a ring shape such that it can easily fit around the wellbore, and have hydraulic pistons or other locking mechanisms that extend inwards from the ring and engage with the outside wall of the wellhead.

[0040] In a different example, which is described in more detail below, at least part of the stator has an outer diameter that is smaller than the inner diameter of the wellhead such that the stator can be received at least partially within the wellhead. The stator comprises one or more expanding members to engage with the internal wall of the wellhead and fix the stator in place.

[0041] The rotor extends form the stator and has a rotating connection with the stator. The rotating connection enables the surface to reach different positions on the external wall of the wellhead. The movement of the rotor relative to the stator can be achieved with a hydraulic motor that activates a drive gear. When the external stator is arranged against the outside wall of the wellhead, the rotor follows the outer perimeter of the outside wall during movement. The external stator and rotor may both have a general ring shape, arranged adjacent to each other, whereby a drive gear enables the movement of the rotor. When the stator is arranged at least partially within the wellbore, the rotor extends radially outwards from the stator, over the datum of the wellhead and downwards to the area of the outside wall that the tool operates on.

[0042] The surface can be moved with respect to the main body of the rotor in radial direction and in the longitudinal direction of the wellhead to reach the location of the external wall of the wellhead the surface needs to operate on. In addition, a rotary motor can drive rotation of the surface.

[0043] The movement of the surface is therefore based on one or more of four possible movements: (a) rotation of the rotor with respect to the stator, (b) radial adjustment, (c) vertical adjustment in axial direction, and (d) rotation or vibration of the surface with respect to the main body of the rotor to carry out a polishing or cleaning operation. Movements (a) and (d) may be carried out at the same time. Adjustment (b) may be carried out before the operation starts, but may be left unchanged during the polishing or cleaning operation given that movement (a) does not change the radial position of the surface. Adjustment (c) may be carried out at the surface, when it is known which part

[0044] 38249088-1 of the wall will be treated and no further vertical adjustment will be required during operation.

[0045] The tool can be operated locally by a processor and a local power supply, such as a battery. Alternatively, the tool is operated hydraulically, whereby a remotely operated vehicle (ROV) provides hydraulic power to actuate the different functions, such as rotation, other movement, locking, unlocking, etc. The ROV can connect with the tool through stab-in connectors and thereby establish hydraulic connections for the different functions.

[0046] Besides the main function of grinding, polishing or removing dirt on the outside wall of the wellhead, cleaning or polishing of the VX seal and / or the datum during rotation of the rotor can be carried out. This function can be achieved by attaching pads to the rotor at an interface between the rotor and the VX seal or the datum. The presence of the stator gives a stable basis from which to access the datum or VX seal, which may otherwise be difficult to clean in subsea conditions without causing damage.

[0047] Fig. 2 illustrates a specific example in detail. A vertical cross section through the wellhead with the wellhead tool attached to the wellhead is schematically illustrated. The wellhead 1 comprises a datum 2 and a VX seal 3, corresponding to datum 103 and VX seal 104 in Fig. 1 . The VX seal is the main seal between the top of the wellhead and the Christmas tree and damage to the VX seal during placement or use of the tool should be avoided. The term ‘VX’ is a term of the art referring to the type of gasket, with other types of gaskets such as ‘AX’ or ‘CX’ being other examples of pressure energised ring joint gaskets. Damage is avoided by retracting any protruding parts from the stator and the rotor, such as the grinding surface on the rotor, or an anti-rotation lock on the stator, and further by providing an interface between the tool and the VX seal that avoids damage. The interface may also be used for polishing the VX seal with a soft pad. Fig. 7 shows details of datum and VX polishing pads 71 and 71 , which are described in more detail below.

[0048] The tool comprises a stator 4 and a rotor 5. The stator and rotor have different hatching in the figure. The stator is at least partially received within the inner bore of the top of the wellhead and the part that is received within the bore has a smaller outer diameter than the bore. The overall shape of the stator part that is received within the bore is disc-

[0049] 38249088-1 shaped. The outer diameter is smaller to allow placement of the stator without damaging the wellhead. The stator is fixed in place using one or more hydraulic anti-rotation locks 6, which extend radially from the stator when activated and engage with the inner wall of the wellhead.

[0050] An axle 7 extends upwards from the disc-shaped part of the stator, and extends in use above the top of the wellhead. The axle is co-axial with the main axis A of the wellbore. The axle is hollow and provides a channel 8 for hydraulic power lines to extend from a stab-in connector 9, such as a ‘hot-stab’ at the top of the axle, to the hydraulic antirotation lock and an hydraulic motor 10 for controlling and driving the rotation of the rotor. The hydraulic motor 10 and the hydraulic anti-rotation lock 6 are both provided within the main disc-shaped body of the stator. The hydraulic motor turns hydraulic pressure into rotational movement of a drive gear 11. The drive gear 11 comprises a wheel 12 arranged on top of the disc-shaped main body. The wheel 12 comprises teeth that mesh with corresponding teeth on a driven gear 13 on the rotor. Alternatively, the drive gear and the driven gear may be connected by a cambelt. The stator further comprises bearings 14 arranged to support the rotor and enable the rotational motion around the rotor’s axis.

[0051] The rotor comprises a sleeve 15 that fits around the axle 7. The sleeve rests on the main disc-shaped body of the stator and extends radially outwards into a collar 16 at the surface of the disc-shaped body and comprises the driven gear 13 at the perimeter of collar 16. The sleeve extends upwards and separates the main body of the rotor from the main body of the stator such that the main body of the rotor is arranged above the datum 2 of the wellhead.

[0052] The main body of the stator comprises an arm 17 that extends outwards from the main axis of rotation, which axis coincides with the main axis A of the wellbore. An optional counterweight 18 is arranged radially opposite to the arm 17 to balance the rotor. The arm 17 extends radially outwards over the datum and then downwards to the outside wall of the wellbore. An interchangeable grinding surface 18 is provided at the end of arm 17. The grinding surface or pad is driven by a hydraulic motor 19 and spins around for polishing or cleaning the outside wall of the riser. Although a hydraulic motor is described and illustrated, an electric motor is used in other embodiments. The depth of the grind setting of the grinding surface is controlled by a floating carrier 20. The radial

[0053] 38249088-1 position of the grinding surface may be controlled by a horizontal carrier 21 within the arm 17. The horizontal carrier is hydraulically controlled. A vertical adjustment mechanism 22 is provided, but the vertical adjustment can be set at the surface prior to deployment of the tool. Alternatively, the vertical adjustment is also controlled hydraulically or electically.

[0054] A hot-stab hydraulic connector 23 is provided at the arm 17. The hydraulic cables attached to the hydraulic connector 23 on the rotor and hydraulic connector 9 on the stator are connected to an ROV and are controlled from the ROV. The rotor is typically not rotated by more than a full turn and moves slowly, so there is no risk of the hydraulic cables becoming entangled. The grinding surface, on the other hand, spins quickly at a particular orientation of the arm, for example 5000rpm. The hydraulic connector 23 may comprise 4 ports: one pair to supply hydraulic fluid in and out for the grinding rotation and a second pair for hydraulic fluid in and out for the horizontal carrier actuation, but further ports can be provided for the floating carrier and / or the vertical adjustment. The horizontal carrier 21 actuation may also use a single port for driving a piston out, while an internal spring provides a force in the opposite direction to urge the arm into a retracted position in the absence of hydraulic pressure.

[0055] The tool may comprise a camera mount 24 and a camera 25, which can be used to inspect the area of the outside wall, in particular for a live feed during the grinding operation.

[0056] Fig. 3 is a perspective view of the tool and wellhead from the top. The stator 4 and rotor 5 can be seen from the top. The stator sleeve 15 and collar 16 extend upwards from the main body of the stator 4. The rotor axle 7 extends above the main plane of the rotor, and defines a channel 8. The stab-in connector 9 extends radially outwards from the top of the axle 7. Hydraulic lines are not shown in the figure. It can be seen that the main body of the rotor is a flat body extending in radial direction with a ring-shaped outer part 31 , connected to a central part 32 by four broad flat spokes 33. A counterweight 18 (not shown in Fig. 3) may be attached to the main body of the rotor on the radially opposite side to the arm 17, or the ring shaped outer part 31 may be sufficiently heavy that a separate counterpart is not required, also keeping in mind that the rotor does not move fast. The main body of the rotor supports arm 17 extending radially outwards. The horizontal carrier 21 is partially attached to one of the spokes and partially attached to

[0057] 38249088-1 the outer part 31. The vertical adjustment mechanism 22 is set at the surface. The vertical adjustment mechanism 22 does not comprise a hydraulic adjustment mechanism and is set at the surface in the illustrated example, but may also comprise a hydraulic adjustment mechanism in other examples. Hydraulic motor 19 is supported on arm 17 by an L-shaped bracket 34. A gearbox 35 is attached underneath the L-shaped bracket and converts the rotational motion of hydraulic motor 19 into rotational motion of the desired speed for the interchangeable grinding surface 36, which is illustrated as a grinding wheel. In Fig. 3, the arm 17 is shown in extended orientation, whereby the wheel 36 does not make contact with the external surface. Support wheels 37 are provided on either side of wheel 36 to control the distance of the wheel 36 to the wall on which it operates. The wheels 37 also stabilise the arm and balance the grinding forces. The wheels 37 rotate freely and are in contact with the outside wall surface during use. The wheels 37 are separated from wheel 36. The axes of the wheels 37 and 36 are all parallel, and are also parallel to the main axis of rotation. However, the grinding wheel may also rotate around a different axis. Fig. 3 also illustrates landing arms 38 extending downwards from ring-shaped outer part 31. The landing arms are tapered towards the lower part and are positioned radially outside the outer wall of the wellhead, such that they assist with steering the tool into the correct position when lowering the tool onto the wellhead. The assembly of wheel 36, wheels 37 and gearbox 35 is spring loaded to urge it against the outer surface of the wellhead, and can pivot around an axis through L- shaped bracket 34.

[0058] Fig. 4 is a perspective view of the wellhead and tool from underneath to show the grinder carrier in more detail. The arm 17 can be seen, with L-shaped bracket 34 supporting gearbox 35 and hydraulic motor 19. The wheels 37 and grinding wheel 36 are in contact with the outer surface of the wellhead. The two wheels 37 and grinding wheel 36 are all contained within the grinder carrier, whereby the rotational axes of the three wheels are parallel. The grinding wheel 36 is arranged in between the other two wheels. The three wheels rotate independently of each other. The three wheels are received between V- shaped top and bottom parts of the grinder carrier. The V-shape follows the curvature of the external wall. The two wheels 37 have a slightly smaller diameter than the grinding wheel. The grinder carrier can rotate around the same axis as the grinding wheel. The axes of the wheels 37 are fixed with respect to the V-shaped top and bottom parts of the grinder carrier. Two of the three landing arms 38 can also be seen extending downwards from the main body of the rotor and having a tapered bottom portion.

[0059] 38249088-1 Fig. 5 is a side view of the wellhead with tool. Rotor axis 7 and stab-in connector 9 can be seen extending above the main part of the rotor. Horizontal carrier 21 is retracted when compared to the orientation of Fig. 3. The vertical adjustment mechanism 22 is set to a lower orientation at the surface, so the hydraulic motor 19 is lowered, and so that wheels 36 and 37 are now in contact with the outside of the wellhead at a lower position near the bottom groove 102. Any damage at this groove, such as metal barbs due to scratches, can be removed. A specific wheel with a V-shaped geometry that matches the shape of the groove can be used if damage within the groove needs to be treated.

[0060] Fig. 6 is a perspective view of the tool on its own without the wellhead or X-mas tree. The stator 4 and rotor 5 are shown as before. The general disc shape of both the stator and the rotor can be seen, whereby the stator has a smaller radius but is thicker compared to the rotor with a larger radius but smaller thickness. The hydraulic motor 10 of the stator can be seen. Stab-in hydraulic connector 23 of the rotor can be seen, whereby the stab-in connector 23 is omitted in some of the preceding figures to avoid blocking other detail. All three landing arms 38 can be seen in this perspective view. A feature that can be seen in this figure is the plurality of datum sliding pads 40. The datum sliding pad may be made of a hard metal, such as stainless steel, and sets the height of the tool besides providing a sliding surface. The tool may be set against the internal wall such that there is a small space between the datum and the datum sliding pad, or the sliding pad may rest on the datum during use. However, a fit against the datum that causes pressure between the datum and sliding pad is preferably avoided to avoid damage during rotation. A single anti-rotation lock 6 is shown. A single lock may be sufficient to set the tool and keep the stator from rotating, but more than one lock can be used if needed. The bottom view of the stator also shows flange 41 of the axle which fixes the axle to the stator by way of screws (shown in cross section of Fig. 8 in more detail).

[0061] Fig. 7 is a close-up perspective view showing a datum sliding pad 40 in more detail, together with an optional additional datum polishing pad 71 and VX seal cleaning pad 72. The VX seal cleaning pad 72 which is angled with respect to the main rotational axis, whereby the angle corresponds to the angle of the VX seal to create optimal contact. Datum polishing pad 71 comprises a surface that is parallel to the main plane of the tool and parallel to the datum in use. The cleaning pads 71 and 72 are adjacent landing arm

[0062] 38249088-1 38 to improve the landing operation, but in other embodiments the two elements are positioned at different rotational positions of the rotor. The datum polishing pad 71 and VX seal cleaning pad 71 are illustrated as integrated with each other, but they may be separate elements. During use, these pads rest on the datum and clear any debris off the datum during rotation. The pads comprise non-abrasive material to avoid any damage to the datum. The sides of datum sliding pad 40 are angled so that the pad is tapered and becomes narrower in radial direction. When the tool rotates, any debris on the datum is pushed to the outside, instead of the inside, as a result of this shape. When performing a datum or VX cleaning operation, any hydraulic hoses or electric power lines to the rotor are not connected, so that the rotor can be rotated 360 degrees without twisting or tangling the hoses or power lines. The hydraulic hoses to the stator lock and hydraulic motor are connected.

[0063] Fig. 8 is a close-up cross section of a detailed section of the stator. The stator 4 and rotor 5 are show. The axle 7 ending in flange 41 can be seen, whereby the flange extends radially outwards from the axle at the lowest part of the axle. The flange 41 is fixed to the main body of the stator 4 with screws 81 . The sleeve 15 can be seen resting on the main disc-shaped body of the stator and extending radially outwards into the collar 16 at the surface of the disc-shaped body and with the driven gear 13 at the perimeter of collar 16. The bearings 14 encompass the collar 16 radially and at the top of the collar to protect the gear mechanism and avoid any debris from entering the gear mechanism. The contact surfaces between stator and rotor can be either plain bearing or roller bearing. Plain bearing may include standard options such as a polymer bearing, coatings or a bronze bushings.

[0064] Fig. 8 further shows a cross section of hydraulic anti-rotation lock 6. The lock is a specific example of a locking member described elsewhere. The lock comprises a hydraulic fluid channel 83 formed within the solid material of the main stator body. The fluid channel terminates at one end at a threaded opening, suitable to be attached to a hydraulic power line. The fluid channel terminates at the other end at a chamber housing a lock piston 85. The lock piston has a first portion with seals 86 that form a sealing connection with the inner walls of the housing, and a second portion with a reduced diameter. The reduced diameter portion extends through a nut 88. The nut 88 forms a stop for the piston and further defines a base for a coil spring 87 surrounding the reduced diameter portion. The coil spring 87 rests against the first portion of the lock piston on the other

[0065] 38249088-1 side, so that the piston is biased into the retracted position in the absence of a hydraulic driving force. When hydraulic pressure is applied, the reduced diameter portion protrudes through the nut and extends beyond the outer wall of the main body of the stator. When placed in the wellhead, the piston will push against the inner wall to keep the stator in place. The biasing force from the coil spring means that only one hydraulic line can be used for controlling the lock piston.

[0066] Fig. 9 is a cross section and illustrates hydraulic motor 10 in more detail. As described previously, the hydraulic motor 10 and the hydraulic anti-rotation lock 6 are both provided within the main disc-shaped body of the stator. The drive gear 11 comprises wheel 12 arranged on top of the disc-shaped main body. The wheel 12 comprises teeth that mesh with corresponding teeth on the driven gear 13 on the rotor.

[0067] Fig. 10 is a perspective view, whereby the elements above the wheel 12 and driven gear 13 are see-through, so that the meshing teeth between the wheel 12 and driven gear 13 can be seen clearly. Parts that are numbered like in previous figures are the same parts and are not described again.

[0068] Fig. 11 is a perspective view of a vertical cross section of the tool. The same elements as described before are numbered likewise.

[0069] Fig. 12 is a vertical cross section through the tool. A detail which is visible in this view is a cross section of the horizontal carrier 21 with a hydraulic piston 121 operating within a piston housing 122. Screws 123 that extend through the top of the main body of the rotor into the sleeve 7 to fix the rotor and sleeve with respect to each other, are also shown in cross section. A further detail that is shown is a cross section through the drive axle 124 of the grinding wheel 36, whereby the drive axle connects to drive shaft 125 of hydraulic motor 19 in a gearbox. The ratio of the gears is chosen to achieve the desired speed of the grinding wheel.

[0070] The grinding wheel is an example of the general concept of a surface described elsewhere. The material of the grinding wheel may be a soft surface, such as a pad comprising plastics for cleaning the wall, or may comprise a hardened steel rough surface, or may comprise a diamond surface to remove a top layer of the wellhead external wall.

[0071] 38249088-1 Fig. 13 illustrates an optional lifting sub 131. The sub 131 comprises a tubular part which can be connected to the tool at the lower end, and an eye 132 at the upper end. The eye 131 can be used for lifting the tool to the surface before or after use.

[0072] Fig. 14 illustrates method steps for operating the tool. A comprises the main steps of: S1 , setting a stator of a wellhead tool at the wellhead; S2, rotating a rotor to position a tool surface attached to the rotor to an area of the external wellhead surface; S3, driving the tool surface against the external wellhead surface; S4, moving the tool surface to treat the wellhead surface.

[0073] Although the invention has been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

[0074] 38249088-1

Claims

CLAIMS:1 . A tool for use in a well system, the tool comprising: a stator and a rotor; the rotor being rotatably connected to the stator, the rotor being arranged to rotate around a main axis of rotation; the rotor comprising a main body and a surface, the surface facing the main axis of rotation, the surface being movable with respect to the main body of the rotor, and the surface being arranged to engage with a wall of the well system.

2. The tool according to claim 1 , wherein the stator is arranged to be at least partially received within the wellhead.

3. The tool according to claim 1 or 2, wherein the stator comprises a locking member for setting the wellhead tool against the internal wall of the wellhead.

4. The tool according to claim 3, wherein the locking member is a hydraulic piston.

5. The tool according to any one of the preceding claims, wherein the stator comprises an axle and the rotor comprises a sleeve, and wherein the sleeve is arranged to rotate around the axle.

6. The tool according to claim 5, wherein the axle defines a channel, and wherein the channel comprises one or more hydraulic fluid conduits.

7. The tool according to claim 5 or 6, wherein: the rotor comprises a collar extending from the axle, the collar comprises a driven gear, the stator comprises a drive gear, and wherein the driven gear meshes the drive gear.

8. The tool according to any one of the preceding claims, wherein the rotor is hydraulically driven by a hydraulic motor, wherein the hydraulic motor is provided at the stator.38249088-19. The tool according to any one of the preceding claims, wherein the stator and the rotor each comprise a hydraulic connector for receiving at least one corresponding hydraulic control line.

10. The tool according to any one of the preceding claims, wherein the rotor comprises a radial adjustment mechanism for adjusting the radial position of the surface, and wherein the radial adjustment mechanism is optionally a hydraulic piston.

11. The tool according to any one of the preceding claims, wherein the rotor comprises a vertical adjustment mechanism for adjusting the vertical position of the surface along the direction of said main axis of rotation.

12. The tool according to any one of the preceding claims, wherein the surface comprises a grinding wheel.

13. The tool according to claim 12, wherein the grinding wheel is received within a grinding carrier, and wherein the grinding carrier comprises one or more further wheels arranged adjacent the grinding wheel for setting the distance of the grinding wheel to said wall.

14. The tool according to claim 13, wherein the rotor comprises a hydraulic motor arranged to rotate the grinding wheel.

15. The tool according to any one of the preceding claims, further comprising a datum polishing pad.

16. The tool according to any one of the preceding claims, further comprising a VX- seal polishing pad.

17. The tool according to any one of the preceding claims, further comprising a lifting sub, the lifting sub comprising an eye at an upper end for lifting the tool to the surface.

18. A method of treating a wall of a well system, the method comprising: setting a stator of a tool at a fixed position with respect to the well system;38249088-1rotating a rotor with respect to the stator to position a surface of the rotor to a portion of the wall of the well system that is to be treated; driving the surface against the portion of the wall of the well system that is to be treated; moving the surface to treat said portion of the wall of the well system.

19. The method according to claim 18, wherein said setting comprises actuating a hydraulic piston within the stator to expand against an internal wall of the well system.

20. The method according to claim 18 or 19, wherein said rotating comprises driving a hydraulic motor to actuate a drive gear within the stator, wherein the drive gear meshes with a driven gear at the rotor.

21. The method according to any one of claims 18 to 20, wherein said driving comprises actuating a hydraulic piston.

22. The method according to any one of claims 18 to 21 , wherein said moving comprises rotating the surface to treat the portion of the wall of the well system.

23. The method according to any one of claims 18 to 22, further comprising adjusting the vertical position of the surface along the direction of the main axis of rotation of the rotor.38249088-1

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