The present application relates, generally, to an apparatus and method relating to a cutting tool and a method of cutting tubular members in a downhole environment.

BACKGROUND OF THE INVENTION

During downhole recovery operations it can be necessary to retrieve sections of tubular members such as casing, lining, drill pipe, mandrels, and other tubing. In order to more easily recover the sections to surface, the tubular members are generally cut into manageable lengths for pulling out of the wellbore.

Conventional cutting tools comprise guillotines, milling tools, or lathe-like cutters, which are run downhole on e-line. These tools require high levels of DC power to be supplied in order to provide the rotational power coupled with the applied force needed to cut through the wall of a downhole tubular member. The use of e-line provides the tool with effectively unlimited power during cutting operations to cut through the target. However, e-line operations require personnel to have higher levels of training to operate tools powered this way due to, for example, increased risks associated with the high voltages supplied.

Such conventional cutting tools can take some time to get through the wall of the tubular member, with higher heat generation and increased power demands the longer a cutting operation goes on. In particular, conventional cutting tools can produce swarf and/or splaying at the edges of the cuts which can interfere with subsequent operations.

Additionally, current cutting tools must be sent downhole with pre-determined settings and may require several trips to the target location to complete the cutting operation if a change in operation parameters is required (for example setting incremental increases to the maximum radial extension of the cutting device to allow it to cut further into the tubular wall).

Due to the limitations with conventional cutting tools it would be beneficial to provide a cutting tool with an alternative power supply that does not need to be run in on e- line, and therefore does not have the additional onerous training requirements. This would allow a far greater number of operators to use such a tool. It would also be beneficial to provide as compact a cutting tool (in terms of its longitudinal length) as possible. More compact tools are desired by operators as they typically reduce the cost and time involved in the running in/pulling out of the wellbore.

Additionally, further improvements in terms of the performance of conventional cutting tools, and also in terms of reducing the costs of such conventional cutting tools, would be highly desirable, particularly given the need in the oil and gas industry to reduce costs wherever possible.

SUMMARY OF THE INVENTION

According to the present invention there is provided a cutting tool for use in an oil or gas well, the cutting tool comprising: a battery powered motive assembly, wherein operation of the motive assembly rotates a drive shaft and modifies fluid pressure within the cutting tool; wherein the drive shaft is configured to rotate a cutting wheel assembly; wherein the cutting wheel assembly comprises a cutting wheel configured to rotate around an axis; and wherein the cutting wheel is actuatable to move radially in response to modification of the fluid pressure.

Optionally the motive assembly comprises a battery pack and a motor. Optionally the motive assembly comprises a power control module (PCM) comprising a battery pack and a motor. Optionally the motive assembly comprises a gearbox. Optionally the motive assembly comprises a PCM comprising a battery pack, an electric motor, and a gearbox.

The PCM, motor, and gearbox can be any kind that are configured to work with a linear actuator. Preferred examples of the PCM, motor, and gearbox are described in WO2019/180462A1, the full contents of which are incorporated herein by reference, and which are manufactured by and available for purchase from Kaseum®, Aberdeen, UK. The PCM may be used as the sole power source for the cutting tool. In other words, the cutting tool may be entirely powered by the battery pack within the PCM.

Accordingly, the cutting tool may advantageously be run in on e-line, slickline, slick e-line, wireline, or any other suitable kind of conveyance method. Optionally, if the cutting tool is run in on e-line, the e-line may be utilised as a means of transmitting commands and/or data between the tool and the surface of the wellbore into which the tool is run. Alternatively, the tool may be pre-programmed with, for example, timing operations that instruct the tool to e.g. start the motor, without necessarily requiring any instructions or signals to be sent from the surface.

Advantageously the use of a battery pack as the sole power source rather than powering the tool through e-line means that there is no requirement for a power convertor. Ordinarily a power convertor would be used to supply power via e-line to the motor, but the use of a battery pack means that the tool can operate regardless of power conversion status.

In particular, the battery pack within the PCM can selectively provide electrical power to an electric motor within the motor sub-assembly. Optionally when power is supplied to the electric motor the motor begins to rotate.

The electric motor may be connected via a first end of an input shaft to the gearbox. Rotation of the motor can rotate the input shaft, and thereby the gearbox. Optionally the input shaft is coupled at its second end with the drive shaft. Optionally the input shaft is coupled at its second end to a drive coupling assembly. Optionally the drive coupling assembly is coupled to the drive shaft. Optionally the rotational movement of the electric motor is transmitted through the gearbox and drive coupling to the drive shaft, which in turn rotates.

Optionally the drive shaft is part of a rotary assembly that further comprises a linear actuator. Optionally the rotary assembly also further comprises a piston, optionally a hydraulic piston.

Preferably the linear actuator comprises a lead screw and lead screw nut, but this is not limiting and alternative arrangements of linear actuators may be used. For example alternatively the linear actuator may comprise a ball screw and ball nut (where lead screw, lead screw nut, and lead screw assembly are used in this disclosure, these terms can be substituted with ball screw, ball nut, and ball screw assembly, and vice versa unless otherwise stated). Optionally the lead screw assembly comprises a housing, a lead screw and a lead screw nut.

Optionally the drive shaft comprises at least one clutch.

Optionally the clutch may be a slip clutch, for example in the form of at least one tolerance ring on an outer surface of the shaft. Optionally the at least one tolerance ring is a circlip, or alternatively a complete ring. Optionally the at least one tolerance ring comprises circumferential projections such as ridges, or a wave-like structure. Optionally the drive shaft comprises portions having projections such as ridges or waves on the drive shaft’s outer surface, where the projections of the drive shaft portions correspond to the projections of the tolerance ring. Optionally the engagement between the projections of the tolerance ring and the drive shaft retain the tolerance ring(s) in position.

Optionally the tolerance ring(s) provide frictional force between the drive shaft and a lead screw within a lead screw assembly. Optionally the tolerance ring(s) are press- fitted between the drive shaft and the lead screw. Optionally the slip clutch utilises spring force to press outwards against the inner surface of the lead screw and thereby provide a frictional force. Optionally the slip clutch is configured to allow the drive shaft and lead screw to rotationally slip with respect to each other when a threshold level of torque is provided by the drive shaft. Optionally the slip clutch is configured so that when the threshold level of torque is reached, it exceeds the spring force of the slip clutch and thereby allows relative movement between the drive shaft and the lead screw. Optionally, when a maximum pressure is reached within the cutting tool, the slip clutch allows the drive shaft and lead screw to slip past each other as described in more detail below.

Optionally the clutch may be an alternative torque-limiting clutch, for example a synchronous torque-limiting clutch, and alternatively arranged in a different configuration within the cutting tool. One suitable clutch may be the EAS®-smartic® clutch from Mayr®, Mauerstetten, Germany. Optionally, instead of being arranged between the drive shaft and the lead screw, the clutch may be disposed at one end of the rotary assembly. Optionally the clutch is at least partially engaged with the drive shaft, for example the clutch may be clamped to a portion of the drive shaft. Optionally an end of the clutch is configured to engage with the lead screw. Optionally the clutch is attached, optionally fixedly attached, to an adapter that is arranged between the clutch and the lead screw, and which is optionally configured to engage the lead screw. Optionally an end of the adapter comprises protrusions which inter-engage with castellations on the corresponding end of the lead screw.

Optionally the clutch is configured to slip at a predetermined threshold level of torque (for example, within the range 10-50 Nm, but this can be set as required). Initially, the clutch acts to rotate the drive shaft and the lead screw together. Once the threshold level of torque is reached and/or exceeded, the clutch is configured to slip and thereby allow relative movement between the drive shaft and the lead screw. As above, optionally when a maximum pressure is reached within the cutting tool, the clutch allows the drive shaft and lead screw to slip past each other as described in more detail below.

Optionally the lead screw comprises a throughbore through which the drive shaft of the linear actuator passes. Optionally the drive shaft and the lead screw are coaxially arranged. Optionally the lead screw surrounds at least a portion of the length of the drive shaft.

Optionally as the drive shaft rotates, the engagement with the lead screw results in rotation of the lead screw at the same time. Optionally the lead screw comprises a threaded portion on its outer surface. Optionally the whole outer surface of the lead screw may be threaded. Alternatively, the lead screw may be at least partially threadless.

Optionally the lead screw nut comprises a throughbore, and the lead screw nut surrounds at least a portion of the lead screw such that at least a portion of the length of the lead screw is located within the throughbore of the lead screw nut, and optionally the lead screw nut, lead screw, and drive shaft are coaxial with an axis of the cutting tool.

Optionally an inner surface of the lead screw nut comprises a threaded portion. Optionally the threaded portion of the lead screw nut engages the threaded portion of the lead screw and is optionally complementary to the threaded portion of the lead screw.

Where a ball screw assembly is used, optionally the threaded section of the ball nut, together with the ball screw, forms a raceway for bearings, preferably ball bearings. Optionally the ball nut further comprises a recirculation mechanism to recirculate the ball bearings.

Optionally as the drive shaft rotates, the lead screw is in turn rotated due to the frictional engagement with the tolerance ring(s) of the drive shaft. As the lead screw rotates, the lead screw nut moves axially along the lead screw.

Optionally the rotary assembly is balanced to well pressure. Optionally the rotary assembly is configured to convert rotary motion to fluid pressure, optionally hydraulic pressure.

Optionally the lead screw nut is coupled at an end, optionally its lower end (i.e. the end of the lead screw nut that is closer to the cutting wheel assembly) to the piston. Optionally the lead screw nut and piston are in a locking arrangement. Optionally the lead screw nut and piston are connected together by screws or other fixings.

Optionally the piston comprises a central bore of a first inner diameter. Optionally an end of the piston comprises an aperture of a second inner diameter smaller than the first inner diameter. The aperture is optionally dimensioned to allow the drive shaft to pass through the aperture. The aperture optionally further comprises at least one inner seal, optionally an annular seal such as an o-ring. Optionally the or each inner annular seal is at least partially disposed in a recess formed in the inner surface of the aperture. Optionally the seal creates a sealing engagement between the aperture and the drive shaft. Optionally the o-ring acts to resist fluid ingress to or egress from either side of the piston. Optionally there is a piston chamber within the rotary assembly, between the hydraulic piston and the cutting wheel assembly and/or the anchor module. This piston chamber may comprise the fluid that is to be compressed by the hydraulic piston.

Optionally as the lead screw nut moves axially the piston travels with the lead screw nut due to the locking arrangement. Optionally as the gearbox rotates in one direction (for example, counterclockwise), the lead screw nut travels in an axial direction towards the cutting wheel assembly. Optionally as the gearbox rotates in the opposing direction (for example, clockwise) the lead screw nut travels axially away from the cutting wheel assembly.

Optionally the piston comprises at least one seal, optionally an annular seal, e.g. an o-ring, on the outer surface of the piston. Optionally the or each outer annular seal is at least partially disposed within a recess formed in the outer surface of the piston. Optionally the piston further comprises at least one seal, optionally an annular seal, in an inner surface of the piston. Optionally the at least one seal on the inner surface of the piston is in sealing engagement with the drive shaft.

Optionally the housing of the lead screw assembly comprises at least one annular groove formed on its inner surface. Optionally the housing of the lead screw assembly comprises at least a first and a second annular groove formed on its inner surface. Optionally the first and second annular grooves are axially spaced apart. Optionally the housing of the lead screw assembly comprises a section with a more narrow inner diameter disposed between the first and second annular grooves. Optionally the piston chamber comprises a more narrow inner diameter than the first and/or second annular grooves. Optionally the inner diameter of the piston chamber is the same as the inner diameter of the section of the lead screw housing between the first and second annular grooves.

Optionally the piston is initially aligned with the second annular groove before any movement of the piston occurs. Optionally as the lead screw nut travels axially and moves the piston, the piston moves past the second annular groove into the piston chamber. Optionally the outer annular seal on the outer surface of the piston is in sealing engagement with the inner surface of the piston chamber.

Optionally the drive shaft comprises a splined end. Optionally the splined end is configured to connect to the cutting wheel assembly. Optionally the cutting wheel assembly comprises a corresponding splined aperture into which the splined end of the drive shaft is inserted. Optionally the splined engagement between the drive shaft and the cutting wheel assembly transmits the rotation of the drive shaft to the cutting wheel assembly. In other words, the drive shaft and the cutting wheel assembly are rotationally engaged, so that when the drive shaft is rotated (in either direction) the cutting wheel assembly also rotates. Optionally the rotation of the cutting wheel assembly is around a longitudinal axis of the cutting tool.

Alternatively, the cutting wheel assembly may comprise a ratchet and pawl arrangement. Optionally the pawl(s) may be narrower at one end, optionally the end that engages the ratchet, and optionally thicker at the opposite end. Optionally the pawl(s) may be paddle- or blade-shaped. Optionally the one or more pawls are each held within or adjacent to a cavity formed within the cutting wheel assembly. Optionally the cavity comprises a biasing device. Optionally the biasing device is configured to bias the or each pawl towards the drive shaft of the tool.

Optionally the drive shaft comprises ridges or teeth that are configured to engage with at least one pawl in the cutting wheel assembly. Optionally the end of the drive shaft acts as a ratchet. Optionally the ridges or teeth on the end of the drive shaft are configured to rotate past the at least one pawl when rotated in one direction, and configured to engage with the at least one pawl when rotated in the other direction. Optionally, engagement of the at least one pawl with the ridges/teeth on the end of the drive shaft drives rotation of the cutting wheel assembly when the drive shaft is rotated in a first direction.

Optionally rotation of the drive shaft in a second direction opposite to the first direction leads to the drive shaft slipping or freewheeling past the at least one pawl. Optionally the or each pawl is pushed against the biasing device by the ridges/teeth on the drive shaft as it passes the or each pawl. Optionally the or each pawl may be hinged or similarly fixed to the cutting wheel assembly, and optionally arranged so that as the drive shaft moves past the or each pawl, a free end of the or each pawl moves in an arc within the cavity. This allows the drive shaft to rotate without corresponding rotation of the cutting wheel assembly. Optionally rotation of the drive shaft in the second direction retracts the hydraulic piston through reversal of the direction of travel of the linear actuator.

The ratchet and pawl arrangement offers the advantage that should the cutting wheel/cutting wheel assembly become trapped, or stalled, in the well bore, the drive shaft can be rotated in the second direction such that the piston is retracted and fluid pressure within the tool is reduced. Once the fluid pressure is relieved, in the case that the cutting wheel is trapped, the cutting wheel can be jarred to free the tool from the tubular and allow retrieval of the tool back to the surface.

Optionally the cutting tool further comprises an anchor module, optionally disposed between the rotary assembly and the cutting wheel assembly. Optionally the anchor module is in fluid communication (optionally selective fluid communication) with the rotary assembly and/or the cutting wheel assembly. Optionally the anchor module comprises a plurality of anchors. Optionally the anchors are symmetrically arranged around the circumference of the anchor module. Alternatively the anchors may be disposed in another part of the cutting tool.

Optionally the anchors are in the form of grooved buttons that move radially outwards from the tool, for example from the anchor module, to anchor the cutting tool. Alternatively the anchors may be anchor pads. Optionally the anchor pads or buttons are disposed radially around the anchor module, optionally in a symmetrical arrangement. Optionally the anchors are actuated by fluid pressure that builds up within the anchor module due to the movement of the piston. Optionally the anchors are configured to engage with the inner surface of the target tubular that is to be cut, e.g. casing, lining etc..

The anchors are configured to rotationally fix the cutting tool relative to the target tubular, allowing rotation of the cutting wheel while resisting rotation of the rest of the tool during cutting operations. Optionally the anchor module comprises an anchor module pressure relief valve, and optionally a check valve. Optionally the cutting wheel assembly comprises the anchor module pressure relief valve, and optionally the check valve.

Optionally the anchor module pressure relief valve resists fluid communication between the anchor module and the cutting wheel assembly when the pressure within the anchor module is under a first pre-determined threshold. Optionally the anchors are configured to radially extend at a pressure greater than zero but less than the first pre-determined threshold. This offers the advantage that the anchors are deployed and in place prior to commencement of a cutting operation as further described below.

Optionally the first pre-determined threshold may be within the range of 100-1000 psi (or greater than or equal to 100 psi; or less than or equal to 1000 psi). In this example of the invention, this broad range encompasses suitable pressures appropriate for the first pre-determined threshold, and at which the anchors can be deployed. Optionally the first pre-determined threshold may be within the range of 100-500 psi (or greater than or equal to 100psi; or less than or equal to 500 psi), which encompasses pressures at which the first pre-determined threshold is preferably set and where the anchors can be deployed. Optionally, the first predetermined threshold may be within the range of 100-300 psi (or greater than or equal to 100psi; or less than or equal to 300psi). This range is particularly suitable for deploying the anchors prior to commencing cutting operations.

Optionally as the lead screw is rotated and the piston moves towards the cutting wheel assembly, the pressure behind the anchor module pressure relief valve increases. Once the pressure exceeds the first pre-determined threshold, fluid may begin to pass through the anchor module pressure relief valve into the cutting wheel assembly.

Optionally as fluid flows into the cutting wheel assembly, the fluid pressure within the cutting wheel assembly increases. Optionally the fluid pressure increases to a second pre-determined threshold, where the second pre-determined threshold is higher than the first pre-determined threshold. Optionally the second pre-determined threshold may be within a range of 200-1500 psi (or greater than or equal to 200 psi; or less than or equal to 1500 psi). This broad range encompasses pressures that are suitable for radially extending the cutting wheel and applying force for cutting operations. Optionally the second pre-determined threshold may be within a range of 400-1200 psi (or greater or equal to than 400 psi; or less than or equal to 1200 psi). This range encompasses pressures that are suitable for radially extending the cutting wheel and applying force for cutting operations. Optionally the second predetermined threshold may be within a range of 800-1200 psi (or greater than or equal to 800 psi; or less than or equal to 1200 psi). This range is particularly useful for cutting operations due to the force provided to the cutting wheel by these fluid pressures (and/or the difference in potential pressure between the first and second pre-determined pressure thresholds allowing the anchors to be deployed at a relatively low pressure, and the second pre-determined threshold to be set at a suitably high pressure).

Optionally when the fluid pressure reaches the second pre-determined threshold, the clutch is configured to permit the drive shaft to effectively disengage from the lead screw, so that the drive shaft may rotate without further rotation of the lead screw as described above. Optionally when the clutch is activated and the drive shaft and lead screw lose mutual frictional force, the fluid pressure within the cutting wheel assembly may reduce (due to increased volume as the cutting wheel and rollers extend radially outwards), or optionally it may stay at or very close to the second predetermined threshold.

Advantageously, by preventing fluid pressure within the cutting wheel assembly exceeding the second pre-determined threshold, the risk of damage to the cutting tool or more particularly to the cutting wheel itself (for example stalling or breakage of the wheel) is significantly reduced. Furthermore, the fluid pressure is maintained at a sufficiently high level to allow the cutting wheel to engage with the tubular that is to be cut - if the fluid pressure was too low, the cutting wheel may not apply sufficient pressure to the tubular and the cutting process could be detrimentally affected.

Alternatively, the tool may not comprise an anchor module pressure relief valve or check valve, and there may be a single pre-determined pressure threshold, at which the drive shaft and lead screw disengage. Optionally the anchors may be actuated at the same time as the cutting wheel and cutting wheel housing.

Alternatively, in addition to, or instead of, a clutch, the cutting tool may comprise a piston pressure relief valve (PRV) to control pressure within the tool. Optionally the piston PRV is located at a distal end of the piston. Optionally the piston PRV extends parallel to the longitudinal axis of the cutting tool. Optionally the piston PRV is disposed within a wall of the piston. Optionally the piston PRV controls fluid communication between the piston chamber and the rotary assembly.

Where the piston PRV is used in place of a clutch mechanism, the lead screw may be fixedly attached to the drive shaft. For example, the lead screw may be attached by screws or other fixings that extend radially at least partially into the drive shaft. Optionally, every complete rotation of the drive shaft advances the piston by a distance equivalent to the pitch of the lead screw.

Optionally the piston PRV is configured to maintain a constant pressure that is fed to the anchor and cutting wheel assembly. Optionally the required pressure may be within a range of 200-1500 psi, for example 800-1200 psi. Optionally the required pressure is set to a particularly preferred value, for example: 1000 psi; 1100 psi; or 1200 psi. Optionally, should the fluid pressure within the piston chamber exceed the pre-determined pressure, the piston PRV opens and optionally, fluid vents from the piston chamber into the central bore of the piston, and/or into a space between the piston and the lead screw assembly housing.

Optionally the cutting wheel assembly comprises at least one roller. Optionally the at least one roller is configured to stabilise, optionally to centralise the cutting wheel assembly. Optionally the at least one roller eases rotation of the cutting wheel assembly. Optionally the at least one roller is disposed opposite to the cutting wheel. Optionally the or each roller comprises a roller wheel that rotates around a roller axle. Optionally the axle is aligned with an axis of the cutting tool. Optionally the roller axle comprises bearings to facilitate rotation.

Optionally the, or each, roller wheel and roller axle are disposed within a roller housing. Optionally the, or each, roller housing is movable, optionally radially movable. Optionally the cutting wheel assembly comprises a chassis in which the cutting wheel and the, or each, roller wheel are disposed. Optionally the or each roller housing is disposed within a cavity or cavities, hereafter the roller cavity/cavities formed in the chassis of the cutting wheel assembly. Optionally the or each roller comprises at least one resilient device configured to bias the roller housing towards a retracted configuration and to resist radial extension of the or each roller.

Optionally there is a fluid pathway from the anchor module pressure relief valve and/or the check valve to the or each roller cavity. Optionally there is no anchor module pressure relief valve or check valve and pressure is controlled via the clutch and/or the piston PRV.

Optionally as fluid pressure builds up in the anchor module and/or the cutting wheel assembly, fluid may flow into the or each roller cavity. Optionally, as the fluid flows into the or each roller cavity, the fluid pressure pushes against the or each roller housing. Optionally as the fluid pressure increases the biasing effect of the resilient device or devices is overcome and the or each roller housing may move radially outwards. Optionally as the roller housing moves radially outwards the roller wheel housed therein then extends beyond the circumference of the cutting wheel assembly chassis and may make contact with the inner surface of the target tubular that is to be cut.

Optionally the cutting wheel assembly comprises two roller wheels that are arranged to be directly opposite the cutting wheel, and positioned such that the roller wheels are on either side of the cutting axis of the cutting wheel. In other words, the roller wheels may optionally be arranged to make contact with the inner surface of the target tubular on either side of any cut that is made to the tubular.

Optionally the cutting wheel is mounted on a cutting wheel axle within a cutting wheel housing. Optionally the cutting wheel axle is aligned with the longitudinal axis of the cutting tool. Optionally the cutting wheel is configured to rotate around the cutting wheel axle. Optionally the cutting wheel axle comprises bearing to facilitate rotation. Optionally the cutting wheel, cutting wheel axle, and cutting wheel housing are disposed in a further cavity, hereafter the cutting wheel cavity. Optionally there is a fluid pathway from the pressure relief valve and/or the check valve to the cutting wheel cavity. Optionally as fluid pressure builds up in the anchor module and/or the cutting wheel assembly, fluid may flow into the or each cutting wheel cavity. Optionally, as the fluid flows into the or each cutting wheel cavity, the fluid pressure pushes against the cutting wheel housing and moves the cutting wheel housing radially outwards. As the cutting wheel housing moves radially outwards, the cutting wheel housed therein then extends beyond the circumference of the cutting wheel assembly chassis to make contact with the inner surface of the target tubular that is to be cut.

Optionally the cutting wheel housing (and therefore the cutting wheel) is extended radially outwards incrementally. Optionally the cutting wheel is moved radially outwards by a first increment under fluid pressure. Optionally as the fluid pressure continues to increase beyond the (optionally second) pre-determined pressure threshold, the clutch (e.g. slip clutch) and/or the piston PRV activates and the pressure reduces, or optionally remains at a constant level. Optionally the cutting wheel housing remains substantially at the position of the first increment as the fluid pressure falls.

The position of the first increment may be sufficient to begin making a first cut in the wall of the tubular. Optionally the cutting wheel extends at least partially into the wall of the tubular. As the cutting wheel assembly rotates around the axis of the cutting tool, the cutting wheel also rotates around the cutting wheel axle. Optionally as the cutting wheel assembly rotates around the axis of the cutting tool, the cutting wheel can thereby make a first 360 degree cut at least partially into the wall of the tubular.

Optionally, as the pressure reduces below the (optionally second) pre-determined threshold the drive shaft and the lead screw re-engage and the fluid pressure increases again as the piston begins axial movement towards the cutting wheel assembly and/or anchor module. The increased fluid pressure optionally moves the cutting wheel housing radially outwards by a second increment.

As the second incremental position optionally extends the cutting wheel housing (and therefore the cutting wheel) further radially outwards from the cutting wheel assembly, the cutting wheel can then cut further into the wall of the tubular to form a deeper 360 degree cut in the wall of the tubular.

Optionally as the fluid pressure again continues to increase beyond the (optionally second) pre-determined threshold, the slip clutch/clutch/piston PRV activates once more and the pressure reduces slightly, or optionally remains at a constant level. Optionally continued radial extension of the cutting wheel and the rollers acts to increase the volume available to fluid within the cutting wheel assembly, which stabilises the fluid pressure. Optionally the housing of the cutting wheel remains substantially at the position of the second increment as the fluid pressure falls. Optionally the housing of the cutting wheel continues to extend outwards in response to the fluid pressure and as the cut being made by the cutting wheel deepens, allowing the cutting wheel to dig further into the wall of the tubular.

This process may optionally repeat until the cutting wheel has fully cut through the wall of the tubular in a 360 degree cut to sever the tubular.

Optionally the cutting tool can be pre-programmed with, for example, a running time that has been pre-determined to provide sufficient time to complete the cutting operation.

When the cutting operation is completed and the cutting tool is to be retrieved from the wellbore, optionally the cutting wheel and the roller wheel(s) can be retracted. Optionally, to achieve this, the rotary assembly can change from a driving configuration to a retraction configuration.

Where the drive shaft comprises a splined end that engages with a splined aperture in the cutting wheel assembly, reversal of the direction of rotation of the drive shaft rotates the cutting wheel assembly in the same direction. In the example of the invention comprising a ratchet and pawl arrangement, reversal of the drive shaft disengages the cutting wheel assembly from the drive shaft and the drive shaft rotates independently of the cutting wheel assembly.

Optionally, in the retraction configuration, the direction of rotation of the drive shaft is reversed. Due to the slip clutch providing a frictional force between the drive shaft and the lead screw, optionally the reversal of rotation of the drive shaft similarly reverses the rotation of the lead screw. The lead screw nut then optionally moves axially in a direction away from the cutting wheel assembly/anchor module. Optionally the hydraulic piston is coupled to the lead screw nut, and the axial travel of the lead screw nut optionally also causes the hydraulic piston to retract from the cutting wheel assembly or anchor module. Optionally as the piston retracts, the volume of the piston chamber within the rotary assembly increases. Optionally as the piston retracts, it passes over the second annular groove which permits fluid passage past the piston. Optionally the piston then passes through the more narrow section of the housing between the first and second annular grooves and reseals against the inner surface of the housing. Optionally, the piston continues to be retracted until the seals of the piston are aligned with the first annular groove. Optionally alignment with the first annular groove allows fluid to move in the space formed between the outer annular seal and the first annular groove. Optionally, once the piston has aligned with the first annular groove, it cannot then be returned to the second annular groove and must be reset at the surface.

Optionally when the cutting tool comprises a piston PRV, when cutting operations are completed and the rotation of the drive shaft is reversed, fluid may be vented in the return direction by the piston. For example the piston may comprise a unidirectional lip seal which permits venting of fluid in the return direction. In this example, when the piston is retracted, the venting of the fluid past the piston seal (and/or through the PRV) offers the advantage that large forces do not build up in the retraction phase of the tool, which may lead to damage to components of the tool.

Optionally, as the piston moves away from the cutting wheel assembly/anchor module, the fluid pressure behind the piston (and in the anchor module/cutting wheel assembly) reduces. Optionally the fluid flows through the check valve into the piston chamber within the rotary assembly. As the fluid pressure reduces in the cutting wheel assembly, the roller(s) and the cutting wheel retract into the chassis of the cutting wheel assembly. The retraction of the cutting wheel and the roller(s) acts to reduce the risk of the cutting tool getting stuck downhole, which would then necessitate intervention measures with the associated loss of operative time and costs. Alternatively, the cutting wheel assembly may comprise a resilient device or devices such as a spring return mechanism configured to retract the cutting wheels. The use of resilient devices biased towards retraction of the cutting wheels may be useful in shallow cut applications, where there is little/no hydrostatic pressure to assist with the retraction of the cutting wheels.

Optionally, when the rotary assembly is in the retraction configuration, and the cutting wheel assembly is being retracted, the first pre-determined threshold is also the maximum pressure difference tolerated during retraction. Optionally during retraction the check valve may permit fluid to flow freely between the cutting wheel assembly and the anchor module. Optionally the check valve is set to a very low pressure such as around 1-5 psi, for example 2 psi, in which case fluid may flow freely through the check valve as soon as the pressure within the anchor module and/or cutting wheel assembly exceed this very low pressure. This may ensure that all hydraulics/pneumatics bleed simultaneously during retraction of the cutting wheel assembly (and subsequently, retraction of the anchors), reducing the risk of a large pressure differential forming and potentially damaging the tool.

Optionally, the pressure within the tool, and more particularly the pressure applied by the piston, is regulated by one or more of the clutch, the pressure relief valve, and the reversible actuator.

Optionally, the tool comprises a shear relief arrangement that allows for emergency venting of the tool should the tool fail. Optionally the shear relief arrangement may be disposed at an end of the anchor module. Optionally, the shear relief arrangement may comprise one or more frangible fasteners, optionally threaded fasteners such as shear screws. Optionally the frangible fasteners pass through apertures in an end of the lead screw assembly housing and into the end of the anchor module connected to the end of the lead screw assembly housing (where optionally the anchor module fits within the inner diameter of the lead screw assembly housing). Optionally the frangible fasteners partially extend into the wall of the anchor module.

Optionally the shear relief arrangement further comprises a spin collar located in a recess formed by the connection between the anchor module and the lead screw assembly housing. Optionally the lead screw assembly housing comprises a milled end forming external and internal recesses in the end of the lead screw assembly housing when the connection with the anchor module is made up. Optionally the spin collar is arranged to encircle the end of the lead screw assembly housing and optionally sit within the external recess in the housing. Optionally the shear relief arrangement further comprises a snap ring which is arranged to encircle the end of the anchor module and optionally sit within the internal recess formed by the end of the lead screw assembly housing. Optionally the internal recess is wider, in an axial direction, than the snap ring. Optionally the snap ring is arranged such that it is at the end of the internal recess closest to the anchor module in the ordinary configuration of the shear relief arrangement.

The end of the anchor module optionally further comprises an annular seal, e.g. an o-ring, disposed within a groove around the outer circumference of the anchor module. The annular seal is optionally located adjacent to the frangible fasteners, optionally on the opposite side of the frangible fasteners to the spin collar and snap ring.

Optionally, in the event that the tool fails - for example it stalls, or it becomes trapped or jammed in the tubular - the tool can be jarred upwards (towards the surface). Jarring the tool breaks the frangible fasteners between the lead screw assembly housing and the anchor module. Optionally the lead screw assembly housing can then move relative to the anchor module. Optionally the lead screw assembly housing moves partially axially away from the anchor module while remaining connected to the anchor module. Optionally the shear relief arrangement including the snap ring and the spin collar moves with the lead screw assembly housing in an uphole direction. Optionally the aperture through the lead screw assembly housing in which the frangible fastener is disposed at least partially aligns with the annular seal around the end of the anchor module, unseating the annular seal from the groove. This allows venting of the fluid within the tool into the wellbore. Where the cutting wheel and rollers comprise resilient devices such as springs, these resilient devices bias the cutting wheel and rollers to radially retract into the cutting wheel assembly. Similarly, the anchor buttons and/or pads may comprise resilient devices to bias the anchor buttons and/or pads to radially retract into the anchor module. The tool may then be recovered to surface. Optionally, the current being provided to the tool by the battery pack can be monitored during the cutting operation. In some circumstances, for example when the tubular is in compression or moves during the cutting operation, this too may result in the cutting wheel being trapped or jammed in the tubular. This can be detected by a spike in the current to the tool (for example, 1-2A during ordinary usage rapidly spiking to 3-5A).

Continuing to increase fluid pressure and apply force to the cutting wheel in the event that the cutting wheel has jammed is undesirable, as this could lead to damage to the tool. Optionally, therefore, a threshold value for the current is pre-set (optionally within the tool, for example within the PCM). Optionally, when the current exceeds the predetermined threshold, rotation of the motor is reversed for a first predetermined period. In particular, where a ratchet and pawl arrangement is used in the cutting wheel assembly as described above, the first predetermined period may be set such that the drive shaft rotates past the nearest pawl. As an example, if three pawls are spaced equidistantly around the drive shaft, the drive shaft may optionally be set to rotate in the reverse direction by a first time period that equates to rotation of 120 degrees to pass a first adjacent pawl.

Optionally, reversal of the motor, and therefore reverse rotation of the drive shaft, reduces fluid pressure within the tool due to retraction of the piston. Optionally, reduction in fluid pressure allows the cutting wheel to retract at least partially. Optionally, reversal of the motor and drive shaft reduces the force applied by fluid pressure on the cutting wheel.

Optionally, once the first predetermined period has ended and the drive shaft has optionally passed an adjacent pawl, the cutting operation may be restarted. Optionally, there may be an additional period of time after completion of the first predetermined period, but before the cutting operation restarts, where no rotation is occurring. Including a rest period between changes in rotational direction may advantageously help to protect the motor and prolong its operational lifetime.

Alternatively, if the cutting wheel remains jammed after completion of the first predetermined period, a second predetermined period of reversed rotation can be carried out. Optionally, the second predetermined period is of the same length of time as the first predetermined period. Optionally, the drive shaft may optionally be set to rotate in the reverse direction by a second time period that may optionally equate to sufficient rotation to pass a second pawl (for example, in the three-pawl arrangement, a further 120 degrees of rotation).

This process can be repeated as often as necessary to free the cutting wheel and either restart cutting operations or, alternatively, recover the tool.

According to the present invention there is provided a method for cutting a tubular in an oil or gas well, the method comprising: deploying a cutting tool into the wellbore to the depth at which the tubular is to be cut, wherein the cutting tool comprises: a battery powered motive assembly, wherein operation of the motive assembly rotates a drive shaft and modifies fluid pressure within the cutting tool; and a cutting wheel assembly comprising a cutting wheel; the method further comprising: rotating the drive shaft and thereby rotating the cutting wheel assembly; rotating the cutting wheel around an axis; and actuating the cutting wheel to radially move the cutting wheel in response to modification of the fluid pressure.

Optionally the cutting wheel is disposed within a housing. Optionally the housing is configured to move radially in response to modification of fluid pressure. Optionally radial movement of the housing thereby radially moves the cutting wheel.

Optionally the method includes, in a first configuration, rotationally engaging the drive shaft and the cutting wheel assembly such that rotation of the drive shaft rotates the cutting wheel assembly. Optionally the method includes, in a second configuration, disengaging the drive shaft and the cutting wheel assembly such that rotation of the drive shaft does not rotate the cutting wheel assembly.

Optionally the drive shaft forms part of a rotary assembly, the rotary assembly further comprising a linear actuator, and wherein the drive shaft comprises at least one clutch, and further optionally the method includes rotating the drive shaft and the linear actuator together until a predetermined threshold of torque is reached. Optionally, the method includes configuring the clutch to slip when said predetermined threshold level of torque is reached, allowing relative movement between the drive shaft and the linear actuator.

Optionally the rotary assembly further comprises a piston configured to move axially with the linear actuator, and the method further includes converting rotary motion to fluid pressure through axial movement of the piston.

Optionally the method includes disposing a piston chamber between the piston and the cutting wheel assembly, the cutting wheel assembly being in fluid communication with the piston chamber. Optionally the method includes increasing the fluid pressure within the cutting wheel assembly by compressing fluid within the piston chamber. Optionally, the method includes radially extending the cutting wheel assembly when the fluid pressure within the cutting wheel assembly reaches a predetermined threshold.

Optionally, the drive shaft and cutting wheel assembly rotationally engage when the drive shaft is rotated in a first direction, and rotationally disengage when the drive shaft is rotated in a second direction.

Optionally the method includes at least partially retracting the cutting wheel by: rotating the drive shaft in the second direction, thereby reversing the axial movement of the linear actuator; retracting the piston; and decreasing fluid pressure within the cutting wheel assembly.

Optionally the method includes at least partially cutting a wall of the tubular by rotating the cutting wheel assembly while the cutting wheel assembly is radially extended within the tubular.

Optionally the method includes radially extending the cutting wheel in predetermined increments.

Optionally the method includes anchoring the cutting tool within the tubular to restrict relative movement of the cutting tool. The accompanying drawings illustrate presently exemplary embodiments of the disclosure and together with the general description given above and the detailed description of the embodiments given below, serve to explain, by way of example, the principles of the disclosure.

In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawings are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. Specific embodiments of the present invention are shown in the drawings, and herein will be described in detail, with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce the desired results.

The following definitions will be followed in the specification. As used herein, the term "wellbore" refers to a wellbore or borehole being provided or drilled in a manner known to those skilled in the art. The wellbore may be ‘open hole’ or ‘cased’, being lined with a tubular string. Reference to up or down will be made for purposes of description with the terms "above", "up", "upward", "upper" or "upstream" meaning away from the bottom of the wellbore along the longitudinal axis of a work string toward the surface and "below", "down", "downward", "lower" or "downstream" meaning toward the bottom of the wellbore along the longitudinal axis of the work string and away from the surface and deeper into the well, whether the well being referred to is a conventional vertical well or a deviated well and therefore includes the typical situation where a rig is above a wellhead and the well extends down from the wellhead into the formation, but also horizontal wells where the formation may not necessarily be below the wellhead. Similarly, ‘work string’ refers to any tubular arrangement for conveying fluids and/or tools from a surface into a wellbore. In the present invention, e-line, slick e-line, slickline or wireline is the preferred work string. The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one embodiment can typically be combined alone or together with other features in different embodiments of the invention. Additionally, any feature disclosed in the specification can be combined alone or collectively with other features in the specification to form an invention.

Various embodiments and aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary embodiments and aspects and implementations. The invention is also capable of other and different embodiments and aspects and its several details can be modified in various respects, all without departing from the scope of the present invention as defined by the claims.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

Accordingly, the drawings and descriptions are to be regarded as illustrative in nature and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including", "comprising", "having" "containing" or "involving" and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents and additional subject matter not recited and is not intended to exclude other additives, components, integers or steps. In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of”, "consisting", "selected from the group of consisting of”, “including” or "is" preceding the recitation of the composition, element or group of elements and vice versa. In this disclosure, the words “typically” or “optionally” are to be understood as being intended to indicate optional or non-essential features of the invention which are present in certain examples but which can be omitted in others without departing from the scope of the invention as defined by the claims.

All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein including (without limitations) components of the downhole tool are understood to include plural forms thereof and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

Figure 1 shows a schematic end view of an example of a PCM which forms part of a cutting tool in accordance with the present invention;

Figure 2 shows a schematic cross-sectional representation of the PCM of Figure 2;

Figure 3 shows a schematic perspective, partially-exploded view of the PCM of Figures 1 and 2;

Figure 4 shows a schematic end view of an example of an electric motor which forms part of a cutting tool in accordance with the present invention;

Figure 5 shows a schematic cross-sectional representation of the electric motor of Figure 4;

Figure 6 shows a schematic perspective view of the electric motor of Figures 4 and 5;

Figure 7 shows a schematic end view of an example of a gearbox which forms part of a cutting tool in accordance with the present invention;

Figure 8 shows a schematic cross-sectional representation of the gearbox of Figure 7;

Figure 9 shows a schematic cross-sectional representation of a first example of a cutting tool in accordance with the present invention, where the cutting wheel assembly is in an extended configuration, the cutting tool comprising a power control module (PCM), electric motor, gearbox, rotary assembly (illustrated with a ball screw assembly in this example), anchor module, and cutting wheel assembly; Figure 10 shows a schematic cross-sectional representation of an example of a rotary assembly comprising a ball screw assembly, anchor module, and cutting wheel assembly which forms part of a cutting tool in accordance with the present invention, where the anchors have been energised and are in an extended configuration, and the cutting wheel assembly is also in an extended configuration;

Figure 11 shows a schematic view of the rotary assembly, anchor module, and cutting wheel assembly of Figure 10;

Figure 12 shows a schematic perspective view of the rotary assembly, anchor module, and cutting wheel assembly of Figures 10 and 11 ;

Figure 13 shows a schematic view of the rotary assembly comprising a slip clutch in the form of tolerance rings;

Figure 14 shows a schematic cross-sectional representation of the rotary assembly of Figure 13;

Figure 15 shows a further schematic cross-sectional representation of the rotary assembly of Figures 13 and 14;

Figure 16 shows a schematic cross-sectional representation of the rotary assembly of Figures 13-15;

Figure 17 shows a schematic perspective view of a drive shaft and tolerance rings which form part of the rotary assembly of Figures 13-16;

Figure 18 shows a schematic end view of an anchor module, with the anchors in the form of ridged or grooved anchor buttons, in an unextended “run-in hole” configuration;

Figure 19 shows a schematic cross-sectional representation of the anchor module of Figure 18;

Figure 20 shows a schematic end view of the anchor module of Figures 18 and 19, with the anchor buttons extended, in an “anchor deployed” configuration;

Figure 21 shows a schematic view of the anchor module of Figure 20;

Figure 22 shows a schematic cross-sectional representation of the anchor module of Figures 20 and 21 ;

Figure 23 shows a schematic perspective view of the anchor module of Figures 20- 22;

Figure 24 shows a schematic perspective view of an alternative example of an anchor module comprising anchor pads, in an extended “anchor deployed” configuration;

Figure 25 shows a schematic view of the anchor module of Figure 24; Figure 26 shows a schematic cross-sectional representation of the anchor module of Figures 24 and 25;

Figure 27 shows a schematic view of a cutting wheel assembly, the cutting wheel assembly comprising a pressure relief valve and check valve;

Figure 28 shows a schematic cross-sectional representation of the cutting wheel assembly of Figure 27, with the cutting wheel in a retracted, “run-in hole” configuration;

Figure 29 shows a schematic cross-sectional representation through the cutting wheel assembly of Figures 27 and 28;

Figure 30 shows a schematic cross-sectional representation through the cutting wheel assembly of Figures 27-29, with the cutting wheel in an extended “deployed” configuration;

Figure 31 shows a schematic cross-sectional representation of the cutting wheel assembly of Figure 30;

Figure 32 shows a schematic view of the pressure relief valve and check valve arrangement in the cutting wheel assemblies of Figures 27-31 ;

Figure 33 shows a schematic perspective view of a second example of a cutting tool in accordance with the present invention, comprising a torque-limiting clutch as part of the rotary assembly, illustrated in this example with a ball screw assembly;

Figure 34 shows a schematic cross-sectional representation of the cutting tool of Figure 33;

Figure 35 shows a schematic view of the cutting tool of Figures 33 and 34;

Figure 36 shows a schematic cross-sectional representation of the rotary assembly, anchor module and cutting wheel assembly of the cutting tool of Figures 33-35;

Figure 37 shows a schematic cross-sectional representation of the rotary assembly of Figures 33-36;

Figure 38 shows a schematic view of the rotary assembly of Figure 37;

Figure 39 shows a further schematic cross-sectional representation of Figure 37;

Figure 40 shows a schematic view of a cross-section through the rotary assembly of Figures 37-39;

Figure 41 shows a close-up schematic cross-sectional representation of part of Figure 37, in particular an end of the rotary assembly showing a portion of the drive shaft, the clutch, adapter, and a portion of the ball screw;

Figure 42 shows a schematic perspective view of the linear actuator, piston, and clutch of the cutting tool of Figures 33-41 ; Figure 43 shows a partially exploded view of Figure 42;

Figure 44 shows a schematic view of a cutting wheel assembly;

Figure 45 shows a schematic cross-sectional representation of the cutting wheel assembly of Figure 44, with the cutting wheel in a retracted, “run-in hole” configuration;

Figure 46 shows a schematic cross-sectional representation through the cutting wheel assembly of Figures 44 and 45;

Figure 47 shows a schematic cross-sectional representation of the cutting wheel assembly of Figures 44-46, with the cutting wheel in an extended “deployed” configuration;

Figure 48 shows a schematic cross-sectional representation through the cutting wheel assembly of Figure 47;

Figure 49 shows a schematic view of a third example of a cutting tool in accordance with the present invention, comprising a piston pressure relief valve (PRV);

Figure 50 shows a schematic cross-sectional representation of the cutting tool of Figure 49;

Figure 51 shows a schematic view of the rotary assembly of the cutting tool of Figures 49 and 50;

Figure 52 shows a schematic cross-sectional representation of the rotary assembly of Figure 51 ;

Figure 53 shows a further schematic cross-sectional representation of the rotary assembly of Figure 51 ;

Figure 54 shows a schematic cross-sectional representation through the rotary assembly of Figures 51-53;

Figure 55 shows a detail view of the piston PRV;

Figure 56 shows a schematic cross-sectional representation of the anchor module of Figures 24-26 connected to a cutting wheel assembly comprising a ratchet and pawl arrangement and an alternative arrangement of the rollers and cutting wheel comprising resilient devices;

Figure 57 shows a schematic cross-sectional view of the ratchet and pawl arrangement of Figure 56;

Figure 58 shows a schematic cross-sectional view of the cutting wheel of Figure 56;

Figure 59 shows a schematic cross-sectional view of a roller of Figure 56;

Figure 60 shows a schematic cross-sectional view of a shear relief arrangement before jarring; Figure 61 shows a schematic cross-sectional view of the shear relief arrangement of Figure 60 after jarring;

Figure 62 shows a schematic perspective view of an alternative linear actuator comprising a lead screw and lead screw nut, piston, and clutch;

Figure 63 shows a partially exploded view of Figure 62;

Figure 64 shows a perspective cross-sectional view of Figure 63; and Figure 65 shows a further cross-sectional view of Figure 63.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION

Figures 1-8 illustrate examples of a power control module (PCM) 1 comprising a housing 2 and a batter pack 3, motor 4, and gear assembly 5 (in this example, a planetary gear assembly) that are configured to work with a linear actuator and are therefore suitable for use with a cutting tool in accordance with the present invention. Examples of these modular components were disclosed in PCT patent application no. WO 2019/180642, the full contents of which are incorporated herein by reference, and which are manufactured by and available for purchase from Kaseum®, Aberdeen, UK.

The use of these components in the cutting tool(s) described below allows the tool to be run into a well on slickline rather than wireline or e-line/slick e-line, as power is supplied to the tool by the PCM as opposed to sent down the line from the surface. However, if the cutting tool is run in on e-line, for example, the e-line may be utilised as a means of transmitting commands and/or data between the tool and the surface of the wellbore into which the tool is run.

Figure 9 shows an example of a cutting tool 100 which may be used to cut casing or other pipes/tubulars in a downhole environment such as an oil well. For simplicity “tubular” will be used as a general term in this description, but the skilled reader will understand that this extends to any form of pipe, tubing, casing etc. that may be used downhole. The cutting tool 100 comprises a PCM 1 , electric motor 4, and planetary gear assembly 5 in a modular arrangement forming a drive assembly 10. The drive assembly 10 connects to a rotary assembly 110, which comprises a linear actuator in the form of a ball screw assembly 120 arrangement, with a central drive shaft 112 that extends from an end of the drive assembly 10 through the tool to an end of cutting wheel assembly 160. The rotary assembly 110 connects to an anchor module 140 which contains anchors 142 to stabilise the cutting tool 100 against the wall of the casing etc. that is being cut. The anchor module 140 then connects to the cutting wheel assembly 160, which contains the cutting wheel 162 that performs the cut. Each of these modules and assemblies are described in more detail as follows.

The gear assembly 5 connects to the drive shaft 112 of the cutting tool 100 via a drive coupling 105 housed within a sub 111 , as shown in Figure 10. An annular race of thrust bearings 107 extends around the circumference of the drive coupling 105, the race of bearings 107 arranged between an upper support thrust washer 106 and a lower support thrust washer 108. The upper and lower washers 106, 108 and the race of thrust bearings 107 are held in position by a split ring 104, which sits within a recess formed on the outer surface of the drive coupling 105. The split ring 104 is immediately adjacent to the upper support thrust washer 106. The lower support thrust washer 108 abuts against a shoulder 111s formed as a step in the inner diameter of the sub 111 and also abuts against a corresponding shoulder 105s formed on the outer diameter of the drive coupling 105. The combination of the shoulder and the split ring 104 acts to resist axial movement of the washers 106, 108 and the race of thrust bearings 107.

The drive shaft 112 connects at its upper end to the drive coupling 105, and a portion of the drive shaft 112 is surrounded by the race of ball bearings 103, configured to facilitate rotation of the drive shaft 112. In addition to the step of the shoulder 111s, a further step and narrowing of the inner diameter of the sub 111 provides an annular recess in which the race of ball bearings 103 is held.

The inner diameter of the sub 111 narrows once more to create a axially-aligned bore through which the drive shaft 112 extends. Slightly spaced apart from the race of ball bearings 103 is an annular wedge seal 102 which is disposed within a recess in the bore formed in the sub 111. The annular wedge seal 102 seals against the outer diameter of the drive shaft 112 to resist fluid entry to the upper components of the drive coupling 105 (i.e. the ball bearings 103, thrust bearings 107, and so on). The inner diameter of the sub 111 then widens to create a chamber 114c.

An aperture 109 extends through the wall of the sub 111 and is configured to permit entry of well fluid into the chamber 114c. There may be three apertures 109 spaced 120° apart around the circumference of the sub 111. Each aperture 109 comprises a filter to resist ingress of debris into the tool 100. Within the chamber 114c there is an annular balance piston 114 with a central bore through which the drive shaft 112 extends. The balance piston 114 has an annular inner seal, in this example a wedge seal 114a, which is disposed within a recess extending around the inner diameter of the bore of the balance piston 114 and seals against the outer surface of the drive shaft 112. The balance piston 114 further comprises an annular outer seal, in this example an o-ring 114b, which seals against the inner surface of the sub 111. The seals together act to resist fluid communication between the well and the upper end of the rotary assembly 120.

The sub 111 is connected to the ball screw assembly housing 119 by a threaded connection. The sub 111 is further locked to the ball screw assembly housing 119 by threaded fixings, in this example by screws 111a spaced apart around the circumference of the sub 111. At its upper end, the ball screw assembly 120 comprises a further race of thrust bearings 121, in this example ball bearings. A circlip 117 and a bearing washer 118 retain the bearings 121 in position at the upper end of the rotary assembly 120. At the opposing side of the bearing race 121 a further bearing washer 123 is positioned, abutting against a first shoulder 119s formed in the inner diameter of the ball screw assembly housing 119 and a second shoulder 122s formed in the outer surface of the ball screw 122.

The drive shaft 112 passes through a central bore in the ball screw assembly 120 formed by the ball screw 122 (and subsequently an aperture in the hydraulic piston 126, described in more detail below). The portion of the drive shaft 112 around which the ball screw 122 is arranged comprises shallow annular recesses into which one or more tolerance rings 113 are fitted. In this example, five tolerance rings 113 are illustrated on the drive shaft 112 as best seen in Figure 17, but this is not limiting. Suitable tolerance rings are, for example, Rencol® Tolerance Rings manufactured by Saint-Gobain Performance Plastics. The tolerance rings 113 are ridged or otherwise textured, which creates a frictional engagement with the inner surface of the surrounding ball screw 122.

The ball screw 122 is threaded on its outer surface with a helical ball groove in which the ball bearings 125 of the ball nut 124 sit. As the drive shaft 112 begins to rotate, the ball screw 122 rotates along with the drive shaft 112 due to the frictional engagement with the tolerance rings 113. Rotation of the ball screw 122 is translated to axial movement of the ball nut 124 as the ball bearings follow the ball screw 122 thread. The ball nut 124 is fixedly connected at an end to a piston, in this example a hydraulic piston 126. Axial movement of the ball nut 124 in turn moves the piston 126 axially, while the fixings resist relative movement between the piston 126 and the ball nut 124.

The piston 126 is disposed within a fluid-filled piston chamber 130 into which an end of the anchor module 140 is connected. The inner diameter of the piston 126 remains substantially constant along its length, with the piston end opposite to the ball nut 124 forming a more narrow diameter that provides an aperture through which the drive shaft 112 passes. This creates an inner chamber 126b within the body of the piston 126, with a smaller volume than the piston chamber 130 on the opposite side of the piston’s end.

The ball screw assembly housing 119 further comprises a retraction bore 129 which is created by first and second annular grooves 129a, 129b formed in the inner surface of the housing 119. At the start of operations, before the ball screw assembly 120 begins to move, the end of the piston 126 is initially aligned with the second groove 129b. Viewing Figures 14 and 15, it can be seen that as the piston 126 is moved axially by the ball nut 124 (left to right in these figures), it passes from the second groove 129b into a more narrow section of the housing 119, which comprises the piston chamber 130. The end of the piston 126 is then sealed against the inner surface of the ball screw assembly housing 119 by an annular seal 128 such as an o-ring, resisting fluid entry from the piston chamber 130 into the retraction bore 129. As the piston 126 continues to move from left to right, along this narrower section, the fluid within the piston chamber 130 increases in pressure.

The piston 126 is also sealed against the outer surface of the drive shaft 112 by an annular wedge seal 127, resisting fluid communication along these surfaces between the piston chamber 130 and the ball screw assembly 120. As the ball nut 124 moves down the ball screw 122 (i.e. in a direction towards the anchor module 140), the piston 126 moves in the same direction within the piston chamber 130, increasing the fluid pressure between the piston 126 and the end of the anchor module 140. The piston 126 includes a piston pressure relief valve (PRV) 131 (best seen in Figure 15) to control the fluid pressure within the piston chamber 130. The piston PRV is configured to allow fluid communication between the piston chamber 130 and the inner chamber 126b, and with the retraction bore 129.

The fluid within the piston chamber 130 is in fluid communication with the anchor module 140. As the fluid increases in pressure within the piston chamber 130, the pressure correspondingly increases in the anchor module 140 as further described below.

A first example of an anchor module 140 is shown in Figures 18-23. The anchor module 140 comprises a race of bearings 135 which sit within a recess formed in an end of the anchor module 140 and are arranged to ease rotation of the drive shaft 112 at the point of entry to the anchor module 140. The anchor module 140 comprises a throughbore 140b through which the drive shaft 112 extends. The bearings 135 are further held in position by a circlip positioned within a groove adjacent to the bearings 135 at an upper end, resisting movement of the race of bearings 135 towards the piston chamber 130.

The anchor module 140 comprises multiple circularly-shaped anchor buttons 142 that radially extend to anchor the cutting tool 100 against the inner wall of the tubular being cut. Figures 18 and 19 show the anchor buttons 142 in their retracted configuration. In this example, two circumferential and equally spaced rows of anchor buttons 142 extend around the anchor module 140, with the buttons on the first and second rows being staggered relative to each other. As shown in Figure 19, the anchor buttons 142 are held within movable housings that form anchor pistons 143, with the anchor pistons 143 and anchor buttons 142 being seated in orifices formed in the body of the anchor module 140. The anchor buttons 142 are each connected to anchor springs 146, disposed within an orifice in each anchor piston 143, that are resiliently biased against movement of the anchor piston 143, retaining the anchor pistons 143, and therefore the anchor buttons 142, in their retracted configuration. The anchor springs 146 facilitate retraction of the anchor buttons 142 in shallow working conditions and/or conditions with low hydrostatic pressure. The anchor buttons 142 are restrained from falling out of the anchor module 140 by retaining plates 141. Each anchor button 142 has an axially-aligned groove on its outer surface into which the restraining plates 141 can fit. The width of the plates 141 and the depth of the grooves on the anchor buttons 142 are selected so that when the anchor buttons 142 extend radially outward from the anchor module 140, the buttons 142 can travel a sufficient distance to make contact with the inner wall of the tubular to anchor the cutting tool 100. The surface of the anchor buttons 142 is further textured with ridges or similar to enhance the frictional contact with the surface of the object being cut and reduce the chance of undesirable movement (rotational or axial) of the cutting tool 100 as it is operational.

When the fluid pressure within the piston chamber 130 is relatively low, the anchor springs 146 act to hold the anchor buttons 142 within the body of the anchor module 140. As the fluid pressure builds up within the piston chamber 130, due to the fluid communication between the chamber 130 and the anchor module 140, pressurised fluid in turn builds up within fluid conduits 148, which direct fluid towards the anchor pistons 143. Each anchor piston 143 has an annular seal 147 disposed within an annular recess in the outer surface of the anchor piston 143 which seals against the orifice in which the anchor piston 143 sits and resists fluid ingress or egress between the wellbore and the fluid conduits 148. The fluid is initially restricted from travelling further through the anchor module 140 into the cutting wheel assembly 160 by a pressure relief valve 150 that is located within the end of the cutting wheel assembly 160 that conjoins to the anchor module 140 (see, e.g., Figures 10 and 28). The pressure relief valve 150 sits adjacent to an optional check valve 155, which adds redundancy in restricting fluid communication from the anchor module 140. As the pressure relief valve 150 prevents fluid escaping from the anchor module 140, the fluid pressure behind the anchor pistons 143 continues to increase as the piston 126 moves downward. Eventually the fluid pressure within conduits 148 reaches a sufficiently high level to overcome the biasing force of the anchor springs 146 (for example, 10-500 psi, where the higher end of the pressure range (e.g. 300 psi) may be used in the example of the invention that comprises the pressure relief valve 150 between the anchor module and the cutting wheel assembly, and the anchors are being deployed before the cutting wheel begins to retract; and lower pressures within the range (e.g. 50 psi) may be used where the anchors are being deployed at the same time as the cutting wheel) and pushes against the anchor pistons 143, radially extending the anchor buttons 142 until they make contact with the inner surface of the tubular and the cutting tool 100 is anchored. Figures 20-23 illustrate the anchor module 140 in a “deployed” configuration with the anchor pistons 143 having been moved outwards in response to fluid pressure, leading to the anchor buttons 142 being radially extended from the body of the anchor module 140.

In this example, the anchors deploy first before there is any movement of the cutting wheel 162, but the anchors may also deploy at the same time as the cutting wheel is extended as will be discussed in the context of alternative examples of the invention below.

An alternative anchor module 240 is illustrated in Figures 24-26 (in an extended, deployed configuration), where the reference numbers are increased by 100 from the numbers used in relation to anchor module 140. Parts that remain the same between the two forms of anchor module will not be described again here for brevity.

In this example, anchor module 240 comprises multiple anchor pads 242 disposed in a single row around the circumference of the anchor module 240. In comparison with anchor buttons 142, the anchor pads 242 of this example are extended in a longitudinal direction. The surface of the anchor pads 242 that contacts the wall of the tubular being cut is grooved, ridged, or otherwise textured to increase frictional contact between the two surfaces. Similarly to the anchor buttons 142, the anchor pads 242 have a longitudinally-extending groove down the centre of the anchor pads 242, aligned with a retaining plate 241. As before, the retaining plate 241 restricts the movement of the anchor pads 242 to prevent the pads 242 (and anchor pistons 243) potentially becoming detached from the anchor module 240 and falling into the well.

As the anchor pads 242 are longitudinally extended they have two anchor springs 264 at each end of each pad 242 resisting movement of the anchor pistons 243 under fluid pressure. Pressurised fluid enters fluid conduits 248 and acts against the anchor pistons 243 and the biasing force of the anchor springs 246, extending the anchor pads 242 radially outwards and against the inner surface of the object being cut (for example, at pressures within the range of 10-500 psi, where the higher end of the pressure range (e.g. 300 psi) may be used in the example of the invention that comprises the pressure relief valve 150 between the anchor module and the cutting wheel assembly, and the anchors are being deployed before the cutting wheel begins to retract; and lower pressures within the range (e.g. 50 psi) may be used where the anchors are being deployed at the same time as the cutting wheel). The anchor springs 264 facilitate retraction of the anchor pads 242 in shallow working conditions and/or conditions with low hydrostatic pressure.

As indicated above and illustrated in Figures 27-31 , the cutting wheel assembly 160 is connected at an end to the anchor module 140, 240 via a coupling 154. Within the coupling 154 there are two annular thrust bearing races 159a, 159b, which mitigate axial loading between the anchor module 140, 240 and the cutting wheel assembly 160 as the drive shaft 112 (and therefore the cutting wheel assembly 160) rotates.

At the same end of the cutting wheel assembly 160, there is a splined orifice 152. The drive shaft 112 has a corresponding splined end 115 that is inserted into the splined orifice 152 for mutual engagement of the drive shaft 112 and the cutting wheel assembly 160. Due to the splined connection, the rotation of the drive shaft 112 drives rotation of the cutting wheel assembly 160. Another type of connection which rotationally fixes the drive shaft 112 and the cutting wheel assembly 160 in such a way that they rotate together would also be suitable.

The splined orifice 152 opens into a fluid conduit through which fluid can travel to or from the anchor module 140. Within this conduit and adjacent to the splined orifice 152 there is housed the pressure relief valve (PRV) 150, and the check valve 155, as best seen in Figures 28, 31 , and 32. As detailed above, the pressure relief valve 150 (and optionally the check valve 155) acts to resist fluid flow when the pressure is below a certain threshold (such as 100-500 psi). Once the fluid exceeds this threshold pressure, the pressure relief valve 150 opens and fluid flows into the cutting wheel assembly 160.

The run-in-hole configuration of the cutting wheel assembly 160 is shown in Figures 27-29. Fluid passing through the PRV enters into a fluid conduit 153 that conducts the fluid into the cutting wheel assembly 160. Within the cutting wheel assembly 160 there are two roller wheels 170 which are each disposed on axles 171 and housed within recesses in roller pistons 173. Fluid passing into the cutting wheel assembly 160 builds up behind the roller pistons 173, as a result of which the roller pistons 173 extend radially outwards from the cutting wheel assembly 160 as shown in Figures 30 and 31. The roller wheels 170 rotate around the axles 171 as the cutting wheel assembly 160 rotates, with the roller wheels 170 making contact with the inner wall of the tubular. This also balances the action of the cutting wheel 162 as it cuts into the tubular, helping to keep the cutting wheel assembly 160 centralised. This in turn means that the cut made in the tubular stays on the same plane through the tubular, reducing the time taken for the cut to be made and reducing the risk of damage to the cutting wheel 162.

The cutting wheel assembly 160 further comprises the cutting wheel 162, which comprises a circular blade with an aperture through which an axle 164 passes. In the examples shown in the Figures the cutting wheel 162 is perpendicular to the longitudinal axis of the cutting wheel assembly 160 (and the cutting tool 100); however, this is not limiting and alternative angles of the cutting wheel may be more suitable for particular cutting operations. The cutting wheel 162 is configured to rotate around the axle 164 as it cuts a tubular. The cutting wheel 162 sits within a recess formed in a cutting wheel piston 166. Similarly to the roller pistons 173, fluid is conducted through the fluid conduit 153 and builds up behind the cutting wheel piston 166 in a chamber 168 that increases in volume as the cutting wheel piston 166 moves radially outwards. As the fluid pressure increases, the cutting wheel piston 166 is pushed out of the cutting wheel assembly 160 and extends radially outwards (as shown in Figures 9-10, 30-31), making contact with the inner wall of the tubular to perform the cut.

As load is applied to the cutting wheel 162, it cuts around the inner diameter of the tubular. As cuts are completed around the tubular with each rotation of the cutting wheel assembly 160, the load applied to the cutting wheel is kept substantially constant, allowing the cutting wheel to cut further into the tubular with each rotation. The cutting wheel assembly 160 continues to rotate, and this process is repeated until the tubular is severed. By way of example, the cutting tool 100 can be pre-set to rotate for 10 minutes with a fluid pressure of 1200 psi applied to the cutting wheel 162, which would provide 30 revolutions of the cutting wheel assembly 160. As an alternative, to provide redundancy in terms of power that can be applied to the cutting tool 100 by the drive assembly 10 and to be completely sure of full severance of the tubular, the tool 100 could be configured to allow for extra revolutions of the cutting wheel assembly 162 - for example, the tool 100 could carry out 80-100 revolutions while downhole. The configuration of the tool 100 can be adjusted to take into account different weights and grades of tubulars as required.

The load is applied to the cutting wheel 162 through the fluid pressure within the piston chamber 130 increasing and this increase being transmitted through the anchor module 140, 240 into the cutting wheel assembly 160. Should the fluid pressure exceed a predetermined threshold (for example 200-1500 psi, and more preferably 800-1200 psi, but this may vary according to the cutting requirements and downhole environment) the tolerance rings 113 disengage from their frictional engagement with the ball screw 122, and the drive shaft 112 rotates while the ball screw 122 does not. The hydraulic piston 126 therefore remains in place and the fluid pressure decreases below the threshold. Maintaining the fluid pressure within the piston chamber 130 at a substantially constant level mitigates the risk of damage to the cutting wheel 162 from too much load being applied during cutting, while maintaining a constant force on the cutting wheel 162 in order to cut the tubular.

The running time of the cutting tool 100 can be pre-set to a length of time that is sufficient to ensure cutting is complete. When cutting is completed, rotation of the drive shaft 112 is reversed. This in turn pulls the ball screw 122 and the hydraulic piston 126 back towards the original configuration. In order to ensure that the cutting wheel 162 is completely retracted, the hydraulic piston 126 is retracted back to a point beyond the hydraulic piston’s 126 original start point within the rotary assembly 110, until the hydraulic piston aligns with the first groove 129a in the ball screw assembly housing 119. This creates a pressure differential, and pulls well fluid from the wellbore into the system to hydrostatically balance the tool 100 with well pressure. Once the cutting wheel 162 is retracted, the cutting tool 100 can be withdrawn from the wellbore.

Alternatively, the cutting wheel piston 126 (and/or the roller pistons 173) may be connected to a spring return mechanism (an example of which is shown in Figures 56 and 58) which may alternatively or additionally retract the cutting wheel piston 126. This may be particularly useful in, for example, shallow cutting operations where there is little to no hydrostatic pressure to assist with the return of the cutting wheel piston 126 and/or the roller pistons 173. A second example of a cutting tool 200 is shown in Figures 33-43.

Figures 33-35 show the entire tool 200, including a drive assembly 10 as described above, which is not described again here for brevity. The tool 200 also comprises an example of anchor module 240. All other features in common with the first embodiment will be identified by the same reference number + 100.

In this example of the cutting tool 200, instead of tolerance rings being used to maintain a constant fluid pressure within the anchor module 240, and more particularly in the cutting wheel assembly 260, an alternative clutch arrangement is shown, in this example a synchronous torque-limiting clutch but this is not restrictive. A suitable clutch that could be used in the cutting tool 200 is an EAS®-smartic® clutch available from Mayr®, Mauerstetten, Germany, but this is not limiting and not the only form of clutch that would provide the required torque limitation function in the tool 200.

Top sub 211 comprises two connected smaller subs, upper sub 211a and lower sub 211b. The upper sub 211a houses the connection between the gear assembly 5 and the drive shaft 212, including thrust bearings 207. The lower sub 211b houses the balance piston 214, clutch 280, and adapter 281. The upper and lower sub arrangement makes manufacture of the cutting tool 200 easier, and also eases maintenance of the clutch 280, should it be required. The clutch 280 is set to slip at a particular pre-determined value, for example 20-50 Nm, to achieve a suitable level of hydraulic pressure (e.g. 200-1500 psi, or more preferably 800-1200 psi, but this can vary according to the cutting requirements and downhole environment) within the cutting wheel assembly 260.

The drive shaft 212 passes through a central orifice in the clutch 280. The clutch 280 is clamped to the drive shaft 212 on the left hand side of the clutch 280 (the location of the side being in reference to the direction of illustration in the Figures, for example Figure 41). The right hand side of the clutch drives the ball screw assembly 220. As best seen in Figures 41-43, the clutch 280 is fixedly connected to an adapter 281 , which again comprises a central aperture through which the drive shaft 212 also passes. The adapter 281 comprises ribs 282 around one side, and is connected by at least one threaded fixing to the clutch 280 on its opposite side. The ribs 282 are arranged around the drive shaft 212 and engage with castellations formed on an end of the ball screw 222. The inter-engagement of the adapter 281 with the ball screw 222 transfers rotational motion from the drive assembly 10 via the drive shaft 212 to the ball screw assembly 220.

As in the first example the ball screw assembly 220 acts to increase fluid pressure within the piston chamber 230, which is then transmitted to the anchor module 240 and the cutting wheel assembly 260. In the present example, and as illustrated in Figures 44-48, there is no pressure relief valve or check valve between the anchor module 240 and the cutting wheel assembly 260. Accordingly, increases in fluid pressure within chamber 230 are reflected by corresponding increases in fluid pressure within the anchor module 240 and the cutting wheel assembly 260. The anchor pads 242 are thus deployed concurrently with the cutting wheels 262 and the rollers 270, and each of these make contact with the inner surface of the tubular substantially simultaneously. The cutting tool 200 is thus anchored at the same time as the cutting wheel 262 begins to cut the tubular. Cutting operations can then be carried out as detailed above to sever the tubular.

Once the tubular has been severed, the cutting wheel piston 264 (and therefore cutting wheel 262), rollers 270, and anchor pads 242 are retracted by reversing the direction of rotation of the drive shaft 212 and retracting the hydraulic piston 230 as before. As retraction of the piston 230 progresses the pressure behind the piston 230 reduces to zero, and then creates a pressure differential to further assist (together with the anchor springs 246) retraction of the radially extended components. Once the extended components, in particular the cutting wheels 262, have been fully retracted, the cutting tool 200 can then be withdrawn from the well.

A third example of a cutting tool 300 is shown in Figures 49-55.

Figures 49 and 50 show the entire tool 300, including a drive assembly 10 as described above, which is not described again here for brevity. The tool 300 also comprises an example of anchor module 240. All other features in common with the first embodiment will be identified by the same reference number + 200. In this example of the cutting tool 300, the fluid pressure within the piston chamber 330 is controlled solely by a piston pressure relief valve (PRV) 331 disposed within a wall of the hydraulic piston 326, best seen in Figure 55. The piston PRV is set to open at a threshold fluid pressure value (for example 200-1500 psi, or more preferably 800-1200 psi, although the threshold value can vary according to cutting requirements and the downhole environment).

The ball screw 322 is fixedly attached to the drive shaft 312 with threaded fixings (although any form of hard mounting of the ball screw 322 to the drive shaft 312 is suitable). This arrangement means that each full rotation of the drive shaft 312 advances the hydraulic piston 326 by a distance equal to the pitch of the ball screw 322.

As fluid pressure builds up in piston chamber 330, the increasingly pressurised fluid is transmitted to the anchor module 240 and the cutting wheel assembly 360 to actuate the anchor pads 242, the cutting wheel piston 366 and cutting wheel 362, and the roller pistons 373 and rollers 370. Should the pressure in the piston chamber 330 exceed the threshold of the piston PRV 331, the valve will open and pressure will be relieved through fluid passing through the piston PRV 331 and entering a chamber 333 on the opposite side of the piston 326 from the piston chamber 330.

Once the cut is complete and the tubular has been severed, the hydraulic piston 326 can be retracted by reversing the direction of rotation of the drive shaft 312, which retracts the ball screw assembly 320. The retraction of the piston 326 is accompanied by hydrostatic pressure pushing against the piston 326. The effect of the retraction is to decrease the fluid pressure experienced by the cutting wheel piston 366, the roller pistons 373, and the anchor pads 242. The pressure behind the hydraulic piston 326 gradually reduces to zero, and then pulls a vacuum, leading to these components returning to their original configurations and allowing the tool 300 to be withdrawn from the well.

Figure 56 shows an alternative cutting wheel assembly 460. Figures 57-59 show cross-sections taken through the cutting wheel assembly 460 at different locations to illustrate different components. The cutting wheel assembly 460 comprises a ratchet and pawl arrangement 490 within an end of the cutting wheel assembly 460 as shown in Figure 57. In this example, there are three pawls 491 arranged circumferentially around the drive shaft 412. The pawls are blade-shaped, with a narrow end and a thicker end, where the pawls 491 are connected to a hinged fixing at their thicker end (or any other suitable fixing that allows the pawl 491 to rotate around an axis of the thicker end).

The pawls 491 are located adjacent to a cavity 494 formed within the cutting wheel assembly. There is a spring 492 seated within each cavity 494 and in contact with the narrow end of the corresponding pawl 491. The springs 492 act to resiliently bias each pawl 491 towards the drive shaft 412.

The drive shaft 412 has teeth 493 formed around its outer circumference at the end of the drive shaft 412. In this example there are three teeth 493 that are formed around the drive shaft 412 and which are spaced apart so that each tooth 493 can engage with a pawl 491. The teeth 493 allows this end of the drive shaft 412 to act as a ratchet.

As the drive shaft 412 rotates in one direction - in this example shown in Figure 57, rotation in an anti-clockwise direction - the teeth 493 engage with the pawls 491 so that the drive shaft 412 and the cutting wheel assembly 460 are rotationally locked. The rotation of the drive shaft 412 in this direction therefore results in corresponding rotation of the cutting wheel assembly 460.

Rotation of the drive shaft 412 in the opposite (i.e. in this example, in a clockwise direction) leads to the drive shaft 412 slipping past each pawl 491. In this direction of rotation, the teeth 493 on the drive shaft 412 push each pawl 491 against each spring 492 as the drive shaft 412 passes each pawl 491. As the drive shaft 412 moves past the or each pawl, the free (narrow) end of each pawl moves in an arc within the cavity 494. This allows the drive shaft 412 to rotate without corresponding rotation of the cutting wheel assembly 460.

In the event that the cutting wheel 462/cutting wheel assembly 460 becomes trapped, or stalled, in the well bore, the drive shaft 412 can be rotated in the clockwise direction to retract the piston and reduce fluid pressure in the tool. Once the fluid pressure is relieved, in the case that the cutting wheel 462 is trapped, the cutting wheel 462 can be jarred to free the tool from the tubular and allow retrieval of the tool back to the surface.

Figure 58 illustrates an example of the cutting wheel assembly 460 where the cutting wheel piston 466 comprises fasteners (e.g. bolts or capscrews) 469 that are disposed within apertures in the cutting wheel piston 466. The fasteners 469 are at least partially surrounded by springs 467 that extend down at least part of each fastener 469 and that are coaxial with each fastener 469. The apertures of the cutting wheel piston 466 comprise a first inner diameter, in which the springs 467 are held, and a second inner diameter smaller than the first inner diameter, through which the corresponding fastener 469 passes. The second inner diameter forms a step or a shoulder that an end of each spring 467 abuts. The opposite end of each spring 467 abuts against a shoulder formed in the fasteners 469 by a wider diameter section of the fastener 469. The springs 467 thus act against the cutting wheel piston 466 at one end and against the fastener 469 at the other end of the spring 467.

The cutting wheel piston 466 moves relative to the fasteners 469, which are connected to the housing of the cutting wheel assembly 460 and remain in position as the cutting wheel piston 466 moves radially. As fluid pressure behind the cutting wheel piston 466 increases, the piston 466 moves radially outwards, forming piston chamber 468 and compressing the springs 467. The springs 467 thus act to resist radial extension of the cutting wheel piston 466, and biases the cutting wheel piston 466 (and cutting wheel 462) towards radial retraction. Accordingly, when the fluid pressure is sufficiently low, the springs 467 retract the cutting wheel piston 466 back into the body of the cutting wheel assembly 460.

Similarly, Figure 59 shows an example of a roller piston 473 connected to two fasteners 474 (as seen in Figure 56; Figure 59 shows a single fastener 474). Each fastener 474 is disposed within an aperture in the cutting wheel assembly 460 and fixed to the roller piston 473 at one end. Similarly to the cutting wheel piston 466, the aperture within the cutting wheel assembly 460 comprises a shoulder at one end, and each fastener 474 further comprises a shoulder spaced apart from the shoulder of the aperture. A spring 475 coaxially surrounds the fastener 474 between these two shoulders. As fluid pressure increases in the cutting wheel assembly 460, the roller wheel piston 473 moves radially outwards, forming piston chamber 478. Radial extension of the roller wheel piston 473 compresses each spring 475. The springs 475 act to resist the radial extension of the roller wheel piston 473 and bias the roller wheel piston 473 (and roller wheel 470) towards radial retraction. Accordingly, when the fluid pressure is sufficiently low, the springs 475 retract the roller wheel piston 473 back into the body of the cutting wheel assembly 460.

Figures 58 and 59 also best illustrate the bearing races 464b, 471b that are disposed around the circumference of the axles 464, 471 , around which the cutting wheel 462 and the roller 470 rotate, respectively. This arrangement facilitates rotation of the cutting wheel 462 and the rollers 470 and is suitable for each example of the invention described herein.

As best seen in Figures 60 and 61 , the tool comprises a shear relief arrangement that allows emergency venting of the tool in the event of failure.

At the end of the ball screw assembly housing 219 that connects to the anchor module 240, the ball screw assembly housing 219 comprises shear screws 219a (for example 8 shear screws 219a) positioned around the circumference of the ball screw assembly housing 219, and extending into an orifice in the outer wall of the anchor module 240.

A spin collar 245 is located in a recess formed in the end of the ball screw assembly housing 219 and extends perpendicularly into a space formed between the anchor module 240 and the ball screw assembly housing 219 when the connection between the two parts is made up. The spin collar 245 encircles the end of the ball screw assembly housing 219. The shear relief arrangement further comprises a snap ring 247 located within a recess formed between the inner surface of the end of the ball screw assembly housing 219 and the outer surface of the anchor module 240. The snap ring 247 is positioned to abut partly against an end of the recess formed in the anchor module 240 and an end of the spin collar 245.

The end of the anchor module 240 further comprises an o-ring seal 249, disposed within a groove around the outer circumference of the anchor module 240. The o- ring 249 sits adjacent to the shear screws 219a, on the opposite side of the shear screws 219a to the spin collar 245 and snap ring 247.

In the event that the tool fails - for example it stalls, or it becomes trapped or jammed in the tubular - the tool can be jarred upwards. Jarring the tool shears the shear screws 219a, allowing the ball screw assembly housing 219 to move axially relative to the anchor module 240. The shear relief arrangement including the snap ring 247 and the spin collar 245 moves with the ball screw assembly housing 219 in an axial direction.

This movement of the ball screw assembly housing 219 aligns the aperture through the ball screw assembly housing 219 in which each shear screw 219a is disposed at least partially aligns with the o-ring 249 around the end of the anchor module 240, unseating the o-ring 249 from its groove. This allows venting of the fluid within the tool into the wellbore for emergency retraction of the anchors, cutting wheel, and rollers (if possible), and recovery of the tool to surface.

Figures 62-65 show an alternative linear actuator assembly. In the illustrated examples, rather than a ball screw assembly 120, 220, a lead screw assembly 520 is used. The lead screw assembly 520 can be directly substituted for the ball screw assembly 120, 220 in the cutting tools 100, 200, 300 described above.

As shown in Figures 62-65, the drive shaft 512 passes through a central orifice in the clutch 580. The clutch 580 may be a synchronous torque-limiting clutch. The clutch 580 is clamped to the drive shaft 512 on the left hand side of the clutch 580 (the location of the side being in reference to the direction of illustration in the Figures, for example Figure 65). The right hand side of the clutch drives the lead screw assembly 520. As best seen in Figure 65, the clutch 580 is fixedly connected to an adapter 581 , which again comprises a central aperture through which the drive shaft 512 also passes. The adapter 581 comprises ribs 582 (best seen in Figure 63) around one side, and is connected by at least one threaded fixing to the clutch 580 on its opposite side. The ribs 582 are arranged around the drive shaft 512 and engage with castellations formed on an end of the lead screw 522. The inter-engagement of the adapter 581 with the lead screw 522 transfers rotational motion from the drive assembly 10 via the drive shaft 512 to the lead screw assembly 520. The outer surface of the lead screw 522 is at least partially threaded. A lead screw nut 524 comprises a complementary thread on its inner surface, and further comprises a central aperture through which the lead screw 522, and the drive shaft 512, pass. The aperture of the lead screw 522 (through which the drive shaft 512 extends) is coaxial with the aperture of the lead screw nut 526.

Connected to an end of the lead screw nut 524 is the piston 526. As previously described, movement of the piston 526 increases and decreases fluid pressure within the lower sections of the tool, not illustrated in Figures 62-65. As the drive shaft 512 rotates, the lead screw 522 is also rotated. Depending on the direction of rotation, the lead screw nut 524 travels axially backwards and forwards up and down the lead screw 522. This in turn moves the piston 526 axially within the piston chamber (c.f. piston chamber 130, 230), increasing and decreasing fluid pressure as the fluid is compressed or decompressed within the piston chamber. Fluid pressure within the cutting wheel assembly 160, 260, 360, 460 increases and decreases accordingly, as detailed above.

Modifications and improvements may be made to the examples and embodiments hereinbefore described without departing from the scope of the invention.