FIELD OF THE INVENTION

The present invention relates to a downhole tool and assembly. More particularly, but not exclusively, the present invention relates to a cartridge assembly for a downhole tool and assembly.

BACKGROUND TO THE INVENTION

in the oil & gas exploration and production industry, in order to access hydrocarbons from a formation, a well borehole is typically drilled from surface and the borehole lined with sections of metal tubular, known as casing. The casing is then typically cemented in place to secure and support the casing within the borehole.

It will be recognised that conventional drilling and casing techniques involve a number of separate steps or trips into the borehole. As a result, techniques for drilling with casing have been developed, whereby the drill bit is connected to the lowermost end of the casing and the casing - together with connected drill bit - is then rotated from surface, such as from the rig floor. In drilling with casing operations, weight is applied to the casing from surface as it rotates, the borehole being formed as the drill bit progresses through the rock strata until the required depth or target location is reached.

However, there are a number of limitations with conventional drilling with casing techniques. For example, casings are generally provided in a number of different sizes/diameters and larger casing sizes are more difficult to rotate due to the larger mass. Moreover, boreholes are often now drilled for significant distances horizontally or at a high angle from vertical which makes manipulation of the casing string problematic or impossible.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to the use of a downhole rotary drive in the drilling, reaming or cutting of a borehole.

According to a first aspect of the present invention, there is provided a cartridge assembly for a downhole tool.

The cartridge assembly may comprise a rotary drive of the downhole tool.

In use, the cartridge assembly may be secured to and run into the borehole with the downhole tool and operable to drive rotation of a cutting member, cutting structure or the like of the downhole tool. Beneficially, providing a rotary drive in the form of a cartridge assembly amongst other things facilitates efficient drill through of the rotary drive of the downhole tool without impacting on the surrounding components of the string where it is desired to extend and/or ream the borehole.

The rotary drive may be of any suitable form and construction.

The rotary drive may comprise a fluid driven rotary drive. The rotary drive may comprise a motor. In particular embodiments, the rotary drive may comprise a positive displacement motor. In other embodiments, the rotary drive may comprise a turbine. In embodiments where the rotary drive comprises a turbine, the turbine may comprise an axial flow reaction turbine.

A body or stator of the rotary drive may be coupled to, or form part of, a housing of the cartridge assembly.

A shaft or rotor of the rotary drive may be disposed within the body or stator and configured for rotation relative to the body or stator. The shaft may comprise a throughbore. The shaft may be hollow.

A fluid flow passage may be defined between the stator and the rotor for driving rotation of the rotor relative to the stator.

A cutting member of the downhole tool may be coupled to, or form part of, the cartridge assembly. In use, the cutting member may be rotated by the rotary drive.

Beneficially, the cutting member of the downhole tool may be rotated at high speed relative to the casing. As such, rotation of the casing can be reduced or the string run into the borehole without rotation.

The cutting member may be of any suitable form and construction.

In some embodiments, the cutting member may comprise a reaming bit.

In some embodiments, the cutting member may comprise a drill bit.

In some embodiments, the cutting member may comprise a coring or sampling tool. The cartridge assembly may be disposed within the housing of the downhole tool.

The cartridge assembly, in particular but not exclusively, the housing of the cartridge assembly, may be coupled to the housing of the downhole tool.

The coupling between the cartridge assembly and the downhole tool may be configured to prevent relative rotation between the cartridge assembly and the downhole tool. The coupling may comprise or form a rotary lock.

The coupling may be of any suitable form and construction.

The cartridge assembly may, for example, be secured to the downhole tool by at least one retainer. The retainer may comprise a pin; a dowel, a grub screw or the like, or a combination of these. The retainer may be radially disposed between the housing of the cartridge assembly and the housing of the downhole tool. For example, axially aligned grooves may be formed in the cartridge assembly housing and the downhole tool housing for receiving the retainer. In some embodiments, the retainer may be breakable. For example, in some embodiments the retainer may comprise one or more shear screw. The retainer may comprise or form part of the rotary lock.

A bore-lining tubular or bore-lining tubular string may be provided. The bore- lining tubular or bore-lining tubular string may comprise a casing or casing string, a completion string or other tubular component or string for deployment into the borehole. The cartridge assembly may be coupled to the bore-lining tubular or bore-lining tubular string. The cartridge assembly may be directly coupled to the bore-lining tubular or bore-lining tubular string. However, in particular embodiments the cartridge assembly may be indirectly coupled to the bore-lining tubular or bore-lining tubular string via the housing of the downhole tool.

Beneficially, in embodiments of the present invention the bore-lining tubular string may be deployed/run into the borehole without or substantially without rotation (from surface).

The housing of the downhole tool may be configured to be coupled to the casing.

The housing of the downhole tool may be directly coupled to the casing. In particular embodiments, the housing of the downhole tool may be indirectly coupled to the casing via a connector sub or the like.

In particular embodiments, the cartridge assembly housing may be coupled to the downhole tool housing which in turn is coupled to the casing via the connector sub. A coupling may secure the housing of the downhole tool to the casing or connector sub. In particular embodiments, the coupling may comprise a threaded coupling. Alternatively, the coupling between the downhole tool and the casing or connector sub may comprise a quick connector, push connector, weld or the like.

A seal may be provided between the housing of the downhole tool and the cartridge assembly. In use, the seal may prevent fluid leakage between the cartridge assembly and the housing of the downhole tool. The seal may be interposed between the inside of the housing of the downhole tool and the outside of the cartridge assembly housing. The seal may be disposed in a groove or recess provided in at least one of downhole tool housing and the cartridge assembly housing.

The seal may be of any suitable form and construction. The seal may comprise an o-ring, for example.

The cartridge assembly may comprise or may be operatively associated with a bearing.

The cartridge assembly may comprise a modular bearing. For example, the bearing may comprise a bearing pack comprising a plurality of bearings. The bearing may comprise or be provided at a bearing sub coupled to the housing of the downhole tool. The bearing sub may, for example, be coupled to the housing of the downhole tool via a threaded connector or the like.

The bearing may be disposed between the cutting member and the housing of the downhole tool. The bearing may be of any suitable form and construction.

The bearing may comprise at least one thrust bearing.

The bearing may comprise at least one radial bearing.

The bearing, or in embodiments where there are more than one bearing at least one of the bearings, may be fluid lubricated.

The bearing may be sealed.

The bearing may be lubricated by fluid from the fluid passage.

Part or all of the cartridge assembly and/or the downhole tool may be configured to facilitate drill through.

Part or all of the cartridge assembly may be constructed from a readily drillable material. The rotary drive may be constructed from aluminium.

In particular embodiments, all or substantially all of the cartridge assembly may be disposed within a drill through diameter of the downhole tool. As such, all of the cartridge assembly may be removable, such as by a further tool, further drill bit, further reaming bit or the like. The bearing, or in embodiments where there are more than one bearing at least one of the bearings, may be disposed outside a drill through diameter of the downhole tool. In particular embodiments, a ball bearing may be provided and disposed outside the drill through diameter. Beneficially, providing a bearing outside the drill through diameter may facilitate more rapid drill through operations to be carried out. Alternatively, or additionally, providing a bearing outside the drill through diameter may permit the integrity of the bearing to be retained, preventing obstructions from being formed which may otherwise inhibit passage of tools through the cartridge assembly and/or the downhole tool.

A clutch may be provided. The clutch may be configured to rotationally fix the rotor to the stator. The clutch may be configured to prevent rotation of the cutting member with respect to a tubular component, such as the bore-lining tubular string.

The clutch may be provided or formed between the cutting member and the rotary drive. The clutch may be provided or formed between the cutting member and the housing. The clutch may be provided or formed between the cutting member and the bearing or bearing sub.

The clutch may of any suitable form and construction.

In particular embodiments, the clutch may comprise a cone clutch, such as that described in Deep Casing Tools US 2013/0319769, the contents of which are incorporated herein in their entirety.

In particular embodiments, the clutch may comprise a cone clutch. The clutch may comprise a male cone. The clutch may comprise a female cone. The male cone may be located within the female cone. In use, the male cone may engage or mate with the female cone to engage the clutch. The male cone and the female cone may be configured to be selectively engaged to rotationally fit the rotor to the housing.

The internal taper angle of the female cone and the external taper angle of the male cone may be matched. The female cone and the male cone may have a self- locking taper angle. For example, the self-locking taper angle may be from 0.1 to 10.0 degrees or more.

The male cone may be integral with, or coupled to, the rotor. The female cone may be integral with, or coupled to, the housing of the rotary drive, or vice-versa.

The male cone and the female cone may be configured to be engaged by application of axial force to the housing of the rotary drive.

One or more axial restraint may be operatively associated with the clutch. The axial restraint may be configured to permit the clutch to be engaged when a selected minimum axial force is applied, that is where the axial force reaches or exceeds a predetermined force threshold. The axial restraint may be configured to be sheared through. The axial restraint may take any suitable form, shape or construction. In particular embodiments, the axial restraint - or in embodiments comprising more than one axial restraint at least one of them - may comprise a shear pin, shear ring or the like.

The clutch may comprise an anti-rotation clutch or lock. In such embodiments, the clutch or lock may be configured to allow free rotation of the rotor - and the connected cutting member - relative to the stator during normal operations of the rotary drive.

The clutch may be configured to permit fluid, such as drilling fluid, to flow over the lock during normal operation. The clutch may comprise an axial slot or slots. The axial slot or slots may extend along - or partially along - the length of the male cone. The axial slot or slots may extend along - or partially along - the length of the female cone. In use, the axial slot or slots may be configured to trap debris carried in the drilling fluid. The axial slot or slots may be configured to receive debris and retain it away from the clutch. The axial slot or slots may be dimensioned to receive an predetermined amount of debris. For example, the axial slot or slots may be configured to drive debris away from the clutch. Beneficially, the axial slots may allow the clutch to operate as designed, unaffected by the presence of any debris that may have been driven into the downhole tool during its operation.

The clutch may be engaged on demand by any suitable method. The clutch may be engaged by applying axial force on the rotor. Axial force applied to the rotor may shear through the one or more axial restraint and permit the clutch to engage. The clutch may be engaged by increasing the rate of fluid flow rate through the rotary drive, increasing the pressure drop in the rotary drive until a predetermined pressure drop is reached. This pressure drop acting on the upper area of the rotor may effect the axial force on the one or more axial restraint, the one or more axial restraint shearing where said axial force reaches or exceeds the required force threshold. Beneficially, this arrangement permits embodiments of the invention to resist forces experienced in normal operation, such as torque forces transmitted from the rotary drive and/or the cutting member, and facilitates selective engagement of the clutch.

The clutch may be configured to be fully engaged on demand by downwards axial movement. The clutch may comprise an axial clearance gap. The axial clearance gap may be an engagement allowance distance. The axial clearance gap may provide axial allowance to engage the clutch. The axial clearance gap may be any suitable distance. For example, the axial clearance gap may be 15 mm. Beneficially, the axial allowance may aid in determining the included angle of the male and female locking cones.

According to a second aspect of the present invention, there is provided a downhole tool comprising a cartridge assembly according to the first aspect.

According to a third aspect of the present invention, there is provided a downhole tool assembly comprising:

a tubular component;

a downhole tool; and

a cartridge assembly according to the first aspect.

The tubular component may be of any suitable form or construction.

The tubular component may comprise a bore-lining tubular or tubular string. In particular embodiments, the bore-lining tubular may comprise a casing or casing string. Alternatively, the bore-lining tubular may comprise a completion string, running string, workover string or the like.

The downhole tool may comprise a borehole cutting tool, such as a drilling tool and/or reaming tool.

According to a fourth aspect of the present invention there is provided a method of running a tubular string into a borehole, the method comprising:

running a downhole tool according to the second aspect or a downhole tool assembly according to the third aspect into a borehole; and

directing fluid, such as drill fluid, through the rotary drive to operate the downhole tool.

The method may comprise inserting the tubular string with the attached apparatus into the borehole to a selected depth.

The method may comprise inserting the tubular string with the attached apparatus into the wellbore to a selected depth while causing the shaft to rotate.

The method may comprise stopping rotation of the shaft when reaching a selected depth.

The method may comprise locking the shaft to the motor housing when reaching a selected depth. Locking the shaft to the motor housing may comprise engaging a lock. Locking the shaft to the motor housing may comprise engaging the male cone and the female cone. The method may comprise engaging a lock by applying axial force to the motor housing. Applying axial force may comprise at least one of applying axial force to hold up the tubular string and applying fluid flow to the motor to cause pressure drop in the motor above a selected threshold.

The method may comprise inserting a second cutting structure into the tubular string. The second cutting structure may be disposed at the end of a pipe string.

The second cutting structure may be configured to drill through at least part of the first cutting structure. The second cutting structure may comprise a drill bit.

According to a fifth aspect of the present invention there is provided a clutch for a downhole tool, the clutch comprising:

a male cone provided on one of a rotor of a downhole tool and a stator of the downhole tool;

a female cone provided on the other of the rotor of the downhole tool and the stator of the downhole tool and being operatively associated with the male cone, the male cone and the female cone configured to engage to rotationally fix the rotor of the downhole tool and the stator of the downhole tool, wherein at least one of the male cone and the female cone comprises at least one axial slot extending at least partially along the length of the male cone and/or the female cone.

The clutch may be configured to permit fluid, such as drilling fluid, to flow over the lock during normal operation. The axial slot or slots may extend along- or partially along - the length of the male cone. The axial slot or slots may extend along- or partially along - the length of the female cone. In use, the axial slot or slots may be configured to trap debris carried in the drilling fluid. The axial slot or slots may be configured to receive debris and retain it away from the clutch. The axial slot or slots may be dimensioned to receive a predetermined amount of debris. For example, the slot or slots may be configured to drive debris away from the clutch. Beneficially, the axial slots may allow the clutch to operate as designed, unaffected by the presence of any debris that may have been driven into the downhole tool during its operation.

The clutch may be engaged on demand by any suitable method. The clutch may be engaged by applying axial force on the rotor. Axial force applied to the rotor may shear through the one or more axial restraint and permit the clutch to engage. Alternatively, or additionally, the clutch may be engaged by increasing the rate of fluid flow rate through the rotary drive, increasing the pressure drop in the rotary drive until a predetermined pressure drop is reached. This pressure drop acting on the upper area of the rotor may effect the axial force on the one or more axial restraint, the one or more axial restraint shearing where said axial force reaches or exceeds the required force threshold. Beneficially, this arrangement permits embodiments of the invention to resist forces experienced in normal operation, such as torque forces transmitted from the rotary drive and/or the cutting member, and facilitates selective engagement of the clutch.

The clutch may be configured to be fully engaged on demand by downwards axial movement. The clutch may comprise an axial clearance gap. The axial clearance gap may be an engagement allowance distance. The axial clearance gap may provide axial allowance to engage the clutch. The axial clearance gap may be any suitable distance. For example, the axial clearance gap may be 15 mm. Beneficially, the axial allowance may aid in determining the included angle of the male and female locking cones.

The clutch may be configured to rotationally fix the rotor to the stator. The clutch may be configured to prevent rotation of the cutting member with respect to a tubular component, such as the bore-lining tubular string.

The clutch may be provided or formed between the cutting member and the rotary drive. The clutch may be provided or formed between the cutting member and the housing. The clutch may be provided or formed between the cutting member and the bearing or bearing sub.

The clutch may of any suitable form and construction.

In particular embodiments, the clutch may comprise a cone clutch, such as that described in Deep Casing Tools US 2013/0319769, the contents of which are incorporated herein in their entirety.

In particular embodiments, the clutch may comprise a cone clutch. The clutch may comprise a male cone. The clutch may comprise a female cone. The male cone may be located within the female cone. In use, the male cone may engage or mate with the female cone to engage the clutch. The male cone and the female cone may be configured to be selectively engaged to rotationally fit the rotor to the housing.

The internal taper angle of the female cone and the external taper angle of the male cone may be matched. The female cone and the male cone may have a self- locking taper angle. For example, the self-locking taper angle may be from 0.1 to 10.0 degrees or more.

The male cone may be integral with, or coupled to, the rotor. The female cone may be integral with, or coupled to, the housing of the rotary drive, or vice-versa. The male cone and the female cone may be configured to be engaged by application of axial force to the housing of the rotary drive.

One or more axial restraint may be operatively associated with the clutch. The axial restraint may be configured to permit the clutch to be engaged when a selected minimum axial force is applied, that is where the axial force reaches or exceeds a predetermined force threshold. The axial restraint may be configured to be sheared through. The axial restraint may take any suitable form, shape or construction. In particular embodiments, the axial restraint - or in embodiments comprising more than one axial restraint at least one of them - may comprise a shear pin, shear ring or the like.

The clutch may comprise an anti-rotation clutch or lock. In such embodiments, the clutch or lock may be configured to allow free rotation of the rotor - and the connected cutting member - relative to the stator during normal operations of the rotary drive.

According to a sixth aspect of the present invention, there is provided a downhole tool comprising a clutch according to the fourth aspect.

According to a seventh aspect of the present invention, there is provided an assembly comprising:

a tubular component;

a downhole tool; and

a clutch according to the fourth aspect.

The downhole tool may comprise a borehole cutting tool, such as a drilling tool and/or reaming tool.

The downhole tool may comprise a rotary drive. In some embodiments, the rotary drive may be provided on a cartridge as outlined above.

The downhole tool may comprise a housing. The housing may be configured to be coupled to a leading end of a bore-lining tubular.

The rotary drive may be disposed in the housing.

The rotary drive may comprise a rotor. The rotary drive may comprise a stator. In some embodiments, the rotor may be disposed around the stator. In other embodiments, the stator may be disposed around the rotor.

The stator may be connected to a leading end of the tubular component. The stator may comprise a flared portion. The flared portion may be locked to the interior surface of the tubular component. The flared portion may be locked to the interior surface of the tubular component by a lock arrangement. The stator may be concentric with the rotor. The stator may locate around the rotor. The rotor may locate around the stator.

The rotor and stator may define a void. The void may be located parallel to the axis of rotation. The void may be configured to receive fluid pumped through the fluid inlet and allow the fluid to travel through the void.

The stator may be hollow. The stator may be tubular in shape. The stator may be radially spaced from the rotational axis of the rotor. The stator may comprise a bore. The bore may extend along the length of the rotary drive. The bore may be coaxial with the axis of rotation of the shaft.

The stator may not extend across the rotor. The rotor may be rotatably mounted on the stator. The rotor may be rotatably mounted on the stator by means of a bearing.

The stator may comprise a fluid inlet. The fluid inlet may be located between an external stator and an internal rotor. The fluid inlet may be radially outwardly spaced from the axis of rotation of the rotor.

The rotor may not extend across the stator. The stator may be rotatably mounted on the rotor. The stator may be rotatably mounted on the rotor by means of a bearing.

The rotor and the stator may be spaced radially outwardly of the rotational axis of the rotor. The rotor and the stator may define an access bore. The access bore may be configured to allow unobstructed access of additional components through the rotary drive.

The downhole tool may comprise a shaft. The shaft may be an output shaft. The shaft may be rotationally coupled to the rotary drive. In some embodiments, the shaft may define the rotor. In other embodiments, the shaft may define the stator.

The shaft may be a tubular shaft. The shaft may comprise a bore. The bore may extend along the length of the rotary drive The bore may be coaxial with the axis of rotation of the shaft. The bore may be parallel but not coaxial with the axis of rotation of the shaft.

The bore may be configured to receive a further object. The further object may be located adjacent the cutting structure. The further object may comprise a second cutting member, a second cutting structure or the like. The further object may comprise a sensing device. The further object may be run into the downhole tool.

The downhole tool may comprise a cutting member, a cutting structure or the like. The cutting member or cutting structure may be coupled to the shaft. The cutting member or cutting structure may be coupled to the shaft by any suitable means, for example threads. The cutting member or cutting structure may be coupled at one end of the shaft. The cutting member or cutting structure may be integral with the shaft. The cutting member or cutting structure may be configured to rotate upon rotation of the shaft. The cutting member or cutting structure may be configured to rotate upon rotation of the tubular component locked to the shaft.

The rotary drive may comprise a motor. The rotary drive may comprise a positive displacement motor, or the like.

In particular embodiments, the rotary drive may comprise a turbine arrangement. The turbine arrangement may comprise an axial flow reaction turbine. The rotor may comprise turbine blades. The turbine blades may be arranged to deflect fluid pumped between the rotor and the stator. The turbine blades may be arranged to convert some of the energy of the fluid into rotation of the rotor.

The cutting member or cutting structure may be of any suitable form or construction. For example, the cutting member or cutting structure may comprise a reamer shoe, a drill bit or a coring tool.

The cutting member or cutting structure may comprise a sacrificial cutting structure. The cutting member or cutting structure may be configured to be sacrificed upon completion of the installation of the tubular component into the borehole.

The cutting member or cutting structure may comprise jetting apertures. The jetting apertures may be configured to allow fluid pumped through the void to exit the first cutting structure. The fluid may be configured to act as a lubricant of the first cutting structure. The fluid may be drilling mud slurry.

The downhole tool may comprise a flow diverter. The flow diverter may be located adjacent the fluid inlet. The flow diverter may be configured to divert fluid pumped down the tubular component radially outwardly so as to flow into the fluid inlet.

The downhole tool may comprise one or more bearing between the rotor and the stator. The bearing or bearings may comprise thrust bearings configured to limit the axial movement between the rotor and the stator while allowing relative rotation of these components. The thrust bearing or bearings may be arranged to allow limited axial movement. The bearings may be positioned in any suitable location.

The downhole tool may comprise a seal. The seal may be configured to resist fluid leakage between the rotor and an end of the tubular component. The seal may take any suitable form or shape. For example, the seal may be a rotating elastomeric seal. The downhole tool may comprise a second cutting structure. The second cutting structure may be coupled to a tubular string. The second cutting structure may be a drill bit or a reamer shoe. The second cutting structure may have a narrower diameter than the (first) cutting structure. The second cutting structure may be configured to be run into the tubular component of the reaming tool. The second cutting structure may be configured to be run into the access bore of the shaft. The second cutting structure may be configured to be run into the access bore of the stator. Beneficially, this allows the second cutting structure to pass through the interior of the motor, the motor components not obstructing the passage of the second cutting structure. The second cutting structure may be configured to cut through the first cutting structure. The second cutting structure may be configured to drill a subsequent section of wellbore.

The reaming tool may comprise a position sensing device. The reaming tool may comprise any suitable inspection or testing device. The device may be configured to be fed through the motor bore defined by the rotor and the stator.

According to an eighth aspect of the present invention, there is provided a downhole tool assembly comprising:

a bore-lining tubular;

a downhole tool; and

a clutch according to the fourth aspect.

According to a ninth aspect of the present invention, there is provided a method of running a tubular string into a borehole, the method comprising:

running a downhole tool according to the seventh aspect or a downhole tool assembly according to the eighth aspect into a borehole; and

directing fluid, such as drill fluid, through the rotary drive to operate the downhole tool.

It should be understood that the features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilised, either alone or in combination with any other defined feature, in any other aspect or embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a diagrammatic view of a downhole tool assembly according to an embodiment of the present invention;

Figure 2 shows a longitudinal half section view of an upper portion of a downhole tool and cartridge assembly according to an embodiment of the present invention;

Figure 3 shows a longitudinal half section view of a mid-section of the downhole tool and cartridge assembly;

Figure 4 shows an enlarged cross-sectional view of the rotary drive shown in Figures 2 and 3; and

Figures 5 and 6 show longitudinal half section views of a lower portion of the downhole tool and cartridge assembly, showing the bearings.

Figure 7 shows a clutch as shown in Figure 5;

Figure 8 shows an alternative clutch for use in embodiments of the invention; and

Figure 9 show the axial slot shown in Figure 8. DETAILED DESCRIPTION OF THE DRAWINGS

Referring first to Figure 1 , there is shown a diagrammatic view of a downhole tool assembly 10 according to an embodiment of the present invention. As shown in Figure 1 , the assembly 10 comprises a bore-lining tubular in the form of a casing section or casing string 12, and a downhole tool 14 comprising a rotary drive 16 and a cutting member 18. In use, the assembly 10 is disposed in a well borehole (shown schematically as B) and the rotary drive 16 operated to drive rotation of the cutting member 18 to cut the borehole B.

Beneficially, the provision of a downhole rotary drive 16 facilitates cutting, such as reaming or drilling, of the borehole B without the requirement to rotate the casing or casing string 12.

In some embodiments, the cutting member 18 comprises a drill bit, the tool assembly 10 being utilised to perform a drilling with casing operation in the borehole B. In other embodiments, the cutting member 18 comprises a reaming bit, the tool assembly 10 being utilised to perform a reaming with casing operation in the borehole B. Referring now to Figures 2 to 7 of the accompanying drawings, there is shown an exemplary downhole tool 14 according to an embodiment of the present invention. As shown in Figure 2, the downhole tool 14 comprises a tubular housing 20. An upper end portion 22 of the housing 20 is coupled to a lower end portion 24 of a tubular connector sub 26 via a threaded connection 28, the upper end portion 22 of the housing 20 defining a recess 30 for receiving the lower end portion 24 of the connector sub 26. An upper end portion 32 of the connector sub 26 defines a threaded box connector 34 for coupling the connector sub 26 to the lower end of a casing section, such as casing string 12 shown in Figure 1. While in the illustrated embodiment, the downhole tool 14 is indirectly coupled to the casing section/casing string 12 it will be recognised that the housing 20 of the downhole tool 14 may alternatively be directly coupled to the casing section/casing string 12.

A cartridge assembly 36 is disposed within the housing 20 of the downhole tool 14, an upper part of which is shown in Figure 2. The cartridge assembly 36 comprises a tubular housing 38 (referred to below as the cartridge assembly housing 38) which is disposed within, and which is coupled to, the housing 20 of the downhole tool 14. In use, the cartridge assembly housing 38 defines a stator of the rotary drive 16.

An upper end portion 40 of the cartridge assembly housing 38 comprises a recess or groove 42 for receiving a seal element 44. In the illustrated embodiment, the seal element 44 comprises an o-ring and in use prevents fluid leakage between the cartridge assembly housing 38 and the housing 20 of the downhole tool 14.

The cartridge assembly 36 is secured to the housing 20 by one or more - and in the illustrated embodiment a plurality of circumferentially arranged - retainers 46 disposed between the cartridge assembly housing 38 and the housing 20. In the illustrated embodiment, the retainer 46 prevents axial and rotational movement of the cartridge assembly 36 relative to the housing 20.

The cartridge assembly 36 further comprises a shaft 48, the shaft 48 in use defining a rotor of the rotary drive 16. As shown in the illustrated embodiment, the shaft 48 is hollow, the shaft 48 comprising a throughbore 50 (see Figure 4).

Referring now also to Figures 3 and 4 of the accompanying drawings, which shows a mid-section of the downhole tool 14 and cartridge assembly 36 shown in Figure 2, the rotary drive 16 formed by the cartridge assembly housing 38 and the shaft 48 comprises a positive displacement motor with a fluid passage 52 defined between the outside of the shaft 48 and the inside of the cartridge assembly housing 38. In use, passage of fluid, such as drill fluid, mud or the like, through the fluid passage 52 drives rotation of the shaft 48 at high speed relative to the cartridge assembly housing 38 - and thus relative to the casing section/casing string 12.

As shown in Figure 3, a u-joint 54 is disposed between the lower end of the rotary drive 16 and the upper end of the cutting member 18, an upper end portion 56 of the u-joint coupled to a lower end portion 58 of the cartridge assembly housing 38 and a lower end portion 60 of the u-joint 54 coupled to an upper end portion 62 of the cutting member 18.

Referring now in particular to Figure 3 and also to Figures 5 and 6 of the accompanying drawings, fluid exiting the rotary drive 16 passes into a fluid flow annulus 64 before passing into cutting member 18 via port 66 (see Figures 5 and 6). Although not specifically shown in the drawings, the cutting member 18 may be provided with jetting nozzles or outlet ports for directing the fluid into an annulus between the downhole tool 12 and the borehole B for return to surface.

As shown in Figures 5 and 6, the cutting member 18 - which in the illustrated embodiment takes the form of a reaming member - comprises a generally tubular body 68 coupled to the u-joint 54 and a nose 70.

A sub 72 comprising a ball bearing package 74 is coupled to the housing 20 as shown in Figure 5. As shown in Figure 5, the ball bearing package 74 is disposed outside a drill through diameter D, such that drilling through can be achieved without the requirement to remove the ball bearing package 74.

A thrust bearing package 76 is disposed around the outside of the cutting member upper portion 62.

A clutch in the form of a cone clutch 78 is disposed between the outside of the cutting member 18 and the housing 20. Beneficially, the cone clutch 78 facilitates mill out or drill through operations to be carried out.

An exemplary arrangement for the clutch 78 is shown in Figure 7 of the accompanying drawings.

In use, the clutch 78 is designed to enable free rotation of the cutting member 18 during normal operation and may be engaged or activated on demand by any suitable method. Beneficially, the clutch 78 prevents or at least mitigates unwanted rotation of the cutting member 18 upon drilling thereof, which may otherwise hinder rotation of the cutting member 18.

In the illustrated embodiment, the clutch 78 takes the form of a cone clutch having a female cone 80 and a male cone 82. In this embodiment, the male cone 82 is integral with output shaft 84 of the rotary drive 16 and the female cone 80 is integral with housing 20. However, it will be recognised that the male cone 82 and /or the female cone 80 may alternatively comprise a separate component and may be coupled to the output shaft 84 and housing 20, respectively. As shown in Figure 7, the rotary drive 16 is coupled to the output shaft 84 by a thread connection 86.

As described above, the housing 20 is coupled to a tubular connector sub 26, the connector sub 26 in turn being couplable to a tubular component, which in the illustrated embodiment comprises a casing string 12 (shown diagrammatically in Figure 7). Lock-up of the output shaft 84 to the housing 20 permits rotation of the cutting member 18 directly by rotation of the casing string 12.

When the clutch 78 is engaged, the male cone 82 is locked into the female cone 80. As shown in Figure 7, taper angle a1 of the female cone 80 and taper angle a2 of the male cone 82 match and in the illustrated embodiment, the taper angles a1 , a2 self-lock.

Axial restraints in the form of shear pins 88 (two of which are shown in Figure 7) are operatively associated with the clutch 78. In use, the shear pins 88 are configured to permit the clutch 78 to be engaged when a selected minimum axial force is applied, that is where the axial force reaches or exceeds a predetermined force threshold.

In some embodiments, the clutch 78 is engaged by applying axial force onto the output shaft 84 or via axial movement of components of the rotary drive 16. Reaching or exceeding a selected force threshold causes the shear pins 88 to shear and allow the female cone 80 and the male cone 82 of the clutch 78 to engage.

However, in the illustrated embodiment, the clutch 78 is engaged by increasing the fluid flow rate through the rotary drive 16. Increasing the fluid flow rate through the rotary drive 16 increases the pressure drop of the rotary drive 16 until a predetermined pressure drop - corresponding to an axial force sufficient to shear the shear pins 88 - is reached.

Referring now to Figures 8 and 9 of the accompanying drawings, there is shown an alternative clutch 178 according to another embodiment of the present invention.

The clutch 178 is similar to the clutch 78 described above and like numerals are represented by like reference signs incremented by 100.

As in the clutch 78, the clutch 178 takes the form of a cone clutch having a female cone 180 and a male cone 182. In this embodiment, the male cone 182 is integral with output shaft 184 of the rotary drive 1 16 and the female cone 180 is integral with housing 120. However, as in the clutch 78 it will be recognised that the male cone 182 and/or the female cone 180 of the clutch 178 may alternatively comprise a separate component and may be coupled to the output shaft 184 and housing 120, respectively. The rotary drive 116 is coupled to the output shaft 184 by a thread connection 186.

The housing 120 is coupled to a tubular connector sub 126, the connector sub 126 in turn being couplable to a tubular component, which in the illustrated embodiment comprises a casing string 1 12 (shown diagrammatically in Figure 8). Lock-up of the output shaft 184 to the housing 120 permits rotation of the cutting member 1 18 directly by rotation of the casing string 112.

When the clutch 178 is engaged, the male cone 182 is locked into the female cone 180. As shown in Figure 8, taper angle a3 of the female cone 180 and taper angle a4 of the male cone 182 match and in the illustrated embodiment, the taper angles a3, a4 self-lock.

Axial restraints in the form of shear pins 188 (two of which are shown in Figure 8) are operatively associated with the clutch 178. In use, the shear pins 188 are configured to permit the clutch 178 to be engaged when a selected minimum axial force is applied, that is where the axial force reaches or exceeds a predetermined force threshold.

As shown in Figure 9, in this second embodiment the clutch 178 comprises an axial slot 90 configured to trap between the female cone 180 and the male cone 182 any debris carried along with drilling fluid. A single slot 90 is shown in Figure 9. However, more than one slot 90 may be provided. The axial slot 90 is configured to receive debris and retain it away from the female and male cones 180, 182 of the clutch 178. The axial slot 90 is dimensioned to receive an expected amount of debris. For example, the slot 90 is configured to drive debris away from the clutch 178. Beneficially, the axial slot 90 may thus allow the clutch 178 to operate as designed, unaffected by the presence of any debris that may have been driven into the downhole tool during its operation.

As shown in Figure 8, the clutch 178 also has axial clearance gap 92. In use, the clearance gap 92 may provide axial allowance to engage the clutch 178. The axial clearance gap 92 may be any suitable distance, but in the illustrated embodiment is 15 mm.

In use, the clutch 178 is designed to enable free rotation of the cutting member 1 18 during normal operation and may be engaged or activated on demand by any suitable method. Beneficially, the clutch 178 prevents or at least mitigates unwanted rotation of the cutting member 118 upon drilling thereof, which may otherwise hinder rotation of the cutting member 118.

It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope of the invention.

For example, it will be recognised that the clutches 78, 178 are not limited in use to the downhole tool and assemblies described above and may be used in a variety of downhole tools, such as for example the tools shown and described in European Patent 1989390, in European Patent 2334890 or the completion system shown and described in International Patent Publication WO 2011/048368, the contents of which are incorporated by reference.