The present invention relates to a device for cutting a downhole object, and to a corresponding method of cutting a downhole object. In particular, but not exclusively, the present invention relates to a device for cutting a downhole object such as a wireline, slickline, coiled tubing, drill pipe or other downhole tubing.

In the oil and gas exploration and production industry, it is frequently necessary to perform a maintenance procedure or to carry out remedial treatments in a producing well. Procedures of this type are known as well intervention or workover procedures. Many workover procedures are carried out using equipment run on wireline, slickline or coiled tubing, thereby reducing the cost associated with carrying out the workover. Typical workover procedures may include running and locating wellbore equipment such as downhole plugs, gauges and valves.

During well intervention operations, a blow-out preventer (BOP) and relevant pressure control equipment is installed

above the wellhead. The BOP is a valve assembly provided at the top of the well, and is closed in the event that there is a loss of control of well fluids. BOPs include separate hydraulically actuated sealing rams, and some also include combined shearing and sealing rams. The sealing rams seal an annulus around, for example, tubing, slickline or wireline extending through the BOP, in the event of a loss of control of well fluids. However, in the event of a serious loss of control, the shear rams are actuated to shear the tubing, slickline or wireline and close the well, to thereby restore control.

During an intervention or workover procedure, the wireline, slickline or coiled tubing is run in through the BOP and into the drilled wellbore. In the event of a loss of control of well fluids occurring during the intervention procedure, the BOP may be operated either to seal around the wireline or the like, or in a more serious event, to shear the wireline. However, it is generally undesired to operate the BOP, save in extreme emergency situations. Accordingly, alternative methods are typically employed to seal around or shear the tubing, slickline or wireline.

For example, wellbore hydrocarbon production is controlled by a series of wellhead valves often referred to as a Christmas Tree, Xmas Tree or simply a Wellhead. These valves are seen as primary well pressure control barriers and since not all BOPs have a shear capability for shearing tubing, slickline or wireline used in well intervention operations, one of the wellhead valves often has limited shear capability and could potentially be used in emergency circumstances. The valve is typically a gate-type valve,

which incorporates a sliding gate that cuts the tubing, wireline or slickline, and blocks fluid flow.

However, since the wellhead valves are seen as primary pressure control barriers and valve manufacturers often do not guarantee shear, seal and re-seal functionality, it is preferable to have an alternative option to shear tubing, slickline or wireline used in well intervention operations. This alternative option may not need to seal as well as shear since the Wellhead valves are certified and tested for their sealing capabilities.

In an alternative example, shear/seal valves have been developed which are placed on the wellhead below the BOP. These shear/seal valves are typically relatively large, and expensive to purchase and maintain. The shear/seal valves typically include a ball valve which is rotatable between an open position, and a closed position where the valve closes fluid flow. The wireline extends through the ball valve, and the ball includes hardened cutting surfaces, for cutting the wireline in the event of a loss of control. By moving the ball valve to the closed position, the ball cuts the wireline between the cutting surfaces and a housing of the valve. The wireline is thus sheared and the portion of the wireline below the valve, and the tool carried by the wireline, falls into the well.

There are various disadvantages associated with cutting wireline using shear/seal valves in this fashion. In particular, the primary function of the ball valve is to close and seal the well. Although the ball is provided with hardened cutting surfaces, using the ball to cut and shear a

wireline causes a deterioration in the structure of the ball and its hydraulic actuating assembly, and impairs the sealing function of the valve.

Furthermore, the cutting surfaces are formed at junctions between an outer spherical surface of the ball and upper and lower extents of a through-bore of the ball, through which the wireline passes. Accordingly, for the ball to cut the wireline against the valve housing during rotation of the ball, the ball has to shift the wireline laterally within the well. Also, the lower cutting surface effectively lifts the portion of the wireline and the tool below the ball by a short distance. The weight of this section of the wireline and the tool may be some thousands of pounds. Accordingly, this can cause damage to the valve components and thus a deterioration in the operational qualities of the valve. Additionally, the ball cuts the wireline in two places, such that a portion of the wireline remains within the ball through-bore. This is generally undesired and causes difficulties during subsequent reopening of the valve.

In addition to intervention or workover, other downhole operations can require similar cutting of downhole objects such as wireline, slickline and coiled tubing.

A compact and cost effective device which could shear tubing, slickline or wireline used in well intervention operations would allow oil companies to continue using seal only BOPs and the seal only capabilities of the wellhead valve. This shear only device would significantly reduce operational, procurement and maintenance costs of shear and seal type BOPs, and shear and seal wellhead valves, as well

as significantly reduce operational risk of using a wellhead valve primary pressure control barrier to shear tubing, slickline or wireline used in well intervention operations.

It is amongst the objects of embodiments of the present invention to obviate or mitigate at least one of the foregoing disadvantages.

According to a first aspect of the present invention, there is provided a device for cutting a downhole object, the device comprising: a main housing; and first and second cutting members each rotatably mounted within the main housing, the first cutting member defining a respective first cutting surface and the second cutting member a respective second cutting surface; wherein the first and second cutting members are adapted for contra-rotation to thereby cut an object.

The invention thus provides a device for cutting a downhole object including first and second cutting members which are rotated relative to one-another to cut an elongate object located between the cutting surfaces defined by the cutting members. This may facilitate cutting of an object such as a wireline, slickline and/or coiled tubing extending through the device. By providing a device designed specifically for cutting a downhole object, the use of wellhead gate valves to cut such a downhole object, or the provision of bulky shear/seal valves, is avoided.

The main housing may include a main housing bore, and the first and second cutting members may be mounted within the

main housing bore and rotatable relative thereto. Axes of rotation of the first and second cutting members may be disposed substantially perpendicularly to the main housing bore.

Preferably, the first and second cutting members are adapted for simultaneous contra-rotation. Accordingly, the first and second cutting surfaces may be adapted for simultaneous movement to cut an object located therebetween. The device may comprise an actuating assembly or actuating means for actuating the first and second cutting members to cut the object, and the actuating assembly may facilitate simultaneous contra-rotation of the cutting members. It will be understood that the first and second cutting members are adapted for contra-rotation in that they are adapted for rotation in respective opposite rotational directions towards and away from each other.

The cutting members may be movable between respective open and respective closed positions, and the cutting surfaces of the cutting members may be adapted to cut the object during movement of the cutting members towards their closed positions. The cutting members may be adapted to cut the object during passage from their respective open positions to their respective closed positions, such that the object is cut before- the cutting members have completed movement -to their closed positions. The cutting members may thus be adapted to move beyond a cutting position where the object is cut, to the closed position, thereby ensuring correct cutting of the object. Alternatively, the cutting members may cut the object only on completing final movement to their respective closed positions.

Preferably, the first cutting member is an outer cutting member and the second cutting member is an inner cutting member, the inner cutting member located within and rotatable relative to the outer cutting member. This may facilitate operation of the device to cut an object and may facilitate minimisation of dimensions of the device. The inner cutting member may thus be adapted for contra-rotation within and relative to the outer cutting member during cutting of an object.

The device may be adapted to cut the object in a scissors cutting action. This may be achieved by arranging the first and second cutting surfaces such that upon rotation of the cutting members, the cutting surfaces are brought into face- to-face opposition around the object, and such that the blades overlap following cutting of the object. Arranging the device to cut the object in a scissors cutting action, where the blades overlap, may facilitate complete and accurate cutting of the object.

The device may be adapted to cut the object at a single location along a length of the object. Following cutting, the device may be adapted to permit the weight of the object to cause any remaining part of the object below the cut to drop into the well. Thus by cutting the object at a single location, following retrieval of a remainder of the object above the cut, no part of the object remains within the device. The first and second cutting members may be located such that on rotation of the cutting members to a position where they cut the object, the first and second cutting surfaces are moved relatively upwardly within the housing to

cut the object at an upper location, the weight of the object then causing any remaining part of the object located within the cutting members to drop into the well. It will be understood that references herein to "upper" and "lower" are made relative to a normal orientation of the device, in use. Typically, the device will be oriented such that a main axis of the housing is vertical and thus movement of the cutting surfaces upwardly is in a vertical sense.

The cutting members may be adapted to cut the object at a position where the object is aligned with a main axis of the device. In this fashion, the object may be cut at a central location within the device, where the object will normally reside, in use. For example, where the object is a wireline, the weight of the wireline (and any associated tool) will typically cause the wireline to hang within the device in a position where it is coaxial with the main axis of the device. It will be understood that the object may be located coaxially within the device in that a main axis of the object is aligned with the main axis of the device. By arranging the device to cut the object in this position, it is not necessary to exert a force on the object to move it to a secondary position where it is to be cut. This may have the effect of reducing consequent forces on the components of the device.

However, the device may comprise a guide assembly for guiding or urging the object to the central location. Thus where the object is initially located spaced or non-coaxial with the device main axis, the object may be moved to the central location for subsequent cutting. The object may be located non-coaxially within the device due, for example, to

deviations in the wellbore. The guide assembly may comprise at least one guide for guiding the object to the central location, and in a preferred embodiment, includes at least one pair of guides, which pair of guides together bring the object to the central location. The pair of guides may comprise a guide formed on or in the first cutting member and a cooperating guide formed on or in the second guide member, rotation of the cutting members causing the guides to together move the object to the central location. The pair of guides may define the respective first and second cutting surfaces, optionally at respective ends thereof, such that following movement of the object to the central location, where the object may be held between the ends of the guides, the object may be cut.

The guide assembly may comprise a second pair of guides, which may include cooperating second guides formed on or in the first and second cutting members, and which may be spaced around the cutting members from the first guides. In use, the first and second guide pairs may be arranged to guide the object to the central location, and the first guide pair to cut the object. The second guides may extend a greater distance around a surface of the respective cutting members. Thus the object may be cut by the cutting surfaces of the first guide pair before the object has reached ends of the second guide pair. This may facilitate cutting of the object at a single location and thus avoiding part of the object remaining in the device following cutting.

The cutting members may each define a respective through- bore, the through-bore of each cutting member having first

and second openings formed in a wall of the respective cutting member. In use and with the cutting members in an open position, the first and second openings may be upper and lower openings. The through-bore of each cutting member may be substantially perpendicular to the respective axis of rotation of the cutting members, about which the cutting members rotate, in use. The cutting members may take the form of tubular sleeves and in embodiments of the invention may be in the shape of a drum, and may thus be generally hollow cylinders. Alternatively, the cutting members may have a generally spherical outer surface or may be of any other suitable shape. The guides may take the form of slots, channels or the like formed in walls of the cutting members. The guides may extend from one or both of the first and second openings in the cutting member walls, and may extend in a common direction around a surface of the cutting member. Where the cutting members are drums or of hollow spherical shape, the guides may extend in a common circumferential direction around the cutting members. The guides of the first and second cutting members may extend in opposite directions. Accordingly, when the cutting members are rotated, the guides may interact to guide the object to the central position.

The device may comprise an actuating assembly or actuating means for selectively actuating the device. The actuating assembly may be adapted to selectively rotate the cutting members, to cut the object. The actuating assembly may comprise an actuating member coupled to the first and second cutting members, for exerting a force on the cutting members to thereby rotate the cutting members. The actuating member may be adapted to simultaneously rotate the first and second

cutting members in respective opposite rotational directions, and thus to contra-rotate the cutting members. In embodiments of the invention, the actuating assembly is a hydraulic actuating assembly, where the actuating member takes the form of a piston. However, it will be understood that the actuating assembly may alternatively be an electric, electronic, mechanical or electro-mechanical actuating assembly.

The actuating assembly may comprise a drive transfer mechanism for transferring force from the actuating member to the cutting members. The drive transfer mechanism may be adapted to convert a translational movement of the actuating member into a rotational movement of the first cutting member, and a contra-rotational movement of the second cutting member. The drive transfer mechanism may comprise first and second drive transfer couplings, each associated with a respective one of the first and second cutting members and coupled to the actuating member. The first and second drive transfer couplings, and thus the associated first and second cutting members, may be rotatable about common axes of rotation. Thus the first and second drive transfer couplings may be located coaxially. Translational movement of the actuating member may be adapted to rotate one of the first and second drive transfer couplings in a first rotational direction and the other one of the first and second drive transfer couplings in a second, opposite rotational direction. This may contra-rotate the cutting members.

The actuating mechanism may comprise a driver coupled to the actuating member and to the first and second drive transfer

couplings. Translational movement of the actuating member may be transferred to the drive transfer couplings through the driver, to thereby contra-rotate the drive transfer couplings. Alternatively, the actuating member may be coupled directly to the drive transfer couplings.

The drive transfer mechanism may comprise a first drive transfer pin coupled between the driver and the first drive transfer coupling, and a second drive transfer pin coupled between the driver and the second drive transfer coupling. The first and second drive transfer pins may be coupled to the respective drive transfer couplings at points spaced from the respective drive transfer coupling axes of rotation. In this fashion, translation of the actuating member may carry the pins, rotating the drive transfer couplings about their axes of rotation. The driver may include a guide slot or channel, and the drive transfer pins may be engaged in the driver channel and coupled to the respective drive transfer coupling. The driver guide slot may be shaped such that translation of the actuating member contra-rotates the drive couplings. In embodiments of the invention, the driver guide slot comprises a slot portion disposed substantially perpendicular to an axis of the actuating member.

The first and second drive "transfer couplings may be located straddling the driver, and thus the driver may be movable between the couplings. To facilitate this, the first and second drive transfer couplings may comprise respective concentrically oriented shafts, and one of the shafts may extend through an aperture in the driver for locating the drive transfer couplings straddling the driver.

The first and second drive transfer couplings may be adapted for rotation between open and closed positions corresponding to the open and closed positions of the cutting members. The drive transfer mechanism may be arranged to restrain the first and second drive transfer couplings in their respective open and closed positions. This may ensure that the drive transfer couplings cannot move further beyond their respective open and closed positions. The first and second drive transfer couplings, and thus the first and second cutting members, may be coupled together such that movement of the drive transfer couplings beyond their open/closed positions is prevented. To achieve this, the first and second drive couplings may each comprise a curved cam track, slot, channel or the like, each of which may be adapted to receive the drive transfer pin which is connected to the other one of the drive couplings. The cam track of one of the drive transfer couplings may permit movement of the pin connected to the other one of the drive transfer couplings, and thus movement between the open and closed positions. However, the pin may be restrained against movement beyond the open and closed positions by abutment with ends of the cam track.

The cutting surfaces may take the form of cutting blades or edges defined by the cutting members, and may be formed integrally with the cutting members or may be removable, for maintenance/repair. The cutting surfaces may be formed at the ends of the respective guides and may be defined between an outer surface of the cutting members and an end wall of the guides.

According to a second aspect of the present invention, there is provided a device for cutting a downhole object, the device comprising: a first cutting member defining a first cutting surface; and a second cutting member defining a second cutting surface; the first and second cutting members adapted to cut an object located between the first and second cutting surfaces in a scissors cutting action.

According to a third aspect of the present invention, there is provided a device for cutting a downhole object, the device comprising: a first cutting member defining a first cutting surface; and a second cutting member defining a second cutting surface; the first and second cutting members adapted to cut an object located therebetween at a single location along a length thereof.

According to a fourth aspect of the present invention, there is provided a device for cutting a downhole object, the device comprising: a main housing having a housing main axis; a first cutting member defining a first cutting surface; a second cutting member defining a second cutting surface; the main housing, the first cutting member and the second cutting member together defining a through-bore; and the first and second cutting members adapted to guide an object located within the through-bore to a location where the object is positioned coaxially with the housing main axis, whereupon the first and second cutting surfaces cut the object.

Further features of the devices of the second to fourth aspects of the invention are defined in relation to the first aspect.

According to a fifth aspect of the present invention, there is provided a method of cutting a downhole object, the method comprising the steps of: running a downhole object into a well such that the object extends through a device for cutting a downhole object; and contra-rotating cutting members of the device to cause first and second cutting surfaces defined by the respective first and second cutting members to cut the downhole object.

According to a sixth aspect of the present invention, there ^■ is provided a method of cutting a downhole object, the method comprising the steps of: running a downhole object into a well such that the object extends through a device for cutting a downhole object; and rotating cutting members of the device to cause first and second cutting surfaces defined by the respective first and second cutting members to cut the downhole object in a scissors cutting action.

According to a seventh aspect of the present invention, there is provided a method of cutting a downhole object, the method comprising the steps of: ^. - . running a downhole object into a well such that the object extends through a device for cutting a downhole object; and rotating cutting members of the device to cause first and second cutting surfaces defined by the respective first and second cutting members to cut the downhole object at a single location along a length thereof.

According to an eighth aspect of the present invention, there is provided a method of cutting a downhole object, the method comprising the steps of: running an object downhole and through a device for cutting a downhole object; locating the object extending through a through-bore of the device defined by a main housing, a first cutting member and a second cutting member of the device; rotating the first and second cutting members to guide the object to a location where the object is positioned coaxially with a main axis of the housing; and subsequently cutting the downhole object.

It will be understood that the features of one or more of the above aspects of the invention may be provided singularly or in combination.

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

Fig. 1 is a perspective view of a device for cutting a downhole object, in accordance with a preferred embodiment of the present invention, taken from above and to one side;

Figs. 2 to 4 are views of the device of Fig. 1 with part of the structure of the device shown in ghost outline, and showing the device during movement to cut a downhole object;

Fig. 5 is a view of the device of Fig. 1 in the position of Fig. 4, shown from above and to the other side;

Figs. 6 to 8 are views of the device of Fig. 1 taken from above, and showing the device during movement to cut a downhole object;

Fig. 9 is a view of the device in the position of Fig. 8, taken from below;

Fig. 10 is an enlarged view of a first cutting member forming part of the device of Fig. 1, taken from one side;

Fig. 11 is an enlarged view of the first cutting member of Fig. 10, taken from the other side;

Fig. 12 is an enlarged view of a second cutting member forming part of the device of Fig. 1;

Fig. 13 is a view of part of an actuating assembly which forms part of the device of Fig. 1, and the first cutting member of Fig. 10, taken from one side and showing part of the actuating assembly in ghost outline;

Fig. 14 is a view of the actuating assembly and the first cutting member of Fig. 13, taken from the other side;

Fig. 15 is a view of part of a further part of the actuating assembly of Fig. 13, and the second cutting member of Fig. 12 ;

Fig. 16 is an enlarged view of an actuator forming part of the actuating assembly of Fig. 13;

Fig. 17 is an enlarged view of a first drive transfer coupling forming part of the actuating assembly of Fig. 13, taken from one side;

Fig. 18 is a view of the first drive transfer coupling of Fig. 17, taken from the other side;

Fig. 19 is an enlarged view of a second drive transfer coupling forming part of the actuating assembly of Fig. 13, taken from one side;

Fig. 20 is a view of the second drive transfer coupling of Fig. 19, taken from the other side;

Fig. 21 is an enlarged view of a torque sub forming part of the actuating assembly of Fig. 13, taken from one side; and

Fig. 22 is a view of the part of the torque sub of Fig. 21 shown from the other side.

Turning firstly to Fig. 1, there is shown a perspective view of a device for cutting a downhole object such as a wireline, slickline or coiled tubing, the device indicated generally by reference numeral 10. The device 10 is also shown in Figs. 2 to 4 at various stages during movement to cut the downhole object which, in the illustrated embodiment, is a wireline 12. Fig. 5 also shows the device 10 in the position of Fig. 4, following cutting of the wireline 12, but from the other side. In Figs. 2 to 5, part of the structure of the device 10 is shown in ghost outline, for illustration purposes.

In general terms, the device 10 comprises a main housing 14, a first cutting member in the form of a hollow outer sleeve or drum 16, and a second cutting member in the form of a hollow inner sleeve or drum 18. Each of the outer and inner drums 16 and 18 are rotatably mounted within the main housing 14, and define respective first and second cutting surfaces in the form of cutting blades or edges 20 and 22. The outer and inner drums 16 and 18 are rotatably mounted within the main housing 14 and are adapted for contra- rotation to cut the wireline 12.

In use, the device 10 is typically provided on a wellhead of a well below a BOP (not shown) , and is coupled to a riser (not shown) which extends from the device 10 to a rig at surface. The wireline 12 is located extending through the device 10 and into the well, for carrying out a downhole procedure, such as an intervention or workover operation. This may involve, for example, running, location and operation of wellbore equipment such as a downhole plug, a gauge or a valve (not shown) . In certain situations, it becomes necessary to cut the wireline 12. For example, in the event of a loss of control of downhole fluids, there is not sufficient time to recover the wireline 12 to surface to enable closure of the well using a gate valve in the wellhead. Accordingly, in order that the well may be closed, the wireline must be cut, abandoning any tool or other equipment in the well. The well can then be safely closed to regain control of well fluids.

The device 10 is operated to cut the wireline 12 by contra- rotating the outer and inner drums 16 and 18, so that the cutting blades 20 and 22 are brought together and cut the

wireline 12 in a scissors cutting action. The outer and inner drums 16 and 18 are shown in Fig. 2 in an open position, and in Fig. 3 during movement towards the closed position where the wireline 12 has been cut, which is shown in Figs. 4 and 5. This movement of the outer and inner drums 16 and 18 is shown more clearly in Figs. 6 to 8, which are views of the device 10 taken from above, and which show the device 10 progressively during movement to cut the wireline 12. Fig. 9 also shows the device 10 in the closed position of Fig. 8, but taken from below. Accordingly, as best seen in Figs. 6 to 8, as the drums 16 and 18 contra- rotate, the cutting blades 20 and 22 are brought together to nip and cut the wireline 12. The severed wireline and any associated tool then falls into the well under its own weight.

Following actuation of the device 10 to cut the wireline and closure of the wellhead gate valve, the well may be stabilised and reopened. This may involve pumping a heavy fluid downhole above the gate valve to kill the well, enabling the safety valve to be reopened, so that the well may be re-entered. To achieve this, the device 10 is returned to the open position by rotating the outer and inner drums 16 and 18 to their starting, open positions. The gate valve is then opened and the severed section of wireline 12 and associated tool is fished from the well and recovered. The device 10 is thus now reset for reuse in a further downhole procedure.

The structure of the device 10 and its method of operation will now be described in more detail, with reference also to Figs. 10 to 22.

The outer drum 16 is shown in more detail in the enlarged views of Figs. 10 and 11, whilst the inner drum 18 is shown in more detail in the enlarged view of Fig. 12. The inner drum 18 is shaped to fit within and to contra-rotate relative to the outer drum 18. The device 10 includes a guide assembly 24 for guiding the wireline 12 into a central location within a through-bore 26 of the device 10 which is defined by the main housing 14, the outer drum 16 and the inner drum 18. During movement to cut the wireline, the wireline 12 is brought to the central location, where the wireline 12 is located coaxially with a main axis 28 of the through-bore 26. This reduces loading on the device 10, as it is not necessary for the device to raise the wireline 12, and any associated tool, in order to perform the cutting action, as is the case with ball-type shear/seal valves.

The guide assembly 24 includes a first pair of guides in the form of a generally elongate channel or slot 30 in the outer drum 16, which extends from a first opening 32 of the drum, and a cooperating wedge or V-shaped channel or slot 34 in the inner drum 18, which extends from a first opening 36 of the inner drum 18. The first openings 32 and 36 are generally circular on one side and elliptical on a side adjacent the channels 30 and 34. The outer drum additionally includes a second opening 38, and the first and second openings 32 and 38 together define a through-bore 40 of the outer drum 16. In a similar fashion, the inner drum 18 includes a second opening 42, and the first and second openings 36 and 42 together define a through-bore 44 of the inner drum 18. The second openings 38 and 42 are each of similar shape to the outer drum first opening 32. Each of

the through-bores 40 and 44 are oriented perpendicularly to respective axes of rotation 46 and 48 of the outer and inner drums 16, 18.

In use, when the outer and inner drums 16 and 18 are in the open position of Fig. 2, the first openings 32 and 36 are aligned and form upper openings, whilst the second openings 38 and 42 are similarly aligned and form lower openings. The through-bores 40 and 44 thus together define part of the main through-bore 26 of the device 10. Contra-rotation of the outer and inner drums 16 and 18 brings the guides 30 and 34 of the first guide pair together, and this carries the wireline 12 into the central location within the main through-bore 26 of the device 10.

The guide assembly 24 additionally includes a second pair of guides in the form of an elongate channel or slot 50 in the outer drum 16, which extends from the second opening 38, and a cooperating channel or slot 52 of similar shape in the inner drum 18, which extends from the second opening 42. The second channels 50 and 52 extend to a greater distance around the circumferences of the respective outer and inner drums 16 and 18 than the first channels 30 and 34. In use, during contra-rotation of the drums 16 and 18, the first and second pairs of guides cooperate to guide the wireline 12 to the central location."

The channels 30 and 34 each define corresponding ends 54 and 56, and the cutting blades 20 and 22 are formed at. a junction between outer surfaces of the respective drums 16 and 18 and the ends 54, 56 of the channels 30 and 34. As the channels 30 and 34 are shorter than the channels 50 and

52, the wireline 12 reaches the ends 54 and 56 of the channels 30 and 34, before it reaches corresponding ends of the channels 50 and 52, as best shown in Fig. 7. Further movement of the drums 16 and 18 towards the closed position of Fig. 8 then nips and cuts the wireline 12. In this way, the wireline 12 is cut at a single location along a length thereof, and this ensures that, following cutting, no part of the wireline remains within the drums 16 and 18. This is because the weight of the severed section of the wireline 12, and any associated tool, causes the section to fall into the well.

The device 10 also comprises an actuating assembly 58, part of which is shown in Fig. 13 and 14, together with the outer drum 16, and part of which is shown in Fig. 15, together with the inner drum 18. Additionally, the actuating assembly 58 is shown in the further enlarged view of Fig. 16.

The actuating assembly 58 is hydraulically operated, and serves for actuating the device to contra-rotate the outer and inner drums 16 and 18, to cut the wireline 12. The actuating assembly includes a piston 60 which is mounted within a cylinder 62, and which is held captive between upper and lower retaining plates 63 and 64 (Fig. 1) which are secured to the main housing 14. The cylinder 62 is coupled to both the outer and inner drums 16 and 18 through a drive transfer mechanism 64, such that translation of the cylinder 62 rotates the drums 16 and 18 between their open and closed positions, to cut the wireline 12.

In more detail, the actuating assembly 58 includes a driver in the form of a shaped plate 68 which is mounted on the cylinder 62, and which is coupled to the drive transfer mechanism 64. The drive transfer mechanism 64 includes first and second drive transfer couplings in the form of a torque plate 70 which is associated with the outer drum 16, and a torque plate 72 which is associated with the inner drum 18. The torque plates 70 and 72 are shown in more detail in the further enlarged views of Figs. 17 and 18, and Figs. 19 and 20, respectively. The torque plates 70 and 72 serve for converting a translational movement of the cylinder 62 into a contra-rotational motion of the outer and inner drums 16 and 18, as will be described below.

The torque plates 70 and 72 are coupled to the outer and inner drums 16 and 18 as follows. A torque sleeve 74, which is also shown in the further enlarged views of Figs. 21 and 22, is coupled to the outer drum 16, as shown in Fig. 13. The torque sleeve 74 includes a flange 76 which extends around part of a circumference of a body 78 of the torque sleeve 74, and which has a cut-out quadrant 80, which is shaped to engage a flange quadrant 82 provided on the outer drum 18. Engagement of the torque sleeve flange 76 with the flange quadrant 82 on the drum 18 permits transfer of a rotational drive force to the drum 18. The torque sleeve 74 carries two hub portions 84 which are shaped to engage" corresponding hub portions on the torque plate 70, for securing the torque sleeve to the torque plate, and which together form a hollow shaft 88.

In a similar fashion, the inner drum 18 has a shaft 90 which carries hub portions 92 that are shaped to engage

corresponding hub portions 94 on the second torque plate 72, for securing the inner drum 18 to the torque plate 72. The drum shaft 90, the shaft hub portions 92 and the torque plate hub portions 94 are shaped to pass through an internal bore 96 which extends through the shaft 88 and the first torque plate 70, for coupling the inner drum 18 to the driver plate 68.

Additionally, the drive transfer mechanism 66 includes respective first and second drive transfer pins 98 and 100, for coupling the first and second torque plates 70 and 72 to the driver plate 68. The driver plate 68 includes a main channel 102 and a cross-channel 104, and the pins 98 and 100 each engage in opposite portions adjacent ends 106 and 108 of the cross-channel 104. In this way, translation of the cylinder 62 and thus of the driver plate 68, rotates the torque plates 70 and 72.

The actuating assembly 58 is assembled as follows. The hollow shaft 88 of the outer drum 16 is coupled to the first torque plate 70, by engagement of the hub portions 84 and 86. The first drive pin 98 is secured in a threaded bore 110 of the .torque plate 70 and is located extending through the end 106 of the driver plate cross-channel 104. The protruding end of the first drive pin 98 engages in a cam track ^" 112 formed in the second torque plate 72. -The shaft 90 of the inner drum 18 is then rotatably mounted within the hollow shaft 88, and extends through the driver plate main channel 102. The second drive pin 100 is secured in a threaded bore 114 of the torque plate 72, and is located extending through the driver plate cross-channel end 108 into a cam track 116 of the first torque plate 70. The

torque plate 72 is then secured to the shaft 90 by engagement of the hub portions 92 and 94. The first and second torque plates 70 and 72 are thus located straddling the driver plate 68, and are coupled to the driver plate 68 by the drive pins 98 and 100. As the drive pins 98 and 100 are located off-centre from the axes of rotation 46 and 48 of the outer and inner drums 16 and 18, and are movable along the cross-channel 104, translation of the driver plate 68 rotates the torque plates 70 and 72, to thereby rotate the drums.

The device 10 thus operates as follows. The device 10 is initially in the open position of Fig. 1, where the through- bore 26 is open. When it is desired to cut the wireline 12, hydraulic fluid is supplied to the cylinder 62 in a region below a lower piston face (not shown) of the piston 60, and is allowed to bleed from an area above an upper piston face (also not shown) . As the piston 60 is captive, this causes the cylinder 62 to translate downwardly relative to the main housing 14. This movement of the piston carries the driver plate 68 downwardly around the inner drum shaft 90, which is received in the main channel 102. During this movement, the drive pin 98 is carried downwardly by its engagement in the cross-channel 104. The off-centre location of the pin 98 causes a corresponding rotation of the outer drum 16 in a first rotational direction towards its closed position, through its connection with the torque plate 70. During this movement of the driver plate 68, the pin 98 translates along the cross-channel 104 between the end 106 and the shaft 90.

Simultaneously, the pin 100 is carried downwardly by its engagement in the cross-channel 104. The off-centre location of the pin 100 causes a corresponding rotation of the inner drum 18 in a second, opposite rotational direction towards its closed position, through its connection with the torque plate 72. During this movement of the driver plate, the pin 100 translates along the cross-channel 104 between ^' the end 108 and the shaft 90. The inner drum 18 is thus contra-rotated relative to the outer drum 16.

During movement of the outer and inner drums 16 and 18 towards their closed positions, the guides 48, 50 and 52, 54 guide the wireline 12 into the central location within the main bore 26, until the drums reach the position shown in Fig. 7. Further movement of the drums 16, 18 towards their closed positions shown in Figs. 5, 8 and 9 then nips and cuts the wireline 12. The drums 16, 18 are restrained against movement beyond their closed positions by the pin 98 abutting an end of the torque plate 72 cam track 112, and the pin 100 abutting an end of the torque plate 70 cam track 116.

The drums 16 and 18 can then be returned to their starting, open positions. This is achieved by supplying fluid to the cylinder 62 above the upper piston face and permitting fluid to bleed from the area below the lower" piston face. This translates the cylinder 62 upwardly towards its starting position, contra-rotating the drums 16, 18 in the opposite direction, back to their starting positions. The drums 16, 18 are then restrained against movement beyond their open positions by the pin 98 abutting an opposite end of the torque plate 72 cam track 112, and the pin 100 abutting an

end opposite end of the torque plate 70 cam track 116. The device 10 is then reset ready for reuse.

If desired, the drums 16, 18 may be locked in their open or closed positions. The drums are locked in their closed positions by locating a retaining pin (not shown) in an aperture 118 in the torque plate 72, which extends through the driver plate main channel 102 and engages in an aligned aperture 120 in the torque plate 70. In a similar fashion, the drums 16, 18 may be locked in their open positions by locating a retaining pin (not shown) in an aperture 122 in the torque plate 72, which extends through the driver plate main channel 102 and engages in an aligned aperture 124 in the torque plate 70.

Various modifications may be made to the foregoing without departing from the spirit and scope of the present invention.

For example, it will be understood that the device may be for cutting any suitable alternative downhole object, such as alternative tubing.

The cutting members may cut the object only on completing final movement to their respective closed positions.

The cutting members may have a generally spherical outer surface or may be of any other suitable shape.

The actuating assembly may alternatively be an electric, electronic, mechanical or electro-mechanical actuating assembly.

The actuating member may be coupled directly to the drive transfer couplings.

The device may optionally cut the downhole object and seal the well. Thus the first and second cutting members may be provided with sealing elements or surfaces, for sealing the -well when the cutting members are in their closed positions.