WO2008107694A1

WO2008107694A1 - Downhole tool

Info

Publication number: WO2008107694A1
Application number: PCT/GB2008/000812
Authority: WO
Inventors: Andrew Ollerenshaw; Mark Russell
Original assignee: National Oilwell Varco, L.P.
Priority date: 2007-03-08
Filing date: 2008-03-10
Publication date: 2008-09-12
Also published as: CA2679547A1; GB0704484D0; GB2447225B; US20100108394A1; EP2132402A1; AU2008222456A1; GB2447225A

Abstract

A downhole tool (10') comprises a body (12') having a longitudinal axis and a body through-bore (14'), a slot (34') communicating the outside of the body with the body through-bore. A sleeve actuator (30') mandrel also has a bore and is selectively axially slidable in the body through-bore. A hollow bar (36') is slidable with a radial component in the slot. At least two levers (210), each pivoted to the mandrel (about a first axis perpendicular the longitudinal axis) extend into the hollow bar and are pivoted thereto (about a second axis parallel the first axis). The levers lie in an actuation plane perpendicular the first and second axes and containing the slot. The levers are disposed at an inclined angle with respect to the longitudinal axis so that longitudinal motion of the mandrel translates into radial movement of the bar.

Description

Downhole Tool

The present invention relates to a downhole tool, in particular an under-reamer.

BACKGROUND

Our pending international application publication number WO2006/072761 (the entire disclosure of which is incorporated herein by reference) discloses a downhole tool comprising: a body having a longitudinal axis and a body through-bore, a slot communicating the outside of the body with the body through-bore; a sleeve actuator mandrel having a sleeve actuator mandrel through-bore and being selectively axially slidable in the body through-bore; a flange on the sleeve actuator mandrel extending into said slot and having one of ribs and channels formed on its sides and inclined at an acute angle to the longitudinal axis; and a hollow bar slidable with a radial component in the slots, the other of channels and ribs being formed on the bar and corresponding with, and engaged in, said one of said ribs and channels of the flange.

The advantage of this arrangement is that the actuating surfaces of the tool, namely the interengaging ribs and channels, are isolated from the drilling fluid. Seals may be provided between the sleeve actuator mandrel and the body beyond both ends of the slot and define, between them and seals around the bars in the slots, a chamber enclosing lubricating oil. In this event, the mutually engaging surfaces are primarily within the confines of the oil chamber, where they are not only protected from contamination by drilling fluid and debris, but also they are washed in lubricant to facilitate their movement and to reduce wear.

It is an object of the present invention to provide an alternative arrangement that has the same benefits of this arrangement.

US-A-4865137 discloses an under-reamer in which cutter arms are pivoted in the body of the tool and a pivot link pivoted to the arm is urged by a hydraulically actuated control piston to pivot each arm outwardly. BRIEF SUMMARY OF THE DISCLOSURE

In accordance with a first aspect of the present invention, there is provided a downhole tool comprising: a body having a longitudinal axis and a body through-bore, a slot communicating the outside of the body with the body through-bore; a sleeve actuator mandrel having a sleeve actuator mandrel through-bore and being selectively axially slidable in the body through-bore; a hollow bar slidable with a radial component in the slot; and at least two levers, each pivoted to said sleeve actuator mandrel about a first axis perpendicular to a line parallel to said longitudinal axis, and each lever extending into said hollow bar and pivoted thereto about a second axis parallel said first axis, wherein an actuation plane of movement of said hollow bar on pivoting of the levers is perpendicular said first and second axes and contains said slot, and the first and second pivot axes at the intersection thereof with said actuation plane define a parallelogram.

Thus, when the sleeve actuator mandrel is actuated to move along said longitudinal axis from a deactuated to an actuated position thereof, said levers are pivoted about their first axes to increase the radial position of said second axes with respect to said longitudinal axis, and whereby said bar slides with a radial component in said slot

A return mechanism is required to guarantee that the bars return to their deactuated position when this is selected. Usually, the strongest mechanism is required to actuate tools, because this will generally involve contact with the hole bore (to start cutting, for example, with an under-reamer), whereas retraction is generally not opposed. On the other hand, when components get worn or contorted by their interaction with the bore hole, they may be difficult or impossible to withdraw.

This might be very problematic with an under-reamer where, to get the tool out through a narrow casing above the reamer, the reamer must be withdrawn (deactuated). Consequently, it is preferred that the levers are captivated by pivot pins forming said first and second pivots between the levers and the sleeve actuator mandrel and the hollow bar respectively. Thus the sleeve actuator mandrel cannot return to its deactuated position without withdrawing the hollow bar into its slot. Preferably, said sleeve actuator mandrel comprises a separate mandrel and sleeve actuator, the sleeve actuator having an actuator through-bore and being axially slidable in the body through-bore between a tool actuated position and a tool deactuated position, the mandrel having a mandrel through-bore and being selectively axially slidable in the body through-bore between a tool actuated position, an interlock position and a sleeve-lock position; wherein: an extension of the mandrel is a close sliding fit inside a first end of the sleeve actuator; said first end captivates a lock element; said body has an internal groove positioned so that, when said sleeve actuator is in said tool deactuated position, said lock element is aligned with said groove and held in engagement therein by said extension while the mandrel is between its interlock and sleeve-lock positions; and said mandrel has an external recess positioned so that, when said mandrel is in said interlock position, said lock element is aligned with said recess, whereupon movement of the mandrel towards said tool actuated position releases said lock element from said groove permitting said sleeve actuator to be moved by the mandrel to said tool actuated position, said mandrel and sleeve actuator being locked together by the body holding said lock element in said recess between said interlock and tool actuated positions of the mandrel.

Put another way, first means may lock the sleeve actuator with respect to the body in said tool deactuated position and while said mandrel is between said interlock and sleeve-lock positions; and second means may lock the sleeve actuator with respect to the mandrel and while said mandrel is between said interlock and tool actuated positions.

Separating the mandrel from the sleeve actuator permits them to move independently when for some stroke movements of the mandrel which is needed for switching between actuation mode and deactuation mode of the tool. Generally, a strong return spring is needed and, by connecting the mandrel with the sleeve actuator during some movements thereof, the return spring for the mandrel can also serve as the return spring for the bars. Since it is normal to provide signalling in the form of pressure pulses, at least when the tool is actuated, then, by connecting the mandrel to the tool actuator, signalling by the mandrel equates to signalling by the tool, at least when they are interconnected.

Preferably, said sleeve actuator mandrel has a port therethrough which aligns with a jet in the body when the sleeve actuator mandrel is in its tool actuated position, whereupon the through-bore of the sleeve actuator is in fluid communication with said jet, and whereby drilling fluid under pressure in said mandrel through-bore is directed onto the well bore in the region of said bar.

Indeed, the applications of the present invention are not limited to under-reamers. Adjustable stabilisers could benefit from the invention.

Preferably, seals between said sleeve actuator mandrel and body beyond both ends of said slot define, between them, and a bar seal around the bar in the slot, a chamber enclosing lubricating oil.

Preferably, the levers are pivoted to a flange connectable to the mandrel sleeve actuator. Preferably there are more than two of said levers in parallel. Preferably, the levers are captivated by pivot pins forming said first and second pivots between the levers and the sleeve actuator mandrel and the hollow bar respectively. Preferably, said pivot pins are captured in blind bores in said hollow arms, said blind bores being formed by elements inserted in said hollow arms. Preferably said elements are welded in said arms. This is desirable because said seal around the arm which seals the arm in said slot is preferably in the same region as the pivots between said levers and arms. That is to say, a projection of said pivot pins in the direction of said second pivot axes preferably intersects said bar seal. Therefore, should the pivot pins be located in through bores of the arms, the pins would interfere with operation of the seal.

Preferably, there are a plurality, preferably three, of said bars, slots and flanges spaced around the longitudinal axis of the tool.

Where the tool is an under-reamer, said bars are provided with cutting elements to effect under-reaming when the tool is actuated in a well bore having a pilot hole receiving the tool. Preferably, said body is thickened in the region of said slots and bars to support said bars. The body may have fins ahead of said slots having dimensions to match said pilot hole and bear against its surface and stabilise the tool, in use, said fins being provided with a hardened wear surface to minimise wear.

Alternatively, the tool may be an adjustable stabiliser, said bars being provided with hardened wear surfaces to minimise wear of the bars, in use.

Furthermore, the tool may be an azimuth controller, in which one or more bars in one or more slots are arranged asymmetrically around the longitudinal axis of the tool. The tool may also comprise one or more static blades.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are further described hereinafter, by way of example only, with reference to the accompanying drawings, in which:

Figures 1a, b and c are side sections through an under-reamer in accordance with the invention in WO2006/072761 in sleeve lock, interlock and tool actuated positions respectively;

Figures 2a_n, a₂, b and c are views of a variation of the tool shown in Figures 1a to c, in corresponding positions, but also in greater detail;

Figures 3a and b are sections along the lines A-A and B-B in Figures 1a and 1c respectively; Figures 4a to d are, respectively two side views, in the directions of Arrows A and B in Figure 4d, a section on the line A-A in Figure 4a, and an end view in the direction of the Arrow D in Figure 4b, of a tool in accordance with the present invention, in a deactuated position thereof;

Figures 5a to d are, respectively two side views, in the directions of Arrows A and B in Figure 5d, a section on the line B-B in Figure 5a, and an end view in the direction of the Arrow D in Figure 5b, of the tool shown in Figures 4a to d, but in an actuated position thereof; and

Figures 6a to f are, respectively a side view, and end view in the direction of Arrow B in Figure 6a, a section on the line C-C in Figure 6b, a section on the line D- D in Figure 6a, a section on the line E-E in Figure 6a, and a perspective, transparent view of an arm and lever mechanism for the tool shown in Figures 4 and 5.

DETAILED DESCRIPTION

In Figures 1 to 3 of the drawings, an under-reamer 10 comprises a body 12 having a through-bore 14 along a longitudinal axis 50 of the tool 10. A mandrel 16 actuates the tool 10 and is a component of an actuation mechanism 18, only one end of which is shown in the drawings. The actuation mechanism 18 is connected at its end 18a to end 12a of the body 12 by a standard screw thread connection 20a. The other end 12b of the tool 10 comprises a female connection 20b.

The actuation mechanism 18 forms no part of the present invention and may be in the form disclosed in WO-A-00/53886, US-A-5483987, US-A-6289999 (the entire disclosures of which are incorporated herein by reference), or any suitable means. Connected to the end of the mandrel 16 is mandrel end 22, which, conveniently, is screw threaded to the mandrel 16. However, in suitable circumstances end 22 may be integral with the mandrel 16 and henceforth is considered a part of the mandrel 16. In the drawings, mandrel 16, and its end 22, is shown in three positions. In Figure 1a, it is shown in a sleeve-lock position. In Figure 1b, it has moved axially rightwardly in the drawings to an interlock position and, in Figure 1c, it has moved further rightwardly to a tool actuated position. The above positions are described further below.

The tool 10 further comprises a sleeve actuator 30 which also has a sleeve through- bore 32. Therefore, it can be seen that a clear passage comprising mandrel through-bore 24, sleeve through-bore 32, and body through-bore 14 through the tool 10 permits unimpeded passage of drilling fluid to a drill bit (not shown) connected to the tool 10.

Neither end 12a,b of the tool 10 is necessarily nearer the drill bit. However, for reasons explained further below, in the present arrangement, end 12a of the tool 10 is preferably arranged nearest the drill bit. The body 12 is provided with three axially disposed, circumferentially spaced slots 34a, b, c, only 34a of which is visible in Figures 1a to 1c. Each slot receives a radially slidable cutter bar 36a, b,c. Although radial, there is no reason why the axis of the slots 34 should not be inclined to the radial. The top surface 38 of each cutter bar is provided with cutting elements, further details of which are not given herein. Suitable form of cutting elements will be known to those skilled in the art. One arrangement is shown in US-A-6732817 (the full disclosure of which is herein incorporated by reference). Each cutter bar 36 is hollow, with an interior space or pocket 46. The interior sides 40a, b (which sides are parallel the longitudinal axis 50) are formed with ribs 42 which are inclined with respect to the axis 50.

The actuator sleeve 30 is provided with three flanges 44a, b,c which are received within the pockets 46 of the hollow bars 36. The flanges 44 are each provided with channels 48 which are also inclined with respect to the longitudinal axis 50 and which cooperate with the ribs 42 in the sides 40a,b of the pocket 46. Indeed, the channels 48 define ribs between them, as do the ribs 42 define channels between them.

With reference to Figures 3a and b, the actuator sleeve 30 has, on its external surface, three open sections 52a, b,c. On assembly of the tool 10, these sections are aligned with the slots 34a,b,c respectively. Each bar 36 with its corresponding flange 44 is then inserted through the slots 34 until a dovetailed base of the flanges 44 abut the open sections 52. The actuator sleeve 30 is also provided with three dovetail sections 56a, b,c disposed between each open section 52a, b,c. When correctly aligned, the sleeve 30 is rotated through 60° about the longitudinal axis 50. An hexagonal section of a nose 31 at second end 67 of the sleeve actuator 30 is adapted to receive a tool for this purpose. Dovetails 58 on the dovetailed sections 56 of the sleeve actuator 30 then lock with corresponding dovetails 60 on the dovetailed base of the flanges 44. In this way, the flanges 44 are locked to, and become an integral part of, the actuator sleeve 30. However, it is required to ensure that the sleeve 30, in operation, does not rotate about axis 50 relative to the slots 34, otherwise this will disengage the dovetails 58, 60. For this purpose, a drilling 64 (64' in Figure 2a₂) in the body 12 is adapted to receive a pin (not shown) adapted to slide in a longitudinal groove 63 on the surface of the sleeve 30. Thus the sleeve 30 is constrained rotationally about the longitudinal axis 50 but is free to move axially. When the actuator sleeve 30 does move axially, as it does between the positions shown in Figure 1b and 1c, the ribs/channels 42,48 on the flanges 44 and inside the bars 36 interact to radially displace the bars 36 from a stowed, deactuated position (as shown in Figures 1a and b), and where the bars are within the confines of the slots 34, to an actuated position as shown in Figure 1c. Here, the bars 36 can bear against and cut the well bore (not shown).

The actuator sleeve 30 is controlled by the mandrel 16. The mandrel end 22 has a cylindrical extension 62 which is a close sliding fit in sleeve 30 at its first end 65. On the end 65 are formed a number of pockets 66 which each receive a lock element in the form of a ball 68. A shoulder 70 is provided in the body 12 and the lock elements 68, sitting on the cylindrical surface of the extension 62, prevent the sleeve 30 from moving rightwardly by engaging the shoulder 70. The sleeve is therefore in a sleeve-lock position because the lock elements 68 prevent any rightward movement of the sleeve 30, while the flanges 44 are at their leftmost position, in which the bars 36 fully withdrawn into the slots 34.

In this position, the mandrel 16 is free to move between the positions shown in Figure 1a and the position shown in Figure 1b without affecting the position of the sleeve 30. However, when the mandrel 16 is moved rightwardly to an interlock position as shown in Figure 1 b, recesses 72 on the surface of the mandrel extension 62 align with the lock elements 68. They are consequently released from engagement with the shoulder 70. Now, further rightward movement of the mandrel moves the actuator sleeve 30 rightwardly in the drawing to actuate the bars 36.

Between the interlock position shown in Figure 1b and the tool actuated position shown in Figure 1c, the internal cylindrical surface 74 of the body 12 locks the lock elements 68 in the recess 72 of the mandrel. Thus, the mandrel is locked to the actuator sleeve 30. Consequently, when the mandrel returns leftwardly in the drawings from the Figure 1c position, the actuator sleeve 30 is constrained to follow it.

This arrangement is also shown in greater detail in Figures 2a to c. A difference, however, between the embodiment shown in Figures 1a to c is that, here, the shoulder 70 is replaced by a circumferential groove 70'. A circumferential gallery 82 is provided around the body bore 14, adjacent the ends of the slots 34. Each slot 34 has an associated jet 84a, b,c (only jet 84a being visible in the drawings). The jets 84 communicate with the gallery 82. The gallery 82 is sealed to the external surface of the sleeve 30 by seals 86a,b. The sleeve 30 is provided with a number of apertures or ports 88. These put the sleeve bore 32 in fluid communication with its external surface. In the deactuated position of the actuator sleeve 30 (Figures 1a and 2a_λ), the apertures 88 are sealed by seals 86a and further seals 86c in the body bore 14. However, when the actuator sleeve 13 moves into its actuated position as shown in Figures 1c and 2c, the ports 88 communicate with the gallery 82 so that drilling fluid under pressure in the actuator sleeve bore can escape to the outside through the ports 88, gallery 82 and jets 84. In issuing from the jets 84, the drilling fluid serves to clear debris caused by the action of the cutters 36 against the well bore.

Each slot 34 is not rectangular in section but has rounded ends 34d, 34e. The bars 36 are correspondingly rounded at their ends and a circumferential groove 90 is formed around the entire periphery of each bar in which a seal (not shown) is disposed.

At its second end 67, the sleeve 30 is received within a liner 92 of the body 12. The liner 92 is sealed to the body 12 by seal 94 and the end 67 is sealed to the liner by seal 96. Thus, between the seals 86b, seals 94,96, and seals 90 around the bars 36, an oil chamber 102 is defined. This can be filled with lubricating oil through a tapping 98 and longitudinal groove 100 in liner 92. In use and after filling, tapping 98 is plugged by means not shown.

Thus the interacting surfaces of the flanges 44 and bars 36 (that is to say, the ribs/channels 42,48), as well as the external surfaces of the bars 36 against the slots 34, and the sliding of the sleeve actuator 30 in the body through-bore 14, are all facilitated by the lubrication. This serves to reduce wear. Also, drilling fluid, particularly that in the annulus surrounding the tool 10 inside the well-bore, is isolated from these components so that the risk of jamming by hard particles carried by the drilling fluid is reduced. However, it will be appreciated that the volume of the chamber 102 changes as the radial position of the bars 36 changes, not to mention the axial position of the sleeve actuator 30. Therefore, several longitudinally arranged drillings 104 are spaced around the circumference of the end 65 of the sleeve actuator 30. These are positioned both to avoid the ports 88 and the pockets 66 and therefore should not strictly be visible in the drawings. However, they are shown in Figures 2a!, b and c for illustrative purposes.

Drillings 104 connect the chamber 102 with the annulus 106 in actuation mechanism 18 and surrounding mandrel 16. The pressure in the annulus 106 is released by a bladder arrangement 108, further details of which are not given as its essential structure is well understood in the art.

The drillings not only relieve pressure in the chamber 102 but also serve to damp movement of the sleeve actuator 30. They also supply the interlock arrangement 72,68,70 with lubricant to facilitate its action as well.

Beyond the pressure relief bladder arrangement 108, a mandrel return spring 110 is visible. Although not shown completely, spring 110 acts between bladder 108 fixed in the body of mechanism 18 and a shoulder on the mandrel 16, urging it leftwardly in the drawings (see Figure 2aJ).

As mentioned above, the direction of orientation in a well bore of the tool 10 is not absolutely determined by its structure: it will operate in either direction; at least, it will if the actuation mechanism 18 operates on fluid pressure. However, it is preferred that it be arranged with the end 12a closest to the drill bit for three reasons. The first is that the jets 84 are more effective being directed immediately at the cutting interface between the cutters 36 and the well bore. Secondly, in the event that the bars 36 (or one of them), jam in their slots 34 and the normal deactuation force applied by the mandrel return spring is inadequate to overcome the jamming, then pulling the tool 10 up against the under edge of the casing (not shown) is considered more likely to nudge the jammed bar(s) back into the slots 34 than from the other direction. Thirdly, in the event of jamming, it would be possible to drop a ball down the well bore so that it closes the end of nose 31 of the sleeve actuator 30. Then, hydraulic pressure above the actuator can supplement the force applied by the mandrel return spring 110.

It is to be noted that there are shown in the drawings three circumferentially spaced bar/flange/slot combinations around the tool. This is for illustrative purposes. The invention includes the possibility of more or less. The possibility of a tool with just one bar exists in the application of an azimuth controller, where it is desired to deflect the drill-string to one side of the well bore so that the azimuth of a motor assembly in the string may be adjusted.

In the case of a stabiliser, the bars 36 are not provided with cutting elements, as shown, but with hardened wear surfaces.

The body 12 is provided with thickened regions 114 to support the slots 34 and bars 36. From another perspective, the tool has thinned regions, where the extra thickness of the body is not required!

In the case of the under-reamer, the thickened regions 114 ahead (in the drilling direction) of the slots 34 have an enlarged diameter surface 116 which is provided with hardened wear elements. In use, the tool here bears against the pilot hole formed by the drill bit on the end of the drill string (not shown) and stabilises the under-reamer keeping it central with respect to the pilot hole.

Turning to Figures 4 to 6, an under-reamer 10' is shown of similar overall construction to the under-reamer 10 of Figures 1 to 3. Like parts are given the same reference number, except with an apostrophe. Thus, with reference to Figure 4c, the under-reamer 10' comprises a body 12' having a through-bore 14' and including a sleeve actuator 30'. The mandrel is not visible in these drawings.

Slots 34a' are provided in thickened regions 114' of the body 12'. Hollow arms 36' slide in the slots 34a'. A flange 44' is similarly connected with the sleeve actuator 30' by corresponding inter-engaging dovetails 58', 60'. However, the flange 44' mounts a series of parallel levers 210 pivoted in a line to the flange 44' about pivot pins 212. The axes of the pivot pins 212 are perpendicular to the longitudinal axis 50 of the tool (or at least, perpendicular to a line (not shown) parallel the longitudinal axis 50) and also perpendicular to respective ones of the radial planes 50a, b,c that contain the longitudinal axis 50, and which also contain the respective slot 34'a,b,c of the respective bar 36'.

The levers 210 are also pivoted about pivot pins 214 to the bars 36'. In Figure 4c, the sleeve actuator 30' is shown in its tool-de-actuated position. Here, the levers 210 are at a minimum inclination with respect to the longitudinal axis 50. This inclination is of about 25°. When the tool is actuated, however, the sleeve actuator 30' moves from the position shown in Figure 4c to that shown in Figure 5c. Here, the levers 210 have been pivoted in an anti-clockwise direction about their axes 212 to adopt almost an orthogonal position with respect to the longitudinal axis 50. Given that this results in a radial extension of the ends of the levers connected to pivot pins 214, the bars 36' are pushed out of the slots 34'a,b,c, in this movement, as can be seen in Figure 5d. This occurs, of course, because the bars 36' are unable to move axially in the slots 34'a,b,c and therefore can only move radially. An advantage of this arrangement is that, when the bars 36' are extended to their maximum extension, and therefore most liable to suffer damage from contact with the bore wall and the like, the maximum retraction force is imposed on the arms 36' when the actuator sleeve 30' begins to move from the tool-actuated position shown in Figure 5c towards the tool-de-actuated position of Figure 4c. Moreover, at the first stages of this movement, there is little axial component of the forces on the bar 36', and therefore less risk of the bar jamming in the slot 34'a,b,c. When the actuator sleeve 30' approaches the position in Figure 4c then, while the geometry becomes unfavourable for further withdrawal of the bars 36', nevertheless, by the time this position is reached, the bars have been withdrawn to a significant extent.

Turning to Figures 6a to f, the structure of the bars 36', flange 44', and the levers 210 is more evident. Flange 44' is a saddle shaped component with a hollow interior 44'a, forming seats or pockets for the levers 210. Pivot pins 212 pass through apertures 216 in the side of the flange 44', as well as through bores 218 in the ends of the levers 210.

The other ends of the levers 210 likewise have eyes 220 receiving their pivot pins

214. These pins are journalled in carrier elements 222 which are welded along line 224 to the inside of the pocket 46' of the arm 36'. This enables the exterior of the arm 36' to be unbroken. The benefit of this is that the axial projection of the pivot pins 214 coincides with the region of the outside surface of the bars 36' where circumferential seal 90 is located. If eyes 228 which support the pins 214 penetrated to the surface, they may compromise the seals 90. Consequently, the bores 228 are 5 "blind". It is to be noted that the levers 210 are all parallel. Moreover, the quadrilateral 250 defined by the axes of the pivots 212,214 where they intersect the plane 50a, b,c of actuation of the bars 36', is a parallelogram. This ensures that the surface of the bars 36' maintain a constant orientation with respect to the bore wall. The parallelogram lies in the plane of actuation of the bar 36', which in the drawings 10 comprises a respective one of the radial planes 501 ,b,c.

However, apart from the simplicity of the design, there is no absolute reason why the bars 36' and slots 34'a,b,c must be radial (in the sense that movement of the bars in the slots must be orthogonally radial with respect to the longitudinal axis 50), or even

15 in an actuation plane that is parallel the longitudinal axis. Similarly, the levers do not necessarily need to be the same length or define a parallelogram. On the contrary, there are several alternative possibilities although these are not preferred as they add considerable complication to the design without necessarily providing any obvious benefit.

2.0

Thus, the actuation plane could be inclined to some degree with respect to the longitudinal axis. This would result in an helically arranged bar 36'. In this event, some sliding connection between the flange 44' and the actuator sleeve 30' would be required, or some rotation of the sleeve 30' must be provided, to enable the

25 movement to occur. The slot would also have to have a helical form.

The actuation plane may be parallel the longitudinal axis, but spaced from it, so that the slots 34'a have a somewhat tangential orientation, rather than a radial one.

30 The slot 34'a in side section is rectangular in the embodiments described above. However, it could be a parallelogram itself, whereby movement of the bars 36' is not radial but also axial to some extent. This might provide a useful feature if the inclination of the slot was upwardly oriented with respect to the borehole in which the tool is employed. Then, should the tool jam, knocking the extended arms onto the

35 bottom of a casing or narrower bore through which the tool is to be retrieved, will have the effect of knocking the arms back into their slots. This might be deemed desirable in some cases.

The levers 210 need not be the same length. In this case the arms 36' move in an arc, rather than in a straight line.

Throughout the description and claims of this specification, the words "comprise" and ^contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A downhole tool comprising: a) a body having a longitudinal axis and a body through-bore, a slot communicating the outside of the body with the body through-bore; b) a sleeve actuator mandrel having a sleeve actuator mandrel through-bore and being selectively axially slidable in the body through- bore; c) a hollow bar slidable with a radial component in the slot; and d) at least two levers, each pivoted to said sleeve actuator mandrel about a first axis, and each lever extending into said hollow bar and pivoted thereto about a second axis parallel said first axis, wherein an actuation plane of movement of said hollow bar on pivoting of the levers is perpendicular said first and second axes and contains said slot.

2. A downhole tool as claimed in claim 1 , in which the first and second pivot axes, at the intersection thereof with said actuation plane, define a parallelogram.

3. A downhole tool as claimed in claim 1 or 2, in which said first and second axes are perpendicular to a line parallel to said longitudinal axis.

4. A downhole tool as claimed in claim 1 , 2 or 3, in which said sleeve actuator mandrel comprises: a) a sleeve actuator having an actuator through-bore and being axially slidable in the body through-bore between a tool actuated position and a tool deactuated position; and b) a mandrel having a mandrel through-bore and being selectively axially slidable in the body through-bore between a tool actuated position, an interlock position and a sleeve-lock position; and wherein: c) an extension of the mandrel is a close sliding fit inside a first end of the sleeve actuator; d) said first end captivates a lock element; e) said body has an internal groove positioned so that, when said sleeve actuator is in said tool deactuated position, said lock element is aligned with said groove and held in engagement therein by said extension while the mandrel is between its interlock and sleeve-lock positions; and f) said mandrel has an external recess positioned so that, when said mandrel is in said interlock position, said lock element is aligned with said recess, whereupon movement of the mandrel towards said tool actuated position releases said lock element from said groove permitting said sleeve actuator to be moved by the mandrel to said tool actuated position, said mandrel and sleeve actuator being locked together by the body holding said lock element in said recess between said interlock and tool actuated positions of the mandrel.

5. A downhole tool as claimed in claim 1 , 2 or 3, in which said sleeve actuator mandrel comprises: a) a sleeve actuator having an actuator through-bore and being axially slidable in the body through-bore between a tool actuated position and a tool deactuated position; b) a mandrel having a mandrel through-bore and being selectively axially slidable in the body through-bore between a tool actuated position, an interlock position and a sleeve-lock position; and wherein: c) first means lock the sleeve actuator with respect to the body in said tool deactuated position and while said mandrel is between said interlock and sleeve-lock positions; and d) second means lock the sleeve actuator with respect to the mandrel and while said mandrel is between said interlock and tool actuated positions.

6. A downhole tool as claimed in claim 5, in which said first and second means comprise a lock element captivated by the sleeve actuator and located in one of a groove in the body or a recess on the mandrel.

7. A downhole tool as claimed in claim 6, in which alignment of said groove and recess occurs in said interlock position of the mandrel, which coincides with said tool deactuated position of the sleeve actuator.

8. A downhole tool as claimed in any of claims 4, 6 or 7, in which said lock element is a ball.

9. A downhole tool as claimed in any preceding claim, in which said sleeve actuator mandrel has a port therethrough which aligns with a jet in the body when the sleeve actuator mandrel is in its tool actuated position, whereupon the through-bore of the sleeve actuator is in fluid communication with said jet whereby drilling fluid under pressure in said mandrel through-bore is directed onto the well bore in the region of said bars.

10. A downhole tool as claimed in any preceding claim, in which the axis of the slot is radial with respect to said longitudinal axis.

11. A downhole tool as claimed in any preceding claim, in which seals between said sleeve actuator mandrel and body beyond both ends of said slot define, between them, and a bar seal around the bar in the slot, a chamber enclosing lubricating oil.

12. A downhole tool as claimed in any preceding claim, in which the levers are captivated by pivot pins forming said first and second pivots between the levers and the sleeve actuator mandrel and the hollow bar respectively.

13. A downhole tool as claimed in claim 12, in which said pivot pins are captured in blind bores in said hollow arms, said blind bores being formed by elements inserted in said hollow arms.

14. A downhole tool as claimed in claims 11 and 13, in which a projection of said pivot pins in the direction of said second pivot axis intersects said bar seal.

15. A downhole tool as claimed in claim 13 or 14, in which said elements are welded in said arms.

16. A downhole tool as claimed in any preceding claim, in which the levers are pivoted to a flange connectable to the mandrel sleeve actuator.

17. A downhole tool as claimed in claim 16, in which said flange is separate from the sleeve actuator mandrel but is locked thereon by circumferential dovetailed slots formed on a sector of the sleeve actuator mandrel adjacent an open sector thereof, and corresponding dovetails on the base of said flange engaged with said dovetailed slots of the sleeve actuator mandrel.

18. A downhole tool as claimed in claim 17, in which the tool is assembled by inserting said flange engaged with said bar in said slot so that said dovetails bear against said open sectors of the sleeve actuator mandrel, and by rotating said mandrel so that said dovetail slots engage said dovetails, means being provided to prevent the sleeve actuator mandrel from rotating in the body during use.

19. A downhole tool as claimed in claim 18, in which said rotation prevention means comprises a pin in the body extending into a slot in the sleeve actuator mandrel.

20. A downhole tool as claimed in any preceding claim, in which there are more than two of said levers in parallel.

21. A downhole tool as claimed in claim 4 or 5, or any of claims 6 to 20 when dependent on claims 4 or 5, in which said sleeve actuator has ports therethrough which align with jets in the body when the sleeve actuator mandrel is in its tool actuated position, whereupon the through-bore of the sleeve actuator is in fluid communication with said jets, and whereby drilling fluid under pressure in said body through-bore is directed into the well bore.

22. A downhole tool as claimed in claim 21 , further comprising a valve operated by the sleeve actuator to restrict drilling fluid flow through the tool past said jets.

23. A downhole tool as claimed in any preceding claim, in which there are a plurality, preferably three, of said bars and slots spaced around the longitudinal axis of the tool.

24. A downhole tool as claimed in claim 23, in which said tool is an under- reamer and said bars are provided with cutting elements to effect under- reaming when the tool is actuated in a well bore having a pilot hole receiving the tool.

25. A downhole tool as claimed in claim 24, in which said body is thickened in the region of said slots and bars to support said bars.

26. A downhole tool as claimed in claim 24 or 25, in which said body has fins ahead of said slots having dimensions to match said pilot hole and bear against its surface and stabilise the tool, in use, said fins being provided with a hardened wear surface to minimise wear.

27. A downhole tool as claimed in claim 23, in which the tool is an adjustable stabiliser, said bars being provided with hardened wear surfaces to minimise wear of the bars, in use.

28. A downhole tool as claimed in any of claims 1 to 23, in which the tool is an azimuth controller, wherein one or more bars in one or more slots are arranged asymmetrically around the longitudinal axis of the tool.

29. A downhole tool as claimed in claim 28, further comprising one or more static blades.