US 20020144815 A1
The present invention provides a down-hole tool guide apparatus 6 suitable for use in controlling movement of a down-hole apparatus 1 provided with a pressurised working fluid supply in a borehole P. The apparatus comprises: a body 7 having a chamber 13 in which is slidably mounted a piston 14. A high pressure end 13 a of the chamber 13 is connected 36 to the pressurised working fluid supply 10 for supplying pressurised working fluid to a high pressure side 32 of said piston 14. A low pressure end 13 b of the chamber 13 is connected with the outside of the guide apparatus 6 and is provided with a spring 16 for applying a biasing force to the low pressure side 17 of the piston 14 corresponding to a predetermined threshold pressure of the pressurised fluid supply at the high pressure side of the piston 14. The body 7 mounts at least one shoe 25 having an engagement face 26. The piston 14 is operatively coupled to a shoe displacement mechanism 18, 19, 28, 29 so that the shoe 25 is held in a stowed position when the piston 14 is urged towards the high pressure end 13 a of the chamber 13 by the spring 16, and is displaced outwardly so that the engagement face 26 projects outwardly of the body 7 when the piston 14 is displaced towards the low pressure end 13 b of the chamber by supply of pressurised working fluid at a pressure higher than said threshold pressure.
1. A down-hole tool guide apparatus suitable for use in controlling movement of a down-hole apparatus provided with a pressurised working fluid supply in a borehole, said apparatus comprising: a body having a chamber in which is slidably mounted a piston, said body being formed and arranged for connection of a high pressure end of said chamber to the pressurized working fluid supply in use of the apparatus for supplying pressurized working fluid to a high pressure side of said piston, said body being further formed and arranged for connecting a low pressure end of said chamber with the outside of said guide apparatus, said body being provided with a resilient biasing device formed and arranged for applying a biasing force to said piston corresponding to a predetermined threshold pressure of the pressurised fluid supply at the high pressure side of said piston, so as to urge said piston towards the high pressure end of the chamber, said body mounting at least one shoe, each said shoe having a radially outwardly facing longitudinally extending engagement face, said piston being operatively coupled to a shoe displacement mechanism formed and arranged so that said shoe is held in a stowed position when said piston is urged towards the high pressure end of said chamber by the resilient biasing means, and said shoe is displaced outwardly so that said engagement face projects outwardly of the body when said piston is displaced towards the low pressure end of the chamber by supply of pressurised working fluid at a pressure higher than said threshold pressure.
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16. A pressurised fluid operated downhole cutting tool apparatus having a pressurised fluid—operated motor drivingly connected to a cutting tool and a pressurised fluid supply, wherein is provided a guide apparatus according to
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19. A pressurised fluid operated downhole apparatus provided with an anchoring tool comprising a guide apparatus according to claim 3.
 The present invention relates to an active downhole cutting tool guide device for use in a hole with sides between which a hole-cutting tool provided with said apparatus may be disposed.
 There is a need for guiding of downhole cutting tools for various purposes including inter alia lateral or kick-off hole cutting, directional drilling, as well as to stabilise an existing cutting tool advance direction against unwanted deviation therefrom. Existing solutions to such problems are generally cumbersome to use and/or unsuitable for use with coiled tubing.
 There is a need for cutting windows in oil/gas well casings used to line the sides of well holes. Well casing is however normally very tough, thick walled steel pipe which is placed inside a borehole of a well as a lining to secure the borehole and prevent the walls thereof from collapsing. Casing—sometimes referred to as casing tubing—may be seamless, spiral welded or seam welded and may, for example, be fabricated from various API grades of steel such as H40, J55, N80 or P110. Sizes typically vary from around 4 inches (101.6 mm) OD to 30 inches (762 mm)OD, while weights typically range from around 11 lb/ft to 200 lb/ft (16.4 kg/m to 298 kg/m approximately) depending on diameter, thickness and grade. It has also been known to employ glass fibre reinforced plastic casing.
 It is known that the cutting of windows in oil well casing, as required for side tracking, is a complicated process, normally requiring the use of a large number of tools not directly related to the cutting of the window itself, such as whipstocks, packers etc. The normal procedure is the setting of cement plug on top of a packer above which a so-called “whipstock” is placed. The whipstock basically consists of a hard metal wedge which guides a window milling drill bit gradually into the casing thus cutting a slot in the casing. As the slope of the whipstock is of a low value the pinching action on the drill bit is very severe therefore requiring extremely high torque and yet a low rate of progress is achieved due to the high friction losses of the drill bit against the whipstock which have to be subtracted from the total energy available for the cutting of the window. Furthermore once the window has been cut the whipstock and packer require to be retrieved which is often a difficult and tedious process. To date the duration of an average window milling job is three to four days and often much longer.
 There is also a need for stabilising drilling tools used to clear well holes which have become obstructed to a greater or lesser degree as a result of deposits on the sides thereof, and/or as a result of deformation of a well hole casing as a result of movement of the surrounding strata. Conventional near bit stabilisers are essentially passive devices, typically comprising a heavy duty ring with four angularly distributed wings which more or less closely approach the hole sides thereby limiting the amount of deviation of the cutting tool possible. With such stabilisers though the resistance to deviation remains substantially constant throughout use of the device i.e. during travel of the cutting tool along clear sections of the hole when ease of travel is desired and stabilisation is not required, as well as during cutting through obstructions, so that in practice the degree of stabilization available when it is required is substantially insufficient for proper stabilisation.
 It is an object of the present invention to obviate or mitigate at least some of the aforementioned problems and disadvantages in the prior art.
 It is a further object of the present invention to provide a cutting tool guide apparatus which may be used with coiled tubing with its inherently shorter positioning and retrieval times against the use of jointed oil field tubing.
 It is another object of the invention to provide a cutting tool guide apparatus suitable for down-hole use in a hole with sides between which a hole-cutting tool provided with said device may be disposed, whereby in use of the device at least one of the angle, the orientation and the lateral offset of a hole-cutting tool relative to the longitudinal axis of the hole in which said tool is disposed, may be controlled.
 The present invention provides a down-hole tool guide apparatus suitable for use in controlling the path of the cutting tool of a down-hole cutting apparatus provided with a pressurised working fluid supply in a borehole, said apparatus comprising: a body having a chamber in which is slidably mounted a piston, said body being formed and arranged for connection of a high pressure end of said chamber to the pressurized working fluid supply in use of the apparatus for supplying pressurized working fluid to a high pressure side of said piston, said body being further formed and arranged for connecting a low pressure end of said chamber with the outside of said guide apparatus, said low pressure end of said chamber being provided with a resilient biasing device formed and arranged for applying a biasing force to said piston corresponding to a predetermined threshold pressure of the pressurised fluid supply at the high pressure side of said piston, so as to urge said piston towards the high pressure end of the chamber, said body mounting at least one shoe, each said shoe having a radially outwardly facing longitudinally extending engagement face, said piston being operatively coupled to a shoe displacement mechanism formed and arranged so that said shoe is held in a stowed position when said piston is urged towards the high pressure end of said chamber by the resilient biasing means, and said shoe is displaced outwardly so that said engagement face projects outwardly of the body when said piston is displaced towards the low pressure end of the chamber by supply of pressurised working fluid at a pressure higher than said threshold pressure.
 Thus with an apparatus of the present invention, it is possible to apply a guiding force to a down-hole cutting tool as and when required, simply by increasing the flow of working fluid. In general the guide apparatus of the present invention is intended for use with a pressurised fluid operated cutting tool apparatus wherein is employed a fluid operated motor such as a turbine or positive displacement motor and pressurised fluid is also supplied to the cutting tool for lubrication thereof, carrying away cuttings etc. Typically the guide apparatus would be mounted between the motor and the cutting tool, the latter normally being supported on a thrust bearing unit. With such a cutting tool apparatus the pressurised fluid pressure applied to the high pressure side of the cylinder(s) can be simply increased by increasing the flow rate of the pressurised fluid supply delivered down the drill string. The pressurised fluid supply is generally provided, downstream of the cylinder , with a flow restrictive nozzle in order to increase the backpressure thereat and the pressure differential obtained for a given pressurized fluid flow rate. By suitable choice of the diameter of the flow restriction nozzle, it is possible to adjust the pressure differential obtained for a given flow rate. This has the advantage of simultaneously increasing the motor torque and/or speed and the fluid supply to the cutting tool which is exactly what is required when kicking-off or cutting through an asymmetric hole obstruction. Conversely when kicking-off or cutting through an obstruction, the guiding apparatus is automatically brought into operation by the working fluid pressure increase which occurs with such operations.
 In one form of the invention there may be used a single shoe. In this case displacement of the shoe into engagement with the hole sidewall to one side of the drill string will force the cutting tool against the hole sidewall to the other side of the drill string. This is useful in cutting windows in well casings by driving the cutting tool, conveniently a milling tool, laterally through the casing to cut a window therethrough. The window may then be elongated longitudinally of the well by driving the drill string forwards. In this type of arrangement, the angular directioning or orientation of the cutting tool (around the well) may be conveniently effected by means of a so-called indexing means (which is a well known remotely operable device used to set the angular orientation of a tool on drill string) to control the angular orientation of the guide device and hence of the shoe around the well prior to operation of the actuator means so that the cutting tool is forced against the well casing at a desired side of the well.
 In another form of the invention at least two angularly distributed, e.g. two diametrically opposed, or three, four or more, symmetrically distributed, shoes may be used. These may be displaced together by a single piston common thereto, or alternatively there may be used two or more separate pistons for the various shoes. In this case when the cylinder(s) is (are) displaced, the existing drill string direction is stabilised against deviation, for example by asymmetrical obstruction to the cutting tool. This is particularly useful when re-boring holes which have become obstructed to a greater or lesser degree e.g. by the formation of deposits therein, or by deformation of the casing which could have arisen, for example, as a result of shifts in the surrounding strata. Where it is merely desired to provide stabilisation of an existing drill string direction, then control of the angular orientation of the guide apparatus with its shoes will not normally be required. Nevertheless if desired the guide apparatus could be used in conjunction with an indexing device.
 It will be appreciated that by varying the preloading of the resilient biasing means it is possible to adjust the fluid pressure threshold required to activate the guide device by displacement of the piston. Typically there could be used a threshold pressure in the region of from 5 to 20 Bar, for example, about 10 Bar, when a positive displacement motor is used. Furthermore by choice of a suitable spring rate, which may moreover be linear or non-linear, it is possible to modify the rate of extension of the shoe(s) with increasing fluid pressure, for example, in order to control the force applied to the cutting tool.
 Any convenient kind of shoe displacement mechanism may be used in accordance with the present invention. Thus, for example, there could be used a cam mechanism, in which a cam is rotated to deploy the shoe(s).
 Conveniently there is used a linkage mechanism captively secured to the piston and comprising a plurality of pivotally connected links. If used as a stabilizer form of guide apparatus of the invention, the shoes will be maintained parallel to the drill string. With the kick-off tool form of guide apparatus the shoe may lie at a slight angle to the drill string as the tool is pushed over to one side of the tube and the tool bends.
 The tool guide apparatus may be connected to the pressurised working fluid supply in any suitable manner. In general the tool guide apparatus will have a working fluid conduit extending axially through its centre which can be coupled to the working fluid conduit(s) exiting the motor stage and running through the thrust bearing assembly to the cutting tool. In such cases there is conveniently employed a perforated connector for coupling the working fluid conduit extending through the guide apparatus to that of the thrust bearing, for tapping off working fluid pressure directly or indirectly into the high pressure end of the guide apparatus chamber. By varying the cross sectional area of the perforation(s), the amount of pressure drawn off in this way can be suitably adjusted.
 Further preferred features and advantages of the invention will appear from the following detailed description given by way of example of some preferred embodiments illustrated with reference to the accompanying drawings in which:
FIGS. 1 and 2 are general side elevations of a bottom hole assembly with a kick-off tool of the invention in its retracted and deployed conditions;
FIGS. 3 and 4 are detailed sectional elevations of the kick-off tool;
FIG. 5 is a detail front elevation of the kick-off tool in its retracted condition;
FIG. 6 is a transverse section of the kick-off tool in the plane VI-VI in FIG.4;
FIG. 7 is a sectional elevation of a centralizing tool of the invention;
FIGS. 8 and 9 are schematic transverse sections through the centralizing tool of FIG. 7 in its deployed and retracted condition; and
FIG. 10 is a longitudinal section of a cutting tool suitable for use with a kick-off tool according to FIGS. 3 to 6 for window milling.
FIGS. 1 and 2 show (schematically) a bottom hole assembly 1 suspended from a coiled tubing drill string 2 and comprising a downhole motor 3 and drill bit 4 supported on a thrust bearing unit 5 with a kick-off tool 6 of the invention mounted between the thrust bearing 5 and the motor 3. In FIG. 1 the kick-off tool 6 is in its inactive or stowed condition, whilst in FIG. 2 the kick-off tool is shown fully extended.
 As shown in FIGS. 3 and 4 the kick-off tool 6 comprises a generally tubular body 7 having a reduced internal diameter upper portion 8 and a larger internal diameter lower portion 9. A fluid supply tube 10 extends along the central longitudinal axis X-X of the body 7 closely fitting the interior 11 of the upper body portion 8 and spaced from the interior 12 of the lower body portion 9 so as to define an annular chamber 13 therebetween. An annular piston 14 is slidably mounted between the fluid supply tube 10 and the interior 12 of the lower body portion 9. A central intermediate diameter body portion 15 houses a helical spring 16 which engages the upper end 17 of the piston 14 for resiliently biasing the piston 14 downwardly.
 The upper end 17 of the piston 14 has secured thereto a connector 18 which is pivotally connected 19 to the lower end 20 of a shoe assembly 21, the upper end 22 of which is pivotally connected 23 to part 24 of the upper body portion 8. In more detail the shoe assembly 21 comprises an elongate shoe member 25 having an outer engagement surface 26 with closely spaced longitudinally extending ridges 27 for positive engagement in use of the tool with the side of a hole or pipe and stabilizing the tool against angular displacement whilst permitting longitudinal displacement—for example, for window milling (longitudinal hole elongation). The ends 25 a, 25 b of the shoe member 25 are connected by respective link members 28, 29 to the piston 14 and upper body portion 8, so that the shoe assembly 21 is movable between a stowed radially retracted configuration as shown in FIG. 3 with the shoe member 25 and link members 28, 29 fully extended longitudinally, and a deployed radially extended configuration as shown in FIG. 4 with the shoe member 25 and link members 28, 29 partially collapsed together longitudinally.
 The working end portion 30 of the piston 14 has a reduced diameter and is slidably received within a sleeve 31 mounted within the annular chamber 13 in order to reduce the surface area of the working end face 32 of the piston 14 thereby to reduce the force exerted on the shoe assembly 21 for a given differential fluid pressure exerted thereon.
 The lower end 33 of the fluid supply tube 10 is connected via a tubular coupling 34 (see FIG. 4) to a further fluid supply tube section 35 extending through a thrust bearing unit 5. The tubular coupling 34 has a number of apertures 36 which connect the interior 37 of the fluid supply tube 10 to the high pressure end 13 a of the annular chamber 13 below the piston working end face 32 for supplying fluid pressure thereto. Inside the coupling 34 is provided a flow restriction nozzle 38 for increasing the fluid pressure diverted to the chamber 13. The back-pressure generated and the pressure differential obtained for a given flow rate can be adjusted by selecting a suitable flow restriction nozzle diameter. The low pressure end 13 b of the annular chamber 13 above the piston 14 is open to the outside of the guide apparatus 6 around the shoe member 25 (see FIGS. 3 to 6).
 In use of the kick-off tool of FIGS. 3 to 6, under normal operating conditions, the shoe member 25 is held in its retracted position by the spring 16. When the differential fluid supply pressure exerted on the working end face 32 is increased by increasing the flow rate of the pressurized fluid, then the piston 14 is forced upwardly thereby partly collapsing the shoe assembly 21 and forcing out the shoe member 25 into a radially outwardly deployed position in engagement with one side 40 of the hole or pipe 41 inside which the bottom hole assembly 1 is disposed and forcing the latter towards the other side 42 of the hole or pipe 41 in order to, for example, bring a window cutting tool (not shown) into engagement therewith, deviate the drilling direction etc.
 FIGS. 7 to 9 show a centralizing tool 43 of the invention for use in centralizing a bottom hole assembly 1 and stabilizing it against unwanted deviations e.g. due to asymmetric obstructions in the hole or pipe 41 or other asymmetric resistance to the advance of the bottom hole assembly 1. The centralizing tool 43 is of essentially similar construction to the kick-off tool 6 of FIGS. 1 to 6 but with three symmetrically angularly distributed shoe assemblies 21A, 21B, 21C instead of the one shoe assembly 21 of the kick-off tool 6, and similar components corresponding generally to those of the latter are indicated by like reference numbers. In this case when the differential fluid supply pressure applied to the piston working end face 32 is increased the shoe members 25 are brought into engagement with the sides 45 of the hole or pipe 41 around the tool 43 so that the bottom hole assembly 1 is held firmly in the centre of the hole or pipe 41 against unwanted deviations therefrom.
 As may be seen in Fig.6, the side 46 of the kick-off tool 6 has a substantially larger radius of curvature (comparable to that of the tool with the shoe assembly 21 in its deployed, radially extended position) than that of the tool 6 in its radially retracted condition. By this means the surface area of the tool side 46 which is forced into engagement with the pipe side 42 in which, for example, a hole is to be cut, is maximized thereby spreading the load thereon, whilst at the same time maximizing ease of movement of the tool 6 along the pipe 41 when the shoe assembly 21 is in its radially retracted condition.
FIG. 10 is a longitudinal section of a cutting tool suitable for use with a kick-off tool according to FIGS. 3 to 6 for window milling. In more detail the cutting tool 47 has an outer generally cylindrical cutting surface 48 which may have carbide inserts or crushed carbide particles or similar cutting materials brazed or attached on to it. This cylindrical cutting surface 48 will cut during the initial perforating operation as the kick-off tool 6 is actuated and pushes laterally the milling tool 47 into the wall of the tubing P (see FIGS. 1-2). The front end face 49 of the tool has a central recess 50 made of a generally conical form. This end face 49 will also be coated with an abrasive cutting coating e.g. crushed carbide. Once the perforation has been made and the BHA starts to advance down the well to elongate axially the perforation to form a window in the tubing P, the end face 49 will be the cutting face. The conical recess 50 of the end face 49 is designed to stabilise the BHA so that it does not drift back into the centre of the tube P, by tending to centralise the cutting 47 in the wall of the tubing P. (If a flat face or an external conical face is used, the tool tends to push back in towards the centre of the tubing).
 It will be appreciated that various modifications may be made to the above described embodiment without departing from the scope of the present invention. Thus, for example, although in FIGS. 3, 4 and 7, the piston-cylinder device 14, 13 is shown connected to the lower end of the shoe assembly, the piston-cylinder device could also be connected to the upper end thereof. It is believed that in use a piston located connected at the lower end could be advantageous as if the tool becomes difficult to operate, e.g. because of contaminants in the pressurized fluid causing a blockage, then in the process of withdrawing the tool from the hole the piston is pushed back by the force of the springs and the lever action of the shoe without having to overcome the effect of the blockage or debris above the piston. To encourage the shoe to retract on pull out of the hole, the angle of the links 28 and 29 at full extension should be less than 90° from centreline of the body and preferably in the range from 30 to 60°.
 Also, if it is desired to provide axial stabilization against longitudinal displacement of the tool—for example in use as a perforating tool, where a hole is to be made in the wall of the casing/tubing but a window is not required, or in use as an anchor, then, instead of longitudinally extending grooves and ridges 27, there could be used part-annular grooves and ridges. In use as an anchor the guide apparatus would be positioned between the downhole motor 3 and the coiled tubing/drill string 2. As a stabiliser the guide apparatus may be positioned between the downhole motor 3 and the coiled tubing/drill string 2 or between the downhole motor 3 and the bearing section 5.
 To reduce the possible bending of the bottom hole assembly 1 between the drill bit 4 and the guide apparatus 6 it may be advantageous to integrate the bearing section 5 and the guide apparatus 6 into a single unit.