DK201470422A1

DK201470422A1 - Underreamer with radial expandable cutting blocks

Info

Publication number: DK201470422A1
Application number: DKPA201470422A
Authority: DK
Inventors: Sigurd Solem
Original assignee: Advancetech Aps
Priority date: 2014-07-07
Filing date: 2014-07-07
Publication date: 2016-01-25
Also published as: CA2954444A1; WO2016004954A1; EP3167145A4; DK179097B1; BR112017000355A2; EP3167145A1; US20170159365A1

Abstract

The present invention relates to a cutting tool for widening the diameter of a borehole and method thereof, where the cutting tool comprises a housing defining an internal chamber in which a moveable activation element is arranged. The activation element is moved in an axial direction and is connected to one or more cutting blocks via a mechanical coupling. The mechanical coupling transfers the axial movement of the action element into a radial movement of the cutting blocks. As the differential pres- sure across the tool drops below the biasing spring force, the activation element is pushed back towards its starting position which in turn causes the cutting blocks to move back into the housing. The cutting blocks extend into one or more cavities formed in the activation element, thereby increasing the travel-to-expansion ratio. The cutting blocks can be replaced by stabilizer blades which are used to stabilize the drill- ing in the expanded borehole.

Description

Underreamer with radial expandable cutting blocks Field of the Invention

The present invention relates to a cutting tool for widening the diameter of a borehole, comprising: - a housing having a longitudinal direction and a transverse radial direction, the housing comprising at least a top end connected to a bottom end by a first outer surface, - at least one moveable cutting block having any number of cutting elements, each cutting block being arranged in a first opening located on the first outer surface and configured to move in the radial direction between a retracted position and an expanded position relative to the housing, and - at least one moveable activation element arranged inside the housing relative to the cutting blocks and configured to move along the longitudinal direction relative to the housing for activation of the cutting blocks.

The present invention also relates to a method for operating a cutting tool in a borehole for widening the diameter of the borehole, the cutting tool comprising at least one moveable cutting block arranged in an outer surface of a housing, the cutting block being connected to an activation element arranged inside the housing, where the method comprises the steps of: - moving the activation element in a longitudinal direction relative to the housing using a differential pressure of a drilling fluid being circulated in the borehole, - moving the cutting block in a transverse radial direction out of the housing towards an expanded position, and - moving the cutting block in the opposite radial direction back into the housing towards a retracted position, e.g. by using a spring force or hydraulic force.

Background of the Invention

Today, it is well-known within the oil, gas and water industries to widen the diameter of a borehole after the initial drilling using an underreamer having expendable blocks with a plurality of cutting elements, such as teeth or cutters. The initial drilling is done by using a cutting tool or drill bit without any expendable cutting blocks, also called a hole opener. The borehole is normally lined with one or more casing elements before the underreamer is inserted into the borehole. The underreamer is lowered into position and the cutting blocks are expanded to widen the diameter of the hole.

US 7900717 B2 discloses an underreamer having a housing with a hollow central tube element allowing drilling fluid to pass through the tool. The housing has three slots extending in the longitudinal direction in which three slidable cutting blades are arranged. The cutting blades are at the lower end in contact with a projecting sleeve on the tube which in turn is held in place by a compression spring. Activation is done by dropping a ball into the drilling fluid which is caught in the central tube, this forces the central tube upwards relative to the housing due to the differential pressure. An angled sliding surface in the slot causes the cutting blades to pivot out of the housing. The cutting blades are retracted due to the compression force of the spring. This solution is sensitive to torsion forces caused by the rotating movement of the tool due to the length of the slots.

US 7594552 B2 discloses an underreamer having a housing in which a central hollow tube is arranged for allowing passage of the drilling fluid. Three or more radially moveable blocks are arranged in the housing relative to the central tube. A flow restricting opening located in the tube causes the incoming drilling fluid to force the tube downwards, the pressure of the drilling fluid above the tube opening pushes the cutting blocks out of the housing. The cutting blocks are forced back into the housing due to the compression force of radially extending springs located between the cutting blocks and the housing. This solution allows for a very limited radial movement since range of movement is limited to the thickness of the housing and thus the tool has a shorter lifespan compared to other underreamer tools.

Cantilever shaped cutting arms can be used instead. However, this mechanism requires long elongated slots to expand and contract the arms making it sensitive to torsion forces. Furthermore, the arms have limited space for the cutting elements thus increasing the wear and reducing the lifespan of the tool.

US 7314099 B2 discloses an underreamer having three cutting blades arranged in elongated slots in an outer housing, wherein the cutting blades are connected to a Z-drive unit located at the bottom of the tool. The Z-drive is arranged around a central tube allowing drilling fluid to pass through the tool unit and uses a piston to push the cutting blades into an expanded position. The cutting blades are moved in a combined longitudinal and radial direction by using guiding grooves and tracks provided on the blades and edges of the slots. A compression spring located around the central tube is used to move the cutting blades back into the housing. This solution is sensitive to torsion forces caused by the rotation of the tool due to the long elongated slots.

Object of the Invention

An object of the invention is to provide a cutting tool having improved torsion properties during operation.

An object of the invention is to provide a cutting tool that allows for an increased range of expansion.

An object of the invention is to provide a cutting tool that allows for a longer lifespan and an increased number of cutting elements.

An object of the invention is to provide a simple and easy method of operating a cutting tool.

Description of the Invention

An object of the invention is achieved by a downhole tool characterised in that: - each cutting block extends inwards into the housing and is moveably connected to the activation element by a mechanical coupling, the mechanical coupling being configured to transfer the longitudinal movement of the activation element into the radial movement of the cutting blocks.

This provides a simple and compact cutting tool in the form of an underreamer with improved torsional and twisting properties as the movement or expansion of the cutting blocks is limited to a radial movement in and out of the housing. The configuration allows for the openings in the housing to have a shape and size that substantially matches the cross-sectional size and shape of the cutting blocks. This eliminates the need for including additional space in order to allow axial movement of the cutting blocks during expansion compared to conventional cutting blocks. It also eliminates the need for any inclined surface or wedge shaped elements to expand the cutting blocks.

The tool is adapted to be placed in any type of borehole in which an underreaming process is desired. The outer size and shape of the housing substantially matches the inner contours of the borehole, preferably allowing for a gap or annular space to be formed between the inner wall of the borehole and the outer surface of the housing. Drilling fluid and loose materials may be led past the tool and back up to a ground level via the gap or annular space. The housing may have a cylindrical shaped outer surface or any other desired shape. The housing may be a solid or hollow housing made of a high strength material, such as steel or any other suitable material.

According to one embodiment, the activation element comprises a second outer surface facing an inner surface of the housing, wherein at least one of the cutting blocks extends into a second opening located on the second outer surface.

This configuration allows for a greater expansion of the cutting blocks compared to conventional cutting tools, as the range/length of expansion is not limited to the thickness of the housing. An inner end of the cutting block may extend into a cavity (a non-through hole) or a through hole in the activation element. Two or more cutting blocks may extend into the same cavity or hole. The outer contours of the cutting block may substantially match the inner contours of the cavity/hole allowing for a tight fit. The cavity/hole is configured to receive and hold the cutting block in at least the retracted position. The inner end of the cutting blocks may be arranged so that it remains inside the cavity/hole in the expanded position. The cavity/hole may extend in the longitudinal direction for allowing the activation element to move axially while maintaining the cutting blocks in their axial positions. The cutting block and/or cavity or hole may have a substantial rectangular, squared, or any other suitable cross-sectional profile.

The housing forms an inner chamber having an inner surface which may substantially match the outer contours of the activation element allowing for a tight fit during movement of the activation element. The inner and/or outer surface may have a circular, elliptical, rectangular/squared, triangular, or any other multi-sided cross-sectional profile. The activation element may alternatively have an outer profile that differs from the inner profile of the housing.

The housing may comprise one or more guiding elements, e.g. a spline system, an axial bearing, a sleeve or another guiding system arranged between the housing and the outer surface of the activation element. One or more spline elements may be arranged on the inner surface of the housing and one or more matching spline elements may be arranged on the outer surface of the activation element. This allows the movement of the activation element to be limited to an axial movement.

In an alternative embodiment, the activation element may extend through an opening of a through hole or cavity in each of the cutting blocks. In this embodiment, the cavi-ty/hole may extend in a radial direction to allow the cutting blocks to move radially while maintaining the activation element in its radial position. Instead, each cutting block may be connected to individual activation elements via individual mechanical couplings.

The activation element and/or cutting block may be made of a high strength material, such as alloy steel, Polycrystalline Diamonds Compacts (PDC), or any other suitable material. The cutting elements may be made of any suitable wear resistance material, such as steel, tungsten carbide, or a composite material.

According to a special embodiment, the mechanical coupling comprises a first set of guiding elements, e.g. tracks, configured to engage a second set of guiding elements, e.g. grooves, wherein one set is arranged on a third surface of the cutting block and the other set is arranged on a fourth surface on the activation element facing the third surface.

This configuration enables the activation element and the cutting blocks to be mechanically connected by means of matching coupling elements. The coupling elements may be arranged between the inner end of the cutting blocks and the outer surface of the activation element and/or between a side surface of the cutting blocks and a side surface of the activation element. One of the side surfaces may be located in the cavi-ty/hole of the respective element. This allows for a simple and direct engagement be tween the activation element and the cutting blocks which eliminates the need for any axially moveable sleeves or elements for expanding the cutting blocks. This allows for a more compact cutting tool since the length of the tool can be reduced compared to conventional cutting tools.

The coupling elements may be configured as any number of tracks, pins or rods and matching grooves or through holes arranged on two opposite facing surfaces. The coupling elements may have any other suitable shape. The rod(s) may extend through the openings of the hole(s) and connected to opposite sides of that element. Alternatively, one or more guiding rollers or wheels may be used and which are configured to move along a rail or groove located in the opposite surface. The elements may each comprise a projecting part having a contact surface facing a matching contact surface of the other element. The contact surface of the activation element may slide along the other contact surface as it is being activated. Other types of guiding systems connecting the activation element with the cutting blocks may be used.

Two or more cutting blocks may be arranged in the same radial plane and angled relative to each other. Alternatively or additionally, two or more cutting blocks may be arranged in two or more radial planes and aligned or offset relative to each other. Two or more of the cutting blocks may have the same size and shape and/or different sizes and shapes. The use of multiple cutting blocks allows the shape and size of the cutting elements to be adapted to the formation surrounding the borehole. This allows for a greater number of cutting blocks and enables the cutting elements to be distributed over a greater number of cutting blocks, thus reducing the wear on each cutting element and increasing the lifespan of tool. This also allows the surface area on which the cutting elements are provided to be increased which in turn further reduces the wear on each cutting element and increases the lifespan of tool.

According to a special embodiment, at least one set of guiding elements is placed in a predetermined angle, e.g. 45 degrees, relative to the longitudinal direction of the respective element.

This configuration enables the guiding elements to be placed in an inclined position relative to the longitudinal direction of one or both elements, thus allowing for a sim- pie and easy transfer of movement between the two elements. The first set of guiding elements may be placed in angled position, e.g. between 30 to 60 degrees, optionally 45 degrees, relative to the longitudinal direction of the activation element. The second set of guiding elements may be placed in angled position, e.g. between 30 to 60 degrees, optionally 45 degrees, relative to the longitudinal direction of the cutting block. Alternatively, the first or second set of guiding elements may be placed in a substantial perpendicular angle, e.g. 90 degrees, relative to the other set of guiding elements or the longitudinal direction of that element. This allows the guiding elements of the cutting blocks to slide or roll along the length of the guiding elements of the activation element as it moves in an axial direction.

According to a special embodiment, the ratio between the relative movement of the activation element and the radial movement of the cutting blocks is between 1:1 and 1:100.

The term” relative movement” is defined as the relative movement between the activation element and the housing in the longitudinal direction. The radial movement is defined by the retracted and expanded positions of the cutting blocks. The ratio may be determined based on the actual axial movement of the activation element from its starting point, i.e. in which the cutting blocks are in their retracted position, to its stopping point, i.e. in which the cutting blocks are in their expanded position. The ratio may instead be determined based on the length of the first set of guiding element. The first or second set of guiding elements may be placed in any angle relative to the respective longitudinal direction of that element capable of providing a travel-to-expansion ratio from 1:1 and 1:100. The present invention allows the travel-to-expansion ratio to be increased compared to conventional cutting tools, meaning that it requires less axial space in order to achieve the same radial expansion.

According to one embodiment, the tool comprises a spring element configured to apply a spring force to the activation element, the spring element being arranged inside the housing and connected to the activation element.

This configuration enables the activation element to be pushed back into its starting position due to the spring force which in turn moves the cutting blocks into the hous ing and back into their retracted position. One or more spring elements may be used to push the activation element or individual activation elements back to its/their starting position. Alternatively or additionally, the hydraulic pressure of the drilling fluid acting on the activation and/or cutting blocks may be used to move the activation back towards the starting position. Drilling fluid may be led into a section of the chamber located between the activation element and the bottom end by a separate inlet or an annular space around the cutting blocks. This allows the tool to automatically retract the cutting blocks as the pressure of the drilling fluid is reduced, thus preventing the tool from getting stuck in the borehole.

The spring element may be a compression spring or another type of spring capable of generating a spring force as it is being deformed due to the movement of the activation element. The spring element may be arranged inside the chamber of the housing at or near the bottom end and/or top end. The spring element may lie against one end of the activation element and a protrusion located inside the chamber or the top/bottom end. The top and/or bottom end may comprise coupling elements, e.g. a threaded coupling, for coupling to a matching coupling element of another tool, e.g. a motor, an agitator, or a drill bit.

Alternatively, one or more spring elements may be arranged between the cutting blocks and the activation element or housing for pushing the cutting blocks back into the housing. This allows the contact surface of the cutting blocks to slide along the other contact surface as the activation element is deactivated.

According to one embodiment, the tool comprises a pressure regulating unit connected to one of the ends of the housing, the pressure regulating unit being configured to regulate the differential pressure over the tool.

This configuration enables the tool to regulate the differential pressure of the drilling fluid passing through the tool which is used to move the activation element along the longitudinal direction towards a stopping position. The pressure regulating unit may be located at either end of the housing and in fluid communication with one or more fluid paths provided in the housing or in the activation element. The fluid path may be a central through hole in the activation element aligned with the centre line of the housing. The fluid path may be connected to an outlet or opening at the other end for leading the drilling fluid out of the tool. The activation element is activated, e.g. pushed towards the bottom end, as the differential pressure exceeds the spring force. The activation element is deactivated, e.g. pushed towards the top end, as the spring force exceeds the differential pressure. The activation level may be determined based on the length of the first guiding elements or the travel-to-expansion ratio.

The pressure regulating unit may be a flow restrictor with fixed flow regulating elements or adjustable flow regulating elements. The flow regulating elements may be pre-set prior to deployment or adjusted during operation by using a downhole link or a communications link if a suitable receiver is located in the tool.

One or more sealing elements may be located in the cutting tool for separating the drilling fluid being led through the central fluid path from the drilling fluid being led back through the annular space at outer surface of the cutting tool. The sealing element may be arranged between the activation element and the housing and/or between the activation element and the cutting blocks. The sealing element may be an O-ring, a deformable lip, a barrier or any other type of sealing element. This generates a differential pressure over the cutting tool which is used to activate the activation element.

According to one embodiment, the cutting tool further comprises at least one guiding block or stabiliser blade extending inwards into the housing, the guiding block or stabiliser blade being arranged in at least one second opening located on the first outer surface and is moveably connected to the activation element.

One or more of the cutting blocks may be replaced by guiding blocks or stabiliser blades with suitable guiding elements, e.g. a convex outer surface or rollers, for guiding the cutting tool during the underreaming process. The tool may comprise at least one set of cutting blocks and another set of guiding blocks or stabiliser blades. One or more guiding blocks or stabiliser blades may be arranged in the same plane as one or more of the cutting blocks. The guiding blocks or stabilizer blades may be expanded and retracted in the same manner as the cutting blocks. This allows the drill string to be stabilised as it is introduced into the expanded borehole.

An object of the invention is also achieved by a method for operating a cutting tool in a borehole in order to widening the diameter of the borehole characterised in that - the longitudinal movement of the activation element is transferred into the radial movement of the cutting blocks by using a mechanical coupling located between the activation element and the cutting block.

This provides a simple and direct activation of the cutting tool without using axially moveable sleeves or elements located in the housing in order to expand the cutting blocks. The present configuration enables the expansion of the cutting blocks to be limited to only a radial movement in and out of the housing unlike conventional cutting tools which move the cutting blocks in an axial direction and pivot/rotate the cutting blocks out of the housing by using an inclined surface or wedge shaped element. This allows the length of the openings in the outer surface of the housing as well as the length of the housing to be reduced which in turn increases the torsional strength of the cutting tool.

According to one embodiment, one end of the cutting block extends into an opening located on the activation element, wherein that one end is at least moved further into a cavity formed in the activation element when the cutting block is moved towards the retracted position.

This enables each cutting block to at least partly be arranged in a cavity formed in the outer surface of the activation element when placed in the retracted position. As the cutting block is expanded, it is moved further out of the cavity and out of the housing by means of the mechanical coupling. One end of the cutting block may remain in the cavity when the block is placed in its expanded position, this reduces the risk of the cutting block turning or falling out of the cavity during operation, thus causing a failure of the tool. This allows for a greater expansion since the range of movement is not limited to the thickness of the housing compared to the cutting tool of US 7594552 B2.

Alternatively or additionally, drilling fluid may be led out of a section of the chamber by a separate outlet or the annular space around the cutting blocks as the activation element is moved towards the bottom end.

According to one embodiment, the transfer of movement is done by a first set of coupling elements located on the activation element moving relative to a second set of coupling elements located on the cutting block, wherein at least one set of coupling elements is placed in a predetermined angle relative to the longitudinal direction of that element.

This provides a simple and reliable way of transferring the axial movement of the activation element into a radial movement without also having to move the cutting blocks in the axial direction. One or both sets of coupling elements are placed in an inclined angle relative to the longitudinal direction of one or both elements so that one set of coupling elements is moved, e.g. slided or rolled, along the length of the other set of coupling elements. This allows for the travel-to-expansion ratio to be increased as it requires axial space to expand the cutting blocks compared to conventional cutting tools.

According to one embodiment, the amount of drilling fluid being led through the cutting tool is regulated by using a flow regulating unit connected to the housing.

This allows the activation level of the activation element to be adjusted by regulating the amount of drilling fluid being diverted through the tool. The difference pressure across the tool is used to move the activation element as it exceeds the spring force of one or more spring elements located in the housing. An operator is able to pre-set the flow regulating unit prior to deploying the cutting tool or able to adjust the configuration of the flow regulating unit during operation. As the force exerted by the difference pressure drops below the spring force, the cutting blocks are moved back into the housing by means of the spring elements.

The cutting tool may also be used as a stabiliser tool in which each of the cutting blocks are placed with a stabiliser blade or a guiding block. In this configuration, the stabiliser tool may be at one end mounted to a cutting tool as described above or another underreamer and at the other end mounted to a drill string or borehole assembly (BHA). When the stabiliser tool is moved into the expanded borehole created by the cutting tool/underreamer, the stabiliser blades or guiding blocks are moved out of the housing and into contact with the inner wall of the borehole as described above. When the differential pressure is reduced, the stabiliser blades or guiding blocks are moved back into the housing as described above and the stabiliser tool can be moved out of the expanded borehole.

Description of the Drawing

The invention is described by example only and with reference to the drawings, wherein:

Fig. 1 shows a first exemplary embodiment of a cutting tool according to the invention in a retracted position,

Fig. 2 shows the cutting tool of fig 1 in an expanded position,

Fig. 3 shows a cross sectional view of the cutting tool of fig. 1, and Fig. 4 shows a cross sectional view of a second exemplary embodiment of the cutting tool.

In the following text, the figures will be described one by one and the different parts and positions seen in the figures will be numbered with the same numbers in the different figures. Not all parts and positions indicated in a specific figure will necessarily be discussed together with that figure.

Reference list 1 Cutting tool 2 Housing 3 Top end 4 Bottom end 5 Side wall 6 Activation element 7 Sealing element 8 Pressure regulating unit 9 Spring element 10 Cavity 11 Cutting block 12 Opening 13 Outer surface 14 Cutting elements 15 Mechanical coupling 16 Longitudinal direction, axial movement 17 Transverse direction, radial movement 18 Fluid path, through hole 19 Annular space 20 Stabiliser blade 21 Inner wall

Detailed Description of the Invention

Fig. 1 shows a first exemplary embodiment of a cutting tool 1 in the form of an underreamer seen from the side. The cutting tool comprises a housing 2 having a longitudinal direction and a transverse radial direction adapted to be placed in a borehole. The housing 2 comprises a top end 3 connected to a bottom end 4 via a cylindrical shaped side wall 5. Part of the housing 2 is cut away for illustrative purposes. The housing 2 is made of high strength material, such as steel. The longitudinal direction extends through the top and bottom ends 3, 4 while the radial direction extends through the side wall 5.

The bottom end 4 comprises a coupling element (not shown) configured to be coupled to an external tool, such as a motor or a drill bit. The coupling element may be a treated coupling arranged on an inner or outer side surface of a projecting side wall (not shown). The top end 3 further comprises a coupling element (not shown) similar to that of the bottom end 4.

The housing 2 forms an internal chamber in which a moveable activation element 6 is arranged. The activation element 6 in the form of a box is configured to be moved axially along the longitudinal direction when activated. One or more sealing elements 7 are arranged on the inner surface of the housing 2 and/or on the outer surface of the activation element 6. The sealing element 7 forms a fluid tight seal which separates the drilling fluid passing into the fluid path (shown in figs. 3-4).

The activation element 6 is at a top end connected to a pressure regulating unit 8 which is configured to regulate the different pressure across the cutting tool 1. The pressure regulating unit 8 may comprise fixed regulating elements or adjustable regu- lating elements for diverting a drilling fluid into one or more fluid paths (shown in figs. 3 and 4) located in the housing 2 or the activation element 6. The fluid paths may be through holes which at the other end are connected to an outlet (not shown). If the cutting tool 1 comprises active regulating elements, an actuator element (not shown) may be connected to the regulating elements for adjusting their position. The actuator element may be controlled remotely by using a wireless communication link or a downhole link, e.g. mud pulses or a constant or varying pressure over predetermined time intervals.

The activation element 6 is at a bottom end connected to a spring element 9, e.g. a compression spring, arranged inside the chamber. The spring element 9 is further connected to the bottom end 4 of the housing 2. The spring element 9 is configured to generate a spring force when it is deformed which is used to bias the differential pressure of the drilling fluid.

The activation element 6 comprises a cavity 10 (not shown in fig. 1 and 2) configured to receive and hold at least a part of a moveable cutting block 11. The cavity 10 is connected to at least one opening located in the outer surface 6a of the activation element 6. The opening faces an opening 12, e.g. a through hole, located in the outer surface 13 of the housing 2. The cutting block 11 comprises a longitudinal direction parallel to the radial direction of the housing 2. The cutting block 11 comprises a plurality of cutting elements 14 at one end configured to perform an underreaming process when brought into contact with the inner surface of the borehole. The other end is configured to be placed in the cavity 10 of the activation element 6. For illustrative purposes, only one cutting block 11 is shown.

A mechanical coupling 15 is arranged between the cutting block 11 and the activation element 6 for transferring the axial movement of the activation element 6 into a radial movement of the cutting blocks 11. The mechanical coupling 15 comprises a first set of coupling elements (not shown) arranged on a side surface of the activation element 6 and a second set of coupling elements (not shown) arranged on a side surface of the cutting block 11. The first coupling elements are grooves configured to engage matching tracks defining the second set of coupling elements. The track and grooves are placed in an inclined angle, e.g. 45 degrees, relative to the respective longitudinal di rections of the elements 6, 11, or any other angle capable of providing a radial expansion rate (travel-to-expansion ratio) from 1:1 and 1:100.

The method of operation will now be described in reference to figs. 1 and 2. Fig. 2 shows the cutting tool 1 in an expanded position while fig. 1 shows the cutting tool in a retracted position. The cutting tool 1 is mounted to a drill string or bottom hole assembly and located into position in the borehole. The pressure in the drilling fluid is increased. As the differential pressure exceeds the activation level of the activation element 6, e.g. the spring force, the activation element 6 is moved/pushed axially downwards (marked with arrow 16) towards a stopping position, thereby compressing the spring element 9. The second coupling elements then slide along the first coupling elements in the mechanical coupling 15 which in turn cause the cutting block 11 to move radially outwards (marked with arrow 17) of the housing 2 and the cavity 10.

When the reaming process is completed, the pressure in the drilling fluid is reduced. As the differential pressure drops below the activation level of the activation element 6, the spring force causes the activation element 6 to move axially upwards (marked with arrow 16) towards its starting position. The first coupling elements are then slid along the second coupling elements which in turn cause the cutting block 11 to move back into the housing 2 and further into the cavity 10. The cutting tool 1 may then be raised to the ground level or moved to a new position.

Fig. 3 shows a cross sectional view of the cutting tool 1’ where the cutting block 11 is placed in its retracted position. The outer surface of the activation element 6 is shaped to substantially match the inner contour of the housing 2 so they form a more or less tight fit. One or more optional guiding elements, e.g. a sleeve, (not shown) are arranged between the inner surface of the housing 2 and the outer surface of the activation element 6. The guiding element is configured to limit the movement of the activation element 6 to an axial movement. The sealing element (shown in figs. 1-2) forms a fluid tight seal which separates the drilling fluid passing into the fluid path 18 from the drilling fluid passing through the annular space 19. The fluid path 18 is formed by a central through hole in the activation element 6 in fluid connection with an inlet and outlet (not shown) located at the ends 3, 4 respectively.

The cavity 10 extends in a longitudinal direction parallel to the longitudinal direction of the activation element. The mechanical coupling 15 is arranged in the cavity 10 between two opposite facing surfaces of the two elements 6, 11. The cutting elements 14 are in the retracted position flushed with or placed in a retracted position relative to the outer surface 13 of the housing 2.

One or more stabiliser blades 20 are arranged in a second opening located on the outer surface 13 of the tool Γ. The stabiliser blade 20 extends into the housing 2 and into a second cavity in the activation element 6, as shown in fig. 3. The stabiliser blade 20 is moveable connected to the activation element 6 by a second mechanical coupling 15. Instead of cutting elements, the stabiliser blade 20 comprises a curved guiding surface 20a or a plurality of rollers for contacting the inner wall 21 of the borehole (marked with a dotted line). The stabiliser blade 20 is expanded and retracted in the same manner as the cutting blocks 11. This stabilises the tool 1 during movement in the expanded borehole.

Fig. 4 shows a cross sectional view of a second exemplary embodiment of the cutting tool 1. In this embodiment the tool 1” comprises two or more cutting blocks 11a, lib, 11c, here three blocks are shown, each of which is arranged in an individual opening 12a, 12b, 12c and cavity 10a, 10b, 10c. The cutting blocks 11 are angled relative to each other, e.g. in 120 degrees intervals and are simultaneously activated, e.g. moved radially, when the activation element 6 is moved axially downwards as described above.

The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention as described in the patent claims below.

Claims

1. A cutting tool for widening the diameter of a borehole, comprising: - a housing having a longitudinal direction and a transverse radial direction, the housing comprising at least a top end connected to a bottom end by a first outer surface, - at least one moveable cutting block having any number of cutting elements, each cutting block being arranged in a first opening located on the first outer surface and configured to move in the radial direction between a retracted position and an expanded position relative to the housing, - at least one moveable activation element arranged inside the housing relative to the cutting blocks and configured to move along the longitudinal direction relative to the housing for activation of the cutting blocks characterised in, that - each cutting block extends inwards into the housing and is moveably connected to the activation element by a mechanical coupling, the mechanical coupling being configured to transfer the longitudinal movement of the activation element into the radial movement of the cutting blocks.

2. A cutting tool according to claim 1, characterised in that the activation element comprises a second outer surface facing an inner surface of the housing, wherein at least one of the cutting blocks extends into a second opening located on the second outer surface.

3. A cutting tool according to claim 1 or 2, characterised in that the mechanical coupling comprising a first set of guiding elements, e.g. tracks, configured to engage a second set of guiding elements, e.g. grooves, wherein one set is arranged on a third surface of the cutting block and the other set is arranged on a fourth surface on the activation element facing the third surface.

4. A cutting tool according to claim 3, characterised in that at least one set of guiding elements is placed in a predetermined angle, e.g. 45 degrees, relative to the longitudinal direction of the respective element.

5. A cutting tool according to claim 3 or 4, characterised in that the ratio between the relative movement of the activation element and the radial movement of the cutting blocks is between 1:1 and 1:100.

6. A cutting tool according to any one of claims 1 to 5, characterised in that the tool comprises a spring element configured to apply a spring force to the activation element, the spring element being arranged inside the housing and connected to the activation element.

7. A cutting tool according to any one of claims 1 to 6, characterised in that the tool comprises a pressure regulating unit connected to one of the ends of the housing, the pressure regulating unit being configured to regulate the differential pressure over the tool.

8. A cutting tool according to any one of claims 1 to 7, characterised in that the cutting tool further comprises at least one stabiliser blade extending inwards into the housing, the stabiliser blade being arranged in at least one second opening located on the first outer surface and is moveably connected to the activation element.

9. A method for operating a cutting tool in a borehole for widening the diameter of the borehole, the cutting tool comprising at least one moveable cutting block arranged in an outer surface of a housing, the cutting block being connected to an activation element arranged inside the housing, where the method comprises the steps of: - moving the activation element in a longitudinal direction relative to the housing using a differential pressure of a drilling fluid being circulated in the borehole, - moving the cutting block in a transverse radial direction out of the housing towards an expanded position, - moving the cutting block in the opposite radial direction back into the housing towards a retracted position, e.g. by using a spring force or hydraulic force, characterised in, that - the longitudinal movement of the activation element is transferred into the radial movement of the cutting blocks by using a mechanical coupling located between the activation element and the cutting block.

10. A method according to claim 9, characterised in that one end of the cutting block extends into an opening located on the activation element, wherein that one end is at least moved further into a cavity formed in the activation element when the cutting block is moved towards the retracted position.

11. A method according to claim 9 or 10, characterised in that the transfer of movement is done by a first set of coupling elements located on the activation element moving relative to a second set of coupling elements located on the cutting block, wherein at least one set of coupling elements is placed in a predetermined angle relative to the longitudinal direction of that element.

12. A method according to any one of claims 9 to 11, characterised in that the amount of drilling fluid being led through the cutting tool is regulated by using a flow regulating unit connected to the housing.