EP3167145A1

EP3167145A1 - Underreamer with radial expandable cutting blocks

Info

Publication number: EP3167145A1
Application number: EP15819749.1A
Authority: EP
Inventors: Sigurd Solem
Original assignee: Advancetech Aps
Current assignee: Advancetech Aps
Priority date: 2014-07-07
Filing date: 2015-07-07
Publication date: 2017-05-17
Also published as: BR112017000355A2; DK201470422A1; WO2016004954A1; US20170159365A1; EP3167145A4; CA2954444A1; DK179097B1

Abstract

A cutting tool (1) for widening the diameter of a borehole and method thereof is disclosed. The cutting tool (1) comprises a housing (2) having cavity (10) in which a moveable activation element (6) is arranged. The activation element (6) is moved in an axial direction and is connected to one or more cutting blocks via a mechanical coupling (15). The mechanical coupling (15) transfers the axial movement of the action element into a radial movement of the cutting blocks. An activation unit (24) pushes the activation element (6) towards a stopping position which in turn causes the cutting blocks (11) to move out of the housing. The activation unit (24) further pulls the activation element back towards its starting position which in turn causes the cutting blocks to move back into the housing. The cutting blocks (11) 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 stabiliser blades (20) which are used to stabilise the drilling 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 and a method for operating the cutting tool. The cutting tool comprises a housing in which a cutting block and an activation element are arranged. Upon activation, the activation element is driven in an axial direction which in turn moves the cutting block in a radial direction from a retracted position to an expanded position via a mechanical coupling. 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 three elongated slots in which three slidable cutting blades are arranged. The cutting blades are at one end connected to a sleeve surrounding a hollow central tube which allows drilling fluid to pass through the tool. A compression spring holds the sleeve in place relative to the central tube. The tool is activated by dropping a ball into the drilling fluid which is caught in the central tube which in turn forces the central tube downwards relative to the housing due to the differential pressure. Drilling fluid is then led into a chamber below the sleeve via corresponding openings which in turn forces the sleeve upwards relative to the housing. An angled sliding surface in each slot then causes the cutting blades to pivot out of the housing. Afterwards the pumping of the drilling fluid is stopped and 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 radially moveable blocks are arranged in the housing relative to the central tube. A flow restricting opening located in the tube is used to activate the tool. Pressure of the drilling fluid above this restrictive opening forces the tube downwards relative to the housing. Drilling fluid is then led into a chamber between the tube and cutting block which in turn pushes the cutting blocks out of the housing. Afterwards the pumping of the drilling fluid is stopped and 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 has 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. Also, the tool must be removed from the downhole in order to reset the tool. 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. US 2010/0108394 Al discloses an underreamer having a housing with openings in which three cutting blocks are arranged and a central tube for allowing drilling fluid to pass through the tool. The tube has three projecting plates each extending into a corresponding cavity in the cutting blocks where the side surfaces of the plate and cavity have engaging inclined grooves and tracks. When activated, a ball is caught by the tube which in turn forces the tube downwards relative to the housing. The cutting blocks are then moved out of the housing due to the engaging grooves and tracks. A compression spring is used to force the tube upwards when the pressure of the drilling fluid is removed which in turn also forces the cutting block back into the housing. In this solution the moveable parts are located in the central hole of the housing, thus a certain pressure differential is required to activate the tool.

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 cutting tool for widening the diameter of a borehole, comprising:

- a housing having a top end, a bottom end and a first outer surface, wherein the housing defines a longitudinal direction and a transverse radial direction,

- at least one moveable cutting block having at least one cutting element, each cutting block being arranged in a first opening located in 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 is arranged relative to the at least one cutting block and configured to move along the longitudinal direction relative to the housing for activation of the at least one cutting block, wherein

- the housing comprises a cavity connected to the first opening in which the at least one cutting block and the at least one activation element are arranged, wherein the cavity is arranged between the first outer surface and an inner surface of the housing. 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. Thus, the overall length of the cutting tool can be reduced. No moveable sleeves or tubes need to be arranged in the central through hole of the housing, thus no additional horsepower or pressure differential is needed to activate the cutting tool. This allows the central hole of the housing to act as a passageway for the drilling fluid, thus the inner diameter of this passageway can be increased. 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. 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. The cutting tool is preferably an underreamer, a back-reamer, a near-bit reamer or any other type of reamer tool. This allows the configuration and dimensions of the cutting tool to be adapted to the desired application.

According to one embodiment, the activation element is further connected to an acti- vation unit arranged in the cavity, wherein the activation unit is configured to drive the activation element.

The present configuration allows the cutting tool to be activated by suitable activating means arranged in the cavity, no Z-drive or ball seats are needed to activate the cutting tool. The activation unit may further comprise suitable control means for controlling the operation of the cutting tool.

The cavity is formed in the outer surface of the housing and in configured to receive and hold the moveable parts used to operate the cutting tool. The cavity has one or more openings. A hatch or removable cover may be provided at these openings for closing off the cavity and protecting the components located inside the cavity. This allows the various parts to be accessed from exterior of the housing for installation, servicing, and replacement. The opening for the cutting block may be located in one of the hatches or covers.

According to a special embodiment, the activation unit is arranged in a chamber inside the cavity, the chamber being sealed off from the rest of the cavity. The cavity may be separated into two or more chambers by means of one or more internal walls and/or sealing elements. The activation unit may be arranged in a first chamber while the cutting block and the activation element may be arranged in a second chamber. The first chamber may be sealed off from the second chamber by using suitable sealing elements, such as O-rings, lip seals, labyrinth seals, rotary seals, fluid barriers or other suitable sealing means. Another set of sealing elements may be arranged between each hatch or cover and surrounding edges of the cavity, or between adjacent hatches or covers. This allows the electrical drive components and other sensitive components to be protected from the surrounding drilling fluid which otherwise may damage these components.

Drilling fluid may enter the second chamber via gaps formed between the activation element and the cutting block, and/or via separate inlets and outlets connected to the second chamber. Said separate inlets and outlets may be used to circulate the drilling fluid inside the second chamber when the activation element and cutting blocks are moved relative to each other. The openings in which the cutting blocks are arranged may be connected to the second chamber. Alternatively, the second chamber may also be sealed off from the drilling fluid by using yet another set of sealing elements, e.g. arranged relative to each cutting block and the surrounding edges of the respective opening. This allows the non-sensitive components to be arranged in the second chamber.

According to another special embodiment, the activation unit comprises a linear actua- tor connected to a control unit configured to control the operation of the activation unit.

The activation element may be driven by suitable drive means arranged in the cavity and relative to the activation element. In a preferred embodiment, the activation ele- ment is connected to a linear actuator via a shaft. The linear actuator may be arranged in the first chamber and the shaft may extend through the inner wall of the cavity. The linear actuator may be driven by a hydraulic, pneumatic, electrical, mechanical or another suitable power source. The linear actuator may be a ball screw, a roller screw, a pneumatic or hydraulic cylinder with a moveable piston, a motor (e.g. an electrical motor), a solenoid with a moveable stem or another suitable linear actuator.

The operation of the linear actuator and power source may be controlled by a control unit arranged in the cutting tool, e.g. in the first chamber in the cavity. The control unit may be electrically connected to the linear actuator and/or power source via wires or a wireless connection. The control unit may be a microprocessor or another electrical circuitry configured to control the operation of the cutting tool. One or more sensors, such as a flow-rate sensor, a pressure sensor or a position sensor, may be electrically connected to the control unit for sensing one or more predetermined parameters, such as the flow-rate or pressure of the drilling fluid or the respective position of the activation element and/or cutting block. This allows the control unit to monitor the operating of the cutting tool.

Optionally a communications module may form part of the control unit for communication with a remote unit, e.g. located at ground level. The communication module may be connected to the remote unit via a wired connection, e.g. data cables, or a wireless connection, e.g. a downhole link or mud pulses.

In a preferred configuration, the control unit monitors the pressure and/or flow-rate of the drilling fluid to detect a stable level within a predetermined time window which in turn is used to activate, deactivate or change the operating mode of the cutting tool. The control method described in DK 178108 B l is hereby incorporated into the application by reference. According to one embodiment, the mechanical coupling comprising a first set of guiding elements, e.g. a pin, configured to engage a second set of guiding elements, e.g. through hole, wherein one of the first and second sets of guiding elements is arranged on a third surface of the at least one cutting block and the other set of guiding elements is arranged on a fourth surface on the at least one activation element facing the third surface.

This 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.

The activation element and cutting blocks are mechanically connected by means of complementary 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 an opposite facing side surface of the activation element. This allows for a simple and direct engagement between the activation element and the cutting blocks which eliminates the need for any axially moveable sleeves or tubes for expansion of the cutting blocks. This allows for a more compact cutting tool and eliminates the need for inclined surfaces or wedge shaped elements to expand the cutting blocks.

The coupling elements may be one or more tracks or pins configured to engage one or more complementary grooves or through holes. The coupling elements, e.g. tracks and grooves, may be arranged on two opposite facing surfaces of the activation element and the cutting block. Alternatively, the coupling elements, e.g. pins, may extend through the other coupling elements, e.g. holes, and may be connected to two opposite sides of the activation element or the cutting block. 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.

Said pins may have a predetermined shear threshold that enables the pins to shear or break when a predetermined force is applied to the pins. The respective cutting block may then fall back into its retracted position. This increases the safety of the cutting tool in an extreme load situation. The pins also reduce the risk of the cutting blocks getting stuck due to solids or other particles in the drilling fluid.

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 ele- ment 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.

The guiding elements may be placed in a predetermined inclined position relative to the longitudinal direction, thus allowing for a simple and easy transfer of movement between the activation element and the cutting blocks. 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 cut- ting 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 one embodiment, the at least one activation element comprises a cavity or through hole located on an outer surface, wherein at least a part of the at least one cutting block extends into the cavity or through hole.

This configuration allows for a greater expansion of the cutting blocks compared to conventional cutting tools, as the range 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 posi- tion, preferably in both the retracted and 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 the cavity or hole may have a substantial rectangular, squared, or any other suitable cross-sectional profile.

In an alternative configuration, the activation element may extend through an opening of a through hole or cavity in each of the cutting blocks. In this embodiment, the cavity/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.

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

The term "relative axial movement" is defined as the relative movement between the activation element and the housing in the longitudinal direction. The "relative 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 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 cutting tool comprises a spring element configured to apply a spring force to the activation element, the spring element being arranged relative to the activation element inside the cavity. The activation element may be pushed back into its starting position due to the spring force which in turn moves the cutting blocks into the housing 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 the second chamber by separate inlets located near one end of the second chamber or by 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 at or near the bottom end and/or the top end of the second chamber. The spring element may lie against one end of the activation element and a protrusion located inside the chamber or the top/bottom end. 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. The top and/or bottom end of the housing may comprise coupling elements, e.g. a threaded coupling, for coupling to a complementary coupling element of another downhole tool, e.g. a motor, an agitator, or a drill bit. According to one embodiment, the cutting tool further comprises at least one guiding block or stabiliser blade arranged in at least one second opening located on the first outer surface, wherein the at least one stabiliser blade is moveably connected to the at least one 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 stabiliser blades may be expanded and retracted in the same manner as the cutting blocks. In this configuration, the stabiliser tool may be at one end mounted to another cutting tool or underreamer. This allows the cutting tool to act as a stabiliser for stabilising the drill string during the introduced into the expanded borehole.

An object of the invention may also be achieved by a cutting tool for widening the diameter of a borehole, comprising:

- at least one moveable activation element arranged relative to the cutting blocks and configured to move along the longitudinal direction relative to the housing for activation of the cutting blocks, wherein

- the activation element comprises a second outer surface facing an inner surface of the housing and each cutting block extends into a cavity in the second outer surface, and wherein each cutting block 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 also 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 that is less than the thickness of the housing. The openings in the housing advantageously have a shape and size that substantially matches the cross- sectional size and shape of the cutting blocks as no addi- tional space is needed to compensate for the axial movement of the cutting blocks during the expansion. It also eliminates the need for any inclined surface or wedge shaped elements to expand the cutting blocks.

This configuration also allows for a greater expansion of the cutting blocks compared to conventional cutting tools, as the range of expansion is not limited to the thickness of the housing. This alternative embodiment differs from the embodiment described above by having the activation element arranged in the central through hole of the housing where the cutting block extends further through openings located on an inner surface of the housing. In this alternative embodiment, the cavity/hole of the activa- tion element may have the same configuration as described above.

In this alternative embodiment, the central through hole of the housing acts as the second chamber described above. The inner surface may substantially match the outer contours of the activation element allowing for a tight fit during movement of the ac- tivation 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 in both embodiments comprise one or more guiding elements, e.g. a spline system, an axial bearing, a sleeve or another guiding system arranged between the inner surface of the chamber and the outer surface of the activation element. One or more spline elements may be arranged on the inner surface of the chamber and one or more complementary 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 this alternative embodiment, the cutting 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 cutting tool.

The pressure regulating unit acts as the activation unit described above. The pressure regulating unit further enables the differential pressure of the drilling fluid passing through the tool to be regulated which in turn is used to move the activation element. The pressure regulating unit may be located at one end of the housing and may be 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 cutting tool. The activation level may be determined based on the length of the first guiding elements, the travel-to-expansion ratio, or the compression force of the spring element.

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. In this alternative embodiment, one or more sealing elements may be used to separate the drilling fluid being led through the central fluid path from the drilling fluid being led back through the annular space at the 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 elements may be O- rings, lip seals, labyrinth seals, fluid barriers or other suitable sealing means. This generates a differential pressure over the cutting tool which is used to activate the activation element. An object of the invention is also achieved by a method for operating a cutting tool as described above, wherein the method comprises the steps of:

- moving the at least one activation element in the longitudinal direction relative to the housing, and further moving the at least one cutting block in the radial direction out of the housing towards an expanded position,

- wherein the at least one activation element is arranged in a cavity in the outer surface, wherein said at least one activation element is driven along the cavity by an activation unit further arranged in the cavity. This provides a simple and direct activation of the cutting tool without using axially moveable sleeves or tubes 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 relative to the housing unlike conventional cutting tools. 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.

The moveable part, i.e. the activation element and the cutting block, is arranged in an outer cavity of the housing. The movement is driven by an activation unit also ar- ranged in this cavity. Thus, no movable parts are arranged in the central through hole of the housing, i.e. defined by the inner surface of the housing, which in turn allows the inner diameter of the fluid passageway to be increased. Also, no additional pressure differential or horsepower is required to activate the cutting tool. The present cutting tool also allows for easy access to the moveable parts by simple removing an outer cover or opening an outer hatch. The respective parts may then be installed, serviced or replaced, and afterwards the cover or hatch is closed again.

According to one embodiment, a linear actuator moves the at least one activation ele- ment, wherein the operation of the linear actuator is controlled by a control unit.

The axial movement of the activation element is carried out using a linear actuator driven by a suitable drive unit as described above. The control unit controls the operation of the linear actuator, e.g. based on one or more measured parameters. This al- lows for a simple and fast activation of the cutting tool. This eliminates the need for a spring element as the movement can be performed solely by the linear actuator.

Alternatively, the control unit may communicate with a remote unit, e.g. at ground level, via a communications module as described above. The control unit may transmit the measured data and/or status information of the cutting tool to the remote unit and receive one or more control signals from the remote unit. The control unit may then adapt the operation of the cutting tool according to the received control signals.

According to one embodiment, the longitudinal movement is transferred into the radi- al movement by using a mechanical coupling located between the at least one activation element and the at least one cutting block.

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. The first and second sets of coupling elements are preferably placed in an inclined angle relative to the longitudinal direction so that one of said sets of coupling elements is moved, e.g. slid 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 reduces the axial space needed to expand the cutting blocks compared to conventional cutting tools. This also increased the radial pressure applied by the cutting block compared to other conventional cutting blocks.

The cutting tool may comprise a built-in safety function as one of the coupling elements may be a pin extending through a hole defining the other coupling element, wherein said pin may be a shear pin having a predetermined shear threshold. In the event of an overload situation, the pin may shear and the cutting block may fall back into the retracted position. The cutting tool may then be retrieved and the pins may be replaced and the cutting tool may be lowered into the downhole again. According to one embodiment, the method further comprises the step of:

- monitoring at least one parameter of the drilling fluid passing through the cutting tool via the control unit, and further detecting when the at least one parameter has reached a predetermined level within a predetermined time window, or - communicating with a remote unit via the control unit, wherein the remote unit and the control unit control the operation of the cutting tool.

The control unit may monitor the pressure and/or flow-rate of the drilling fluid pass- ing through the drilling tool. The control unit may further determine if the pressure and/or flow-rate have reached a stable predetermined level within a predetermined time window which in turn is used to activate or deactivate the cutting tool or switch between operating modes, such as described in DK 178108 B l. Additionally or alternatively, the control unit may communicate with the remote unit for displaying status information to an operator or later analysis. The operator may transmit control signals to the cutting tool via the communication path, e.g. a wired or wireless connection as described above. The control unit then controls the operation of the cutting tool according to the received control signals. This allows the operator to monitor the operation and optionally adjust the operation if needed.

According to one embodiment, one end of the cutting block extends into an opening located on the at least one activation element, wherein the one end is at least moved further into the activation element when the at least one cutting block is moved to- wards 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.

An object of the invention may also be achieved by a method for operating a cutting tool as described above for widening the diameter of the borehole, wherein 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 the radial direction out of the housing towards an expanded position,

- wherein 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, wherein

- one end of the cutting block extends into an opening located on an outer surface of the activation element, wherein the one end is moved further into the activation ele- ment when the cutting block is moved towards the retracted position.

This configuration also allows for a greater expansion of the cutting blocks compared to conventional cutting tools, as the range of expansion is not limited to the thickness of the housing. Thus, a simple and compact cutting tool can be formed. This embodi- ment differs from the embodiment described above by having the activation element arranged in the central through hole of the housing where the cutting block extends further through openings located on an inner surface of the housing. In this embodiment, the cavity/hole of the activation element may have the same configuration as described above. In this embodiment, the central through hole of the housing acts as the second chamber described above.

In this alternative embodiment, the amount of drilling fluid being led through the cutting tool is regulated by using a flow regulating unit connected to the housing. 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 cutting tool. The difference pressure across the cutting tool moves the activation element when it exceeds the spring force of the 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 ele- ments. This allows the pressure regulating unit to act as the activation unit described above.

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,

Fig. 4 shows a cross sectional view of a second exemplary embodiment of the cutting tool

Fig. 5 shows a third exemplary embodiment of the cutting tool in a retracted position,

Fig. 6 shows the cutting tool of fig. 5 in an expanded position,

Fig. 7 shows the cutting tool of fig. 5 seen in the radial direction, and

Fig. 8 shows a cross-section of the cutting tool of fig. 5.

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

22 Cutting tool

23 Cavity

24 Actuator unit

25 Wall

26 Shaft

27 Linear actuator

28 Control unit

Detailed Description of the Invention

Fig. 1 shows a first exemplary embodiment of a cutting tool 1 in the form of an un- derreamer 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 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 regulating 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 by a control unit (shown in fig. 5).

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 par- allel 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 extend into 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 complementary 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 directions 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. The spring force causes the activation element 6 to move axially upwards (marked with arrow 16) towards its starting position as the differential pressure drops below the activation level of the activation element 6. 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 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 configured to limit the movement of the activation element 6 to an axial movement may be arranged between the inner surface of the housing 2 and the outer surface of the activation element 6. 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 . 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, l ib, 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.

Fig. 5 shows a third exemplary embodiment of the cutting tool 22 in a retracted position where fig. 6 shows the cutting tool 22 in an expanded position. The cutting tool 22 has a cavity 23 formed in the outer surface 13 of the housing 2' in which the activation element 6 and the cutting block 11 are arranged. An activation unit 24 is further arranged in the cavity 23 and connected to the activation element 6 via a shaft 25. An inner wall 26 separates the cavity 23 into a first chamber and a second chamber, wherein the shaft 25 extends through the inner wall 26. The activation unit 24 comprises a linear actuator 27 connected to a control unit 28 which controls the operation of the cutting tool 22. The activation unit 24 is accessible via a cover removable connected to the housing 2' . The control unit 28 communicates with a remote unit (dotted lines) via a communications module arranged in the cavity 23.

When activated, the control unit 28 send a control signal to the linear actuator 27 which in turn moves the activation element 6 and the cutting block to their expanded position as described in figs. 1 and 2. After completing the underreamer process, the control unit 28 then sends another control signal to the linear actuator 27 which moves the activation element 6 and the cutting block to their retracted position as described in figs. 1 and 2. In this configuration, the drilling fluid is able to pass freely through the cutting tool 22 as the central trough hole of the housing 2' acts as the fluid passageway 18'.

Fig. 7 shows the cutting tool 22 seen in the radial direction where the housing 2' is omitted for illustrative purposes. As illustrated, the cavity 23 is connected to three openings which can be closed off by a cover or hatch (not shown). The coupling elements 15 are here shown as a through hole in the cutting block 11 and a pin extending through the hole. The pin is connected to two opposite facing surfaces on the activation element 6. The cavity 10' of the activation element 6 is an elongated cavity which at least corresponds to the axial movement of the activation element 6.

Fig. 8 shows a cross-section of the cutting tool 22 and the cavity 23 in which the activation element 6 and the cutting block 11 are arranged. The inner diameter of the through hole 18' is greater than the inner diameter of the through hole 18 shown in figs. 3 and 4. Thus, more drilling fluid may be led through the cutting tool 22 without any significant loss of pressure. 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 top end, a bottom end and a first outer surface, wherein the hous- ing defines a longitudinal direction and a transverse radial direction,

- at least one moveable activation element arranged relative to the at least one cutting block and configured to move along the longitudinal direction relative to the housing for activation of the at least one cutting block

characterised in, that

- the housing comprises a cavity connected to the first opening in which the at least one cutting block and the at least one activation element are arranged, wherein the cavity is arranged between the first outer surface and an inner surface of the housing.

2. A cutting tool according to claim 1, characterised in that the activation element is further connected to an activation unit arranged in the cavity, wherein the activation unit is configured to drive the activation element.

3. A cutting tool according to claim 2, characterised in that the activation unit is arranged in a chamber inside the cavity, the chamber being sealed off from the rest of the cavity.

4. A cutting tool according to claim 2 or 3, characterised in that the activation unit comprises a linear actuator connected to a control unit configured to control the operation of the activation unit.

5. A cutting tool according to any one of claims 1 to 4, characterised in that the mechanical coupling comprising a first set of guiding elements, e.g. a pin, configured to engage a second set of guiding elements, e.g. through hole, wherein one of the first and second sets of guiding elements is arranged on a third surface of the at least one cutting block and the other set of the guiding elements is arranged on a fourth surface on the at least one activation element facing the third surface.

6. A cutting tool according to any one of claims 1 to 5, characterised in that the at least one activation element comprises a cavity or through hole located on an outer surface, wherein at least a part of the at least one cutting block extends into the cavity or through hole.

7. A cutting tool according to any one of claims 1 to 6, characterised in that the ratio between the relative axial movement of the at least one activation element and the relative radial movement of the at least one cutting block is between 1: 1 and 1: 100.

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

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

10. A method for operating a cutting tool according to any one of the preceding claims, wherein the method comprises the steps of:

- characterised in, that

- the at least one activation element is arranged in a cavity in the outer surface, where- in said at least one activation element is moved along the cavity by an activation unit further arranged in the cavity.

11. A method according to claim 10, characterised in that a linear actuator drives the at least one activation element, wherein the operation of the linear actuator is controlled by a control unit.

12. A method according to claim 10 or 11, characterised in that the longitudinal movement is transferred into the radial movement by using a mechanical coupling located between the at least one activation element and the at least one cutting block.

13. A method according to any one of claims 10 to 12, characterised in that the meth- od further comprises the step of:

- monitoring at least one parameter of the drilling fluid passing through the cutting tool via the control unit, and further detecting when the at least one parameter has reached a predetermined level within a predetermined time window, or

- communicating with a remote unit via the control unit, wherein the remote unit and the control unit control the operation of the cutting tool.

14. A method according to any one of claims 10 to 13, characterised in that one end of the at least one cutting block extends into an opening located on the at least one activation element, wherein the one end is at least moved further into the at least one acti- vation element when the cutting block is moved towards the retracted position.