Multi cycle downhole tool

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national stage application of PCT/GB2014/053509 filed Nov. 27, 2014 and entitled “Multi Cycle Downhole Tool,” which claims priority to British Application No. GB 1321137.0 filed Nov. 29, 2013 and entitled “Multi Cycle Downhole Tool,” both of which are hereby incorporated herein by reference in their entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

This invention relates to a downhole tool with an activation member for multiple use downhole, and associated methods; and in particular, but not exclusively, to a downhole tool having extendable members, such as an under-reamer, casing cutter or adjustable stabiliser.

BACKGROUND OF THE INVENTION

In the oil and gas industry, downhole tools are used to perform various operations during exploration, production, maintenance or decommissioning. The tools often form part of a tool string that travels downhole, such as a drill string for drilling a bore in an underground formation. Typically the downhole tools perform different functions during different stages of downhole operations. For example, downhole tools are often transported to and from a particular location in a bore and only activated for use at the particular location for a specific interval, such as to perform a local operation such as packing or reaming or perforating, or the like.

It is often unsuitable to transport the downhole tools in an active configuration. For example, there are numerous downhole tools that feature radially extendable members. Blades or cutters such as on an underreamer are radially extendable to allow the underreamer to pass through a restriction or a casing with the blades in a relatively compact radial configuration. When the undereamer passes out of the end of the casing in a bore, the blades are extended to allow the bore to be drilled to a diameter greater than the internal diameter of the casing.

During an underreaming operation the blades can be subjected to high radial forces so, to ensure effective cutting, the blades are radially supported in the extended configuration. Examples of underreamers are described in applicant's International (PCT) Application Publication No.s WO 2004/097163 and WO 2010/116152, the disclosures of which are incorporated herein by reference. Upon completion of an underreaming operation, the blades are retracted to allow the toolstring including the undereamer to be retrieved from the bore. Failure to retract the blades, or to retain the blades in a retracted configuration during retrieval of the underreamer, causes the blades to contact the existing casing. A blade retraction failure of the underreamer makes it difficult, sometimes impossible, to retrieve the underreamer and can also cause damage to the casing or other equipment in the bore.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a tool, such as an under-reaming tool. The tool may comprise a body. The tool may comprise one or more laterally extendable member/s. The laterally extendable members may comprise a plurality of extendable cutters mounted on the body. The tool may be configured to be cycled between a first configuration in which the one or more laterally extendable member/s are retracted and a second configuration in which the one or more laterally extendable member/s are movable between retracted and extended positions. The tool may configured to prevent extension of the one or more laterally extendable member/s by an external fluid in the first and/or second configuration/s.

The tool may configured to prevent extension of the one or more laterally extendable member/s by an external fluid pressure in the first and/or second configuration/s.

The tool may configured to prevent extension of the one or more laterally extendable member/s by an external fluid entering the tool in the first and/or second configuration/s.

According to a further aspect of the invention, there is provided a drill-string comprising a tool according to any other aspect.

The tool may be configured to allow extension of the cutters only in the second configuration. The cutters may be extendable only in the second configuration. The tool may be configured to allow extension of the cutters only in response to an internal fluid pressure within the body and/or an internal fluid flow through or within the body. The tool may be configured to allow extension of the cutters only in response to a toolbore pressure, or toolbore overpressure. The tool may be configured to allow extension of the cutters only in response to an internal fluid pressure within the body exceeding the external fluid pressure.

The tool may comprise an internal fluid passage. The internal fluid passage may comprise an axial fluid passage. The fluid passage may comprise an internal bore. The internal bore may comprise a tool bore. The internal bore may comprise a throughbore. The body may comprise the internal fluid passage. The tool bore may form part of a drill-string bore. The tool bore may be configured to be in fluid communication with one or more other drill-string components or assemblies.

The tool may be configured to only allow extension of the cutters in response to a higher internal pressure relative to an external pressure. The tool may be configured to prevent extension of the cutters when the external pressure exceeds an internal pressure.

The tool when configured such that the cutters are driven or biased to the retracted position can be defined as set in the first configuration.

The tool when configured such that the cutters are driven to the extended position can be defined as set in the second configuration.

Providing such a tool may prevent unwanted extension and/or ensure retraction of cutters. For example, such a tool may prevent extension of cutters when encountering a higher than expected external fluid pressure. Such a tool may prevent extension and/or ensure retraction of cutters during tripping in hole when high external hydrostatic pressure annular to tool body may exceed the hydrostatic pressure within the tool bore. Such a tool may obviate or at least mitigate against the possibility of cutter blades extending into casing bore and hanging up drill string during trip in hole.

The tool may be configured to be subjected to a plurality of pressure conditions. The tool may be configured to be subjected to at least three pressure conditions.

A first pressure condition may be defined as internal pressure, such as tool bore pressure, being greater than the pressure external to the tool body.

A second pressure condition may be defined as the pressure external to the tool body being greater than the internal or tool bore pressure.

A third pressure condition may be defined as the internal or tool bore pressure being equal to the pressure external to the tool body.

Although referred to as first, second and third pressure conditions, it will be appreciated that the tool may be subjected to pressure conditions in any other order. For example, the tool may be initially subjected to the second or third pressure conditions, such as when running-in; and subsequently subject to the first pressure condition.

The first pressure condition (e.g. high internal or tool bore pressure relative to low pressure external to the tool body) may be achieved when a drilling fluid is pumped through the tool bore.

The tool, such as an under-reamer, may be positioned in a bottom hole assembly of a drill string. The under-reamer may be positioned above one or more drilling components. Downhole of the under-reamer tool there may be a drill bit. The drill-string may also include additional components, such as selected from one or more of: a rotary steerable tool and/or a measurement while drilling tool (MWD) and/or a logging while drilling tool (LWD). The drill-string may be configured such that a fluid flowing through the drill string bore generates a pressure drop across each bottom hole assembly component. The pressure drop may effectively be the pressure differential between the tool bore pressure and the annular pressure external to tool body. The pressure differential between the drill string bore and the annulus external to the drill string may increase cumulatively above each bottom hole assembly component.

The tool may comprise one or more piston/s. The/each piston may be configured to act within the under-reamer in an axial direction. The axial direction of action of the/each piston may be dependent upon a polarity of the pressure differential between the tool bore pressure and the annular pressure external to the tool body.

The tool may comprise an activation member. The activation member may comprise a first piston. The first piston may comprise an activation piston. The activation piston may be configured within the under-reamer to act in an axial direction to drive, such as directly drive, the cutters to the extended position. The activation piston may comprise or be operatively associated with, such as attached to, a cam mechanism to drive the cutters. The cam mechanism may be configured to convert or translate the axial movement and/or force of the activation piston to a movement and/or force with at least a radial component to extend the cutters laterally. The first piston may be configured to provide a negligible or no axial bias when not selected or activated, such as in the first configuration. The first piston may be configured to provide a bias, such as a hydraulic bias, when selected or activated.

The tool may comprise a second piston. The second piston may comprise a retraction piston. The retraction piston may be configured within the under-reamer to act in an opposing axial direction to the activation piston. The retraction piston may be used against the activation piston to drive, such as directly drive, and/or bias the cutter blades to the retracted position.

The tool may comprise a third piston. The third piston may comprise a conditional piston. The conditional piston may comprise a counterpiston.

The conditional piston may be configured to act in the opposing direction to the retraction piston, at least as a result of fluid pressure/s. The conditional piston may be configured to act in the opposing direction to the retraction piston at least when the tool is subject to the first pressure condition. The conditional piston may be configured to act in the same direction as the activation piston, at least as a result of fluid pressure/s. The conditional piston may be configured to act in the same direction as the activation piston, at least when the tool is subject to the first pressure condition. The conditional piston may be configured to act in the same direction as the activation piston, at least when the tool is in the second configuration.

The conditional piston may be configured to act in an opposite direction when the tool is subject to the second pressure condition compared to when the tool is subject to the first pressure condition. The conditional piston may change direction when the pressure condition changes between the first and second pressure conditions.

The retraction piston may be configured to exert a different magnitude of bias than the conditional piston. The retraction piston may be configured to exert a smaller bias force than the conditional piston. The conditional piston may be configured to resist movement of the activation member in one direction (e.g. the first or second direction, such as uphole or downhole), at least when subject to the second pressure condition in the first and/or second configurations. The retraction piston may be configured to resist movement of the activation member in the same direction (e.g. the first or second direction, such as uphole or downhole) when the tool is subject to the first pressure condition.

The first configuration may comprise an inactive configuration. The second configuration may comprise an active configuration. The tool may be configured to retract and/or prevent extension of the cutters when the tool is in the first configuration. The tool may be configured to retract and/or prevent extension of the cutters when the tool is in the first configuration and subjected to the first and/or second and/or third pressure condition/s. The tool may be configured to retract and/or prevent extension of the cutters when the tool is in the second configuration and subjected to the second and/or third pressure condition/s. The three pistons may combine within the under-reamer tool such that when the under-reamer is set in the first configuration the cutters remain retracted when the internal or tool bore pressure exceeds the external or annular pressure. The three pistons may combine within the under-reamer tool such that when the under-reamer is set in the first configuration the cutters remain retracted when the external or annular pressure exceeds the internal or tool bore pressure.

The tool may be configured to extend and/or maintain the cutters in the extended position only when the tool is in the second configuration and subjected to the first pressure condition. The tool may be configured to retract and/or prevent extension of the cutters when the tool is in the second configuration and subjected to the second and/or third pressure condition/s. The three pistons may combine within the tool such that when the tool is in the second configuration the cutters will move and/or be biased to the extended position only when the internal or tool bore pressure exceeds the external or annular pressure.

The tool may comprise a mechanical biasing member. The mechanical biasing member may act in combination with one or more of the pistons to ensure the cutter blades remain retracted when the internal or tool bore pressure and the external or annular pressure are substantially equal.

The tool may comprise one or more internal fluid chambers. The tool may comprise one or more internal fluid chambers and/or lateral or diametric area/s exposed to internal or tool bore pressure.

The plurality of pistons may be configured to utilise the fluid chamber/s and/or diametric area/s in various combinations of external pressure or internal or tool bore pressure to selectively produce a single net piston force in a variety of axial directions. The plurality of pistons may be configured to utilise variations in relative pressures between the respective fluid chambers to vary the single net piston force (e.g. a single net piston force resultant from

The net piston force may be defined to act in a first direction. The first direction may be axial. The first direction may be defined in a direction such as to retract the blades. The first direction may be uphole. Alternatively, the first direction may be downhole.

The net piston force may be defined or redefined to act in a second direction. The second direction may be defined or redefined in a direction such as to extend the cutter blades. The second direction may be axial. The second direction may be substantially opposite to the first direction. The second direction may be downhole. Alternatively, the second direction may be uphole.

The under-reamer tool may comprise a first fluid chamber and a second fluid chamber.

The activation piston may be positioned within the under-reamer such that is subject, at least partially, to pressure from or in the first fluid chamber and pressure from or in the second fluid chamber. The activation piston may be positioned between the first and second fluid chambers. The activation piston may be axially positioned between the first and second fluid chambers.

The under-reamer tool body may comprise one or more ports. The/each port may communicate external fluid pressure to the internal fluid chambers and/or vice versa.

The tool body may comprise one or more ports communicating external fluid to and/or from the first fluid chamber, such as a first fluid chamber port.

The tool body may comprise one or more ports communicating external fluid to and/or from the second fluid chamber, such as a second fluid chamber port.

The first fluid chamber port/s may define a first fluid flow area.

The first fluid flow area may allow fluid flow or fluid pressure to enter the first fluid chamber from the annular volume external to the tool body.

The first fluid flow area may allow fluid flow or fluid pressure to exit the first fluid chamber to the annular volume external to tool body.

The first fluid chamber may comprise one or more port or ports enabling fluid communication between the first fluid chamber and the internal or tool bore, such as one or more further first fluid chamber ports. The one or more further first fluid chamber ports may comprise a configurable port/s. The one or more further first fluid chamber ports may define a second fluid flow area.

The first fluid chamber port may provide fluid communication between the first fluid chamber and the internal or tool bore in the first and/or second configurations.

Where the first fluid chamber port does not provide fluid communication between the first fluid chamber and the internal or tool bore in the first configuration, the first fluid chamber may be effectively sealed from the internal or toolbore pressure. Accordingly the first fluid chamber may be isolated from the internal pressure, such as subject to the external pressure. The further first fluid chamber port may be substantially replaced and/or supplemented by an opening or an increased opening of the first fluid chamber port in the second configuration relative to the first configuration.

The second fluid flow area may allow fluid flow or fluid pressure to enter the first fluid chamber from the internal or tool bore.

The second fluid flow area may allow fluid flow or fluid pressure to exit the first fluid chamber to the internal or tool bore.

The second fluid flow area may define a fluid flow area substantially larger than the first fluid flow area.

The first and/or second fluid flow area/s may define a larger total flow area between the first fluid chamber and the internal or tool bore in the second configuration than in the first configuration.

The activation piston may comprise a first sealing area between the internal or tool bore and the first fluid chamber.

The activation piston may comprise a second sealing area between the first fluid chamber and the second fluid chamber.

The activation piston may comprise a third sealing area between the internal or tool bore (pressure) and the second fluid chamber.

The first and third sealing areas may each and/or in combination define a relatively small sealing or piston area/s compared to the second sealing area.

The second sealing area may define a significantly larger sealing or piston area than the first and/or third sealing area/s, combined and/or individually.

The first and third sealing areas may define sealing or piston areas that are substantially equal or of marginal difference.

The tool may comprise a selection member or device. The selection member or device may be configured to control a pressure differential across the activation piston. The selection member or device may be configured to control fluid flow or pressure in the first and/or second fluid chamber/s. The selection member or device may be configured to control fluid flow through the second fluid flow area.

The selection member or device may be selectively operable to allow the activation piston to activate the tool and/or the cutters. The selection member or device may be selectively actuated to allow the tool to be reconfigurable between the first configuration and the second configuration.

The selection member may be configured to prevent or restrict fluid flow through the first and/or second fluid flow area/s into the first fluid chamber when the tool is in the first configuration.

The selection member may be configured to prevent or restrict internal or tool bore fluid or pressure from entering the first fluid chamber when the tool is in the first configuration. The selection member may comprise a port cover. The selection member may comprise a sleeve, such as a retractable or extendable sleeve. The selection member may comprise a valve, such as a configurable valve.

Alternatively, the selection member may be configured to restrict or prevent fluid communication through the first chamber external port in the second configuration such that fluid pressure in the first fluid chamber varies between external fluid pressure in the first configuration and internal fluid pressure in the second configuration.

The first fluid area may allow external fluid and/or pressure to enter and/or exit the first fluid chamber when the tool is in the first configuration.

The first fluid chamber may be or comprise or be configured to exposed or subjected to external pressure when the tool is in the first configuration. Fluid pressure in the first fluid chamber may be substantially the same as external fluid pressure when the tool is in the first configuration.

The selection member may be configured to allow fluid flow through the second fluid flow area when the tool is in the second configuration, such as only when the tool is in the second configuration.

The selection member may be configured to substantially increase the second fluid flow area when the tool is transitioned or reconfigured to the second configuration.

The second fluid flow area may be substantially larger than the first fluid flow area, at least when the tool is in the second configuration.

When the tool is in the second configuration, fluid flow from the internal or tool bore may be relatively unrestricted into the first fluid chamber. When the tool is in the second configuration, fluid flow between, such as exiting, the first fluid chamber and external to the tool body, such as the annular volume, may be substantially or relatively restricted or prevented.

When the tool is in the second configuration there may be minimal or zero pressure drop across the second flow area between the internal or tool bore and the first fluid chamber.

When the tool is in the second configuration there may be significant pressure drop across the first flow area between the first fluid chamber and external to the tool body, such as the annular volume.

The first fluid chamber may effectively comprise or be at internal or tool bore pressure when the tool is in the second configuration.

The second fluid chamber port may allow external fluid to enter and/or exit the second fluid chamber.

The second fluid chamber port may allow external pressure to enter and/or exit the second fluid chamber.

The second fluid chamber may be at or comprise external pressure when the tool is in the first and/or second configuration/s.

The first fluid chamber and second fluid chamber may define the pressure differential across the second sealing area.

The first fluid chamber and the second fluid chamber may both comprise or be at external pressure when the tool is in the first configuration.

The second sealing area may be subject to zero or marginal pressure differential when the tool is in the first configuration.

The activation piston may be subject to negligible force generated from the second sealing area when the tool is in the first configuration.

The internal or tool bore pressure and the first fluid chamber pressure may define the pressure differential across the first sealing area.

The first fluid chamber may comprise or be at external pressure when the tool is in the first configuration.

The first sealing area may be subject to a pressure differential between the internal or tool bore pressure and the external pressure when the tool is in the first configuration.

When the tool is in the first configuration and subject to the first pressure condition, the activation piston may be subject to a force generated from the first sealing area acting in the second direction.

The internal or tool bore pressure and the second fluid chamber pressure may define a pressure differential across the third sealing area.

The second fluid chamber may comprise or be at external fluid pressure.

When the tool is in the first configuration and subject to the first pressure condition, the activation piston may be subject to a force generated from the third sealing area acting in the first direction.

When the tool is in the first configuration, the activation piston may be subject to a force generated from the first sealing area acting in the second direction and from the third sealing area acting in the first direction. When the tool is in the first configuration, the activation piston may be subject to zero or negligible force generated from the second sealing area. The first and third sealing areas may be of equal area or marginally different in area, acting in opposing direction. The tool may be configured such that the forces generated from the first and third sealing areas are substantially balanced, at least in the first configuration.

When the tool is in the first configuration the activation piston generates zero force or marginal force due to the pressure differential between the internal or tool bore pressure and pressure external to tool body. In the first configuration, a variation in the pressure differential between the internal or toolbore pressure and the external pressure has no substantial variation on the force generated by the activation piston. The tool may be configured to maintain the force generated by the activation piston in the first configuration irrespective of variations in the internal and/or external pressure/s. The maintained force generated may be substantially zero.

The first fluid chamber pressure and the second fluid chamber pressure may define the pressure differential across the second sealing area.

The first fluid chamber may comprise or be at internal or tool bore pressure when the tool is in the second configuration.

The second fluid chamber may comprise or be at external pressure when the tool is in the second configuration.

When the tool is in the second configuration and subject to the first pressure condition, the second sealing area may be subject to the pressure differential between the internal or tool bore pressure and pressure external to the tool body.

The internal or tool bore pressure and the first fluid chamber pressure may define the pressure differential across the first sealing area.

The first fluid chamber may effectively comprise or be at tool bore pressure when the tool is in the second configuration.

The first sealing area may be subject to zero or minimal pressure differential when the tool is in the second configuration.

When the tool is in the second configuration and subject to the first pressure condition, the activation piston may be subject to zero or negligible force generated from the first sealing area.

The internal or tool bore pressure and the second fluid chamber pressure may define the pressure differential across the third sealing area.

The second fluid chamber may comprise or be at external fluid pressure.

When the tool is in the second configuration and subject to the first pressure condition, the activation piston may be subject to a force generated from the third sealing area acting in the first direction.

When the tool is in the second configuration and subject to the first pressure condition, the activation piston may be subject to a force generated from the second sealing area acting in the second direction. When the tool is in the second configuration and subject to the first pressure condition, the activation piston may be subject to a force generated from the third sealing area acting in the first direction. When the tool is in the second configuration and subject to the first pressure condition, the activation piston may be subject to zero or negligible force generated from the first sealing area. The second sealing area may be substantially larger than the third sealing area. Accordingly, when the tool is in the second configuration and subject to the first pressure condition, the second sealing area may generate a net activation piston force acting in the second direction.

When the tool is in the second configuration and subject to the first pressure condition, the activation piston may generate a force acting in the second direction.

When the tool is in the first configuration and subject to the first pressure condition, the activation piston may generate a zero force or marginal force.

The under-reamer tool may comprise a third fluid chamber.

The tool body may comprise a port communicating external fluid and/or fluid pressure to the third fluid chamber, such as a third fluid chamber port.

The third fluid chamber port may allow external fluid to enter and/or exit the third fluid chamber.

The third fluid chamber port may allow external pressure to enter and/or exit the third fluid chamber.

The third fluid chamber may comprise or be at external pressure when the tool is in the first and/or second configuration/s.

The retraction piston may comprise or be operatively associated with a (fourth) sealing area between the internal or tool bore and the third fluid chamber.

The retraction piston may comprise or be operatively associated with a (fifth) sealing area between the internal or tool bore and the third fluid chamber.

The fourth sealing area and the fifth sealing area may be located at opposing ends of the third fluid chamber. Accordingly, when the third fluid chamber is exposed to a pressure the fourth and fifth sealing areas may generate opposing forces on the retraction piston.

The fourth sealing area, when subject to the first pressure condition, may result in a net force on the retraction piston (due to the pressure differential across the fourth sealing area) that acts in the first direction. Accordingly, the fourth sealing area may act to retract or maintain retraction of the cutters.

The fifth sealing area, when subject to the first pressure condition, may result in a net force on the retraction piston (due to the pressure differential across the fifth sealing area) that acts in the second direction. Accordingly, the fifth sealing area may act to extend or maintain extension of the cutters.

The fourth sealing area may be substantially larger than the fifth sealing area. Accordingly, when subject to the first pressure condition, the retraction piston may act with a net force in the first direction. Accordingly, the retraction piston may act to retract or maintain retraction of the cutters when subject to the first pressure condition.

The activation piston and the retraction piston may be configured within the under-reamer tool such that they act in opposition, such as in opposing axial directions. The activation piston and the retraction piston may be configured within the under-reamer tool such that they act directly against each other. The activation piston and the retraction piston may be configured within the under-reamer tool such that they act indirectly against each other.

The retraction and activation pistons may be operatively disengaged and/or disengageable. The retraction and activation pistons may be operatively disconnected in at one or more of the first and/or second configuration/s and/or when the cutters are extend and/or retracted. The retraction and activation pistons may configured to indirectly and/or releasably engage each other.

The activation piston and the retraction piston may not be attached or secured to each other. The activation piston and the retraction piston may be connected, such as contacting loosely (e.g. with opposing end faces).

Alternatively, the activation piston and the retraction piston may be secured to each other, such as by a threaded connection. The retraction and activation pistons may configured to directly and/or non-releasably engage each other.

When the tool is in the first configuration and subject to the first pressure condition, the activation piston may generate zero force or marginal force (in either direction).

When the tool is in the first configuration and subject to the first pressure condition, the retraction piston may act with a force in the first direction. When the tool is in the first configuration and subject to the first pressure condition, the retraction piston may act to retract and/or maintain retraction of the cutters. When the tool is in the first configuration and subject to the first pressure condition, the retraction piston may act against the activation piston with opposing force. The retraction piston force may be greater than the activation piston force. Accordingly, in the first configuration, the retraction piston force and the activation piston force may result in a net force such that the retraction piston drives the activation piston toward the first direction, such as to retract or maintain retraction of the cutters.

When the tool is in the second configuration and subject to the first pressure condition, the activation piston may act with a force in the second direction. When the tool is in the second configuration and subject to the first pressure condition, the activation piston may act to extend or maintain extension of the cutters.

When the tool is in the second configuration and subject to the first pressure condition, the retraction piston may act in the first direction with less force than the activation piston acting in the second direction.

When the tool is in the second configuration and subject to the first pressure condition, the activation piston may act, such as acting directly, against the retraction piston with opposing force. When the tool is in the second configuration and subject to the first pressure condition, the activation piston force may be substantially greater than the retraction piston force. When the tool is in the second configuration and subject to the first pressure condition, the relative retraction and activation piston forces may result in a net force driving the activation piston in or towards the second direction. Accordingly, when the tool is in the second configuration and subject to the first pressure condition, the activation piston may extend or maintain extension of the cutters.

The under-reamer tool may comprise a mechanical biasing member. The mechanical biasing member may act between the under-reamer tool body and the activation piston.

The mechanical biasing member may be configured to act against the activation piston acting in the first direction. The mechanical biasing member may be configured to act in the second direction. The mechanical biasing member may be configured to bias the activation piston against cutter extension. The mechanical biasing member may be configured to bias the tool towards cutter retraction.

When the tool is in the first and/or second configuration/s and subject to the third pressure condition, the mechanical biasing member may act with a force, such as a dominant or determinant force, against the activation piston acting in the first direction. When the tool is subject to the third pressure condition, the biasing member may bias and/or drive the cutters to the retracted position. When the tool is in the first and/or second configuration/s and subject to the third pressure condition, the mechanical biasing member may act with or provide a force, such as a dominant or determinant force, such that the cutters are and/or remain retracted.

The mechanical biasing member may comprise one or more of: a spring, a helical spring, a Belleville washer, a resilient member, and/or the like. The mechanical biasing member may comprise a compressive biasing member (e.g. a compression spring). Alternatively, the mechanical biasing member may comprise a tensile biasing member (e.g. a tension spring).

When subject to the second pressure condition, the pistons may act in reverse directions relative to the first pressure condition (e.g. due to tool bore pressure and external annular pressure switching polarity compared to the first pressure condition).

When the tool is in the first configuration and subject to the second pressure condition, the activation piston may generate zero force or marginal force in either direction.

When the tool is in the first configuration and subject to the second pressure condition, the retraction piston may act with substantial force in the second direction. When the tool is in the first configuration and subject to the second pressure condition, the retraction piston may act with substantial force in the direction of cutter blade extension.

When the tool is in the first configuration and subject to the second pressure condition, the activation piston and the retraction piston may be configured to act individually or independently from each other.

The tool may be configured to prevent or at least inhibit that the cutters are driven unintentionally to the extended position.

When the tool is in the first configuration and subject to the second pressure condition the activation piston may generate zero force or marginal force in either direction. The activation piston may be configured as a separate component or device, such as separate from the retraction piston. The mechanical biasing member may act against the activation piston, such as to supply a substantial force acting to drive the activation piston to the first direction (e.g. mechanical biasing member may directly drive the actuation piston towards the direction of retraction).

When the tool is in the first configuration and subject to the second pressure condition, the retraction piston may act with a substantial force in the direction of cutter extension. When the tool is in the first configuration and subject to the second pressure condition, the retraction piston may transfer no force, such as directly, to the activation piston. The retraction piston may be configured as a separate component or device, such as separate from the activation piston.

Accordingly, the tool of the present invention may be configurable to prevent extension of the of the exendable member/s when the tool is subject to the second pressure condition, such as when the tool is in the first configuration. Such a configuration or (re)configurability may be advantageous over other tools that may otherwise be prone to unintended or undesired extension of members when a piston acts in an opposite direction, such as due to a differential pressure other than intended or desired (e.g. a higher annular pressure and/or a lower toolbore pressure).

When the tool is in the first configuration and subject to the second pressure condition the retraction piston may be biased and/or translate axially away from the activation piston.

When the tool is in the first configuration and subject to the second pressure condition, the activation piston may require or receive assistance from the mechanical biasing member to act in the intended direction of cutter retraction. The retraction and/or maintenance of retraction, such as with the aid of the mechanical biasing member, may be supplemented or improved further by the inclusion of the third piston. The third piston may be configured to prevent extension of the cutters when the tool is in the second configuration. The third piston may be configured to bias and/or drive the activation piston in the first direction. The third piston may only be active, or only actively hydraulically biasing, when the tool is subject to the second pressure condition. The third piston may be configured to act or to transmit force to the activation piston and/or retraction piston only when the tool is subject to the second pressure condition. The third piston may be configured to transmit force to the activation piston and/or retraction piston only when the tool is subject to the second pressure condition, such as to transmit hydraulically-generated force to the activation piston and/or retraction piston only when the tool is subject to the second pressure condition.

The conditional piston may be configured to exert a bias in a substantially opposite direction to the retraction piston. The conditional piston may be configured to exert a different magnitude of bias than the retraction piston. The conditional piston may be configured to exert a larger bias force than the retraction piston. The conditional piston may be configured to exert a smaller bias force than the retraction piston. The retraction piston may be configured to resist movement of the activation member in a first direction (e.g. uphole or downhole). The conditional piston may be configured to resist movement of the activation member in a second direction (e.g. downhole or uphole). The first and second directions may be substantially opposite. The direction of resistance may be dependent upon the pressure condition and/or the configuration of the tool.

The tool may comprise a fourth fluid chamber. The fourth fluid chamber may be an internal chamber.

The tool may comprise a port or a plurality of ports communicating internal or tool bore pressure to the fourth fluid chamber.

The fourth fluid chamber may be positioned or located within the tool, such as between the second fluid chamber and the third fluid chamber. The fourth fluid chamber may be located on an opposite axial side of the third piston. The third piston may divide an internal volume, such as a cylinder, into the third and fourth chambers. The third piston may be configured to be subject to a pressure differential between the third and fourth chambers.

An external diameter of the conditional piston may locate against an internal diameter of the tool body.

Alternatively an additional component, such as a cartridge case, may be located between the external diameter of the conditional piston and the internal diameter of the tool body.

The internal diameter of the conditional piston may locate against an external diameter of the retraction piston. The internal diameter of the conditional piston may define the fifth sealing area. The internal diameter of the conditional piston may locate on the external diameter of the retraction piston which defines the fifth sealing area.

The tool may comprise an axial stop, such as an axial end stop between the retraction and conditional pistons. The retraction piston may comprise a boss, flange, shoulder or protrusion at the far end of the fifth sealing area shaft. The boss, flange or protrusion may form the distal axial end stop between the retraction piston and the conditional piston.

The outer diameter of the conditional piston may locate on an internal bore of the tool body. The tool may comprise a stop between the conditional piston and the tool body. A face or protrusion configured to engage the conditional piston, such as at the external diameter of the conditional piston (e.g. at the end of the bore on the tool body or the additional component, such as the cartridge case), may form a distal axial end stop between the conditional piston and the tool body.

The conditional piston may slide axially along or within the tool between the distal end stop on the retraction piston and the distal end stop on the tool body.

The outer diameter of the conditional piston may define the sixth sealing area.

The conditional piston may be positioned, within the tool, between the third fluid chamber and the fourth fluid chamber such that one end face of the conditional piston is subject to annular pressure from the third fluid chamber and the opposite end face of the conditional piston is subject to internal or tool bore pressure from the fourth fluid chamber, in the first and/or second configurations.

The mechanical biasing member may be located within the third fluid chamber. The mechanical biasing member may be located between the conditional piston and the tool body bore, such as axially located between an end face of the conditional piston and an end face of the tool body bore or an end face of a cartridge case located inside the tool body bore.

The mechanical biasing member may act between an end face on the main tool body and an end face of the conditional piston applying force to locate the conditional piston against the distal axial end stop on the retraction piston.

The mechanical biasing member may apply a force on the conditional piston to act in the first direction. The mechanical biasing member may be configured to bias the conditional piston towards the direction of cutter retraction.

The cartridge case component may be mounted within the under-reamer such that it is secured axially within the main tool body. Load transferred from the retraction piston and/or the conditional piston and/or the mechanical biasing member to any end face on the cartridge case may be transferred through the cartridge case component to the main tool body.

The tool may comprise a retraction module. The retraction module may comprise the retraction piston, the conditional piston and the mechanical biasing member. The cartridge case may be used to house the retraction piston, conditional piston and mechanical biasing member as an assembly or sub assembly, which may be defined as the retraction module.

The retraction module may provide a fluid communication path between external fluid (e.g. annular fluid), such as from the third fluid chamber port, and a fluid chamber within the retraction module, such as the third fluid chamber.

The retraction module may be housed within the tool body such that the cartridge case is restrained from axial movement within the tool body. The retraction module may be housed within the tool body such that axial movement of the retraction piston and/or the conditional piston is allowed.

The retraction piston may be free to move, within the tool body, between two axial distal stops. Load exerted from the retraction piston may be transferred to the tool body through either axial distal stop.

The conditional piston may be free to move in the second direction to a tool body distal stop. Load may be transferred from the conditional piston to the tool body, such as through the axial stop.

The conditional piston may be free to move in the first direction to a distal stop located on the retraction piston. Load may be transferred from the conditional piston to the retraction piston, such as through the distal stop on the retraction piston.

The mechanical biasing member may be configured to supply force on the conditional piston acting in the first direction, such as transferring load through the conditional piston to the distal stop on the retraction piston.

When subject to the first pressure condition, the retraction piston may act in the first direction with significant force.

When subject to the first pressure condition, the conditional piston may act in the second direction acting, such as directly, against the mechanical biasing member. When subject to the first pressure condition, the conditional piston may have sufficient force to overcome the mechanical biasing member. Accordingly, when subject to the first pressure condition, the conditional piston may translate axially to the distal end stop, thus transferring load through to the tool body.

When subject to the first pressure condition, the conditional piston may move in an opposing axial direction to the retraction piston. When subject to the first pressure condition, zero force may be exchanged between the conditional piston and the retraction piston.

When subject to the second pressure condition, the retraction piston may act in the second direction.

When subject to the second pressure condition, the conditional piston may act in the first direction.

When subject to the second pressure condition, the conditional piston may act, such as directly act, against the retraction piston. The conditional piston may act with greater force than the retraction piston. Accordingly, the conditional piston may bias and/or drive the retraction piston in or towards the first direction.

When subject to the third pressure condition, both the retraction piston and conditional piston may act with zero force due to zero pressure differential between the internal or tool bore pressure and the pressure external to the tool body.

When subject to the third pressure condition, the mechanical biasing member may act on, such as dominantly act on, the conditional piston. In turn, the conditional piston may acts against and supply a substantial force for the retraction piston to act in the first direction.

The retraction piston may act in or towards the first direction when subject to any of the first pressure condition, the second pressure condition or the third pressure condition.

The retraction piston may act in or towards the first direction when the internal or tool bore pressure is greater than the pressure external to tool body, such as annular pressure.

The retraction piston may act in or towards the first direction when the pressure external to tool body, such as annular pressure, is greater than the internal or tool bore pressure.

The retraction piston may act in or towards the first direction when the internal or tool bore pressure equals the pressure external to the tool body, such as annular pressure.

The retraction piston may act in or towards the first direction in the first and/or second tool configurations, such as for all pressure conditions.

The tool may comprise the configurable activation piston and the retraction module. The configurable activation piston may act, such as directly, against the retraction module.

The activation piston may loosely contact the retraction module, such as by adjacent end faces.

Alternatively, the activation piston may be secured to the retraction module, such as by a threaded connection.

When the tool is in the first configuration and subject to the first pressure condition, the activation piston may act with zero force or marginal force. When the tool is in the first configuration and subject to the first pressure condition, the retraction module may act in the first direction with a substantial or dominant force. When the tool is in the first configuration and subject to the first pressure condition, the activation piston may be driven and/or biased by the retraction module to act in the first direction with a substantial or dominant force.

When the tool is in the first configuration and subject to the first pressure condition, the cutters may be driven and/or biased to the retracted position with the substantial or dominant force.

When the tool is in the first configuration and subject to the second pressure condition, the activation piston may act with zero or marginal force. When the tool is in the first configuration and subject to the second pressure condition, the retraction module may act in the first direction with a substantial or dominant force. When the tool is in the first configuration and subject to the second pressure condition, the activation piston may be driven and/or biased by the retraction module to act in the first direction, such as with the substantial or dominant force.

When the tool is in the first configuration and subject to the second pressure condition, the cutters may be driven and/or biased to the retracted position, such as with the substantial or dominant force.

When the tool is in the first configuration and subject to the third pressure condition, the activation piston and the retraction module may generate zero or marginal force. The mechanical biasing member may drive and/or bias the retraction module and the activation piston to act in the first direction with a substantial or dominant force.

When the tool is in the first configuration and subject to the third pressure condition, the cutters may be driven and/or biased to the retracted position with a substantial or dominant force.

When the tool is in the second configuration and subject to the first pressure condition, the activation piston may act in the second direction, such as with a significant force. When the tool is in the second configuration and subject to the first pressure condition, the retraction module may act in the first direction with substantially less force than the activation piston acting in the second direction. When the tool is in the second configuration and subject to the first pressure condition, the activation piston may generate a substantially greater force than the retraction module. Accordingly, when the tool is in the second configuration and subject to the first pressure condition, the activation piston may act in the second direction, such as with a significant force.

When the tool is in the second configuration and subject to the first pressure condition, the cutters may be driven to the extended position, such as with a substantial or dominant force.

When the tool is in the second configuration and subject to the second pressure condition, the activation piston may act in the first direction, such as with a significant force. When the tool is in the second configuration and subject to the second pressure condition, the retraction module may act with in the first direction, such as with a significant force. Accordingly, when the tool is in the second configuration and subject to the second pressure condition, the activation piston may act in the first direction with a combined force of the activation piston and the retraction module.

When the tool is in the second configuration and subject to the second pressure condition, the cutters may be driven and/or biased to the retracted position, such as with a significant force.

When the tool is in the second configuration and subject to the third pressure condition, the activation piston and the retraction module may generate zero or marginal force (e.g. due to a lack of pressure differentials). When the tool is in the second configuration and subject to the third pressure condition, the mechanical biasing member may act against the activation piston, driving the activation piston to act in the first direction, such as with significant force.

When the tool is in the second configuration and subject to the third pressure condition, the cutters may be driven and/or biased to the retracted position, such as with significant force.

When the tool is in the first configuration, the cutter blades may be driven to the retracted position regardless of any pressure differential polarity between the internal or tool bore pressure and the pressure external to tool body, such as annular pressure.

When the tool is in the first configuration, the cutters may be driven to the retracted position regardless of any pressure differential magnitude between the internal or tool bore pressure and the pressure external to tool body, such as annular pressure.

When the tool is in the first configuration, a retraction force may be increased or maximised, such as by increasing the pressure differential (e.g. between a relatively high internal or tool bore pressure and a relatively low pressure external to tool body, such as annular pressure).

When the tool is in the first configuration, the retraction force may be increased or maximised, such as by increasing a fluid flow rate through the tool bore.

When the tool is in the second configuration, the cutters may be driven and/or biased to the extended position only when the internal or tool bore pressure is greater than the pressure external to tool body, such as annular pressure.

When the tool is in the second configuration, the cutters may be driven and/or biased to the extended position only when the internal or tool bore pressure is greater than the external or annular pressure and with sufficient net force to overcome the mechanical biasing member.

When the tool is in the second configuration and subject to the first pressure condition, the conditional piston may act, such as directly, against the mechanical biasing member. The conditional piston may act independently from the activation piston.

When subject to the first pressure condition, the conditional piston may counteract or overcome the mechanical biasing force. When the tool is in the second configuration and subject to the first pressure condition, the conditional piston may reduce or eliminate or negate the mechanical biasing member force acting against the activation piston. Accordingly, when the tool is in the second configuration and subject to the first pressure condition, the conditional piston may effectively increase the net activation piston force.

The activation piston may be configured to provide a negligible or no axial bias when not selected or activated, such as in the first configuration. The activation piston may be configured to provide a bias when selected or activated. The activation piston may be configured to provide an uphole (or alternatively downhole) bias when selected. The activation piston may be configured to provide a bias when selected, such as in the second configuration, according to an operation parameter, such as a fluid differential (e.g. between the internal or toolbore pressure and the external or annular pressure). The activation piston may be configured to selectively provide either of a bias or a negligible bias in the second configuration according to an operation parameter.

The tool may be configured to expose at least a portion of the activation piston to a fluid pressure differential only in the second configuration. The tool may be configured to prevent or at least limit exposure of the activation piston to a pressure differential in the first configuration. The tool may be configured to expose the at least a portion of the activation piston to a pressure differential in the second configuration. The under-reaming tool may be configured to expose the at least a portion of the activation piston to a pressure differential between an internal fluid pressure and the external fluid pressure (only) in the second configuration. The tool may be configured to allow the activation piston to move between an inactive position with the cutters retracted and an activated position with the cutters extended only in the second configuration. The tool may be configured to allow selection or activation of the activation member by selectively exposing the at least a portion of the activation member to the fluid pressure differential. The tool may be reconfigured between the first configuration and the second configuration by selectively exposing the at least a portion of the activation piston to the fluid pressure differential. Accordingly, the activation and retraction pistons may be controlled to provide a net bias in alternate directions dependent upon the pressure condition, at least when the tool is in the second configuration.

The tool may comprise a control mechanism configurable to prevent cycling between the first and second configurations and thus maintain the tool in a selected one of the first and second configurations. The control mechanism may comprise the selection member.

One of several methods of controlling the cycling may be used. For example, the configuration of the tool may be controlled using an indexer, such as actuated by flow rate cycles through the tool and/or a drop-ball/s and/or an electronic shifting mechanism and/or a fluid flow activated mechanism. The configuration of the tool may additionally or alternatively by controlled using an electric motor triggered by a signal. The signal may be sent to the tool via any telemetry method, including the telemetry method based on detection of drill string rotation, such as disclosed in U.S. patent application Ser. No. 61/803,696 assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference.

According to a further aspect of the invention, there is provided a downhole tool comprising:

a body; and

an activation member at least partially located within the body;

wherein the tool is configured to selectively vary an effective sealing area of the activation member to selectively vary a hydraulic bias of the activation member.

Providing such a downhole tool wherein the tool is configured to selectively vary an effective sealing area of the activation member to selectively vary a hydraulic bias of the activation member may permit the activation member to exert a selective force as a result of a fluid pressure. Such a downhole tool may permit a movement of the activation member as a result of the fluid pressure, such as an activating or deactivating movement.

The effective sealing area may be an effective cross-sectional sealing area. For example, the tool may further comprise a first seal defining a first cross-sectional sealing area perpendicular to a longitudinal axis of the activation member. The first seal may encompass the first sealing area.

The tool may be configured to selectively vary a magnitude of the hydraulic bias.

The tool may be configured to selectively vary a direction of the hydraulic bias.

The hydraulic bias may be a substantially axial bias. For example, the hydraulic bias may be towards a first axial direction.

The tool may be configured to selectively vary the hydraulic bias of the activation member without a substantial variation in an internal body fluid pressure, such as a toolbore pressure. The tool may be configured to selectively vary the hydraulic bias of the activation member at substantially the same internal body fluid pressure.

The tool may further comprise a second seal, wherein the tool is configured to selectively vary an effective sealing area of the activation member by selectively transferring effective sealing of the activation member from the first seal to the second seal.

The first seal may provide an effective seal between the activation member and the body in a first configuration, and the second seal may provide an effective seal between the activation member and the body in a second configuration.

The first seal may inhibit fluid communication between the internal body fluid and the second seal in the first configuration. The first seal may prevent fluid communication between the internal body fluid and the second seal in the first configuration. The first seal may permit a partial fluid communication between the internal body fluid and the second seal in the first configuration.

In the first configuration, there may be an effective pressure differential across the first seal and in the second configuration there may be an ineffective pressure differential across the first seal. In the first configuration, there may be an ineffective pressure differential across the second seal and in the second configuration there may be an effective pressure differential across the second seal.

The ineffective pressure differential may be substantially no pressure differential.

The ineffective pressure differential may be relatively small.

The tool may be configured to fluidly communicate the second seal with the internal body fluid via a first fluid chamber, such as a first fluid passage.

The tool may be configured to selectively vary fluid pressure in the first fluid chamber. For example, the tool may comprise at least a first flow restriction, such as a first port, between the second seal and the internal body fluid, such as between the first fluid chamber and a fluid supply in a body internal bore. In the first configuration the first flow restriction may inhibit fluid communication between the internal body fluid and the first fluid chamber more, relative to the first flow restriction in the second configuration. For example, the first flow restriction may comprise a relatively small opening in the first configuration, compared to a relatively large opening in the second configuration.

The tool may be configured to generate a greater pressure differential across the first flow restriction in the first configuration than in the second configuration. The tool may be configured to generate a greater pressure differential across the first flow restriction in the first configuration than in the second configuration.

A pressure in the first fluid chamber may be substantially less than the internal body fluid pressure in the first configuration, at least when subject to the first pressure condition.

A pressure in the first fluid chamber may be substantially the same as the internal body fluid pressure in the first configuration, at least when subject to the third pressure condition.

A pressure in the first fluid chamber may be substantially more than the internal body fluid pressure in the first configuration, at least when subject to the second pressure condition.

A pressure in the first fluid chamber may be substantially the same as the internal body fluid pressure in the second configuration, when subject to the first and/or second and/or third pressure conditions.

Alternatively, the pressure in the first fluid chamber may be substantially less than the internal body fluid pressure in the second configuration, when subject to the first and/or second and/or third pressure conditions.

Further alternatively, pressure in the first fluid chamber may be substantially more than the internal body fluid pressure in the second configuration, when subject to the first and/or second and/or third pressure conditions.

The first flow restriction may substantially limit fluid communication between the first fluid chamber and the internal body fluid in the first configuration.

The first flow restriction may substantially prevent fluid communication between the first fluid chamber and the internal body fluid in the first configuration.

The first flow restriction may be effectively negated in the second configuration. For example, there may be substantially no pressure differential across the first flow restriction in the second configuration.

The first fluid chamber may be in substantially unrestricted fluid communication with the internal body fluid in the second configuration.

The first flow restriction may be altered during the transformation of the tool from the first configuration to the second configuration. For example, the first flow restriction may be opened, or enlarged, as the tool transitions from the first configuration to the second configuration.

The first flow restriction may be effectively bypassed in the second configuration. For example the tool may further comprise a first flow restriction bypass, the bypass configured to be substantially closed in the first configuration and substantially open in the second configuration.

The tool may comprise a first cross-sectional flow area between the internal body fluid and the first fluid chamber in the first configuration; and a second cross-sectional flow area between the internal body fluid and the first fluid chamber in the second configuration. The first cross-sectional flow area may be substantially smaller than the second cross-sectional flow area. For example, the tool may comprise at least a second flow restriction, such as a second port, between the first fluid chamber and the internal body fluid. In the first configuration the second flow restriction may inhibit fluid communication between the internal body fluid and the first fluid chamber more, relative to the second flow restriction in the second configuration. For example, the second flow restriction may be substantially closed in the first configuration.

The tool may further comprise a first chamber external port between the first fluid chamber and a body exterior, such as an annulus between the body and a bore. The first chamber external port may provide fluid communication between

The tool may comprise a fourth seal. The fourth seal may provide for a hydraulic counterbias. For example, the fourth seal may provide for a fourth sealing area, such as a fourth cross-sectional sealing area.

The hydraulic counterbias may act in the opposite direction to the hydraulic bias.

The hydraulic counterbias may act in the same direction as the hydraulic bias.

The hydraulic counterbias may act in the opposite direction to the hydraulic bias in the first configuration.

The hydraulic counterbias may act in the opposite direction to the hydraulic bias in the second configuration.

The hydraulic counterbias may act in the same direction as the hydraulic bias in the first configuration.

The hydraulic counterbias may act in the same direction as the hydraulic bias in the second configuration.

The hydraulic counterbias may be greater than the hydraulic bias.

The hydraulic counterbias may be less than the hydraulic bias.

The hydraulic counterbias may be greater than the hydraulic bias in the first configuration.

The hydraulic counterbias may be less than the hydraulic bias in the second configuration.

The hydraulic counterbias may be less than the hydraulic bias in the first configuration.

The hydraulic counterbias may be greater than the hydraulic bias in the second configuration.

The tool may be configured to exert a net hydraulic force on the activation member.

The net hydraulic force may comprise the hydraulic bias.

The net hydraulic force may comprise the hydraulic counterbias.

The tool may further comprise a mechanical biasing member. For example, the tool may further comprise a spring. The mechanical biasing member may be configured to provide a mechanical force in a same direction as the net hydraulic force.

The mechanical biasing member may be configured to provide a mechanical force in an opposite direction to the net hydraulic force.

The mechanical biasing member may be configured to provide a greater force than the net hydraulic force.

The mechanical biasing member may be configured to provide a lesser force than the net hydraulic force.

The mechanical biasing member may be configured to provide a greater force than the net hydraulic force in the first configuration.

The mechanical biasing member may be configured to provide a lesser force than the net hydraulic force in the first configuration.

The mechanical biasing member may be configured to provide a lesser force than the net hydraulic bias in the first configuration.

The mechanical biasing member may be configured to provide a greater force than the net hydraulic force in the first configuration.

The tool may be configured for multiple reconfiguration downhole.

The tool may be configured to selectively cycle between the first and second configurations.

The tool may comprise a first or an activation piston. For example, the activation member may comprise a shaft, such as a hollow shaft, configured for axial movement within the body. The activation piston may be a fluid-actuated piston.

The first seal may be an annular seal. The second seal may be an annular seal. The third seal may be an annular seal. The fourth seal may be an annular seal.

The tool may comprise a reamer. The tool may comprise an underreamer. The tool may comprise a drillbit. The tool may comprise an injector, such as an acidifying injector.

The activation member may permit the passage of fluid through the tool in multiple configurations, such as in an active and an inactive configuration.