EP4413230A1

EP4413230A1 - Hydraulically actuated tool

Info

Publication number: EP4413230A1
Application number: EP22785751.3A
Authority: EP
Inventors: Scott Henderson
Original assignee: Odfjell Technology Invest Ltd
Current assignee: Odfjell Technology Invest Ltd
Priority date: 2021-10-04
Filing date: 2022-09-26
Publication date: 2024-08-14
Also published as: MX2024004154A; WO2023057253A1; GB202114212D0; CA3232942A1; CN118140036A; AU2022360496A1

Abstract

Disclosed is a downhole tool and method of use. The tool has a sleeve assembly slideable within the body between a first position and a second position. A master hydraulic reservoir is defined between the sleeve assembly and the body to a first end of a control portion. A bleed conduit extends between the master hydraulic reservoir and a slave hydraulic system defined, at least in part, by the body. An electromechanical control valve across the bleed conduit is configured to regulate fluid flow along the bleed conduit. When the sleeve moves between the first and second positions, the volume of the master hydraulic reservoir and the slave hydraulic system each change; and the combined volumes of the master hydraulic reservoir and the slave hydraulic system is substantially constant. The volume change can be used to effect control over downhole tool functionality.

Description

HYDRAULICALLY ACTUATED TOOL

Field of the Invention

The invention relates to a downhole tool having a hydraulic actuation mechanism that is selectively lockable.

Background of the Invention

In the oil and gas industry drilling operations provide drilled wells to hydrocarbon reserves.

Drilling, completion, maintenance and extraction operations associated with such wells require the use of a wide variety of equipment run into the well on a work string. Such equipment frequently includes mechanical tools which must be controlled remotely from the surface, for example to switch the apparatus between one or more states.

Many such operations require fluid circulation to a particular part of the well, such as drilling fluid, steam or chemical treatments. Fluids are normally pumped through the work string.

Control over some tools can be effected using fluid in the work string, by dropping objects such as a ball or a dart into the work string to selectively block the bore of a tool and apply a back pressure to actuate a mechanism. For example, a ball may land on a seat and pressure may displace the seat and an associated sleeve downhole or re-direct fluid, to actuate a mechanism operatively coupled to the sleeve. Many tools utilise this general means of actuation, including for example circulation tools with circulation ports openable by moving a sleeve; or underreamers or cleaning/scraping tools having reaming or cleaning members which are actuated by moving a sleeve.

A problem with tools operable by selectively blocking a bore through the drill string is that the bore is then unavailable for other operations. This can be addressed by blowing the ball or dart through the hole, but since a typical well can only tolerate a limited number of such objects, this in turn normally requires the ball or dart to be caught and retrieved, or drilled through. A further problem is that is it desirable to run in multiple tools on a single work string, to minimise the number of trips. Where several tools share generally the same principle of actuation, this may limit the number of tools that may be run in together, adding to overall time and cost of downhole operations.

LIS2010/089583 describes an under-reaming tool in which a central piston is hydraulically displaced to deploy the tool’s milling arms. A chamber is defined between the piston and the tool body, which is divided into upper and lower parts by a wiper seal. As the piston is displaced, fluid bleeds between the upper and lower parts of the chamber via a passage, to accommodate their changing volume. A solenoid valve in the passage is actuated to open the passage and permit the piston to move. This arrangement takes up a significant radial thickness of the tool, however.

There remains a need for a means to actuate or control a downhole tool that addresses or mitigates one or more of these issues.

Summary of the Invention

According to a first aspect of the invention there is provided a downhole tool, comprising: a body having a through bore; a sleeve assembly slideable within the body between a first position and a second position; and the body comprising a control portion; wherein a master hydraulic reservoir is defined between the sleeve assembly and the body to a first end of the control portion, and wherein the control portion further comprises a bleed conduit extending between the master hydraulic reservoir and a slave hydraulic system defined, at least in part, by the body; and an electromechanical control valve across the bleed conduit configured to regulate fluid flow along the bleed conduit; wherein, when the sleeve moves between the first and second positions, a volume of the master hydraulic reservoir and a volume of the slave hydraulic system changes; and the combined volumes of the master hydraulic reservoir and the slave hydraulic system is substantially constant.

When the control valve is open, liquid is able to pass through the bleed conduit between the master hydraulic reservoir and the slave hydraulic system, to allow the sleeve assembly to move between the first and second positions, for example under the action of hydraulic pressure in the through bore and/or resilient biasing. The master hydraulic reservoir, bleed conduit and the slave hydraulic system define a closed system. When the volume of the master hydraulic reservoir decreases, the volume of the slave hydraulic system increases, and vice versa. The volume change of the slave hydraulic system can be used to effect control over downhole tool functionality, regulated by the control valve.

When the control valve is closed, liquid is not able to pass into or out of the master hydraulic reservoir and the volume of the master hydraulic reservoir is prevented from changing. Opening and closing of the control valve can thereby be used to regulate movement of the sleeve assembly. In addition, the control valve can be closed so as to hydraulically lock the sleeve in position - either the first position, the second position or indeed any intermediate position.

The sleeve assembly motion can in turn be used to control one or more tool functions, and the said functions can be regulated by opening and closing of the control valve.

The slave hydraulic system may comprise at least one actuation chamber. The, or each, actuation chamber may have a variable volume.

The, or each, actuation chamber may comprise an actuation element.

The, or each, actuation chamber may be defined, at least in part, by the actuation element (i.e. one or more surfaces thereof).

The actuation element may be movable within or in relation to a cavity or aperture defined by the body. Movement of the actuation element may correspond to a change of the volume of the actuation chamber. The actuation element may be slideable within the cavity or aperture. The tool may comprise a seal between the actuation element and the cavity or aperture.

The, or each, actuation chamber may be defined by the actuation element and the cavity/aperture walls and, in some embodiments, the sleeve assembly and/or control portion.

The actuation element may be moveable between a first position of the actuation element (which the actuation element adopts when the sleeve assembly is in the first position) and a second position of the actuation element (which the actuation element adopts when the sleeve assembly is in the second position). In use, actuation element may function as a piston, moveable within a cavity or aperture defined by the body. It will be understood that the volume of the, or each, actuation chamber changes as the actuation element moves.

The actuation element may be moveable generally radially, or the actuation element may be moveable generally longitudinally. The actuation element may be a sliding sleeve, or sleeve portion (i.e. extending partially around a circumference of the tool).

The actuation element may comprise or consist of a deployable tooling element, such as a cleaning element. For example, an inner face or faces of a deployable tooling element may in part define the actuation chamber, and an outer portion may be adapted for a particular downhole function.

By way of non-limiting example, deployable tooling element, such as an outer portion of a deployable tooling element may comprise; a cleaning formation, such as one or more scraper blades, brushes or the like; a milling formation, such as having an abrasive surface or surfaces, or other milling formation known in the art; a casing anchor, comprising for example one or more retaining formations such as teeth or the like; a packer, comprising a resiliently deformable, optionally inflatable, formation for sealing against a casing wall; a wiper plug, for engaging with a casing wall and retaining fluid flow or pressure in one direction past the tool.

The deployable tooling element may be moveable between a retracted position and an extended position. Movement between the retracted and extended positions may be effected by movement of the sleeve assembly between the first and second positions.

Movement between the retracted and extended positions may be radial.

In the retracted position, the tooling element may be recessed within the body.

By recessed within the body, we include housed within the body, within an aperture or cavity, or having a radially outermost surface level with or within the radius of a radially outermost surface of the body, or a radially outermost surface of a longitudinally adjacent portion of the body. In the extended position, the deployable tooling element may extend or further extend (in comparison to the retracted position) from an outer surface of the body. That is to say, in the extended position, a radially outermost surface of the deployable tooling element may extend radially beyond a radially outermost surface of the body.

An actuation element or a deployable tooling element may be mounted within an aperture or cavity of the body, wherein the aperture or cavity is open to an outside of the tool. In such embodiments, the actuation member or tooling element may be retained to the body by any suitable means.

For example, in some embodiments, an actuation element or tooling element may be retained via a pin that extends through and is slideable within a slot through the element and the pin is secured to the body (e.g. threadably). A pin may extend laterally and a slot may extend radially for example, to facilitate radial motion of the element. In some embodiments an actuation element or tooling element may be provided with a lip or flange having a larger dimension than a portion of the recess or aperture, to prevent the element from being ejected therefrom.

The actuation element may be operatively coupled to a deployable tooling element, or to more than one tooling element.

For example, an actuation element may abut a tooling element or be pivotally or otherwise mechanically connected thereto.

An actuation element may be operable to cause the tooling element to rotatably deploy upon radial or longitudinal motion of an actuation element. For example, a deployable tooling element may comprise a pivotable connection to the body and be caused to pivot around said connection under the action of the actuation member.

An actuation element may comprise a tapered surface, and be operable to slideably engage with a surface (optionally also tapered) of a deployable tooling element to cause the deployable tooling element to deploy.

The, or each, actuation chamber may communicate directly or indirectly with the bleed conduit. In some embodiments, a branched bleed conduit may extend between the master hydraulic reservoir and two or more actuation chambers. A branched bleed conduit may have a control valve disposed between the master fluid reservoir and a branch in the branched bleed conduit, such that a single control valve may regulate fluid between the master hydraulic reservoir and multiple actuation chambers.

The slave hydraulic system may comprise a primary slave hydraulic reservoir and one, or more than one, actuation chamber in fluid communication with the primary slave hydraulic reservoir.

In some embodiments, the primary slave hydraulic reservoir is generally annular and may extend around all or substantially all of a circumference of the tool.

The primary slave hydraulic reservoir may fluidly communicate directly with the bleed conduit.

The, or each, actuation chamber may be in fluid communication with the primary slave hydraulic reservoir via a connecting conduit or channel. The connecting conduit or channel may extend through, or be defined by, the body, along at least a part of its length.

The connecting conduit may extend radially, along at least a part of its length.

The connecting conduit may extend longitudinally, along at least a part of its length.

The primary slave hydraulic chamber may fluidly communicate with multiple actuation chambers. In effect, the primary slave hydraulic reservoir may function as a manifold within the slave hydraulic system.

By directly fluidly communicate with we mean that an end of a conduit or channel, for example the bleed conduit, may extend from the reservoir or chamber in question, or that reservoirs or chambers may extend from one another without any intermediate fluid pathway. By indirectly, we include that there may be an intermediate reservoir, or chamber or other fluid pathway. For example, an actuation chamber may communicate indirectly with the bleed conduit via the primary slave hydraulic reservoir and optionally one or more connecting conduits or channels. The master hydraulic reservoir may be generally annular and extend around all or substantially all of a circumference of the tool.

The tool may comprise more than one master hydraulic reservoir. The more than one master hydraulic reservoirs may each be part-annular. The more than one master hydraulic reservoir may be distributed around a circumference of the tool.

The tool may comprise more than one primary slave hydraulic reservoir. The more than one primary slave hydraulic reservoirs may each be part-annular. The more than one primary slave hydraulic reservoirs may together be distributed around a circumference of the tool.

In embodiments having more than one master hydraulic reservoir and/or more than one primary slave hydraulic reservoir or actuation chamber, it will be understood that a variety of bleed conduit configurations may be implemented, extending between master hydraulic reservoirs and actuation chambers or primary slave hydraulic chambers of the slave hydraulic system with any suitable connectivity.

In some embodiments, multiple bleed conduits may extend from the master hydraulic reservoir, directly or indirectly, to each of two or more actuation chambers, each bleed conduit being provided with a control valve.

Where more than one control valve is present, movement of the sleeve assembly may be regulated by operation of the control valves together with one another. Furthermore, where multiple valves are present, different control valves may be in control lines that communicate (directly or indirectly) with different actuation chambers or groups of chambers and so may provide for actuation elements of different actuation chambers or groups thereof to be selectively actuated.

For example, master hydraulic reservoirs and primary slave hydraulic reservoirs, or actuation chambers, may be connected in pairs via corresponding bleed conduit each with a control valve.

In some embodiments, multiple bleed conduits may extend from a master hydraulic reservoir to each of two or more primary slave hydraulic reservoirs, each bleed conduit being provided with a control valve. In some embodiments, tool may comprise one or more branched bleed conduits extending between the (or a said) master hydraulic reservoir and two or more primary slave hydraulic reservoirs or actuation chambers. A branched bleed conduit may have a control valve disposed between the master fluid reservoir and a branch in the branched bleed conduit, such that a single control valve may regulate fluid between the first fluid reservoir and actuation chambers or primary slave hydraulic reservoirs.

In embodiments comprising more than control valve, each control valve may be operable to open and close independently of one another, so as to effect independent control over different actuation chambers or groups of actuation chambers. In this way, different parts of the tool, such as different tooling elements may be controlled independently of one another.

It will be understood that in embodiments having more than one master and/or primary slave reservoir and/or more than one actuation chamber, the total volume of the master hydraulic reservoir or reservoirs, and the slave hydraulic system is substantially constant.

The (or each) bleed conduit may extend through or be defined by the body, along at least a part of its length.

The bleed conduit may extend extending longitudinally between the master hydraulic reservoir and the slave hydraulic system, along at least a part of its length. The bleed conduit may extend generally radially, along at least a part of its length.

The control portion may comprise the entire of the bleed conduit.

The master hydraulic reservoir may be defined between a first end of the control portion and the body. The primary slave hydraulic reservoir or a said actuation chamber, may be defined between a second end of the control portion and the body.

The master hydraulic reservoir, primary slave hydraulic reservoir and/or the or each actuation chamber, may be defined in part by adjacent surfaces of the sleeve assembly.

The tool may comprise one or more sensors, configured to detect a signal or series of signals. The electromechanical control valve may communicate with one or more said sensors and be operable to open and/or close on detection of a pre-determined control signal or signals detected by said sensor or sensors. The tool may comprise any suitable sensor or combination of sensors. The tool may comprise one or more sensors configured to detect a down hole condition, such as pressure, flow rate, temperature, etc. The tool may comprise a pressure sensor, flow sensor, accelerometer, acoustic sensor or the like.

Accordingly, where the tool comprises a pressure and/or flow sensor, control over the electromechanical control valve may be affected from the surface by pumping, to increase hydrostatic pressure in the bore and/or to create fluid flow in the bore and/or outside of the tool. Where the tool comprises an accelerometer, control over the electromechanical control valve may be affected by moving the tool longitudinally or rotationally; in use by stroking or rotating the work string to which the tool is connected.

In some embodiments the electromechanical control valve is connected or connectable to a wireline, and control signals may be transmitted via the wireline, in use.

The tool may further comprise a control system configured to open and close the control valve. The control system may communicate with the electromechanical control valve and said one or more sensors or wireline, as the case may be.

It will be understood that the electromechanical control valve, or the control system in particular, may be configured to respond to a combination of such control signals and/or a combination of signals from more than one sensor, to assist in eliminating any unwanted actuation of the electromechanical control valve.

In some embodiments, for example, the tool comprises an accelerometer configured to detect rotational signals, and the control system is configured to actuate the valve responsive to a series of two or more periods of rotation and/or counter rotation separated by predetermined time intervals.

The processing resource or logic control required for the control system to effect such control over the electromechanical control valve will be well known to one skilled in the art.

The sleeve assembly may be slideable between the first and second positions under the action of hydraulic pressure and/or a biasing arrangement.

The sleeve assembly may be resiliently biased towards one or other of the first and second positions, by a resilient biasing member. The, or each, actuation element may be resiliently biased towards the first position of the actuation element, or the second position of the actuation element.

A biasing member (or members) may act between the sleeve assembly and the body. For example a spring or other suitable resilient biasing member or members may be disposed in the master hydraulic and/or within the slave hydraulic system. Resilient biasing may be between opposed lips or shelves (for example an annular lip) within the master hydraulic reservoir or slave hydraulic system, or any other suitable formation, as known in the art. One or more resilient biasing members may be provided to act between the body and the sleeve assembly elsewhere within the tool, other than in the said hydraulic reservoirs.

A biasing member (or members) may act between the actuation element and the body, or between the actuation element and the sleeve assembly. A biasing member may be disposed in the or each actuation chamber.

The sleeve assembly may be slidable under the action of a hydrostatic pressure within the bore, that is to say a static pressure differential between the bore and an outside of the tool body. Accordingly, the sleeve may be moved by pressurising the bore.

For example, an outer surface or surface of an actuation element, such as a deployable tooling element may be exposed in use to fluid within the well, external to the tool. Such pressure may be overcome by pressurising the through bore, which pressure may be transmitted to an inner surface of the actuation element within the actuation chamber,

The sleeve assembly may be slidable under the action of a hydrostatic pressure within the bore, whereby when the bore is pressurised, forces applied longitudinally to the sleeve assembly may overcome opposed forces applied to the sleeve assembly by virtue of resilient biasing members acting between the sleeve assembly and the body, or between the actuation elements and the body.

In some embodiments, the master hydraulic reservoir may fluidly communicate with the bore.

The tool may further comprise a tertiary hydraulic volume defined, at least in part, between the sleeve assembly and the body and separated from the master hydraulic reservoir by a slideable balance piston. The tertiary hydraulic volume may communicate with the bore. Provision of the tertiary hydraulic volume and balance piston separates the master hydraulic reservoir from fluid in the bore or well and may prevent debris or chemical treatments from entering, which might otherwise cause blockage or damage to the bleed conduit and control valve in certain downhole applications.

The tertiary hydraulic volume may be at least partially open ended and be in fluid communication with the through bore. The tertiary hydraulic volume may communicate with the bore via one or more pressure ports through the sleeve assembly.

The balance piston may be integrally formed with the adjacent part of the sleeve assembly, or may be fixed thereto. For example, first balance piston may be form generally as a collar around the sleeve assembly, retrained by retaining screws, bolts or the like.

The balance piston may be slidable with respect to the sleeve assembly and the body between a first upper end stop and a first lower end stop. Such slidable relationship may provide for a degree of damping.

The sleeve assembly may be slidable under the action of a dynamic pressure differential along (i.e. longitudinally) the tool. A dynamic pressure differential may be generated by flowing fluid through the through bore. A dynamic pressure differential may be generated by a flow restriction within the bore defined by the sleeve assembly.

At least a part of the length of the through bore may be defined by the sleeve assembly. At least a portion, and in some embodiments all, of the portion of the through bore defined by the sleeve assembly may have a diameter that is less than an upstream portion of the work string, whether that be an upstream portion of the tool, or a length of tubular upstream of the tool, etc.

Provision of each of: a flow restriction; fluid or pressure communication of the master hydraulic reservoir (or tertiary volume as the case may be) with the through bore; and, in some embodiments, pressure communication of the slave hydraulic system with an outside of the body; provides for the sleeve assembly to be moved under the action of either a hydrostatic pressure in the bore and/or a dynamic pressure differential as disclosed herein. The control portion may be or form part of a control collar portion disposed around the sleeve assembly.

The control portion may be formed integrally with an adjacent portion of the body. The control portion may be attached to the body, for example within or around a through bore extending through the body.

The control portion may be attached to the body by a lock key threaded through the body in to the control portion or by any other suitable means such as welding, grub screws or the line.

The master and primary slave hydraulic reservoirs may be defined in part by upper and lower ends of the control portion, and adjacent surfaces of the sleeve assembly. A control collar portion may comprise first and second flange portions, extending radially outward, wherein an upper face of the first flange portion defines a lower end of the master hydraulic reservoir or primary slave hydraulic reservoir; and wherein a lower face of the second flange portion defines an upper end of the other of the master hydraulic reservoir or primary slave hydraulic reservoir.

The control portion, and in particular the first and second flange portions of a control collar portion may be provided with one or more seals for sealing against an inner surface of the body, for example one or more O-rings. The control portion may comprise one or more internal seals for slideably sealing between the control portion and the adjacent portion of the sleeve assembly, such as wiper seals.

The bleed conduit may extend generally longitudinally through one or more parts of the control portion. In some embodiments, the first and second flange portions may comprise upper and lower end regions of the bleed conduit. An intermediate region of the bleed conduit may be defined by one or more hydraulic lines, optionally connected to the flange portions (by threaded compression fittings for example), or extending therethrough. The electromechanical control valve may be connected to one or more said hydraulic lines.

The control portion may include one or more recesses, or more reduced diameter portions of a control collar portion. One or more recesses may be defined between the control portion or the body. The body may comprise one or more recesses proximate the control portion. A said recess may be annular or part annular, in some embodiments. Said recesses may provide space for additional apparatus to be housed. At least an intermediate region of the bleed conduit may be located in a said recess , for example. In some embodiments, the electromechanical control valve is located in a said recess. In some embodiments a control system may be located in a said recess.

As discussed above the electromechanical control valve may be powered by and controlled via wireline from the surface.

In some embodiments, however, the electromechanical control valve is battery powered. The tool may accordingly comprise a battery pack. The control portion may comprise the battery pack. The battery pack may be located in a said recess.

Where present, the control system and one or more sensors me communicate with and be powered from the battery pack.

Movement of the sleeve assembly between the first and second positions may change the tool between a deactivated and an activated condition.

The tool may comprise one more circulation ports. Movement of the sleeve assembly between the first and second positions may open and close the one or more circulation ports (i.e. changes the ports between deactivated (closed) and activated (open)).

The sleeve assembly may comprise one or more sleeve ports communicating with the through bore through the sleeve assembly to an outside of the sleeve assembly. The body may comprise one or more circulation ports extending radially through the body to an outside of the body.

In one of the first and second positions of the sleeve assembly, the one or more sleeve ports and the one or more circulation ports may be longitudinally misaligned, such that the tool is in a deactivated condition in which fluid in the through bore does not communicate with outside of the body.

In the other of the first and second positions of the sleeve assembly, the one or more sleeve ports and the one or more circulation ports may be longitudinally aligned, with each other or with an intermediate chamber defined between the sleeve assembly and the body, such that the tool is in an activated condition in which fluid in the through bore communicates with fluid outside of the body. In the activated condition fluid can be pumped through the work string and circulated via the one more sleeve ports and the one or more circulation ports to an outside of the tool.

The sleeve assembly may be operatively connected to an actuator, such as a linear actuator or a hydroelectic piston actuator, so as to change the condition of further apparatus between a deactivated and an activated condition. The sleeve assembly may be directly operatively coupled to further apparatus to change the condition of the further apparatus between a deactivated and an activated condition (in addition to effecting movement of the actuation elements, disclosed herein).

The further apparatus may include any downhole apparatus, including but not limited to an expandable stabilizer, an expandable packer (e.g. radially expandable by longitudinal compression under the action of the sleeve assembly), deployable arms of an underreaming apparatus, a whipstock or other wellbore departure tool. The range of further down whole apparatus and available means of operatively connecting to a sliding sleeve will be well known to one skilled in the art.

In some embodiments, the tool can be used as a casing cleaner or scraper, with deployable cleaning elements distributed around an outside of the body in one or more helical arrays, optionally extending from apertures in the body through outwardly extending ribs separated by flutes, generally as described in PCT/EP2015/056540 or PCT/EP2019/053345, which are incorporated herein by reference.

As disclosed herein, the tool may comprise one or more actuation elements (optionally comprising or operatively coupled to one or more deployable tooling elements), circulation ports and/or one or more than one further downhole apparatus.

Movement of the sleeve assembly between the first and second positions may change the condition of the actuation elements, one or more further downhole apparatus and circulation ports between their respective first/second, extended/retracted, deactivated/activated or open/closed conditions, as the case may be.

The condition of the respective actuation elements, circulation ports and/or further downhole apparatus may change generally simultaneously as the sleeve assembly moves between the first and second positions. In some embodiments, the sleeve assembly is operable to move between the first and second positions and one or more defined third positions. The sleeve assembly may be operable to move between the first position, the second position and a defined third position that is intermediate the first and second positions. The tool may for example be configured to move an activation element, such as to extend deployable cleaning elements, on the movement of the sleeve assembly between the first and third positions, and to open circulation ports or activate a further downhole apparatus, on movement of the sleeve assembly between the third and second positions.

In some embodiments the one or more third positions may be defined by closing the electromechanical control valve and hydraulically locking the sleeve assembly in a defined third position. The tool may comprise a sensor such as an optical sensor or a mechanical switch to detect when the sleeve assembly is at the third position and cause the electromechanical control valve to close.

The tool may be configured to cause the electromechanical control valve to automatically close under certain circumstances. For example, the electromechanical control valve may be configured to close after a predetermined amount of time has elapsed since the electromechanical control valve has been opened.

Alternatively, or in addition, be configured to automatically close when the sleeve assembly arrives at the first and/or second position.

The tool may be equipped with one or more sensors for detecting the position of the sleeve assembly. In some embodiments an accelerometer or acoustic sensor used to detect control signals may also be configured to detect the position of the sleeve assembly, for example when the sleeve assembly contacts an end stop and creates a vibration or sound.

The control system may be configured to effect such automatic closing of the electromechanical control valve.

The sleeve assembly may be of unitary construction (with any ancillary apparatus, such as seals or the like).

The sleeve assembly may comprise a single sleeve. The sleeve assembly may comprise multiple sleeves connected end to end; for example threadably connected to one another.

The body may be of unitary construction (i.e. formed as a single piece, optionally with the exception of the control portion and, where present, any downhole apparatus which may be mounted or coupled to the body). The body may be a generally tubular mandrel. The body may comprise multiple body portions connected to one another end to end.

The body may include connectors for connecting the tool to the work string above and below the tool. Any suitable connectors may be used such as threaded pin connectors, as known to one skilled in the art.

According to a second aspect of the invention there is provided a method of moving a sliding sleeve assembly of a downhole tool between a first position and a second position, wherein a master hydraulic reservoir is defined between the sleeve assembly and a body of the tool to a first end of a control portion of the body, and the control collar portion comprises a bleed conduit extending between the master hydraulic and a reservoir slave hydraulic system; the method comprising: generating a hydrostatic pressure differential between the through bore and an outside of the tool; and/or generating a dynamic pressure differential in the through bore across the tool or across a flow restriction defined by the sleeve assembly; opening a control valve (such as an electromechanical control valve) disposed in the bleed conduit; flowing hydraulic fluid between the master hydraulic reservoir and the slave hydraulic system along the bleed conduit via the control valve; and closing the control valve to hydraulically lock the sleeve assembly in the first or second position.

The steps may be conducted in any suitable order. For example the pressure differential may be created before, or after the control valve is opened.

The method may comprise changing the volume of the master hydraulic chamber and the slave hydraulic system, wherein the combined volume thereof is substantially constant.

The method may comprise, while the sleeve assembly moves, increasing the volume of the slave hydraulic system and decreasing the volume of the master hydraulic system. The method may comprise, while the sleeve assembly moves, decreasing the volume of the slave hydraulic system and increasing the volume of the master hydraulic system.

The method may comprise, when the control valve is open, flowing fluid into or out of one or more actuation chambers to thereby move an actuation element. The method may comprise moving the sleeve from the first position to the second position and thereby moving the actuation element from a first position of the actuation element, to a second position of the actuation element.

Moving an actuation element may comprise moving a deployable tooling element between a retracted position to an extended position.

The method may comprise increasing or decreasing the volume of the slave hydraulic system by moving an actuation element (or elements).

The method may comprise, when the control valve is open, flowing fluid through the bleed conduit into a primary slave hydraulic reservoir, and from the primary slave hydraulic reservoir into one or more actuation chambers (to thereby effect movement of an actuation element).

The method may comprise issuing a control signal or signals to open and/or close the control valve. That method may comprise issuing a control signal or signals to one or more sensors in communication with the electromechanical control valve. The method may comprise creating a downhole condition in order to issue a control signal to a said sensor. The downhole condition may for example comprise pressurising the bore pumping fluid through the bore, moving the tool longitudinally and/or rotationally, e.g. by stroking the work string or rotating the work string as disclosed herein in relation to the first aspect.

For example the tool may comprise an accelerometer in communication with the electromechanical control valve and the method may comprise issuing a rotational signal to the accelerometer by rotating the tool.

In some embodiments, the electromechanical control valve, or a control system communicating therewith, is configured to respond to one or more sequences of rotational signals (or other downhole conditions or wireline signals), such as a predetermined sequence of rotations and/or counter rotations separated by non-rotating periods. The method may comprise controlling the electromechanical control valve via a wireline connection, the method may comprise controlling the control valve via more than one of the said downhole conditions or wireline.

The sleeve assembly may be resiliently biased towards one of the first or the second position. Accordingly, the method may comprise moving the sleeve assembly from the first to the second position under the action either the hydraulic pressure differential or a resilient biasing member; and moving the sleeve assembly from the second to the first position under the action of the other of the hydraulic pressure differential or resilient biasing member.

Where the method includes multiple steps of moving the sleeve assembly between the first and second positions camera will be understood that the method may comprise additional steps of opening and or closing the control valve.

The pressure differential may be a hydrostatic pressure differential between the bore and an outside of the tool. The method may comprise generating the hydrostatic pressure differential by generating a hydrostatic pressure within the bore.

The pressure differential may be a dynamic pressure differential. The method may comprise generating a dynamic pressure differential across the tool or through a flow restriction defined by the sleeve assembly.

The tool may comprise one more circulation ports. Movement of the sleeve assembly between the first and second positions may open and close the one or more circulation ports.

The method may comprise opening and or closing one or more circulation ports by moving the sleeve assembly between the first and second positions. The method may for example comprise aligning and misaligning one or more sleeve ports extending from the bore through the sleeve assembly with one or more circulation ports extending through the body to an outside of tool, by moving the sleeve assembly between the first and second positions. The method may comprise aligning and mis aligning the sleeve ports with an intermediate chamber in communication with the circulation ports, by moving the sleeve assembly between the first and second positions.

The sleeve assembly may be operatively coupled to one or more further downhole apparatus. The method may comprise changing the condition of one or more further downhole apparatus between a deactivated and an activated condition, by moving the sleeve assembly between the first and second positions, as disclosed herein in relation to the first aspect.

The method may comprise attaching the tool to a work string. The method may comprise running the work string into a well.

The method may comprise the use of the downhole tool of the first aspect of the invention.

Optional features of each aspect of the invention correspond to optional features of any other aspect of the invention. In particular the method of the second aspect of the invention may comprise the use of any features described in relation to the tool of the first aspect of the invention; and the tool of the first aspect of the invention may comprise any features or apparatus required to carry out the method of the second aspect of the invention.

The term “longitudinally” refers to an orientation generally along the work string, and thus generally along a length of the tool, between the upper and lower ends thereof. It will be understood that the tool is of generally cylindrical configuration and thus may be considered to have a longitudinal axis extending along the tool. The term “radially” refers to an orientation perpendicular to the longitudinal orientation, for example radially in relation to the longitudinal axis. Whilst the tool may have a longitudinal axis, it will need not be entirely symmetrical around the longitudinal axis, and downhole apparatus, components of the control collar portion etc. may be distributed non symmetrically around the longitudinal axis.

Reference herein to an “end” (e.g. a first end or a second end) of a feature of the tool, such as the body, sleeve assembly, control collar portion, etc. relate to the longitudinal dimension. Thus a first end of a given feature is necessarily longitudinally spaced apart from the second end.

Terms such as “above” and “below” are used in relation to the longitudinal orientation of work string or tool. Where a feature that is above another feature is positioned along the work string (or tool) closer to the surface and a feature that is below another feature is positioned along the work string (or tool) further from the surface - regardless of the orientation of the well or borehole in relation to vertical.

Description of the Drawings Non-limiting example embodiments will now be described with relation to the following drawings in which:

Fig.lA shows a cross sectional side view longitudinally through an embodiment of a downhole tool with a sleeve assembly in a first position;

Fig. 1 B shows a cross sectional view of the downhole tool of Fig 1 A with the sleeve assembly in a second position;

Fig. 2A shows a cross sectional side view longitudinally through another embodiment of a downhole tool with a sleeve assembly in a first position;

Fig. 2B shows a cross sectional view of the downhole tool of Fig. 2A with the sleeve assembly in a second position;

Fig. 3 shows a perspective of the control collar portion of the downhole tool;

Fig. 4 shows a perspective view of a sleeve assembly of the downhole tool of Fig 1 A and 1 B, with the control collar portion omitted for clarity and a lower sleeve having a circulation port attached thereto;

Fig. 5 shows a perspective cross sectional view of the body of the downhole tool.

Detailed Description of Example Embodiment

With reference to Figs. 1A, 1B and 3-4, the downhole tool includes a body 100 and a through bore 102, 102a. The body includes a control portion 15, in the embodiment shown a control collar portion formed as a separate unit (see Fig. 3) which is secured within the body 100 by a lock key 6, which engages with a recess 31 on the outer surface of the control collar 15.

A sleeve assembly 200 (shown in perspective view in Fig. 3), consists generally of an upper sleeve 4 that is optionally threadably coupled to a lower sleeve 8, via respective outer threaded region 19 of the upper sleeve and inner threaded region 20 of the lower sleeve 8. The upper and lower sleeves 4, 8 are provided with hex formations 71 , 74 to facilitate such coupling. In alternative embodiments the sleeve assembly may comprise a single sleeve, such as sleeve 4 only, or a greater number of sleeves. A portion 102a of the through bore 102 is defined by the sleeve assembly. The diameter of the bore 102a through the sleeve assembly is less than the diameter of the bore 102 above and below the sleeve assembly defined by the body 100.

The control collar portion 15 is disposed around a lower region 74 of the upper sleeve 4.

As shown in Fig. 4, in the embodiment shown, the body 100 includes lower 1, middle 2, and upper 3 sections which are threadably coupled together via conventional male 25 and female 24 pin connectors. The middle section only is shown in Figs 1A and 1 B. The upper and lower sectionals are optional and, in use the middle section may be coupled directly into a work string.

A master hydraulic reservoir 29 is defined between the sleeve assembly 200 and the body 100 above the control collar portion 15 (to the left in Figs. 1A and B). A bleed conduit (discussed in further detail below, with reference to Figure 3) extends from the master hydraulic reservoir to a slave hydraulic system 30.

The slave hydraulic system 30 includes a primary slave hydraulic reservoir 30a, defined between the sleeve assembly 200 and the body 100 below the control collar portion 15 (to the right in Figs. 1A and B). The slave hydraulic system 30 further includes actuation chambers 30c, that are formed as cavities in the outer surface of the body 2. The actuation chambers 30c are each connected via a connecting channel 30b, through the body, to the primary slave hydraulic reservoir 30a.

The primary slave hydraulic reservoir 30 and the master hydraulic reservoir 29 are annular.

Actuation elements 90 are slideably mounted in the cavities, actuation chambers 30c. A sliding seal 92 extends around the actuation element to provide a fluid tight seal. The actuation elements may be secured by way of a pin extending laterally through a radial slot, as known in the art. These features are omitted from the figures, for clarity.

Each actuation chamber 30c is defined in part by the body and in part by an inner face 91 of the actuation element 90. An outer face 93 of the actuation element can be provided with a tooling surface (not shown) such as an abrasive or cutting surface, or a tooling formation such as an anchor, as disclosed herein. The actuation elements 90 are biased inward by springs within the actuation chamber 30c (not shown). In alternative embodiments the springs with actuation chambers are omitted, and control over the position of the actuation elements (discussed below) is entirely hydraulic.

In the embodiment shown, the master hydraulic reservoir 29, and the primary slave hydraulic reservoir 30a are defined by the upper and lower ends 60, 61 of the control collar portion, adjacent outer surfaces of the upper sleeve 4 and inner surfaces of the body 100. The master hydraulic reservoir is also in part defined by ends of a balance piston 10, discussed in further detail below. The lower end of the primary slave hydraulic reservoir is defined by a sealing collar 5, fixed around the sleeve 4. In alternative embodiments, the sleeve comprises a outer shoulder, or the body an inner shoulder, defining the lower end of the reservoir 30a.

The sleeve assembly 200 is slidable within the body 100 between a first position, shown in Fig. 1A and a second position, shown in Fig 1 B. In the first position, the upper end 33 of the sleeve 4 abuts the lower end 32 of upper body section 3, which functions as an end stop. In alternative embodiments and end stop is not provided and the limit of motion is defined by the volume of fluid within the master hydraulic reservoir 29 and the slave hydraulic system 30.

In the second position, a stop shoulder 13 around the upper sleeve 4 encounters an opposing stop shoulder 14 extending from the upper end of the control collar 15.

The sleeve assembly 200 is spring biased towards the first position shown in Fig. 1A, by a coiled spring 23. The spring is disposed in the first hydraulic reservoir 29 and acts between the upper face 60 of the control collar 15 and a shoulder 204 around the upper sleeve 4.

The tool also includes a balance piston 10. The balance piston 10 is, in the embodiment shown, slideable in relation to the sleeve assembly 200 and body 100 and includes inner and outer seals 58, 59. It will be understood that the balance cylinder is optional. In alternative embodiments, the balance cylinder 10 is fixed in relation to the sleeve, analogous to sealing collar 5, or is replaced by a shoulder extending from one or other of the sleeve or the body, to define an end of the master hydraulic reservoir.

A lower end of the first balance cylinder 10 defines the upper end of the first hydraulic reservoir 29. An upper end of the first balance cylinder 10 defines a lower end of a tertiary hydraulic volume 108, between the body and the sleeve 4. The tertiary hydraulic reservoir communicates with the bore 100 at its upper end, via an annulus defined between the upper sleeve 4 and the upper body section 3.

The balance cylinder 10 is slideable along the sleeve 4 between the shoulder 204 and the lower end of the upper body section 3.

The body 100 includes fill ports 28, 22 by which the master hydraulic reservoirs 29 and the slave hydraulic system 30 are filled with hydraulic fluid. The ports are then plugged. The tertiary hydraulic volume 108 communicates with fluid in the bore 100. The balance piston 10 and sealing collar 5 isolate the master hydraulic reservoir 29 and the slave hydraulic system 30 from ingress of unwanted fluids or debris. The master hydraulic reservoir 29 and the slave hydraulic system 30, and the bleed conduit therebetween define a closed hydraulic system.

In the first position of Fig. 1 A, the volume of fluid within the actuation chambers 30c is at its minimum and the actuation or tooling elements 90 are in a first position thereof, recessed within the tool body 2 (i.e. their radially outermost surfaces are radially aligned with or within the outermost surface of the body. Thus, the tooling surface 93 cannot contact a casing wall as the tool is run in. The volume of fluid in the master hydraulic reservoir 29 is, in the first position, at a maximum.

In the second position, of Fig. 1 B, the volume of volume of fluid in the master hydraulic reservoir 29 is at its minimum and fluid has flowed therefrom, via the bleed conduit, into the slave hydraulic system 30, into the primary slave hydraulic reservoir 30a, through the channels 30b and into the actuation chambers 30c. The volume of fluid in the actuation chambers 30c increases and the actuation elements 90 are displaced radially outward from the body, to a second position of the actuation elements. In their second position, the tooling surfaces 93 extend radially outward of the body, whereby the tooling surfaces can contact a casing wall, for cleaning or cutting operations.

An alternative embodiment of the tool is shown in Figures 2A (first position) and 2B (second position). Features in common with the tool of Figs 1A and 1B are provided with like reference numerals.

Actuation element 90a is mounted in the cavity, actuation chamber 30c. The actuation elements are elastomeric sealing elements operable to function as packers. The sealing elements 90a and cavity 30c are annular and the sealing elements 90a seal at their upper and lower ends with the body 2. The cavity 30c and the primary slave hydraulic reservoir 30a are connected via radially extending channels 30b.

The actuation chamber 30c is defined in part by the body and in part by an inner face 91 of the actuation element 90.

In the first position of Fig. 2A, the volume of fluid within the actuation chamber 30c is minimal and the elastomeric element 90a is recessed within the tool body 2 (i.e. the radially outermost surface 93a is radially aligned with or within the outermost surface of the body. Thus, the surface 93 cannot contact a casing wall as the tool is run in and the element 90a is thus not damaged. The volume of fluid in the master hydraulic reservoir 29 is, in the first position, at a maximum.

In the absence of any forces applied thereto, the elastomeric elements 90a adopt their first positions shown in Fig. 2A and thereby provide an elastomeric biasing force towards that position.

In the second position, of Fig. 2B, the volume of volume of fluid in the master hydraulic reservoir 29 is at a minimum and fluid has flowed therefrom, via the bleed conduit, into the slave hydraulic system 30, into the primary slave hydraulic reservoir 30a, through the channels 30b and into the actuation chamber 30c. The volume of fluid in the actuation chambers 30c increases and the elastomeric element 90a inflates radially outwardly to extend from the body to its second position. In the second position, the outer surface 93a extends radially outward of the body, whereby the elastomeric element 90a can contact a and seal against a casing wall, to isolate a region of the well.

Figure 3 shows the control collar 15 in further detail.

The control collar portion 15 comprises a bleed conduit that extends between the first and the second hydraulic reservoirs 29, 30. The bleed conduit is defined in part by apertures extending through the control collar 15 and in part by hydraulic lines.

The collar has upper and lower flange portions 15a, 15b at the first and second ends of the collar 15. The flange portions 15a, 15b define the respective first and second ends 60, 61 of the collar 15. An upper channel 56 extends through the upper flange portion, and extends from the upper end face 60, exiting at a recess 15c between the flange portions 15a, 15b. Similarly, a lower channel 57 extends through the lower flange portion 15b, extending from the lower end face 61 and exiting to the recess 15c. The upper and lower channels thus communicate with the master hydraulic reservoir 29 and the slave hydraulic system 30. Hydraulic lines 53 positioned within the recess 15c are connected by threaded compression couplings 52 to the upper and lower channels 56, 57. The hydraulic lines 53 each also connect to a solenoid valve 51, having a solenoid 54.

End regions of the bleed conduit are thus defined by the upper and lower channels 56, 57 and an intermediate region of the bleed conduit is defined by the hydraulic lines 53, with the solenoid valve 51 being positioned in the bleed conduit.

The solenoid (i.e. electromechanical) valve 51 includes an accelerometer (not shown) and a control system (not shown), by which control over the valve 51 can be effected by way of rotational signals received by the accelerometer, as disclosed herein.

The control collar 15 also includes a battery pack 55 which communicates with and powers the valve 51. The battery pack is housed within an adjacent recess between the upper and lower flange portions of the collar 15.

The control collar has a central bore sized to slideably receive the sleeve assembly 200 (and the lower part 74 of the upper sleeve in particular. The flange portions 15a, 15b are sized to be received within the body 100. Seals 58 are provided around the flange portions to seal between the collar 15 and the body 100. Seals 59 are also provided to slideably seal between the control collar 15 and the sleeve assembly 200.

Movement of the sleeve assembly between the first and second positions will now be described with reference to Figs. 1A and 2A, 1 B and 2B.

In use, the tool will be connected to a work string and run into a well.

The electromechanical control valve is opened by rotating the tool (from the surface, via the work string) to transmit rotational control signals to the accelerometer.

Fluid is pumped through the work string.

The section 26 of the bore 102 that is defined by the upper body section 3 above the upper end 33 of the sleeve assembly 200 is of wider diameter than the bore 102b through the sleeve assembly. Fluid flow through the bore 102 to the narrower section 102a defined by the sleeve assembly 200 creates a dynamic pressure differential. Hydrostatic pressure in the bore 102, 102a also increases, resulting in a static pressure differential between the bore and the wellbore outside of the body. When either the static pressure differential, the dynamic pressure differential or their combined effects overcomes the resistance of the spring 23 (and, in the embodiments shown, the biasing of the tooling element 90 or elastomeric element 90a), the sleeve moves towards the second position. The actuation chambers 30c accordingly increase in volume and the tooling element 90 and elastomeric element 90a move to their extended, second positions shown in Figs. 1B and 2B.

With the control valve 51 open, hydraulic fluid is able to flow generally longitudinally from the master hydraulic reservoir 29, along the bleed conduit 56, 53, 57 and to the slave hydraulic system 30.

It should be noted that if the valve 51 is closed, such fluid pumping through the work string (as might be required for other downhole operations, e.g. in relation to other equipment run in on the work string) would not cause movement of the sleeve, since fluid would not be able to flow along the bleed conduit between the master hydraulic reservoir and the slave hydraulic system, and the sleeve would be hydraulically locked.

If, as is typically the case, the balance cylinder 10 is at its upper end stop, or between their upper and lower end stops, fluid is also exchanged between the bore and the tertiary hydraulic volume 108. One or other of the exchange of fluid between the master hydraulic reservoir 29 and the slave hydraulic system 30 and the exchange of fluid between the bore 102 and the volume 108 may be rate limiting (typically the bore may be pumped/pressurised such that flow through the bleed conduit is rate-limiting), such that the movement of the balance cylinder 10 independent of the sleeve 4 provides for a degree of damping.

When the sleeve assembly 200 reaches the second position shown in Figs. 1 B and 2B, the solenoid control valve 51 is closed. This prevents flow of fluid along the bleed conduit and hydraulically locks the sleeve assembly in the second position. With the valve closed, subsequent pressure changes in the bore 100 or the wellbore outside of the tool and acting upon the outer surfaces 93, 93a of the actuation elements 90, 90a, cannot cause further movement of the sleeve assembly.

Closure of the control valve can occur automatically, after a predetermined time sufficient for the sleeve to have moved has elapsed since opening. Alternatively, or in addition, further rotational signals can be transmitted to the accelerometer to close the control valve 51. The accelerometer (or optionally further sensors or trip switches) may also be configured to detect landing of the sleeve at the second position. The control valve’s control system may be configured to effect closure of the valve under any or all of these circumstances.

When the control valve 51 is again opened (e.g. by rotation of the tool), and pumping/circulation of fluid in the bore 100 has ceased, the spring 23 (and biasing of the elements 90, 90a) urges the sleeve back towards the first position shown in Figs 1A and 2A and fluid flows from the slave hydraulic system 30 back into the master hydraulic reservoir 29 along the bleed conduit 57, 53, 56. The actuation chambers 30c accordingly reduce in volume and the tooling element 90 and elastomeric element 90a revert to their retracted, first positions.

In use, as discussed above, the total volume of the enclosed system comprising the master hydraulic reservoirs 29, bleed conduit 56, 52, 57 and the slave hydraulic system 30 is constant.

Movement of the sleeve between the first and second positions may also change the condition of additional tool functions from a deactivated condition to an activated condition.

With reference to Figs. 4 and 5, the tools of Figs 1A B may further include a circulation port, for example. In such embodiments, the sleeve assembly 200 may further include a lower sleeve 8 with an array of sleeve ports 18 which extend through the lower sleeve 8 to the bore 102a. The sleeve ports 18 are separated from the primary slave hydraulic chamber 30c by the sealing collar 5.

The lower body section 1 is provided with an array of upwardly oriented circulation ports 7. To either side thereof are positioned internal seals 59, which seal around the sleeve 8.

When the sleeve is in the first position, the sleeve ports 18 are misaligned with and above the circulation ports 7, and separated therefrom by the internal seals 59a. The seals 59a isolate the bore 102a from the ports 7 and thus the outside of the tool. The circulation tool is in a deactivated condition, when the sleeve is in the first position.

When the sleeve assembly is in the second position, the sleeve ports 18 are moved into alignment with the circulation ports 7 such that the bore 102a communicates with the outside of the tool via the ports 7, 18 and the circulation tool is in an activated condition. In alternative embodiments, the circulation tool can be arranged to be in a deactivated condition when the tool is in the second position. Whilst exemplary embodiments have been described herein, these should not be construed as limiting to the modifications and variations possible within the scope of the invention as disclosed herein and recited in the appended claims.

Claims

1. A downhole tool, comprising: a body having a through bore; a sleeve assembly slideable within the body between a first position and a second position; and the body comprising a control portion; wherein a master hydraulic reservoir is defined between the sleeve assembly and the body to a first end of the control portion, and wherein the control portion further comprises a bleed conduit extending between the master hydraulic reservoir and a slave hydraulic system defined, at least in part, by the body; and an electromechanical control valve across the bleed conduit configured to regulate fluid flow along the bleed conduit; wherein, when the sleeve moves between the first and second positions, a volume of the master hydraulic reservoir and a volume of the slave hydraulic system changes; and the combined volumes of the master hydraulic reservoir and the slave hydraulic system is substantially constant.

2. The downhole tool of claim 1 , wherein the slave hydraulic system comprises at least one actuation chamber and wherein the, or each, actuation chamber comprises an actuation element.

3. The downhole tool of claim 2, wherein the, or each, at least one actuation chamber is defined, at least in part, by the actuation element.

4. The downhole tool of claim 2 or 3, wherein the, or each, actuation element is movable within or in relation to a cavity or aperture defined by the body.

5. The downhole tool of claim 4, wherein the, or each, actuation element is slideable within the cavity or aperture.

6. The downhole tool of claim 4 or 5, wherein the tool comprises a seal between the actuation element and the cavity or aperture.

7. The downhole tool of any one of claims 2 to 6, wherein the actuation element is moveable radially.

29

8. The downhole tool of any one of claims 2 to 7, wherein actuation element comprises or consists of a deployable tooling element; or wherein the actuation element is operably coupled to a deployable tooling element.

9. The downhole tool of claim 8, wherein the deployable tooling element, or outer portion thereof, comprises; a cleaning formation; a milling formation; a casing anchor; a packer, comprising a resiliently deformable or inflatable formation for sealing against a casing wall; a wiper plug, for engaging with a casing wall and retaining fluid flow or pressure in one direction past the tool.

10. The downhole tool of claim 8 or 9, wherein deployable tooling element is moveable between a retracted position and an extended position, effected by movement of the sleeve assembly between the first and second positions.

11. The downhole tool of any preceding claim, wherein the slave hydraulic system comprises a primary slave hydraulic reservoir and one, or more than one, actuation chamber in fluid communication with the primary slave hydraulic reservoir.

12. The downhole tool of claim 11 , wherein primary slave hydraulic reservoir is generally annular.

13. The downhole tool of claim 11 or 12, wherein primary slave hydraulic reservoir fluidly communicates with the bleed conduit and wherein the, or each, actuation chamber is in fluid communication with the primary slave hydraulic reservoir via a connecting conduit or channel.

14. The downhole tool of any one of claims 11 to 13, wherein the slave hydraulic system comprises multiple actuation chambers and the primary slave hydraulic chamber fluidly communicates with the multiple actuation chambers.

15. The downhole tool of any preceding claim, wherein the master hydraulic reservoir is generally annular.

16. The downhole tool of any preceding claim, wherein tool comprises one or more sensors, configured to detect a signal or series of signals, wherein the

30 electromechanical control valve communicates with one or more said sensors and is operable to open and/or close on detection of a pre-determined control signal or signals detected by said sensor or sensors.

17. The downhole tool of any preceding claim, wherein the tool further comprises a control system configured to open and close the control valve.

18. The downhole tool of any preceding claim, wherein sleeve assembly is slideable between the first and second positions under the action of hydraulic pressure.

19. The downhole tool of any preceding claim, wherein sleeve assembly is resiliently biased towards one or other of the first and second positions, by a resilient biasing member.

20. The downhole tool of claim 2 or any one of claims 3 to 19 when dependent on claim 2, wherein the, or each, actuation element is resiliently biased towards a first position of the actuation element, or a second position of the actuation element.

21. The downhole tool of claim 20, wherein a biasing member is disposed in the or each actuation chamber.

22. A method of moving a sliding sleeve assembly of a downhole tool between a first position and a second position, wherein a master hydraulic reservoir is defined between the sleeve assembly and a body of the tool to a first end of a control portion of the body, and the control collar portion comprises a bleed conduit extending between the master hydraulic reservoir slave hydraulic system; the method comprising: generating a hydrostatic pressure differential between the through bore and an outside of the tool; and/or generating a dynamic pressure differential in the through bore across the tool or across a flow restriction defined by the sleeve assembly; opening a control valve (such as an electromechanical control valve) disposed in the bleed conduit; flowing hydraulic fluid between the master hydraulic reservoir and the slave hydraulic system along the bleed conduit via the control valve; and closing the control valve to hydraulically lock the sleeve assembly in the first or second position.

23. The method of claim 22, comprising changing the volume of the master hydraulic chamber and the slave hydraulic system, wherein the combined volume thereof is substantially constant.

24. The method of claim 23, comprising, while the sleeve assembly moves, increasing the volume of the slave hydraulic system and decreasing the volume of the master hydraulic system, or vice versa.

25. The method of claim 23 or 24, comprising, when the control valve is open, flowing fluid into or out of one or more actuation chambers to thereby move an actuation element.

26. The method of claim 25, wherein moving an actuation element comprises moving a deployable tooling element between a retracted position to an extended position.

27. The method of claim 25 or 26, comprising increasing or decreasing the volume of the slave hydraulic system by moving an actuation element or elements.

28. The method of any one of claims 22 to 27, comprising, when the control valve is open, flowing fluid through the bleed conduit into a primary slave hydraulic reservoir, and from the primary slave hydraulic reservoir into one or more actuation chambers.

29. The method of any one of claims 22 to 28, comprising issuing a control signal or signals to open and/or close the control valve.