Patent Description:
Gauge hangers are used in the oil and gas industry to support instruments such as pressure and temperature measuring gauges inside tubing whilst the instruments gather data. The gauge hanger and instruments are then recovered to surface at the end of the monitoring period. Typically, the gauge hanger and measurement instrument are installed and retrieved with a cable deployed setting tool. Such a gauge is disclosed for example in the <CIT>.

Traditionally there have been two types of gauge hangers: those that work by wedging themselves inside the tubing by various expanding gripper means, and those that are seated in a special profile in the tubing string. When deployed, either of these means may prevent further access to the wellbore via the tubing string.

It is known to use a magnetic field to attach a downhole instrument to tubing in a wellbore. Gauge hangers that attach magnetically to the side of the tubing may allow long-term deployment of instruments whilst retaining access to the wellbore for other intervention tools. However, known magnetic attachment mechanisms tend to be complicated, and may require the use of several permanent magnets or electromagnets in order to switch between an activated and deactivated state. Furthermore, existing mechanisms may require a cable to be permanently attached to the downhole instrument or may risk the cable detaching before the gauge hanger is attached to the tubing.

It would therefore be desirable to provide a gauge hanger which can be reliably attached to the tubing wall at the required depth and then released from its setting tool. It would also be desirable to provide a gauge hanger which can be easily retrieved at the end of the monitoring period.

According to one aspect of the present invention there is provided a gauge hanger for deployment in a wellbore using a setting tool, the gauge hanger comprising:.

The present invention may provide the advantage that, by arranging the switchable magnet and the coupling assembly to be actuated by a common actuator, a less complex system requiring fewer parts may be provided. Furthermore, this arrangement may help to ensure that the setting tool can only be disengaged from the gauge hanger once the gauge hanger is attached to the wall.

The switchable magnet and the coupling assembly are preferably mechanically linked. For example, the switchable magnet and the coupling assembly may be linked by a rotatable member (such as a shaft), which may be rotatable by the common actuator. In this case, the switchable magnet and the coupling assembly may both be actuated by rotation of the rotatable member. This may facilitate actuation of the switchable magnet and the coupling assembly by the common actuator.

The gauge hanger is preferably arranged to be lowered into the wellbore using the setting tool. Once at the required depth, the gauge hanger is preferably arranged to be attached to the wellbore wall and released from the setting tool. The setting tool can then be lifted to surface.

The switchable magnet is preferably switchable between a deactivated state and an activated state. In the activated state, the switchable magnet preferably produces an external magnetic field sufficient to attach the gauge hanger to the wellbore wall. In the deactivated state the switchable magnet preferably produces no external magnetic field, or insufficient external magnetic field to attach the gauge hanger to the wellbore wall.

The coupling assembly is preferably switchable between an engaged state and a disengaged state. In the engaged state, the gauge hanger is preferably attached to the setting tool, preferably in such a way that the setting tool can support the gauge hanger. In the disengaged state, the setting tool can preferably be detached from the gauge hanger.

Preferably, switching the switchable magnet to an activated state also switches the coupling assembly to a disengaged state. This may allow the gauge hanger to be detached from the setting tool as part of the same action as attaching the gauge hanger to the wellbore wall. This may help to provide a less complex system requiring a single actuator and/or fewer parts than might otherwise be required.

Preferably, during setting, the coupling assembly is not switched to the disengaged state until the switchable magnet is switched to an activated state. This may help to ensure that the setting tool is only detached from the gauge hanger once the gauge hanger is attached to the wall.

The gauge hanger may be arranged to be retrieved from the wellbore using a retrieval tool. The retrieval tool may be the same as the setting tool, or a separate retrieval tool may be used. The retrieval tool may be lowered into the wellbore until it encounters the gauge hanger. The gauge hanger may be arranged to be attached to the retrieval tool and detached from the wellbore. The retrieval tool and gauge hanger may then be lifted to surface.

Preferably, during retrieval, switching the coupling assembly to an engaged state also switches the switchable magnet to a deactivated state. This may allow the gauge hanger to be detached from the wellbore wall as part of the same action as attaching the gauge hanger to the retrieval tool. This may help to provide a less complex system requiring a single actuator and/or fewer parts than might otherwise be required.

Preferably the switchable magnet is not switched to a deactivated state until the coupling assembly is switched to the engaged state. This may help to ensure that the gauge hanger is only detached from the wellbore wall once the gauge hanger has been attached to the retrieval tool.

The switchable magnet preferably comprises one or more permanent magnets in a configuration that allows an external magnetic field to be turned on or off. For example, the switchable magnet may comprise a rotatable core, and the rotatable core may comprise one or more permanent magnets. The rotatable core may be provided in a base comprising at least one block of high magnetic permeability material and a block of low magnetic permeability material. Rotation of the rotatable core (relative to the base) may switch the switchable magnet between an activated state and a deactivated state. This may allow an external magnetic field to be easily switched on and off without requiring an electromagnet.

Preferably the coupling assembly comprises a rotatable element, and rotation of the rotatable element switches the coupling assembly between an engaged state and a disengaged state. This may help to provide a simple mechanism for attaching and detaching the setting tool to the gauge hanger.

Preferably the rotatable element is rotated synchronously with a rotatable core in the switchable magnet. Thus, the gauge hanger may comprise means, such as a rotatable shaft, for transferring rotation between the rotatable element and the rotatable core. This may allow a single actuator such as a motor to be used to attach the gauge hanger to the wellbore wall and to decouple the setting tool from the gauge hanger.

In one embodiment, the coupling assembly comprises an engagement member (for example, one or more dogs) for engagement with the setting tool. In this case, the rotatable element may comprise a cam which is arranged to displace the engagement member. For example, the cam may be arranged to displace the engagement member radially as the cam rotates. Displacement of the engagement member may be, for example, through an aperture such as a slot in the coupling assembly. The coupling assembly may also comprise means for causing the engagement member to follow the cam. For example, the coupling assembly may comprise a slot and pin arrangement which causes the engagement member to follow the profile of the cam. However, if desired, any other means for causing the engagement member to follow the cam, such as a spring, may be used instead or as well.

The engagement member may be arranged, for example, to engage with an aperture such as a slot in the setting tool. This may provide a convenient mechanism for engaging and/or disengaging the gauge hanger with and/or from the setting tool.

In one embodiment, the coupling assembly comprises two engagement members, which may be arranged to move in opposite directions. In this case, the cam may comprise two lobes and each lobe may act on one of the engagement members. Each of the engagement members may be arranged to move radially outwards into a corresponding aperture in the setting tool. This may help to provide a secure mechanism for holding the setting tool and the gauge hanger together. Alternatively, if desired, any other appropriate number of engagement members and/or lobes, such as three, four or more, may be provided, and the engagement members may be arranged to move in any appropriate direction. Furthermore, rather than a cam, any other appropriate means for urging an engagement member outwards may be provided.

The coupling assembly may comprise means for limiting rotation of the rotatable element. For example, where the rotatable element is a cam, the coupling assembly may comprise a lobe shaped cavity for limiting rotation of the cam. This may help to ensure that the cam is not over-rotated. This in turn may help to ensure that the switchable magnet remains in the desired state (e.g., fully activated or fully deactivated) and/or that the coupling assembly remains in the desired state (e.g., fully engaged or fully disengaged).

The gauge hanger may further comprise a secondary retention mechanism for holding the setting tool and the gauge hanger together when the coupling assembly is in a disengaged state. The secondary retention mechanism may comprise, for example, a snap ring on the gauge hanger which is arranged to engage with a groove on the setting tool, or vice versa, or alternatively any other type of releasable retention means. This may help to ensure that the setting tool and gauge hanger are held together as the coupling assembly is engaged/disengaged. It may also help to ensure that the two engagement members are accurately aligned with the corresponding apertures of the setting tool.

If desired, a single switchable magnet could be used to attach the gauge hanger to the wellbore wall. However, in a preferred embodiment, the gauge hanger comprises a plurality of switchable magnets for attaching the gauge hanger to the wellbore wall. For example, the gauge hanger may comprise two switchable magnets, one at or towards the top of the gauge hanger and one at or towards the bottom of the gauge hanger. Alternatively, three or more switchable magnets could be used, in which case one or more switchable magnets may be provided at one or more intermediate locations along the length of the gauge hanger. Use of a plurality of switchable magnets may help to ensure that the gauge hanger remains attached to the wellbore wall. For example, where the gauge hanger is deployed in production tubing, this may help to prevent the gauge hanger from being dislodged by passing liquid or gas flow. Furthermore, this may help to prevent the gauge hanger from being dislodged by other tools passing the gauge hanger in either direction. Furthermore it may help the gauge hanger mate with a variation of internal curvature of the wellbore using different curvatures of the switchable magnet housings.

The gauge hanger is preferably used to support one or more instruments such as a measuring gauge. In one embodiment, a switchable magnet is provided on either side of the instrument. In this case, the instrument may also be used to transfer rotation between the switchable magnets. This may help to provide a simple and convenient way of activating and/or deactivating both switchable magnets. However, if desired, another mechanism such as a rotatable shaft could be used to transfer rotation between the switchable magnets.

The gauge hanger may further comprise means for removably connecting the coupling assembly to an actuator in the setting tool. The means for removably connecting the coupling assembly to the actuator may be arranged to transfer rotation between the actuator and the gauge hanger when engaged. For example, the gauge hanger may comprise a socket and the setting tool may comprise a shaft arranged to seat inside the socket, or vice versa. This may allow rotation to be transferred between an actuator, such as a motor, in the setting tool and the gauge hanger, while allowing the setting tool to be detached from the gauge hanger.

The socket and shaft are preferably arranged to transfer rotation between the two. For example, the shaft may be a hexagonal shaft, in which case the socket may be a hexagonal socket. Alternatively, any appropriate shape of socket and/or shaft, such as square, rectangular, triangular, star-shaped, octagonal, or any other multi-sided polygonal shape may be used instead. Furthermore, any other appropriate arrangement which allows rotation to be transferred when engaged (such as holes and pins) may be used instead of a socket and shaft.

According to another aspect of the invention, there is provided a deployment assembly comprising a setting tool and a gauge hanger in any of the forms described above.

According to another aspect of the invention, there is provided a deployment assembly comprising:.

In one embodiment, the coupling assembly is provided in the gauge hanger. However, in another embodiment, the coupling assembly is provided in the setting tool rather than in the gauge hanger. In this case, the coupling assembly may comprise an engagement member for engagement with the gauge hanger and the gauge hanger may comprise an aperture for receiving the engagement member. The coupling assembly may otherwise be in any of the forms described above.

In any of the above arrangements, the setting tool may comprise an actuator arranged to actuate the coupling assembly and the switchable magnet. The actuator may be for example a motor arranged to supply torque to the coupling assembly and the switchable magnet.

The setting tool (or gauge hanger) may comprise a collar arranged to slide over the coupling assembly. The collar may comprise one or more of:.

The setting tool may be arranged to deploy the gauge hanger in the wellbore. Furthermore, the setting tool may be arranged to retrieve the gauge hanger from the wellbore.

The setting tool may comprise a guide arranged to locate the setting tool in the wellbore relative to the gauge hanger. The guide may be for example in the form of an elliptical hoop structure arranged at an angle to the vertical axis. The guide may be arranged to ride over the gauge hanger and to rotate the setting tool relative to the gauge hanger. This may help to ensure that the setting tool is correctly aligned with the gauge hanger when it is being used for retrieval.

Alternatively, a separate retrieval tool may be used to retrieve the gauge hanger, in which case the guide may be provided on the retrieval tool.

Corresponding methods may also be provided. Thus, according to another aspect of the invention there is provided a method of deploying a gauge hanger in a wellbore, the method comprising:.

The actuator may be for example a motor arranged to rotate a rotatable element in the gauge hanger (or setting tool) and a rotatable core in the switchable magnet. Rotation of the rotatable element may cause the setting tool to decouple from the gauge hanger. The rotatable element may be, for example, a cam arranged to act on an engagement member.

Preferably the setting tool is not decoupled from the gauge hanger until the switchable magnet is activated.

According to a further aspect of the invention there is provided a method of retrieving a gauge hanger from a wellbore, the method comprising:.

Preferably the switchable magnet is not deactivated until the retrieval tool is coupled to the gauge hanger.

Features of one aspect of the invention may be provided with any other aspect. Apparatus features may be provided with method aspects and vice versa.

Preferred embodiments of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:.

<FIG> shows an overview of a wellbore system in one embodiment. Referring to <FIG>, the system comprises wellbore <NUM>, casing <NUM>, well head structure <NUM> and tubing <NUM>. The tubing <NUM> may be the conduit through which oil and gas are brought from the producing formations to the surface. The tubing <NUM> is typically made from a metallic material such as mild steel. An instrument <NUM> such as a pressure and temperature measuring gauge is located inside the tubing <NUM> in order to gather data. The instrument <NUM> may store the data in memory for later retrieval and/or transmit data to the surface, for example, using acoustic telemetry or other means of communication. The instrument <NUM> is supported by a gauge hanger <NUM> which attaches to the wall of the tubing <NUM>. The gauge hanger <NUM> is set in place using a setting tool <NUM>. The setting tool <NUM> is lowered and raised using a deployment wire connected to a surface hoist (not shown). In this example, the tubing <NUM> is production tubing, although the principles described herein may be used with any type of tubing, such as drilling tubing or production tubing, which may be permanently or temporarily deployed in the wellbore.

Traditionally there have been two types of gauge hangers: those that work by wedging themselves inside the tubing by various expanding gripper means; and those that are seated in a special profile in the tubing string. When deployed, either of these may prevent further access to the wellbore via the tubing string.

For example, access may be required by other wireline conveyed tools, coiled tubing conveying tools or small diameter 'spaghetti' strings of tubing. If the duration of deployment of a gauge hanger assembly is long, this can lead to a conflict in operational requirements, often requiring the instruments and hangers to be removed from the wellbore prematurely.

In embodiments of the invention, a gauge hanger is provided that attaches magnetically to the side of the tubing, allowing other tools to be run past it. A setting tool is used to deploy the gauge hanger at the required depth. This can provide a means of long-term deployment of instruments whilst retaining access to the wellbore for other intervention tools.

The magnetic force required to hold the gauge hanger against the wall should only be generated at the desired setting depth to prevent the device from attaching to the nearest metallic item it encountered when being run in hole. Furthermore, the magnetic force holding the gauge hanger against the wall should be able to be removed at the set depth during retrieval. In embodiments of the invention, a switchable magnet is used to attach the gauge hanger to the tubing wall. A switchable magnet is a device that uses one or more permanent magnets in a configuration that allows the external field to be turned on or off.

<FIG> illustrate the principles of a switchable magnet in one exemplary embodiment. In <FIG>, cross-sections through an exemplary switchable magnet are shown. The switchable magnet comprises base <NUM> and switching core <NUM>. The base <NUM> comprises two blocks <NUM> of ferromagnetic material, such as iron, with a block <NUM> of non-ferrous material, such as brass or aluminium, between the two. A cylindrical cavity runs through the centre of the base <NUM>, intersecting the two blocks <NUM> of ferromagnetic material and the block <NUM> of non-ferrous material. The switching core <NUM> is a cylindrical permanent magnet which is located inside the cavity. The poles of the magnet are on diametrically opposite sides of the switching core. The switching core <NUM> can be rotated inside the base <NUM> between an "off" position and an "on" position.

When the switching core <NUM> is in the "off" position, as shown in <FIG>, the poles of the magnet are orientated towards the block <NUM> of non-ferrous material.

In this position, the blocks <NUM> of ferrous material act as keepers, allowing the magnetic flux to bridge the poles. Thus, in the "off" position, little or no external magnetic field is created. However, when the switching core <NUM> is in the "on" position, as shown in <FIG>, the blocks <NUM> of ferrous material act as an extension of the magnet. Thus, in the "on" position, an external magnetic field is created, with the magnetic flux passing through the blocks <NUM>. The external magnetic field can be used to attach the device to a metallic object such as a tubing wall.

In one embodiment, a gauge hanger and a setting tool form a deployment assembly for deploying the gauge hanger in a wellbore. The deployment assembly is preferably provided with the following functional features:.

<FIG> shows parts of a deployment assembly in an embodiment of the invention. Referring to <FIG>, the deployment assembly comprises a gauge hanger <NUM> and a setting tool <NUM>. The setting tool <NUM> is used to set the gauge hanger <NUM> at the appropriate location in the wellbore tubing. The setting tool <NUM> is attached to a deployment wire <NUM> connected to a surface hoist (not shown).

The setting tool <NUM> comprises a motor <NUM>, a battery <NUM>, a control unit <NUM> and a communications module <NUM>. The motor <NUM> is powered by the battery <NUM> and controlled by the control unit <NUM>. The control unit <NUM> comprises a processor and associated memory programmed with the appropriate software to control operation of the motor <NUM>. The communications module <NUM> can receive and transmit data and commands for use by the control unit <NUM>. The communications module <NUM> communicates with equipment at the surface, for example, through the wire <NUM> or using any other appropriate means of transmission, such as a separate communications wire, radio frequency transmission or acoustic transmission.

The motor <NUM> is connected to a drive shaft <NUM> which is used to transfer torque to the gauge hanger <NUM>. The setting tool <NUM> includes a collar <NUM> which fits over a coupling assembly in the gauge hanger <NUM>.

The gauge hanger <NUM> comprises a coupling assembly <NUM>, an upper magnet assembly <NUM> and a lower magnet assembly <NUM>. The coupling assembly <NUM> is used to removably attach the gauge hanger <NUM> to the setting tool <NUM>. The upper magnet assembly <NUM> and the lower magnet assembly <NUM> are used to attach the gauge hanger <NUM> to the tubing wall. The upper and lower magnet assemblies <NUM>, <NUM> are connected by means of two torsion bars <NUM>. The torsion bars <NUM> are used to hold the upper magnet assembly <NUM> and the lower magnet assembly <NUM> together and prevent rotation between the two. One or more instruments <NUM> such as a measuring gauge is located between the upper magnet assembly <NUM> and the lower magnet assembly <NUM>.

Each of the magnet assemblies <NUM>, <NUM> comprises a switchable magnet with a switching core. The switchable magnets may be, for example, in the form described above with reference to <FIG>. Thus, the magnetic forces holding the gauge hanger <NUM> against the wall are switchable, allowing the device to be set at the required depth and subsequently removed.

In the arrangement of <FIG>, both the upper magnet assembly <NUM> and the lower magnet assembly <NUM> are used to attach the gauge hanger <NUM> to the tubing wall. This helps to ensure secure attachment using a streamlined device. Furthermore, by attaching both the top and the bottom of the gauge hanger, other tools passing in either direction are less likely to dislodge the gauge hanger from the tubing wall. The magnetic forces between the gauge hanger and tubing wall are designed to be sufficient to resist the gauge hanger being dislodged by high flow rates of liquid or gas as well as to resist pushing or pulling forces applied by a tool passing by it.

The motor <NUM> in the setting tool <NUM> is used to rotate the switching core in the upper magnet assembly <NUM> between an "off" position and an "on" position via the drive shaft <NUM>. The instrument <NUM> is also attached to the switching core in the upper magnet assembly <NUM>. This allows rotation to be transferred through the instrument <NUM> to the lower magnet assembly <NUM>. Thus, the upper magnet assembly <NUM> and the lower magnet assembly <NUM> can be switched simultaneously between the "off" position and the "on" position. The torsion bars <NUM> hold the upper magnet assembly <NUM> and the lower magnet assembly <NUM> in place relative to each other and ensure that the magnets are always aligned.

The coupling assembly <NUM> is designed such that activating the magnetic fields in the upper and lower magnet assemblies <NUM>, <NUM> also releases the gauge hanger <NUM> from the setting tool <NUM>, as will be explained below. This allows the setting tool <NUM> to be removed once the gauge hanger <NUM> has been set at the required depth.

The coupling assembly <NUM> is also designed to attach to a retrieval tool, which may be the same as the setting tool. Attaching the coupling assembly to the retrieval tool also deactivates the magnetic fields in the upper and lower magnet assemblies <NUM>, <NUM>. This allows the gauge hanger to be released and lifted to the surface when it is no longer required.

<FIG> shows parts of the upper magnet assembly and the coupling assembly in more detail. Referring to <FIG>, the upper magnet assembly <NUM> comprises magnetic mount <NUM>, base <NUM>, switching core <NUM> and upper instrument mount <NUM>. In the assembled state, the base <NUM> is located inside the magnetic mount <NUM>, and the switching core <NUM> is located inside the base <NUM>. The base <NUM> and the switching core <NUM> together form a switchable magnet. For example, the base <NUM> and the switching core <NUM> may be substantially in the form described above with reference to <FIG>, although other types of switchable magnet may be used instead. The magnetic mount <NUM> is used to hold the base <NUM> in place. The outside surface of the base <NUM> is slightly curved, so as to substantially conform to the inside surface of the tubing with which the gauge hanger is to be used.

In the arrangement of <FIG>, the coupling assembly <NUM> comprises barrel <NUM> and rotator shaft <NUM>. The coupling assembly <NUM> is used to attach the gauge hanger to the setting tool, and to rotate the rotator shaft <NUM>. The switching core <NUM> is in the form of a hollow cylinder with a cavity <NUM> extending longitudinally through its centre. The rotator shaft <NUM> extends into the cavity <NUM> and is used to rotate the switching core <NUM> inside the base <NUM>. The magnetic mount <NUM> includes a hole <NUM> which engages with a collar <NUM> on the barrel <NUM>. The magnetic mount <NUM> is attached to the barrel, so that the barrel <NUM> remains stationary with respect to the magnetic mount <NUM> and the base <NUM>. The magnetic mount <NUM> also includes holes <NUM> which are used to attach the torsion bars <NUM> (see <FIG>).

In <FIG>, the rotator shaft <NUM> extends the entire way through the switching core <NUM>, through a hole <NUM> in the magnetic mount <NUM>, and into the instrument mount <NUM>. There is a slight clearance between the rotator shaft <NUM> and the hole <NUM>, so that the rotator shaft <NUM> can rotate inside the hole <NUM>. The instrument mount <NUM> is fixed to the rotator shaft <NUM>, for example using a worm screw. Thus, the rotator shaft <NUM> can be used to rotate both the switching core <NUM> and the instrument mount <NUM>. The instrument mount <NUM> is used to connect an instrument and to transfer rotation of the rotator shaft <NUM> though the instrument <NUM> to the lower magnet assembly <NUM>.

<FIG> is a cross-section through the upper magnet assembly and the coupling assembly in the assembled state. Referring to <FIG>, the rotator shaft <NUM> extends from the coupling assembly <NUM>, through the switching core <NUM> to the instrument mount <NUM>. The rotator shaft is connected to the switching core and instrument mount, so that rotation of the rotation shaft causes the switching core and the instrument mount to rotate. The instrument mount <NUM> is arranged to connect to an instrument, for example, using a threaded connection.

<FIG> shows parts of the lower magnet assembly in more detail. Referring to <FIG>, the lower magnet assembly <NUM> comprises magnetic mount <NUM>, base <NUM>, switching core <NUM> and lower instrument mount <NUM>. The magnetic mount <NUM> is used to hold the base <NUM> in place. The base <NUM> and the switching core <NUM> together form a switchable magnet. The magnetic mount <NUM>, base <NUM> and switching core <NUM> may be substantially the same as the corresponding components in the upper magnet assembly <NUM>, although it would also be possible for them to have different sizes, materials and/or constructions.

The lower instrument mount <NUM> is designed to be mounted to the bottom of the instrument <NUM>. Thus, rotation of the instrument <NUM> causes the lower instrument mount <NUM> to rotate. The lower instrument mount <NUM> includes a rotator shaft <NUM>. The rotator shaft <NUM> extends into a cavity in the switching core <NUM> and is used to rotate the switching core <NUM> inside the base <NUM>. The magnetic mount <NUM> includes a hole <NUM> which accommodates a collar <NUM> on the lower instrument mount <NUM>. There is a slight clearance between the hole <NUM> and the collar <NUM>, so that the collar <NUM> can rotate inside the hole <NUM>. The magnetic mount <NUM> also includes holes <NUM> which are used to attach the torsion bars <NUM>. This allows the magnetic mount <NUM> and base <NUM> to be held in place (relative to the upper magnet assembly) while the switching core <NUM> rotates.

The rotator shaft <NUM> extends the entire way through the switching core <NUM> and through a hole <NUM> in the magnetic mount <NUM>. There is a slight clearance between the rotator shaft <NUM> and the hole <NUM>, so that the rotator shaft <NUM> can rotate inside the hole <NUM>. A nut <NUM> is screwed to the bottom of the rotator shaft <NUM>, with a washer <NUM> provided between the nut <NUM> and the bottom of the magnetic mount <NUM>. The nut and washer allow the shaft <NUM> and switching core to rotate, while holding the assembly together.

<FIG> is a cross-section through the lower magnet assembly in the assembled state. Referring to <FIG>, The lower instrument mount <NUM> is arranged to connect to an instrument, for example, using a threaded connection. Rotation of the instrument transfers rotation to the rotator shaft <NUM>. The rotator shaft <NUM> extends through the switching core <NUM> and through the hole <NUM> to the nut <NUM>. The switching core <NUM> is connected to the rotator shaft <NUM>, so that rotation of the rotator shaft causes the switching core to rotate.

<FIG> is an exploded view of a coupling assembly in an embodiment of the invention. Referring to <FIG>, the coupling assembly <NUM> comprises setting nut <NUM>, washer <NUM>, rotator <NUM>, dogs <NUM>, barrel <NUM>, snap ring <NUM>, locator pins <NUM>, and rotator shaft <NUM>. The snap ring <NUM> fits into a circumferential groove <NUM> on the outside of the barrel <NUM>. The locator pins <NUM> fit into holes <NUM> on the outside of the barrel <NUM>.

The setting nut <NUM> comprises a head <NUM> and a shank <NUM>. The head <NUM> includes a socket <NUM> which is arranged to engage with the drive shaft <NUM> in the setting tool. In this example, the socket <NUM> is a hexagonal cavity and the drive shaft <NUM> is a hexagonal shaft, although it will be appreciated that other shapes may be used instead. Furthermore, if desired, the socket could be in the setting tool and the shaft on the gauge hanger.

The shank <NUM> passes through a hole in the centre of the washer <NUM>, and into a hole <NUM> in the rotator <NUM>. The shank <NUM> is attached (firmly screwed in) to the rotator <NUM>, so that rotation of the setting nut <NUM> causes rotation of the rotator <NUM>. The washer <NUM> is attached to the rotator <NUM> by two spring pins (not shown on <FIG>) and rotates together with the rotator <NUM> and the setting nut <NUM>.

The rotator <NUM> comprises a head <NUM> and a shank <NUM>. The shank <NUM> extends into a hole <NUM> which runs through the centre of the barrel <NUM>. There is a slight clearance between the shank <NUM> and the hole <NUM>, so that the shank <NUM> can rotate inside the hole <NUM>. The shank <NUM> is connected to the rotator shaft <NUM>, so that rotation of the rotator <NUM> causes rotation of the rotator shaft <NUM>.

The head <NUM> of the rotator <NUM> is in the form of a cam. The cam has two lobes orientated at <NUM>° to each other. The lobes of the cam <NUM> engage with the dogs <NUM>. The rotator <NUM> is rotatable between a position in which the lobes are at <NUM>° to the dogs <NUM> and a position in which the lobes face the dogs. Rotation of the lobes towards the dogs <NUM> causes the dogs to be pushed radially outwards. The dogs <NUM> include holes <NUM>. The holes <NUM> receive pins (not shown) which fit into slots <NUM> in the washer <NUM>. The slots <NUM> and pins are used to assist with the inward and outward radial movement of the dogs <NUM>, as will be explained below. The dogs <NUM> are arranged to engage with slots in the setting tool <NUM>.

<FIG> is a cross-section through the coupling assembly <NUM> in the assembled state. In the view shown in <FIG>, the lobes of the cam <NUM> are orientated perpendicular to the plane of the paper. Referring to <FIG>, the setting nut <NUM> is connected to the rotator <NUM>, and the rotator <NUM> is connected to the rotator shaft <NUM>. The washer <NUM> is also connected to the rotator <NUM>. The snap ring <NUM> is located in the groove <NUM> on the outside of the barrel <NUM>. The locator pins <NUM> are in the holes <NUM> on the outside of the barrel <NUM>. Rotation of the setting nut <NUM> causes rotation of the rotator <NUM>, washer <NUM> and rotator shaft <NUM> relative to the barrel <NUM>.

<FIG> shows the barrel <NUM> of the coupling assembly <NUM> in more detail. Referring to <FIG> and <FIG>, the barrel <NUM> includes two protrusions <NUM> which extend axially in the direction of the setting nut <NUM>. Each of the protrusions <NUM> has a straight edge on the inside of the barrel. The two edges face each other and run parallel to each other. Thus, the two edges define a slot <NUM> which runs radially through the barrel <NUM>. The radial slot <NUM> accommodates the dogs <NUM>.

Also visible in <FIG> is a lobe-shaped cavity <NUM> in the barrel <NUM> immediately inwards of the radial slot <NUM>. The cam <NUM> on the rotator <NUM> is located partially in the slot <NUM> and partially in the cavity <NUM>. The lobe-shaped cavity <NUM> is used to limit rotation of the cam <NUM> on the rotator <NUM>.

<FIG> shows one of the dogs in more detail. Referring to <FIG>, the inside edge of the dog <NUM> engages with a lobe of the cam <NUM>. The dog <NUM> acts as a cam follower, that is, it follows the profile of the cam lobe, moving inwards and outwards as the cam rotates. The dog <NUM> has flat sides <NUM> which allows it to slide radially inside the slot <NUM> in the barrel <NUM>. This prevents the dog from skewing. The inside edge of the dog matches the shape of the cam <NUM>, so that the dog <NUM> can be completely stowed when the lobe of the cam is at <NUM>° to the dog. When fully expanded, the tip of the lobe "locks" into a trough <NUM> on the inside of the dog to prevent the cam from slipping rotationally.

In the arrangement described above, the upper switching core <NUM> is fastened (for example, glued or pinned) to the rotator shaft <NUM> with the poles of the core orientated specifically relative to the rotator shaft <NUM> such that when the lobes of the cam <NUM> (and therefore rotator shaft) are rotated fully to their stop point where the engagement members (dogs <NUM>) are retracted, the magnet is fully energised. This may require the rotator shaft to firstly be firmly fixed to the rotator before fixing the core to the rotator shaft or some other means of achieving the correct alignment.

The lower rotator shaft <NUM> and switching core <NUM> can be fixed together in any orientation but the lower instrument mount <NUM> should be fixed to the instrument <NUM> such that the lower core <NUM> and the upper core <NUM> are exactly aligned so that they engage and disengage magnetically simultaneously. This may require shimming of the lower instrument mount to the instrument or some other means of achieving accurate rotational makeup of the two.

Referring back to <FIG>, it can be seen that the collar <NUM> of the setting tool <NUM> fits over the coupling assembly <NUM> in the gauge hanger. The collar <NUM> includes slots into which the dogs <NUM> can expand. This allows the setting tool <NUM> to hold the gauge hanger <NUM> as it is being deployed.

<FIG> shows the collar <NUM> of the setting tool in one embodiment. In this embodiment, the collar is a separate component which attaches to the bottom of the setting tool, although it would also be possible for the collar to be an integral part of the setting tool. Referring to <FIG>, the collar <NUM> is in the form of a hollow cylinder. Recesses <NUM> are provided on the outside of the collar which allow it to attach to the bottom of the setting tool. The inside diameter of the collar <NUM> is slightly larger than the outside diameter of the coupling assembly <NUM> in the gauge hanger. The collar <NUM> also has an internal taper to help it ride over the coupling assembly. In addition, the collar <NUM> has two V-shaped slots <NUM> on its sides. The V-shaped slots <NUM> open towards the coupling assembly <NUM>. The slots <NUM> engage with the locator pins <NUM> on the coupling assembly to assist with location of the collar on the coupling assembly.

The collar <NUM> includes two opposing slots <NUM>. Each slot <NUM> runs partially around the collar in a circumferential direction and forms an aperture through the collar <NUM> in a radial direction. The dimensions of the slots <NUM> are slightly larger than those of the dogs <NUM>. The slots are sized and located such that the dogs <NUM> can expand into them.

The collar <NUM> also includes two opposing grooves <NUM> on its inside surface. The grooves <NUM> are arranged to engage with the snap ring <NUM> on the coupling assembly <NUM>.

In this embodiment, a guide <NUM> is shown attached to the collar <NUM>. The guide <NUM> has an outside diameter which corresponds to the diameter of the tubing in which the gauge hanger is to be deployed. The guide <NUM> helps to ensure that the setting tool is correctly orientated in the tubing. The guide <NUM> is attached to the collar <NUM> using a bolt <NUM>. The guide <NUM> can be removed from the collar <NUM> and replaced with one of a different size. This can allow the setting tool to be used with tubulars of different diameters. Alternatively, when the gauge hanger is being set, it may be possible to dispense with the guide <NUM>.

When an instrument is to be deployed in the tubing of a wellbore, the gauge hanger and instrument are first assembled at the surface. This is achieved by connecting the top of the instrument <NUM> to the instrument mount <NUM> in the upper magnet assembly <NUM>, connecting the bottom of the instrument <NUM> to the instrument mount <NUM> in the lower magnet assembly <NUM>, and then connecting the torsion bars <NUM> between the upper and lower magnet assemblies <NUM>, <NUM>. If two or more instruments are to be deployed, then these may be connected in series between the upper and lower magnet assemblies <NUM>, <NUM>.

Prior to fitting the gauge hanger to the setting tool, the dogs <NUM> are withdrawn (if this is not already the case). This is achieved by rotating the rotator <NUM> such that the lobes of the cam <NUM> face away from the dogs <NUM>. The rotator <NUM> may be rotated, for example, using a wrench inserted into the hexagonal cavity <NUM> in the setting nut <NUM>, or by rotating the instrument <NUM>, or in any other way. This also ensures that the switchable magnets are deactivated.

The setting tool <NUM> is then attached to the gauge hanger <NUM>. With the dogs <NUM> withdrawn, the collar <NUM> of the setting tool can be slid over the coupling assembly <NUM>. This process is assisted by the internal taper on the collar <NUM>. The V-shaped slots <NUM> engage with the locator pins <NUM> to help ensure correct alignment between the setting tool and the coupling assembly. The snap ring <NUM> on the coupling assembly <NUM> engages with the grooves <NUM> on the inside surface of the collar <NUM>. This provides a secondary retaining mechanism to hold the setting tool in place on the gauge hanger while the dogs <NUM> are engaged.

When the setting tool <NUM> is attached to the gauge hanger <NUM>, the hexagonal drive shaft <NUM> in the setting tool fits into the hexagonal socket <NUM> in the setting nut <NUM> in the gauge hanger. This allows the motor <NUM> in the setting tool <NUM> to rotate the setting nut <NUM>, and hence the rotator <NUM>.

Once the collar <NUM> has been fitted to the coupling assembly <NUM>, the dogs <NUM> can be expanded into the slots <NUM> in the collar. The snap ring <NUM> and grooves <NUM> ensure that the dogs <NUM> are aligned with the slots <NUM> in an axial direction. Furthermore, the locator pins <NUM> and the V-shaped slots <NUM> ensure that the dogs <NUM> are rotationally aligned with the slots <NUM>.

The dogs <NUM> are expanded into the slots <NUM> by rotating the rotator <NUM> such that the lobes of the cam <NUM> face towards the dogs <NUM> and push them outwards. The rotator <NUM> may be rotated, for example, using the motor <NUM>, or in any other way. With the dogs <NUM> expanded into the slots <NUM> in the collar, the setting tool <NUM> is able to hold the gauge hanger <NUM> as it is being deployed in the tubing.

The magnetic force required to hold the gauge hanger against the tubing wall should only be generated at the desired setting depth. Thus, the upper magnet assembly <NUM> is arranged such that, when the dogs <NUM> are expanded (with the lobes of the cam facing towards the dogs), the switching core <NUM> is orientated with respect to the base <NUM> such that the external magnetic field is switched off. Likewise, the lower magnet assembly <NUM> is arranged such that, with the dogs <NUM> expanded, the switching core <NUM> is orientated with respect to the base <NUM> such that the external magnetic field is switched off. This can allow the deployment assembly (comprising setting tool and gauge hanger) to be lowered into the tubing without attaching to the tubing wall or other objects.

Once the setting tool <NUM> has been attached to the gauge hanger <NUM>, the deployment assembly is lowered into the tubing using the deployment wire <NUM>. The deployment wire <NUM> is connected to a surface hoist, which lowers the deployment assembly until it is at the required depth. Suitable surface hoists are known in the art and thus not described further. As the deployment assembly is being lowered into the tubing, the dogs <NUM> are held in the expanded position by the cam <NUM>. This ensures that the setting tool remains attached to the gauge hanger as it is being lowered.

Once the deployment assembly has reached the desired depth, the switchable magnets in the upper magnet assembly <NUM> and the lower magnet assembly are activated. This is achieved using the motor <NUM> in the setting tool <NUM>. The motor <NUM> rotates the drive shaft <NUM>, and hence the setting nut <NUM>, rotator <NUM> and rotator shaft <NUM> in the coupling assembly <NUM> and the switching core <NUM> in the upper magnet assembly <NUM>. Rotation of the switching core <NUM> relative to the base <NUM> activates the external magnetic field, causing the upper magnet assembly <NUM> to attach to the wall of the tubing. At the same time, the switching core <NUM> in the lower magnet assembly <NUM> is rotated respect to the base <NUM> via rotation of the instrument <NUM>. Rotation of the switching core <NUM> relative to the base <NUM> activates the external magnetic field, causing the lower magnet assembly <NUM> to attach to the wall of the tubing.

Operation of the motor <NUM> is controlled by the control unit <NUM> using signals received by the communications module <NUM> from a surface operator. This can allow the surface operator to deploy the gauge hanger at the required depth. Alternatively, the communications module may be dispensed with, and the setting tool <NUM> may be arranged to deploy the gauge hanger <NUM> after a certain time delay or in response to certain measurements such as depth measurements.

As the switching cores <NUM>, <NUM> in the upper and lower magnet assemblies <NUM>, <NUM> are rotated, the rotator <NUM> and the washer <NUM> also rotate. As the rotator <NUM> and the washer <NUM> rotate, they start drawing the dogs <NUM> inwards. The coupling assembly is arranged such that the dogs <NUM> remain engaged with the slots <NUM> in the collar <NUM> until sufficient magnetic force has been generated to reliably attach the gauge hanger to the tubing wall. Further rotation of the rotator <NUM> and the washer <NUM> draws the dogs <NUM> out of the slots <NUM>, releasing the setting tool from the gauge hanger.

<FIG> illustrate operation of the coupling assembly as the magnets are activated. In <FIG>, a top view of the coupling assembly is shown, with the washer <NUM> partially cut away.

<FIG> shows the coupling assembly when the gauge hanger is in the rest state prior to activation of the switchable magnets. In this state, the switching cores <NUM>, <NUM> are oriented relative to their respective bases <NUM>, <NUM> such that no external magnetic field is produced. At the same time, the lobes of the cam <NUM> are orientated towards the dogs <NUM>, forcing them outwards. In this state, the width of the gauge hanger between the outer edges of the two dogs <NUM> is W<NUM>. This width is wider than the internal diameter of the collar <NUM>, ensuring that the dogs <NUM> remain in the slots <NUM>.

Also shown in <FIG> are pins <NUM>. The pins <NUM> are fitted into the holes <NUM> in the dogs <NUM> and extend into the slots <NUM> in the washer <NUM>. The slots <NUM> run in a generally circumferential direction and are orientated such that one end of the slot is radially outwards of the other (with respect to the axis of rotation). The washer <NUM> is attached to the rotator <NUM> using screws <NUM>, so that the washer rotates together with the cam <NUM>. In the state shown in <FIG>, the dogs <NUM> are in the extended position, and the pins <NUM> are at the radially outwards ends of the slots <NUM>. In this state, the distance between the two pins is D<NUM>.

<FIG> shows the coupling assembly when the shaft has been rotated through <NUM>° relative to the rest state shown in <FIG>. In the state shown in <FIG>, the switching cores <NUM>, <NUM> have been rotated through <NUM>° relative to their respective bases <NUM>, <NUM>. In this position, a significant proportion of the total available external magnetic field is already produced. Thus, in this position, the upper and lower magnetic assemblies produce sufficient external magnetic field to attach themselves to the tubing wall.

In <FIG>, the washer <NUM> has been rotated such that the pins <NUM> are midway between the two ends of the slots <NUM>. At this point, each pin <NUM> is in a part of the slot <NUM> which is radially inwards with respect to the rest state shown in <FIG>. Thus, rotation of the washer <NUM> pulls the pins <NUM> and thus dogs <NUM> radially inwards.

In the <NUM>° state shown in <FIG>, the distance between the two pins is D<NUM> where D<NUM> < D<NUM>. Furthermore, the cam <NUM> has been rotated such that its lobes are orientated at <NUM>° to the dogs <NUM>. This allows the dogs <NUM> to be partially drawn into the coupling assembly. The width between the outer edges of the two dogs <NUM> is W<NUM>, where W<NUM> < W<NUM>. In this example, the width W<NUM> is approximately equal to the internal diameter of the collar <NUM>. Thus, in this position, the dogs <NUM> are at the point of being withdrawn from the slots <NUM> in the setting tool.

<FIG> shows the coupling assembly when the gauge hanger is in the engaged state with the external magnetic fields activated. In this state, the switching cores <NUM>, <NUM> have been rotated through <NUM>° relative to their respective bases <NUM>, <NUM>. The total available external magnetic field is produced, ensuring that the gauge hanger remains attached to the tubing wall.

In the state shown in <FIG>, the washer <NUM> has been rotated such that the pins <NUM> are at the radially inwards ends of the slots <NUM>. Thus, rotation of the washer <NUM> pulls the pins <NUM> and thus dogs <NUM> radially inwards. The distance between the two pins is D<NUM> where D<NUM> < D<NUM>. Furthermore, the cam <NUM> has been rotated such that its lobes are orientated at <NUM>° to the dogs <NUM>. This allows the dogs <NUM> to be completely drawn into the coupling assembly.

In the <NUM>° position shown in <FIG>, the width between the outer edges of the two dogs <NUM> is W<NUM>, where W<NUM> < W<NUM>. The width W<NUM> is less than the internal diameter of the collar <NUM>. Thus, in this position, the dogs <NUM> are completely withdrawn from the slots <NUM>. Thus, in this position, the setting tool <NUM> can be disengaged from the gauge hanger <NUM>.

The coupling assembly is arranged such that sufficient magnetic force to attach the gauge hanger to the tubing wall is produced before the setting tool is released from the gauge hanger. For example, in one exemplary embodiment it has been found that <NUM>% of the magnetic holding force is developed when the switching core is rotated <NUM>° from the "off" position. In this embodiment, the coupling assembly is designed to remain functionally engaged with the setting tool until at least <NUM>° of rotation to ensure the setting tool cannot be disengaged before the magnets are set. Of course, it will be appreciated that these values are given by way of example only, and different values may be used as appropriate. For example, the shape and/or orientation of the cam <NUM> and the slots <NUM> may be varied in order to vary the point at which the dogs are withdrawn from the slots <NUM> in the setting tool.

As mentioned above, the cam <NUM> extends partially into a lobe shaped cavity <NUM> immediately inwards of the radial slot <NUM> in the barrel <NUM>. The lobe shaped cavity <NUM> provides a positive stopping mechanism, so that rotation of the cam <NUM> is limited to <NUM>°. This prevents over rotation of the rotating components, ensuring that the switchable magnets remain fully activated and the dogs remain fully withdrawn. Thus, in this embodiment the cam is used both to actuate the dogs and to provide a stopping mechanism.

When the dogs <NUM> have been withdrawn from the slots <NUM>, the snap ring <NUM> and grooves <NUM> provide a secondary retention mechanism, holding the setting tool in place on the gauge hanger. A light upwards jarring action on the deployment wire <NUM> disengages the snap ring and separates the setting tool from the gauge hanger. Once the setting tool has been disengaged from the gauge hanger, it can be drawn upwards out of the wellbore using the deployment wire <NUM>.

It will be appreciated from the above that the action of rotating the switching cores in the magnet assemblies in order to engage the switching magnets also draws in the dogs from the slots in the setting tool. Thus, the same action which is used engage the magnets is also used to disengage the setting tool from the gauge hanger. This allows a single actuator (the motor <NUM>) to be used to perform both tasks simultaneously and ensures that the setting tool can only be disengaged from the gauge hanger when the magnets are set.

When it is desired to retrieve the gauge hanger from the wellbore, a retrieval tool is lowered into the tubing and attached to the gauge hanger. The retrieval tool is used to deactivate the magnetic force holding the gauge hanger to the tubing wall, and to lift the gauge hanger to the surface.

In a preferred embodiment, the setting tool described above is also used as a retrieval tool to retrieve the gauge hanger. The retrieval tool is lowered into the tubing using a deployment wire <NUM> (such as a slickline) connected to a surface hoist.

When the gauge hanger is in the wellbore, it will be lying against the side of the tubing in an unknown orientation. The retrieval tool therefore needs to be correctly orientated over the gauge hanger in order to engage with it. This is achieved using a collar and guide attached to the bottom of the retrieval tool. In one embodiment, the collar and guide are in the form shown in <FIG>.

Referring back to <FIG>, the guide <NUM> is an elliptical hoop structure and is fixed to the collar <NUM> at an angle of <NUM>° to the vertical axis. The outside diameter of the guide <NUM> corresponds to the diameter of the tubing in which the gauge hanger is deployed. The collar has a smaller diameter than the guide, and is located off-centre of the guide. The guide <NUM> ensures that, as the retrieval tool is being run into the tubing, it is located adjacent to the tubing wall. Once the retrieval tool encounters the gauge hanger, the guide <NUM> slides past the top of the coupling assembly <NUM>. Downward movement of the guide past the coupling assembly rotates the retrieval tool in the tubing until it is aligned with the coupling assembly. The collar <NUM> then slides over the coupling assembly <NUM>. The collar <NUM> has an internal taper to help it ride over the coupling assembly. The two V-shaped slots <NUM> on the collar <NUM> ride over the locating pins <NUM>. This ensures that the dogs <NUM> are aligned with the slots <NUM> rotationally and axially.

To engage the snap ring <NUM> with the grooves <NUM>, some downwards force is required. The retrieval tool is therefore provided with sufficient weight to snap the ring into place as the collar <NUM> slides over the coupling assembly <NUM>.

In addition to mating the snap ring <NUM> and locating pins <NUM>, the hexagonal shaft <NUM> from the retrieval tool must also seat inside the hexagonal socket <NUM> on top of the coupling assembly. Gentle up and down movement of the retrieval tool (via the slickline) may be required to assist the process of mating the snap ring, locator pins and hexagonal shaft. Alternatively, the retrieval tool could be provided with vibration producing means which cause the tool to vibrate once contact was made, which would assist in mating the three elements. The vibration may be produced, for example, by the motor <NUM> or using a separate vibrator.

Once the retrieval tool is seated on the gauge hanger, the motor <NUM> is used to rotate the drive shaft <NUM>, and hence the setting nut <NUM>, washer <NUM>, rotator <NUM> and rotator shaft <NUM> in the coupling assembly <NUM> and the switching cores <NUM>, <NUM> in the upper and lower magnet assemblies <NUM>, <NUM>. The rotation is in the opposite direction to that which was used to activate the magnets and disengage the dogs from the slots during the setting process. Operation of the motor <NUM> is controlled by the control unit <NUM> using signals received by the communications module <NUM> from a surface operator. Alternatively, the retrieval tool may be arranged to rotate the motor after a certain time delay or in response to a measurement signal.

As the washer <NUM> and the rotator <NUM> rotate, the lobes on the cam <NUM> rotate towards the dogs <NUM>, pushing the dogs outwards into the slots <NUM> in the collar <NUM>. This process is the reverse of that described above with reference to <FIG>. At the same time, the switching cores <NUM>, <NUM> in the upper and lower magnet assemblies <NUM>, <NUM> are rotated. This begins the process of deactivating the switchable magnets. However, the magnet assemblies <NUM>, <NUM> are arranged such that sufficient magnetic force to attach the gauge hanger to the tubing wall is still produced at least until the dogs <NUM> have reliably engaged with the slots <NUM>. This ensures that the magnets do not disengage before the retrieval tool is attached to the gauge hanger. Further rotation of the switching cores <NUM>, <NUM> then deactivates the switchable magnets, releasing the gauge hanger from the tubing wall. The lobe shaped cavity <NUM> in the barrel <NUM> provides a positive stopping mechanism, so that rotation of the cam <NUM> is limited to <NUM>° (i.e., at the rest position shown in <FIG>). This prevents over rotation of the rotating components, ensuring that the switchable magnets remain deactivated, and the dogs fully expanded.

When the gauge hanger is released from the tubing wall, the weight of the gauge hanger is taken by the retrieval tool and the slickline. At this point, the weight of the gauge hanger is noticeable on a weight indicator on the slickline. This provides an indication to the operator that the retrieval tool is connected to the gauge hanger and the gauge hanger is disengaged from the tubing wall. The retrieval tool and gauge hanger can then be lifted to the surface using the slickline.

It will be appreciated from the above that the action of rotating the cam to expand the dogs into the slots also rotates the switching cores in the magnet assemblies. However, the mechanism is arranged such that the switchable magnets are not deactivated until the dogs are engaged with the slots. Thus, the same action which is used secure the retrieval tool to the gauge hanger is also used to deactivate the magnets, disengaging the gauge hanger from the tubing wall. This allows a single actuator (the motor <NUM>) to be used to perform both tasks simultaneously and ensures that the gauge hanger is only disengaged from the tubing wall once the retrieval tool is attached.

When retrieving a gauge hanger that has been in a well for some time, some close-fitting parts may have become encrusted with scales and contaminants. In this case, some force may be required to rotate the magnetic cores and to push the dogs out through the slots in the retrieving tool.

In some embodiments, a hammering rotating mechanism is provided in the retrieval tool to overcome "stiction" in the rotating components. This may be in the form of an impact driver driven by an electro-mechanical device. In this case, the driver will hammer for several cycles in the clockwise direction (when viewed from above as in <FIG>) and then stop in that position with the cam firmly rotated to a stop in the internal lobe with the dogs pushed out in the retrieval tool slots.

Claim 1:
A gauge hanger (<NUM>) for deployment in a wellbore using a setting tool (<NUM>), the gauge hanger comprising:
a switchable magnet (<NUM>, <NUM>) for attaching the gauge hanger to a wellbore wall; and
a coupling assembly (<NUM>) for coupling the gauge hanger to the setting tool;
wherein the switchable magnet (<NUM>, <NUM>) and the coupling assembly (<NUM>) are arranged to be actuated by a common actuator (<NUM>).