WO2021053341A1

WO2021053341A1 - Sensor apparatus

Info

Publication number: WO2021053341A1
Application number: PCT/GB2020/052258
Authority: WO
Inventors: Lawrence Mcallister; Andrew Fraser; Jack Willis; Christopher Wells
Original assignee: Accsensum Ltd.
Priority date: 2019-09-19
Filing date: 2020-09-17
Publication date: 2021-03-25
Also published as: GB201913537D0; GB2588370B; GB2588370A

Abstract

Sensor apparatus for locating at a downhole position in a well. The sensor apparatus has an electronics module (2) and a battery (5) provided in a housing (1), the electronics module (2) including: a logging memory; and an electrical contact (3) for contact with the battery (5) when the sensor apparatus is located at the downhole position in the well. The sensor apparatus has one or more sensors configured to generate sensor data. When the battery (5) is provided in the housing, a first electrical circuit is formed including the battery (5), the electrical contact (3) and the logging memory. When the electronics module (2) is powered by the battery (5) via the electrical contact (3), it is configured to store the sensor data in the logging memory. The electronics module (2) is electrically connected to an interrogation device to output the sensor data stored in the logging memory to the interrogation device.

Description

SENSOR APPARATUS

[0001] This invention relates to a downhole tool, in particular a downhole logging tool, for example for logging temperature.

BACKGROUND

[0002] Downhole tools are used for performing desired functions in a well. In some examples, the downhole tools include one or more sensors for monitoring environmental conditions in the well. Among the environmental conditions to be monitored is temperature. Previously, many downhole tools measured temperature using a mercury thermometer, provided as a thermometer module in a downhole tool. A maximum and minimum temperature reading on the mercury thermometer was typically only readable when the downhole tool containing the thermometer was raised up to the surface. Typically, the mercury thermometer was previously provided in a recess defined in an outer surface of the downhole tool, and was not configured to be provided with any power connector to receive power from the downhole tool (because a mercury thermometer did not typically require power to function).

[0003] The use of mercury is now restricted or even completely prohibited in some countries.

[0004] It is in this context that the present invention has been devised.

BRIEF SUMMARY OF THE DISCLOSURE

[0005] In accordance with an aspect of the present disclosure there is provided a sensor apparatus for locating downhole, such as at a downhole position in a well. The sensor apparatus comprises a housing for having a battery provided therein, an electronics module provided in the housing, and one or more sensors configured to generate sensor data. The electronics module comprises a logging memory, and an electrical contact for contact with the battery when the sensor apparatus is located at the downhole position in the well. When the battery is provided in the housing, a first electrical circuit is formed including the battery, the electrical contact and the logging memory. The electronics module, when powered by the battery via the electrical contact, is configured to store the sensor data in the logging memory. The electronics module, when electrically connected to an interrogation device, is configured to output the sensor data stored in the logging memory to the interrogation device. To connect the interrogation device to the electronics module, the first electrical circuit is to be broken and reformed into a second electrical circuit including the interrogation device, the electrical contact and the logging memory.

[0006] Thus, the sensor apparatus can be made particularly compact because one or more of the components forming the first electrical circuit can be re-used in the second electrical circuit, rather than needing a completely new circuit for extraction of the data as for powering the sensor apparatus. A compact sensor apparatus is particularly useful in a space-constrained environment downhole in a well. Furthermore, the present disclosure is particularly suited to a retrofit application, where the sensor apparatus is for fitting into a pre-existing opening provided in a downhole tool, and previously having provided therein an obsolete sensor, such as a mercury thermometer (sometimes referred to as an analogue thermometer).

[0007] It will be understood that in some embodiments, the logging memory may be configured to be connected to a further battery if necessary to ensure the data stored therein remains stored, even after the first electrical circuit is broken. In some embodiments, one or more components forming part of the first electrical circuit can be removed to break the first electrical circuit. The one or more components to be removed may include the battery.

[0008] It will be understood that the electronics module is substantially any single component or collection of components of the sensor apparatus that provides the features and described functionality of the electronics module.

[0009] It will be understood that the downhole position can be considered to be substantially any position in the well, typically a position away from the surface.

[0010] It will be understood that in some embodiments, the circuit need not be broken to extract the data to the interrogation device from the logging memory.

[0011] In some examples, the interrogation device may be electrically connected to the electronics module by contact between the interrogation device and the electrical contact.

[0012] Viewed from another aspect, the present disclosure provides a sensor apparatus for locating at a downhole position in a well. The sensor apparatus comprises a housing for having a battery provided therein, an electronics module provided in the housing, and one or more sensors configured to generate sensor data. The electronics module comprises a logging memory and an electrical contact for contact with the battery when the sensor apparatus is located at the downhole position in the well. The electronics module, when powered by the battery via the electrical contact, is configured to store the sensor data in the logging memory. The electronics module, when electrically connected to an interrogation device via the electrical contact, is configured to output the sensor data stored in the logging memory to the interrogation device via the electrical contact.

[0013] Thus, the same electrical contact as used for supplying power to the electronics module from the battery (when present) can also be used to provide an electrical connection between the logging memory of the electronics module and the interrogation unit. In some examples, the battery may be a removable battery. Access to the electrical contact by the interrogation device may only be possible after removal of the removable battery.

[0014] The electrical contact may comprise a first portion for contacting the battery and a second portion for contacting the interrogation device. The second portion of the electrical contact may be substantially inaccessible to the interrogation device whilst the battery is in the housing and in contact with the first portion of the electrical contact.

[0015] In other words, the sensor apparatus may be configured such that a portion of the electronics module for contacting the battery is provided at the same end of the electronics module as the same or a further portion of the electronics module for contacting the interrogation unit.

[0016] The second electrical circuit may be configured to be formed only when the battery is removed from the housing.

[0017] The housing may define a first end having the electronics module provided thereat and a second end, opposite the first end, and through which a portion of the interrogation device can be inserted for connection to the electronics module. The housing may be configured to allow insertion of the battery through the second end.

[0018] The second end may be openable to permit access into the housing. The sensor apparatus may further comprise a closure member for closing the housing at the second end when the battery is provided in the housing. The first electrical circuit may further include the closure member. The housing may be enclosed at the first end and between the first end and the second end. Thus, the housing may be substantially sealed by closure of the housing at the second end using the closure member. Therefore, an internal space of the housing, including the electronics module, can be environmentally sealed from an outer environment of the housing when the housing is closed. In some examples, the closure member includes a seal.

[0019] The second electrical circuit may not include the closure member. In other words, of the first electrical circuit and the second electrical circuit, the closure member may only be included in the first electrical circuit.

[0020] The sensor apparatus may further comprise a resiliently deformable member configured to urge the battery against the electrical contact in the first electrical circuit. Thus, an electrical conduction between the battery and the electrical contact can be resistant to any mechanical shocks experienced by the sensor apparatus, thereby reducing the likelihood that the electronics module will lose power as a result of movements of the sensor apparatus, such as mechanical shocks. The resiliently deformable member may be a spring. The resiliently deformable member may be conductive to form part of the first electrical circuit. In some examples, the resiliently deformable member may be configured to be in direct contact with the battery. The resiliently deformable member may be provided between the battery and the closure member. The resiliently deformable member may be provided between the battery and the electronics module. In some examples, the resiliently deformable member may be provided between the electronics module and the housing. The resilient member may form the contact on the electronics module.

[0021] The sensor apparatus may be configured such that the portion of the interrogation device is to be inserted through the second end of the housing to connect the interrogation device to the electronics module via contact with the electrical contact. In other words, the portion of the interrogation device is sufficiently long and sufficiently thin so as to pass through the opening at the second end to be closed by the closure member and to contact the electrical contact. It will be understood that to facilitate this, the electrical contact must be accessible by the interrogation device from the second end of the housing.

[0022] The electrical contact may be arranged to be recessed in the electronics module. Thus, only a protruding contact on the battery and/or the interrogation device can be capable of making contacting the electrical contact. Advantageously, this makes it difficult for the electronics module to be damaged by insertion of the battery in an incorrect orientation.

[0023] The first electrical circuit and the second electrical circuit may each include at least a portion of the housing. Typically, the first electrical circuit and the second electrical circuit each include substantially the same portion of the housing. Thus, the portion of the housing forming part of the first electrical circuit can be re-used to form the second electrical circuit, reducing if not removing the need for additional components to be provided in the sensor apparatus only for use in the second electrical circuit.

[0024] The one or more sensors may include a temperature sensor to generate temperature data indicative of a plurality of temperature readings when the sensor apparatus is located at the downhole position. Thus, the mercury thermometer of the prior art can be replaced by a digital thermometer.

[0025] The one or more sensors may include an accelerometer. The one or more sensors may include a magnetic sensor. The one or more sensors may include a gyroscope sensor. The one or more sensors may include a radiation sensor. The one or more sensors may include an acoustic sensor. The one or more sensors may include a pressure sensor. [0026] At least one of the one or more sensors may be provided in the housing. Thus, the one or more sensors can be protected from an external environment of the sensor apparatus.

[0027] At least one of the one or more sensors may be provided outside the housing. Thus, a sensor provided outside the housing can obtain more accurate and/or direct measurements of environmental characteristics of the sensor apparatus. The at least one sensor provided outside the housing may be in data communication with the logging memory via a physical electrical connection. In other words, the physical electrical connection requires that data communication signals between the sensor provided outside the housing and the logging memory may be solely via a physical medium of the sensor apparatus, such as through wires and/or through one or more conductive portions of the housing. In some examples, the at least one sensor provided outside the housing may be at an end of the housing away from the second end, such as at the first end. In this way, the provision of a sensor outside the housing need not block access to the housing for insertion or removal of the battery and/or for access by the interrogation device to the electrical contact. In some examples, the one or more sensors may all be provided substantially away from the second end of the housing. Thus, of the one or more sensors and the electrical contact, only the electrical contact is provided at the second end of the housing, ensuring that the sensor apparatus can be sufficiently thin to fit into a relatively thin opening, such as that used for the provision of an analogue thermometer in a downhole tool.

[0028] The housing may be arranged to receive an AAA battery as the battery. In particular, the housing may be arranged to receive any battery having a diameter substantially identical to a standard diameter of an AAA battery as the battery. Thus, the housing can be relatively compact. An AAA battery typically provides sufficient energy storage for powering the one or more sensors for a suitable duration. The power consumption of the electronics module can be limited to provide a relatively long duration of battery life. Advantageously, the power consumption of the electronics module will be low enough (less than 2mW) to permit at least 45 days continuous operation from a single AAA lithium Cell. The housing may be sized so as to be slightly larger than the size of the AAA battery. The housing may be sized so as to be receivable into a recess in a legacy downhole tool, the recess previously intended to receive a mercury thermometer. Specifically, the housing may have a length of less than 16 centimetres. The housing may have a length of less than 13cm. The housing may have an outer extent, such as a diameter, of less than 2 centimetres. The housing may have an outer extent, such as a diameter, of less than 13mm. [0029] The electronics module may further comprise a supply reservoir capacitor configured to store sufficient charge to maintain power in a microprocessor of the electronics module during brief disconnection between the battery and the electrical contact. Thus, when the sensor apparatus is being deployed downhole, and brief disconnection between the battery and the electrical contact occur due to sudden movement of the sensor apparatus (such as shocks cause by knocks against a wall of the well or similar), the power can be maintained in the electronics module by the energy reserve stored in the supply reservoir capacitor.

[0030] The electronics module may be configured to determine a data communication message from the interrogation device in dependence on a voltage of a signal from the interrogation device to the sensor apparatus. In one example, the voltage of the signal from the interrogation device can be modulated to encode a data communication message. The electronics module may be configured to determine the data communication message based on a determination of a modulation of the voltage of the signal from the interrogation device. Thus, messages can be encoded relatively simply.

[0031] The electronics module may be configured to encode a data communication message from the electronics module to the interrogation device by modulating the current drawn from the interrogation device by the electronics module. Thus, the current drawn by the electronics module can be modulated to encode a data communication message. The electronics module may be configured to modulate a current drawn from the interrogation device in dependence on an intended communication message. Thus, messages can be encoded relatively simply. Furthermore, it will be understood that modulation of the current drawn by the electronics module can be achieved using a relatively simple electrical circuit, such as using an NPN transistor and a current setting emitter resistor, thereby ensuring a compact and simple arrangement of electronics in the electronics module.

[0032] The electronics module may be selectively retained in the housing. The apparatus may further comprise a resiliently deformable retention member for retaining the electronics module within the housing. Thus, the electronics module can be held in place in the housing. The retention member may be electrically conductive and may form part of the first electrical circuit and the second electrical circuit. The retention member may be arranged to electrically connect the electronics module to the housing by a route not including the electrical contact. The electronics module can be slidably moveable out of the housing by overcoming a resilient bias of the retention member. Thus, the electronics module can be removed from the housing for replacement/maintenance as necessary. The electronics module may be provided with a fastener portion for engagement with a portion of a removal tool for removing the electronics module from the housing. [0033] The sensor apparatus may further comprise an electrical magnetic field generator provided at the housing to generate a magnetic field detectable outside the housing. It will be understood that the electrical magnetic field generator may be present even in examples of the sensor apparatus not powered by a battery, but instead by some other power source. It will also be understood that an electrical magnetic field generator is substantially any electrical component arranged to generate a magnetic field detectable outside the housing in dependence on electrical power being applied to the electrical component. The magnetic field detectable outside the housing may have a peak strength of at least 2 x 10⁵ tesla at the housing. In other words, the magnetic field detectable outside the housing, measured at the housing, may be at least as large as the Earth’s own magnetic field, measured substantially at the surface.

[0034] The magnetic field generated by the electrical magnetic field generator may be a varying magnetic field. The magnetic field generated by the electrical magnetic field generator may be an alternating magnetic field. Thus, the magnetic field can induce an alternating current in a wire.

[0035] The sensor apparatus may further comprise a magnetic field detector to be positioned outside the housing and configured to be responsive to the magnetic field generated by the electrical magnetic field generator. Thus, the magnetic field detector can be used to indicate that the electronics module is operational, by detecting the magnetic field. Advantageously, no visual or audible signal is required from the housing, allowing for the housing to be substantially completely sealed from an external environment, and need not include openings and/or non-opaque regions for permitting sound and/or light to escape the housing.

[0036] The magnetic field detector may be a passive magnetic sensor, directly responsive to the magnetic field. The passive magnetic sensor may be a compass. In some examples, the passive magnetic sensor may be responsive to a constant magnetic field. In some embodiments, the magnetic field detector may be an electronic component, for example a gauss meter.

[0037] The magnetic field detector may comprise a third electrical circuit into which an electric current can be induced by the magnetic field. The third electrical circuit may include an electrical component configured to generate a notification signal when the current is induced therethrough. It will be understood that the inducement of a current requires that the magnetic field is an alternating magnetic field. The notification signal may be any one or a combination of light, sound and wireless transmission.

[0038] The sensor apparatus may further comprise the interrogation device. [0039] The interrogation device may comprise: a first contact; and a second contact. When the interrogation device is to be electrically connected to the electronics module, the first contact may be configured to electrically connect to the electronics module via the electrical contact of the electronics module, and the second contact maybe configured to electrically connect to the housing. The first contact and the second contact may be included in the second electrical circuit. Thus, the interrogation device can become part of the second electrical circuit via the housing and the electrical contact of the electronics module.

[0040] The first contact may be resiliently biased outwardly from the end of the interrogation device. Thus, good electrical contact between the first contact of the interrogation device and the electrical contact of the electronics module can be provided. The first contact may define a contact point or contact serrations to further ensure good electrical contact between the first contact of the interrogation device and the electrical contact of the electronics module. The interrogation device may comprise a spring to resiliently bias the first contact outwardly from the end of the interrogation device.

[0041] Viewed from another aspect, the present disclosure provides a method of obtaining sensor data from a downhole position in a well. The method comprises: providing the sensor apparatus as described hereinbefore, including the battery to form the first electrical circuit; lowering the sensor apparatus into the well to the downhole position; after sensor data has been recorded, raising the sensor apparatus away from the downhole position; breaking the first electrical circuit; electrically connecting an interrogation device to the electronics module of the sensor apparatus to form the second electrical circuit; and receiving sensor data at the interrogation device from the logging memory of the electronics module.

[0042] Thus, the sensor apparatus can be used to obtain sensor data from a downhole position in a well.

[0043] Viewed from another aspect, the present disclosure provides an electronic temperature sensor apparatus for retrofitting into an analogue thermometer compartment of a downhole tool. The analogue thermometer compartment is for receiving therein an analogue thermometer for measuring a temperature of an environment of the downhole tool. The electronic temperature sensor apparatus comprises: a housing sized to fit into the analogue thermometer compartment; an electronics module provided in the housing, comprising a logging memory; and an electronic temperature sensor configured to generate temperature data. The electronics module is configured to store the temperature data in the logging memory. The electronics module, when electrically connected to an interrogation device, is configured to output the temperature data stored in the logging memory to the interrogation device.

[0044] Thus, the electronic temperature sensor apparatus is retrofitted into an existing compartment in a downhole tool, originally arranged for receiving an analogue thermometer therein. In other words, the electronic temperature sensor apparatus can be provided in the space originally intended for the mercury thermometer, thereby extending the life of many existing downhole tools. Furthermore, the electronic replacement for the thermometer is capable of logging many samples of temperature against time providing far more temperature information than the established mercury thermometer. As described herein, it may also be advantageous for the electronic temperature sensor apparatus to also log other parameters, for example pressure or acceleration.

[0045] It will be understood that the electronic temperature sensor apparatus may comprise substantially any of the features of the sensor apparatus described hereinbefore, and may be operated, and/or configured to be operated in substantially any of the ways described hereinbefore in relation to the sensor apparatus.

[0046] Viewed from another aspect, the present disclosure provides a method of retrofitting an electronic temperature sensor into an analogue thermometer compartment of a downhole tool. The analogue thermometer compartment is for receiving therein an analogue thermometer for measuring a temperature of an environment of the downhole tool. The method comprises: removing any analogue thermometer from the analogue thermometer compartment; and inserting the electronic temperature sensor as described hereinbefore into the thermometer compartment of the downhole tool.

[0047] It will be understood that the logging memory is advantageously a non-transitory computer readable storage medium. The non-transitory computer readable storage medium may be a non-volatile storage medium, such as FLASH, EEPROM or FRAM memory. In other examples, the non-transitory computer readable storage medium may include substantially any computer readable memory, including a volatile storage medium such as RAM.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 shows a section view of a sensor apparatus as described herein, in a data logging configuration;

Figure 2 shows a section view of the sensor apparatus of Figure 1 , in a data download configuration; Figure 3 shows a section view of a further example of a sensor apparatus as described herein, in a data logging configuration;

Figure 4 shows an exploded view of a sensor apparatus as described herein, in a data logging configuration, along with a summary of parts;

Figure 5 shows an exploded view of an electronics module of the sensor apparatus shown in Figure 4, along with a summary of parts;

Figure 6 shows an example of an interrogation device for the sensor apparatus as described herein;

Figure 7 shows an exploded view of the interrogation device shown in Figure 6; and

Figure 8 shows an extraction tool, also including an exploded view of the extraction tool for use with the sensor apparatus described herein.

DETAILED DESCRIPTION

[0049] Figure 1 shows a section view of a sensor apparatus as described herein, in a data logging configuration. In particular, the sensor apparatus comprises a housing 1 for containing at least some of the other components of the sensor apparatus, as described herein. The housing 1 can be located at, for example attached to, a downhole tool (not shown) and is used to log sensor data whilst the downhole tool is at a downhole location in a well. Typically, the housing 1 is to be installed in a cavity of the downhole tool, previously configured for housing an analogue thermometer (in particular a mercury thermometer) of the downhole tool. In this way, it can be seen that the sensor apparatus can be retrofitted into downhole tools originally configured to be provided with only a mercury thermometer in a separable thermometer module for logging a maximum (and potentially minimum) temperature when the downhole tool is provided in the downhole location in the well.

[0050] The housing 1 is configured, when sealed, to isolate components provided therein from an external environment of the sensor apparatus. In particular, the housing 1 can at least partially protect components provided therein from extremes of pressure and chemicals that may be experienced by the housing 1.

[0051] An electronics module 2 is provided within the housing 1. The electronics module 2 may contain various internal sensors. In particular, the electronics module 2 comprises an electronic temperature sensor (not shown) for measuring a temperature of the housing. It will be understood that the temperature of the housing 1 may be indicative of a temperature of an external environment of the sensor apparatus. In some examples, the electronic temperature sensor may be configured to be responsive to a temperature of an outer portion of the housing 1. As explained hereinbefore, provision of an electronic temperature sensor allows the use of mercury thermometers to be discontinued. Nevertheless, it will be understood that the sensor apparatus can alternatively or additionally comprise substantially any sensor that can operate within the module without external connection. The sensors may include accelerometers, giros, radiation (typically gamma) sensors, acoustic sensors, and magnetic sensors.

[0052] The electronics module 2 further comprises a logging memory (not shown) for storing sensor data output by one or more sensors of the electronics module 2. The logging memory is substantially any form of computer-readable and computer-writable memory, such as a non-transitory computer-readable storage medium, for example a non volatile computer-readable storage medium.

[0053] The electronics module 2 is also provided with an electrical contact 3 to contact with a first terminal 4 of a power supply 5, in the form of the button 4 of a battery 5 for powering the electronics module 2. As will be described further hereinafter, a second terminal of the power supply 5 (in particular the battery 5) is also connected to the electronics module 2 via a different route, such as via the housing 1.

[0054] An inside diameter of the housing 1 may be relatively small, typically only just sufficient to permit the use of a common AAA size battery 5 as the battery 5 to power the sensor apparatus. It will be understood that in such space-constrained environments, there is typically insufficient space to run a conductor or wire between the battery 5 and the housing 1 from the second terminal of the battery 5 to the electronics module 2. Therefore, as explained hereinbefore, the housing 1 is used as part of the electrical circuit. The electrical circuit including the electronics module 2 and the battery 5 is referred to herein as a first electrical circuit. The housing 1 is sealed by a closure member 8 in the form of a sealing cap 8. In this example, the sealing cap 8 seals an internal cavity of the housing 1 from an external environment using a sealing member, such as in the form of a resiliently deformable O-ring 7, provided in a corresponding seal groove defined in the sealing cap 8. It will be understood that substantially any form of known seal may be used to ensure the cavity of the housing 1 is isolated from the external environment of the sensor apparatus.

In the present example, the sealing cap 8 comprises a threaded portion for engaging with a threaded region on the internal surface of the housing 1 to retain the sealing cap 8 in position in the housing 1. Nevertheless, it will be understood that the sealing cap may be retained in position by substantially any means including being screwed or pinned to the housing 1, or perhaps by pressure exerted thereon by an external structure, such as the portion of the downhole tool in which the sensor apparatus is mounted. [0055] A resiliently deformable member 6 in the form a spring 6 is provided to bias the battery 5 against the electrical contact 3. In this example, the spring 6 is provided between the second terminal of the battery 5 and the sealing cap 8. Thus, when the sealing cap 8 is in place the spring 6, battery 5 and electronics module 2 are in compression between pressure cap 8 and an opposite end of the housing 1 , against which the electronics module 2 abuts. Whilst the spring 6 is shown in the preferred location between the pressure cap 8 and the battery 5, where it could be advantageously attached to the pressure cap for ease of replacement of the battery 5, it will be understood that the spring 6 could, in other examples, be fitted between the battery 5 and electronics module 2. In this alternative arrangement, the spring 6 would be advantageously attached to the electronics module 2 which could also aid easy replacement of the battery 5. Another alternative location for the spring would be between electronics module 2 and housing 1 , although this is typically less preferable as it requires the electronics module 2 to move and it may be advantageous that the electronics module 2 remain stationary in the housing 1.

[0056] The spring 6 is typically relatively strong, exerting sufficient force to resist the risk of shock (rapid deceleration of the tool when it hits something) momentarily interrupting the supply of power from the battery to the electronics module 2 of the sensor apparatus. In some embodiments, the spring 6 provides a compressive force in excess of 100 times the weight of the battery 5 and electronics module 2. In some examples, the arrangement can be turned 180 degrees such that the spring 6 is at the top pushing the battery 5 and electronics module 2 down. This is because, when running into the oil well, the main shock that would be experienced will tend to primarily accelerate the masses in the housing 1 downward. Advantageously, the electronics module 2 can further comprise a capacitor in the form of a supply reservoir capacitor, having a capacitance of greater than 20 pF to smooth out short power supply interruption resulting from impact shock. It will be understood that the exact capacitance of the capacitor may vary depending on the electrical power requirements of the electronics module 2.

[0057] When the housing 1 is sealed with the sealing cap 8, the button 4 at the end of the battery 5 is pressed against the electrical contact 3 at the end of the electronics module 2, ensuring an electrical connection between the button 4 of the battery 5 and the electronics module 2 via the electrical contact 3. As described hereinbefore, the electronics module 2 has a return connection (not shown) via the housing 1 which is electrically connected to the sealing cap 8 and thus to the second terminal of the battery (via the spring 6 in this example). Therefore, Figure 1 shows a complete first electrical circuit to power the electronics module 2 using energy from the battery 5. The electronics module 2 may be electrically connected to the housing 1 by substantially any suitable means, including using either a single connection or multiple connections between the electronics module 2 and the housing 1. In an example, electrical connection of the electronics module 2 to the housing 1 may be provided by the pressure of the electronics module 2 against the end of the housing 1 from the spring action of the spring 6. In other examples, the electrical connection may be provided by one or more spring contact pins, and/or a canted spring around the module, and/or being threaded into the housing by a conductive thread. Advantageous, in some examples, the same means that electrically connects the electronic module 2 to the housing 1 can also retain the electronics module 2 in the housing 1.

[0058] It will be understood that a canted spring is a spring capable of resilient deformation in a direction transverse to an axial direction of the spring (the direction around which the spring is coiled) and is arranged to be provided in a groove in a component for providing electrical contact and resisting movement between two components abutted against one another. The types, manufacture and uses of a canted spring are well known to the skilled person.

[0059] The contact 3 in this example is a round, substantially planar contact 3, and is recessed in an insulating shroud as shown by the shape of the electronics module 2 in Figure 1. The insulating shroud of the electronics module 2 is sized such that the contact button 4 on the end of the AAA battery 5 can still be pressed against the contact 3 making electrical connection without fouling the insulating shroud. Nevertheless, it will be understood that if the battery 5 were inserted the wrong way round, the substantially flat second terminal of the battery 5 would not make an electrical connection with the electrical contact 3, therefore providing protection against incorrect power supply polarity. It may be advantageous, for example given the limited space, and/or to minimise parts, if the shroud is integrally formed with and potentially part of a main body of the electronics module 2 so that it may provide an insulated chamber or recess for the individual electronic components (not shown) of the electronics module 2. Typically the shroud and main body of the logger module 2 is formed from plastics, or any other suitable insulative material.

The present inventors have found that polyether ether ketone (PEEK) is a suitable choice of material for high temperature operation. The surface of the electrical contact 3 that makes contact with the button 4 on the battery 5 may, in some examples, have one or more serrations provided thereon to assist in breaking through any surface contamination that may otherwise detract from good electrical connection between the battery 5 and the electrical contact 3 of the electronics module 2. [0060] It will be appreciated that the connection between the button 4 on the battery 5 and the electrical contact 3 typically only serves to press the electronics module 2 into the housing 1 and removal of the battery 5 does not typically provide any force sufficient to pull the electronics module 2 from the housing 1. This is advantageous here as the electronics module 2 can be retained in the housing 1 with minimal force allowing various forms of detent or clip method to be used to reliably retain the electronics module 2 in the housing 1, even when the battery 5 is being removed therefrom. Providing the electronics module 2 in the housing ensures both mechanical and electromagnetic protection of the electronics therein. Advantageously, one or more canted springs may be used to both retain the electronics module 2 in the housing 1 through friction and to provide electrical connection between the electronics module 2 and the housing via the conductive canted springs. In some examples, as described further hereinafter, the end of the electronics module 2 proximate to the electrical contact 3 may have defined therein a connector portion, for example in the form of a circumferential groove that would enable a special tool to be inserted to engage with said groove and allow the electronics module 2 to be pulled from the housing 1 for replacement or service.

[0061] When the sensor apparatus has been operational at the downhole location in the well for a desired time period, and has data stored in the logging memory of the electronics module 2, it is necessary to retrieve the sensor data stored in the logging memory. As will be appreciated, the limited space makes it difficult to put a connector on the electronics module 2 for the sole purpose of connecting to extract data stored in the logging memory whilst the battery 5 is still present in the housing 1. Therefore, the present inventors have realised that it is advantageous to re-use portions of the first electrical circuit that the battery 5 uses to connect power to the electronics module 2 to also provide both power and communications connection between an interrogation device (sometimes referred to as a download tool and shown in Figure 2) and the electronics module 2.

[0062] Figure 2 shows the use of an interrogation device comprising an outer body 11 that is typically large enough to offer any practical means of computer connection (ie standard USB connection) thereto (such as from a further device arranged to be in data communication with the interrogation device), a probe portion 10 that is inserted into the housing 1 to bring a probe contact 9 to the electrical contact 3 on the electronics module 2 still located inside the housing. The probe contact 9 is typically resiliently biased outwardly, for example by a spring as shown in Figure 2, to ensure good electrical contact between the probe contact 9 and the electrical contact 3 on the electronics module 2. Thus, the electrical contact 3 on the electronics module 2 can remain simple and compact. In particular, it will be understood that a simple form of the electrical contact 3 is typically preferred to a socket into which a pin would need to be inserted and which would disadvantageously increase the length of the contact 3 and consequently also increase the length of the electronics module 2 (and the sensor apparatus). Furthermore, it will be understood that a small socket would also require a small pin for engagement therewith, which could be particularly vulnerable to mechanical damage. In this example, there is a mechanical shroud 17 at the end of the probe portion 10 which provides some protection of the probe contact 9 which only needs a small travel and can be made moderately robust in its own right.

[0063] An advantage of using a contact held against the electrical contact 3 of the electronics module 2 in compression is that withdrawal of the interrogation device does not provide any significant force pulling the electronics module 2 from the housing 1. As with the contact between the battery 5 and the electronics module 2, this enables the electronics module 2 to be retained in the housing 1 with minimal force allowing various forms of detent or clip methods to be used to retain the electronics module 2 in position in the housing 1, as disclosed earlier in this document.

[0064] The probe contact 9 is typically a single contact, in this example in the form of a single electrically conductive pin, insulated from the probe portion 10, so that when pressed against the electrical contact 3 on the end of the electronics module 2 an electrical connection is established between the electronics module 2 and the interrogation device via the probe contact 9. The end of the probe contact 9 may be provided in the form of a point or may have one or more serrations thereon to assist in breaking through any surface contamination that may otherwise detract from making electrical connection between the probe contact 9 and the electrical contact 3 of the electronics module 2. Typically, it is just the probe contact 9 that is sprung as depicted in Fig 2, although a spring could be inserted in the probe portion 10 or between the probe body 11 and the probe portion 10.

[0065] To form an electrical circuit the interrogation device must also connect electrically to another portion of the electronics module 2, as with the battery 5. As with the battery 5, the interrogation device is configured to electrically connect also to the electronics module 2 via the housing 1. It will be understood that electrical connection between the interrogation device and the housing 1 can be accomplished in a variety of way, for example using one or more sprung contacts protruding from the interrogation device, such as from the probe portion 10 of the interrogation device, and engaging with the housing 1 , or perhaps a screw connection between the probe portion 10 and the housing 1, or a screw fastener. It will be understood that were a screw connection is used, the threads of the screw connection are to be formed form a conductive material to ensure an electrical connection can be provided therethrough. Preferably, one or more canted springs 16 are used on the probe portion 10 to provide electrical connection to the housing 1 via the canted springs 16. Advantageously, the friction force of these canted springs 16 would be chosen to substantially retain the interrogation device in the housing 1 of the sensor apparatus.

[0066] It will be understood that there exist alternative ways of retaining the interrogation device in the housing 1 other than friction from the canted springs 16. One possibility, though not a preferred option, involves reliance on an operator to hold the probe portion 10 of the interrogation device in the housing 1.

[0067] One or more elastomeric, for example resiliently deformable, O-rings may be used on the interrogation device to provide additional friction to hold the probe portion 10 of the interrogation device within the housing 1. The one or more O-rings may also serve to substantially seal the internal cavity of the housing 1 from an external environment, even when the sensor apparatus is raised up from the downhole position in the well. Thus, contaminants may be prevented from entering into the cavity in the housing 1.

[0068] In other examples where the interrogation device or a portion thereof is sufficiently large to stand on a surface with the probe portion 10 pointing upward, the user can simply place the sensor apparatus onto the probe portion 10 and gravity will hold it in place. The interrogation device then powers the electronics module 2 via the contact between the probe contact 9 and the electrical contact 3 of the electronics module 2, and also via the contact between the interrogation device and the electronics module 2 via the housing 1. The interrogation device can also communicate with the electronics module 2 over the same single electrical circuit, also referred to herein as a second electrical circuit. In particular, it will be understood that in order to form the second electrical circuit including the electrical contact 3 of the electronics module 2 and the interrogation device (and also the logging memory of the electronics module 2), the first electrical circuit is broken and components forming part of the first electrical circuit (such as the electrical contact 3) can be re-used in the second electrical circuit.

[0069] Any applicable means of providing bidirectional data communications over power may be used to provide communication between the interrogation device and the electronics module 2 of the sensor apparatus. However, the limited space and need for the parts used in the electronics module 2 to be robust favours a simple means especially in the electronics module 2. One particularly suitable approach is the use of a simple current and voltage modulation scheme. In this approach the interrogation device modulates the voltage provided to the electronics module 2 to send messages from the interrogation device to the electronics module 2. Similarly, the electronics module 2 modulates the current it draws from the interrogation device to send messages back to the interrogation device.

[0070] It will be understood that the interrogation device comprises electrical components for interfacing with the electronics module 2 of the sensor apparatus when the interrogation device is connected to the electronics module 2 of the sensor apparatus via the electrical contact 3. In one example, the interrogation device may include a standard computer connector, such as a USB connector to connect to a further device for receiving the sensor data from the logging member via the interrogation device. The USB connector may be used to supply power to the interrogation device from the further device as necessary. In another example, the interrogation device may include a wireless communication unit, such as a wireless transceiver, for example Bluetooth ® or any other suitable wireless communication technology, including via a cellular network or via Internet of Things (loT). Thus, the sensor data transferred from the logging memory to the interrogation device may be further transferred to a further device via the wireless communication unit. In the case of wireless data transfer from the interrogation device to a further device, it will be understood that the interrogation device may be provided with power in a number of ways, for example from a battery, or from a dedicated, wired power supply.

[0071] Another example of the sensor apparatus is shown in Figure 3, in which an external sensor 13 is also provided in data communication with the electronics module 2.

In particular, the external sensor 13 is mounted at an end of the housing 1 opposite the open end to be closed by the closure member 8. It will be understood that such an arrangement would not be possible in examples of the sensor apparatus where a connection to the electronics module 2 is to be provided even when the battery 5 remains in the housing 1 , via the end of the housing 1 opposite the end closed by the closure member 8. In other words, the provision of the external sensor 13 at the opposite end of the housing 1 is enabled by the dual use of electrical contact 3 both for connecting to the battery 5 and for power and communication exchange with the interrogation device. Of course, the connection to the electronics module 2 via the housing 1 should also be electrically connectable to both the battery 5 and the interrogation device. In particular, a connection 14 is provided at a distal end of the electronics module 2 to a proximal end of the electronics module 2 provided with the electrical contact 3 for connecting to the battery 5. The connection 14 is electrically connected to the external sensor 13 for providing power and communication exchange between the external sensor 13 and the electronics module 2. In some examples, the addition of the external sensor 13 requires further provision of a seal 15 at the housing 1 to substantially prevent ingress of external particles or contaminants from the external environment of the sensor apparatus within the housing 1. The seal 15 may be substantially any known sealing method, either temporary or permanent, which might include O-ring seals, various elastomeric sealing methods or, in some examples, a metal seal. In some examples, the external sensor 13 is welded to the housing 1.

[0072] The connection 14 between the external sensor 13 may be selectively disconnected, allowing the electronics module 2 to be removed from the housing 1 as necessary, although there is limited space to fit a standard connector here. Therefore, preferably, the external sensor 13 is permanently connected to the electronics module 2 via a permanent connection 14. The external sensor 13 must be retained firmly in a way that resists the external pressure acting to force the sensor into the housing 1. Therefore, the retention method can be considered to effectively retain the electronics module 2 within the housing 1.

[0073] In some examples, it is useful to provide an indication to an operator and/or a user that the sensor apparatus is operating when the battery 5 is provided in the housing 1. Therefore, a confidence indicator can be provided by a component on the sensor apparatus in some examples. When the battery 5 is first loaded in the housing 1 and the sensor apparatus is made up ready for operation, for example by closing the open end of the housing 1 using the closure member 8, it is desirable that the operator can be confident that the sensor apparatus is operating correctly before it is deployed to the downhole location in the well. This is particularly important for this kind of tool where the electronics module 2 remains in the housing 1 and other forms of confidence indicator (eg LED) are not practicable. For example, it is typically not desirable to provide transparent or semi-transparent portions or openings or ports through the housing for permitting the emission of a visual or audible indicator therethrough.

[0074] One suitable configuration of the sensor apparatus for providing a confidence indicator is disclosed herein, and makes use of a small wire winding on a high permeability core inside the electronics module 2. In particular, this is an example of a magnetic indicator, where the electronics module 2 comprises an electrical magnetic field generator. Provided the housing 1 is of sufficiently low permeability, the magnetic field resulting from an electric current in the small wire winding can be detected outside the housing 1. Nevertheless, it will be understood that other designs of electrical magnetic field generator are possible.

[0075] A static magnetic field may be used to indicate the tool is operating. A static magnetic field can be detected using a magnetic field detector, such as a gauss meter or compass, and observing a change in the static field or direction of the compass in the vicinity of the sensor apparatus. [0076] Additionally or alternatively, indication that the sensor apparatus is operating can be provided with the use of a changing magnetic field. The modulated magnetic field may be detected in many ways using various magnetic sensors, as will be apparent to the person skilled in the art. One of the simpler methods is to use a low frequency (<1 Hz) alternating current in the winding and detect this with a gauss meter or common magnetic compass which will swing back and forth with the alternating field. This gives a more positive indication to the operator than simply detecting the presence of a static field. An advantage of this approach over a higher frequency is the low frequency minimises losses due to induction coupling to the housing, thereby reducing the energy requirements to produce the magnetic field, extending the battery life of the sensor apparatus.

[0077] As is widely known, an alternating magnetic field can be used to induce an alternating current in a wire positioned in the alternating magnetic field. Therefore, by modulating the current in the small wire winding, an alternating magnetic field is produced that can be detected outside the housing 1. Whilst various forms of modulation may be used, a particularly simple and effective example uses an alternating current with symmetrical positive and negative drive characteristics. Another indicator operating method is to use an alternating current having a frequency within the audible range in the small wire winding and an external pickup coil and suitable amplifier and listening device to detect the current induced by the resulting alternating magnetic field. One example of a suitable listening device is an old-fashioned telephone listener, though there are many that would be apparent to the skilled person. Preferably, the small wire winding may be supplied with a combination of low frequency (<1Hz) AC may be used with bursts of high frequency enabling the use of a compass or detection coil, depending on operator preference.

[0078] It will be understood that the electronic module 2 may be configured to supply power to the electrical magnetic field generator for some of the time, for example for a preconfigured amount of time after initial power on, thereby increasing the battery life of the sensor apparatus.

[0079] Figures 4 to 8 illustrate a further example of a sensor apparatus as described herein. The reference numerals used in relation to Figures 4, 5, 7 and 8 are applicable only to each of those figures respectively.

[0080] In particular, Figure 4 shows an exploded view of a sensor apparatus provided in a data logging configuration. The sensor apparatus comprises a housing 1 into which is received an electronics module 5 and a battery 4, in this example an AAA lithium cell capable of operating at up to 150°C. A closure member 2 in the form of an end cap 2 is provided to close the housing 1, and includes a resiliently deformable member in the form of a spring to engage against the battery 4 to retain the battery 4 in contact with an electrical contact in the form of an electrode (not labelled) of the electronics module 5. A fastener 3 in the form on a pin screw 3 is used to retain the end cap 2 in place closing the housing 1.

[0081] Figure 5 shows an exploded view of the electronics module (labelled 5 in Figure 4) of the sensor apparatus shown in Figure 4, along with a summary of parts. As can be seen, the electronics module comprises a chassis 1 that is typically plastic and supports an electrical assembly 6 in the form of a PCB assembly 6, including at least a microprocessor, a logging memory and one or more sensors. In this example, the one or more sensors includes an electronic temperature sensor configured to output temperature data to the logging memory. An electrical contact 5 of the electronics module is provided by a contact button 5 in electrical contact with the components of the PCB assembly. The electronics module further comprises a ferrite rod 2 for having a thin wire coiled therearound, as described hereinbefore. A canted contact spring ring 4 is provided at the electronics module for providing electrical contact and mechanical retention between the electronics module and the housing (not shown in Figure 5). The electronics module is further provided with a chassis contact cap 3, typically made from metal and connected by wire (not shown) to the electrical assembly 6, to retain the canted contact spring ring 4 in contact with the electronics module.

[0082] Figure 6 shows an example of an interrogation device for the sensor apparatus as described herein. Figure 7 shows an exploded view of the interrogation device shown in Figure 6. As labelled in Figure 7, the interrogation device comprises an outer body 5 in the form of an outer housing 5 arranged to remain outside the sensor apparatus when the interrogation device is to be used to extract sensor data from the logging memory of the electronics module of the sensor apparatus. The interrogation device further comprises a probe portion 4 to be connected to the outer housing 5 and configured to be insertable within the housing of the sensor apparatus, as described hereinbefore. In this example, two O-rings 6 are provided at an outer end of the probe portion 4 for ensuring mechanical retention of the probe portion 4 within the housing of the sensor apparatus. An inner end of the probe portion 4, opposite the outer end, is provided with a probe contact 3 for contacting the electrical contact of the electronics module of the sensor apparatus. The probe contact 3 is resiliently movable within a contact holder 1, sometimes referred to as a spring contact holder 1 arranged to resiliently bias the probe contact 3 outwardly from the spring contact holder 1 towards the electrical contact of the electronics module of the sensor apparatus. A collar 2 is provided to surround the probe contact 3 and provide at least some protection for the potentially delicate probe contact 3 when the probe portion 4 of the interrogation device is not provided within the housing of the sensor apparatus. A canted contact spring ring 8 is also provided at the probe portion 4 for providing electrical connection between the interrogation device and the housing of the sensor apparatus into which the probe portion 4 is to be inserted. Within the outer housing 5, there is provided an interrogation electronics module 12, in the form of a PCB 12 to provide power and communications messages to the sensor apparatus and for receiving sensor data and any other communications messages therefrom when the probe portion 4 is inserted in the housing of the sensor apparatus such that the probe contact 3 is in contact with the electrical contact of the electronics module of the sensor apparatus. The outer housing 5 is closed by an end cap 7. The outer housing 5 is secured to the probe portion 4 and the end cap 7 is secured to the outer housing 5 by screw fasteners 9. The PCB 12 is secured in the outer housing 5, in this example to the probe portion 4, by a further screw fastener 11, through a washer 10. The interrogation electronics module 12 is connected to the contact 3 via a wire connection (not shown) through the probe portion 4. The interrogation device is operated substantially as described hereinbefore.

[0083] Figure 8 shows an extraction tool, also including an exploded view of the extraction tool for use with the sensor apparatus described herein. The extraction tool is for use removing an electronics module of the sensor apparatus from the housing of the sensor apparatus. The extraction tool comprises a clasp 1 for engaging with a portion of the electronics module, and a clasp cover 2 that slides on the clasp 1 and is retained and biased toward the collet end of the clasp 1 by spring 4 and handle 5 that screws onto the clasp 1 . The clasp cover 2 can be moved relative to the claspl by movement of pull cap 3 relative to handle 5 affixed to an end of the removal clasp 1 and resiliently biased relative to the clasp 1 by a coil spring 4. The coil spring 4 is braced between the handle 5 and a pull cap 3, affixed to the clasp cover 2. The operator uses manual hand action to pull the clasp cover 2 towards the handle 5, thus freeing collet fingers at the distal end of the clasp 1 to spring open when pushed over a groove on the electronics module. When engaged with the electronics module within the housing the operator releases the pull cap 3 attached to clasp cover 2 which is sprung over the collet end of the clasp locking the collet fingers around the electronics module and allowing the operator to pull the extraction tool and electronics module from the sensor apparatus housing.

[0084] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0085] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A sensor apparatus for locating at a downhole position in a well, the sensor apparatus comprising: a housing for having a battery provided therein; an electronics module provided in the housing, the electronics module comprising: a logging memory; and an electrical contact for contact with the battery when the sensor apparatus is located at the downhole position in the well; and one or more sensors configured to generate sensor data, wherein, when the battery is provided in the housing, a first electrical circuit is formed including the battery, the electrical contact and the logging memory, wherein the electronics module, when powered by the battery via the electrical contact, is configured to store the sensor data in the logging memory, wherein the electronics module, when electrically connected to an interrogation device, is configured to output the sensor data stored in the logging memory to the interrogation device, and wherein, to connect the interrogation device to the electronics module, the first electrical circuit is to be broken and reformed into a second electrical circuit including the interrogation device, the electrical contact and the logging memory.

2. The sensor apparatus as claimed in claim 1 , wherein the battery is removable and wherein the second electrical circuit is to be formed only when the battery is removed from the housing.

3. The sensor apparatus as claimed in claim 1 or claim 2, wherein the housing defines a first end having the electronics module provided thereat and a second end, opposite the first end, and through which a portion of the interrogation device can be inserted for connection to the electronics module.

4. The sensor apparatus as claimed in claim 3, wherein the second end is openable to permit access into the housing, wherein the sensor apparatus further comprises a closure member for closing the housing at the second end when the battery is provided in the housing, and wherein the first electrical circuit further includes the closure member.

5. The sensor apparatus as claimed in claim 4, further comprising a resiliently deformable member configured to urge the battery against the electrical contact in the first electrical circuit.

6. The sensor apparatus as claimed in any of claims 3 to 5, when dependent on claim 2, wherein the sensor apparatus is configured such that the portion of the interrogation device is to be inserted through the second end of the housing to connect the interrogation device to the electronics module via contact with the electrical contact.

7. The sensor apparatus as claimed in any preceding claim, wherein the first electrical circuit and the second electrical circuit each include at least a portion of the housing.

8. The sensor apparatus as claimed in any preceding claim, wherein the one or more sensors include a temperature sensor to generate temperature data indicative of a plurality of temperature readings when the sensor apparatus is located at the downhole position.

9. The sensor apparatus as claimed in any preceding claim, wherein the one or more sensors include one or more of: an accelerometer, a magnetic sensor, a gyroscope sensor, a radiation sensor, an acoustic sensor and a pressure sensor.

10. The sensor apparatus as claimed in any preceding claim, wherein at least one of the one or more sensors is provided in the housing.

11. The sensor apparatus as claimed in any preceding claim, wherein at least one of the one or more sensors is provided outside the housing and is in data communication with the logging memory via a physical electrical connection.

12. The sensor apparatus as claimed in any preceding claim, wherein the housing is arranged to receive a battery having a diameter substantially identical to an AAA battery as the battery.

13. The sensor apparatus as claimed in any preceding claim, wherein the electronics module further comprises a supply reservoir capacitor configured to store sufficient charge to maintain power in a microprocessor of the electronics module during brief disconnection between the battery and the electrical contact.

14. The sensor apparatus as claimed in any preceding claim, wherein the electronics module is configured to determine a data communication message from the interrogation device in dependence on a voltage of a signal from the interrogation device to the sensor apparatus.

15. The sensor apparatus as claimed in any preceding claim, wherein the electronics module is configured to encode a data communication message from the electronics module to the interrogation device using current modulation in the current drawn from the interrogation device by the electronics module.

16. The sensor apparatus as claimed in any preceding claim, further comprising an electrical magnetic field generator provided at the housing to generate a magnetic field detectable outside the housing.

17. The sensor apparatus as claimed in claim 16, wherein the magnetic field is an alternating magnetic field.

18. The sensor apparatus as claimed in claim 16 or claim 17, further comprising a magnetic field detector to be positioned outside the housing and configured to be responsive to the magnetic field generated by the electrical magnetic field generator.

19. The sensor apparatus as claimed in claim 18, wherein the magnetic field detector is a passive magnetic sensor, such as a compass, directly responsive to the magnetic field.

20. The sensor apparatus as claimed in claim 18, when dependent on claim 17, wherein the magnetic field detector comprises a third electrical circuit into which an electric current can be induced by the magnetic field, the third electrical circuit including an electrical component configured to generate a notification signal when the current is induced therethrough.

21. The sensor apparatus as claimed in any preceding claim, further comprising the interrogation device.

22. The sensor apparatus as claimed in claim 21 , wherein the interrogation device comprises: a first contact; and a second contact, wherein, when the interrogation device is to be electrically connected to the electronics module, the first contact is configured to electrically connect to the electronics module via the electrical contact of the electronics module, and the second contact is configured to electrically connect to the housing, and wherein the first contact and the second contact are included in the second electrical circuit.

23. A method of obtaining sensor data from a downhole position in a well, the method comprising: providing the sensor apparatus of any of claims 1 to 20, including the battery to form the first electrical circuit; lowering the sensor apparatus into the well to the downhole position; after sensor data has been recorded, raising the sensor apparatus away from the downhole position; breaking the first electrical circuit; electrically connecting an interrogation device to the electronics module of the sensor apparatus to form the second electrical circuit; and receiving sensor data at the interrogation device from the logging memory of the electronics module.

24. An electronic temperature sensor apparatus for retrofitting into an analogue thermometer compartment of a downhole tool, the analogue thermometer compartment for receiving therein an analogue thermometer for measuring a temperature of an environment of the downhole tool, the electronic temperature sensor apparatus comprising: a housing sized to fit into the analogue thermometer compartment; an electronics module provided in the housing, comprising a logging memory; and an electronic temperature sensor configured to generate temperature data, wherein the electronics module is configured to store the temperature data in the logging memory, and wherein the electronics module, when electrically connected to an interrogation device, is configured to output the temperature data stored in the logging memory to the interrogation device.

25. A method of retrofitting an electronic temperature sensor apparatus into an analogue thermometer compartment of a downhole tool, the analogue thermometer compartment for receiving therein an analogue thermometer for measuring a temperature of an environment of the downhole tool, the method comprising: removing any analogue thermometer from the analogue thermometer compartment; and inserting the electronic temperature sensor apparatus as claimed in claim 24 into the thermometer compartment of the downhole tool.