WO2014076440A1

WO2014076440A1 - Camera assembly for use in a subterranean well

Info

Publication number: WO2014076440A1
Application number: PCT/GB2012/000838
Authority: WO
Inventors: Nigel Halladay; Mathew Davis; Mark Alan Robert KNEEBONE
Original assignee: CALIDUS ENGINEERING Ltd
Current assignee: CALIDUS ENGINEERING Ltd
Priority date: 2012-11-15
Filing date: 2012-11-15
Publication date: 2014-05-22
Anticipated expiration: 2015-05-15

Abstract

A camera assembly (6, 102, 202) for use in a subterranean well (2) is provided, the camera assembly (102) comprising a pressure resistant outer housing (104) defining a chamber (106) therein, at least a portion (126) of the chamber (106) being thermally insulated; an optical sensor (142) disposed within the thermally insulated portion (126) of the chamber (106) in the outer housing (104); a pressure resistant optical window (116) for receiving light from outside the assembly to be conveyed to the optical sensor (142); a lens assembly (140) disposed to receive light entering the assembly through the optical window (116); and a gradient index lens relay (146) extending between the lens assembly (140) and the optical sensor (142) for conveying light received through the optical window (116) from the lens assembly (140)to the optical sensor (142).

Description

CAMERA ASSEMBLY FOR USE IN A SUBTERRANEAN WELL The present invention relates to camera assembly for use in a subterranean well.

The drilling of subterranean boreholes or wells are required for a variety of reasons, including, but not limited to, the production of oil and gas, the production of water, the recovery of geothermal energy, and the like. Such boreholes and wells are referred to herein generally as 'wells'.

During the drilling, operation or maintenance of wells, it is desirable to visually log the well, in particular the walls of the well. To this end, it is known to deploy cameras downhole to allow a visual inspection of the well at depth. The camera is typically incorporated into a visual logging tool that is lowered into the well, in particular at the distal end of a cable, along which data from the camera is transmitted to the surface for viewing and/or recording.

A particular problem arises with the use of camera assemblies for the visual logging of wells in this manner. Generally, the temperature within the well increases with increasing depth.

US 4,855,820 discloses a down hole video tool apparatus and a method for visual well bore recording. The video tool apparatus comprises a wide angle video apparatus at its lower end, when disposed in the bore and deployed for use. An upper section of the apparatus comprises an array of components, including a power suppl /triplexer, a telemetry board, an FM modulator video amplifier transmission board, a gyroscope data interface board and a gyroscope. Data from the gyroscope regarding the orientation of the apparatus and image data from the video apparatus are transmitted to the surface, when in use, for use in a visual logging of the walls of the bore. The wide angle video apparatus comprises a wide angle video lens and a wide angle video camera. A light source is provided to illuminate the walls of the bore. US 4,855,820 discloses that the apparatus is provided with a housing resistant to both pressure and temperature, with the ability to withstand temperatures of up to 200 . However, it is disclosed that heat within the bore, such as when logging a geothermal borehole, can damage the instrumentation within the housing of the apparatus. It appears that US 4,855,820 does not address the issue of heat affecting the operation of the components within the housing and their efficient operation under conditions of high temperature existing at depths within subterranean wells and boreholes. It is indicated that the apparatus may be deployed and used up to depths of 10,000 feet underground.

A more recent development is disclosed in US 5,519,543, relating to an optic system for a down hole camera assembly. The optic system comprises an elongated, generally tubular housing formed from a thermally insulating material. The housing contains a lens assembly comprising a front lens group and a rear lens group disposed at opposing ends of the housing. The front and rear lens groups are thermally isolated from one another by two spaced apart optical windows disposed within the housing therebetween. The windows are preferably sealed to the housing, allowing the cavity defined between the windows to be partially evacuated. A path for light is defined within the housing extending from the front lens group, through the first and second windows, to the second lens group. The optic assembly is disposed within an outer housing, formed from tubular steel. Light from the optic assembly is received by an imaging assembly, also disposed within the inner housing and thermally insulated from the outer housing and the exterior of the apparatus. A power supply/transmission assembly is also disposed within the inner housing. US 5,519,543 indicates that the optical path provided for light received by the optic system to the imaging assembly provides a conduit for heat to reach the thermally sensitive imaging components. It is suggested in US 5,519,543 that the optic system housing within the inner housing and comprising the thermally insulating window assembly insulates the imaging components from the heat within the wellbore, when the apparatus is in use. However, the assembly of US 5,519,543 is particularly complex to construct. Further, it appears that the optic assembly of the apparatus of US 5,519,543, by being disposed within the inner housing, provides only a narrow field of view.

Accordingly, there is a need for an improved camera assembly for the visual logging of wells. In particular, it would be Useful if the improved camera assembly could provide a wider field of view than the prior art systems, while still insulating the sensitive imaging components from the elevated temperatures at downhole locations.

It has been found that an improved camera assembly for downhole logging of wells may be constructed by providing an image sensing assembly and a lens assembly within a pressure resistant outer housing, by having the image sensing assembly disposed within a thermally insulating inner housing, while having the lens assembly located within the outer housing but outside the inner housing. A conduit providing an optical path extends from the lens assembly to the image sensing assembly within the inner housing. By selectively insulating the image sensing assembly within the inner housing, the operation of the camera assembly under conditions of elevated temperatures prevailing at depths in the well bores may be maintained, while at the same time allowing the lens to have a wide field of view. According to the present invention there is provided a camera assembly for use in a subterranean well, the camera assembly comprising:

a pressure resistant outer housing defining a chamber therein, at least a portion of the chamber being thermally insulated;

an optical sensor disposed within the thermally insulated portion of the chamber in the outer housing;

a pressure resistant optical window for receiving light from outside the assembly to be conveyed to the optical sensor;

a lens assembly disposed to receive light entering the assembly through the optical window; and

a gradient index lens relay extending between the lens assembly and the optical sensor for conveying light received through the optical window from the lens assembly to the optical sensor.

The camera assembly of the present invention is for use in surveying or logging subterranean wells, including but not limited to oil and gas wells, geothermal wells and the like. As noted above, the temperature within a well increases with increasing depth. The camera assembly of the present invent/on has been arranged to provide protection to the thermally sensitive components of the assembly, in particular the optical sensor or camera components. To this end, as will be described, thermal insulation is provided to protect such components. The arrangement is such that those components that are less sensitive to high temperatures can be displaced from the thermally sensitive components and may be provided with less or no thermal insulation, as required. This has the advantage of increasing the flexibility of the design of the assembly, as well as reducing the thermal insulation requirements within the device. As will be described in more detail hereinafter, the use of a gradient index lens as the conduit for light between the optical window and associated lens assembly and the optical sensor provides this flexibility in design.

The camera assembly of the present invention comprises a pressure resistant housing. In general, the pressure of fluid within a subterranean well increases with increasing depth. The housing of the assembly is thus formed to withstand the fluid pressures expected to be encountered at the working depth of the camera assembly, in particular the hydrostatic pressures prevailing at the operating depths in a liquid- filled well. Accordingly, the particular design and configuration of the housing will depend upon such factors as the depth to which the assembly is to be deployed in use, as well as other conditions prevailing within the well, such as temperature, the presence of corrosive or abrasive materials within the well, and the like.

Suitable materials for construction of the housing are known in the art and include alloys of steel, in particular stainless steel.

The housing may have any suitable configuration. In a particularly preferred embodiment, the housing is generally cylindrical. In one embodiment the camera assembly is incorporated into a tool, in known manner, to be deployed downhole individually or as part of a tool string. In such cases, the size and shape of the housing may be selected to conform with other components of the tool and/or other tools in the string.

The housing defines a chamber therein. At least a portion of the chamber within the housing is thermally insulated. The housing itself will provide some insulation of the chamber from heat outside the housing. However, this is generally insufficient to adequately thermally insulate the most sensitive components of the assembly, in particular the optical sensor. Accordingly, the interior of the housing is most preferably provided with thermal insulation to provide the required level of thermal insulation for at least a portion of the chamber. The form of the thermal insulation will be determined by such factors as the maximum operating temperature intended for the camera assembly, in turn determined by the depth to which the assembly is to be deployed and the conditions prevailing within a given well.

Suitable insulating materials for use in insulation the chamber within the housing are known in the art and include such materials as syntactic glass foams. In one preferred embodiment, the assembly comprises a vacuum heat shield within the housing, the vacuum heat shield having an insulated chamber therein. The vacuum heat shield comprises an inner wall and an outer wall, both walls defining an annular cavity therebetween. . The annular cavity is evacuated to a partial vaccum, to thereby reduce the transfer of heat from outside the heat shield to the insulated chamber within the heat shield. It is an advantage of the present invention that the camera assembly may be arranged to have the size of the vacuum heat shield at a minimum necessary to house the most thermally sensitive components, most importantly the optical sensor. The heat shield may have any suitable form that fits within the chamber in the housing. In a preferred embodiment, the heat shield is generally cylindrical, more preferably having an outer diameter or dimension that is substantially the same as the diameter of the chamber within the housing. Alternatively, additional insulating material may be disposed between the heat shield and the inner wall of the housing, as required to provide the requisite degree of insulation for components within the heat shield.

The camera assembly further comprises an optical sensor disposed within the insulated portion of the chamber within the housing. Suitable optical sensors and camera assemblies are known in the art and are commercially available.

The optical sensor is disposed within the insulated portion of the chamber and is thereby shielded from the high temperatures prevailing outside the housing when the camera assembly is deployed in the well. Typical operating temperatures of the optical sensor are up to about 100°C, but can extend to about 125°C, depending upon the type and design of the optical sensor or camera assembly. Such operating temperatures are significantly below the temperatures prevailing in downhole locations in a subterranean well.

The camera assembly further comprises an optical window. Light from outside the housing passes through the optical window and is conveyed to the optical sensor as described hereinafter. The optical window may be of any suitable arrangement that is sufficiently transparent to the passage of light therethrough, but able to resist the conditions, such as elevated temperature and pressure prevailing within the wellbore at the intended operating depth of the assembly. Suitable optical windows are known in the art. Materials of construction of the optical window include glass and quartz. The configuration of the optical window is such as to receive light to pass the lens assembly and will be determined in part on the form of lens assembly being employed, for example the field of view of the lens assembly. For example, the optical window may be planar, providing a relatively narrow field of view, or convex, providing a wider field of view, for example for use in conjunction with a wide angle or fish eye lens. The optical window may be disposed in any suitable position in the camera assembly. Most preferably, the optical window is disposed at the distal end of the assembly, that is the end of the assembly that faces downwards or is lowermost when the assembly is deployed in a wellbore. As noted, the camera assembly further comprises a lens assembly for receiving light entering through the optical window. Again, suitable lens assemblies are known in the art. The lens assembly may comprise one or a plurality of lenses, as required to collect and focus the incident light. The lens assembly may have any desired field of view, for example being wide angle or fish-eye, giving a field of view of up to 170° or greater. As noted, the optical window will shaped and configured to be consistent with the field of view of the lens.

To convey light from the lens assembly to the optical sensor, the camera assembly of the present invention employs a relay lens, in particular a gradient index lens. The gradient index lens employed in the present invention is a generally elongate, cylindrical lens along which light is transmitted by internal reflection from the surface of the lens. Suitable gradient index relay lenses are known in the art. For example, gradient index of refraction (GRIN) optical relays are described in US 5,361 ,166. Further, suitable gradient index relay lenses are commercially available, for example endoGRIN® gradient relays, ex Gradient Lens Corporation.

It has been found that gradient index (ens relays allow light to be conveyed from the lens assembly to the optical sensor, but have a very low heat conductivity. Generally, the extent to which heat is transmitted along the gradient index lens relay is inversely proportional to the length of the relay and thus decreases as the length of the relay increases. In known camera assemblies, while it has been possible to provide a housing construction that suitably thermally insulates an optical sensor disposed within, the need to have an opening in the housing through which light can pass to reach the optical sensor compromises the integrity of the housing and provides a path for heat to reach the thermally sensitive components. By employing a gradient index lens relay, the passage of heat along the light path is significantly reduced, such that the thermal integrity of the housing and insulation is not compromised.

As noted, the gradient index lens relay is a generally cylindrical conduit for the light. The relay is formed from a transparent material, for example glass. In one embodiment, the glass is treated in an ion exchange process, to provide the glass rod with the properties to transmit light efficiently therealong, with little or no losses.

The length of the gradient index lens may be selected according to the thermal sensitivity of the optical sensor and the intended operating temperature of the camera assembly. Thus, for an assembly intended for deployment at greater depths, and hence operation at higher temperatures, a longer gradient index lens will be required, compared with an assembly intended for use closer to the surface and/or one in which a more t erma y robust optical sensor is employed. For example, the gradient index lens may have a diameter of from 2 to 20 mm, more preferably from 2 to 10 mm, and a length of from 10 cm to 200 cm, preferably from 25 cm to 150 cm. Gradient index lenses having a length longer than the minimum required to provide the necessary thermal insulation may be employed as required, for example depending upon the configuration of the overall assembly and the relative positions of the optical window, the lens assembly and the optical sensor.

The camera assembly may employ a single gradient index lens relay extending between the lens assembly and the optical sensor. Alternatively, the assembly may comprise a plurality of gradient index lens relays extending substantially parallel to one another between the lens assembly and the optical sensor. For example, if a plurality of gradient index lens relays is employed, the assembly may comprise two or more, preferably four or more, still more preferably eight or more relays. The or each relay may consist of a single gradient index lens or may comprise two or more individual lenses arranged end to end and connected by a suitable optical junction to provide a path for light between the lens assembly and the optical sensor.

One or more further lens assemblies, each comprising one or more lenses, may be disposed between the gradient index lens relay and the optical sensor, for example to focus the incoming light onto the light sensitive array of the optical sensor, as required.

In one embodiment, the optical sensor, lens assembly and gradient index relay are disposed within a single housing, with the housing being provided with an optical window, as described above. Alternatively, the assembly may comprise a first pressure resistant housing within which the optical sensor is disposed, as described hereinbefore, and a second pressure resistant housing having the optical window and lens assembly disposed therein. In this arrangement the gradient index lens relay extends between the first and second housings, to provide a light path between the lens assembly and the optical sensor. The gradient index lens relay is preferably disposed within a suitable conduit to provide protection from damage.

The first and second housings may have any suitable configurations, as described above, and are preferably generally cylindrical. In one embodiment, the camera assembly is provided with a light source for emitting light from the assembly. The light source may be disposed at any suitable position in the assembly, preferably adjacent or in the region of the optical window. In this way, the wellbore may be illuminated, to aid inspection of the interior of the well. Any suitable means may be employed to provide the emitted light. Such means may be disposed within the housing of the assembly, in which case a further optical window is required, in order to allow light to be emitted from the housing to illuminate the wellbore. Details of the optical window, including materials of construction are as described above.

Most preferably, the light source comprises one or more bulbs. Light emitting diodes (LEDs) may be employed at lower operating temperatures. LEDs have the advantage of being efficient at generating light with low power consumption and without generating significant amounts of heat. This is advantageous when the light source is disposed within the housing, as heat generated by components within the housing must also be prevented from reaching the thermally sensitive components. However, at temperatures above about 120°C, it is necessary to use incandescent bulbs. As incandescent bulbs generally emit significant amounts of heat, provisions must be made to thermally isolate the bulbs from other components in the assembly, in particular the optical sensor.

In a further aspect, the present invention provides a logging tool for use in a wellbore comprising a camera assembly as hereinbefore described. As noted above, the present invention employs a gradient index lens as an optical relay for transmitting light to the optical sensor of the camera assembly, while keeping the optical sensor thermally insulated. Accordingly, the present invention provides in yet another aspect the use of a gradient index lens as an optical relay for transmitting light from an optical window to the optical sensor of a downhole camera assembly.

Embodiments of the present invention will now be described, by way of example only, having reference to the accompanying drawings, in which: Figure 1 is a diagrammatical representation of a camera assembly of an embodiment of the present invention deployed in the bore of a well for performing a visual logging of the well; Figure 2 is a cross-sectional view of a camera assembly of one embodiment of the present invention;

Figure 3 is a perspective view of a camera assembly of a second embodiment of the present invention;

Figure 4 is a longitudinal perspective cross-sectional view of the assembly of Figure 3;

Figure 5 is an enlarged view of the portion V of Figure 4; and

Figure 6 is an enlarged view of the portion VI of Figure 4.

Turning to Figure 1 , there is shown a camera assembly of the present invention deployed in the bore of a well. In particular, there is shown a subterranean wellbore 2, hereinafter referred to as a 'well', extending downwards into rock strata, generally indicated as 4. The well is formed in conventional manner using known techniques and may be a well for the production of hydrocarbons, such as oil and/or gas, the production of water, or for the recovery of geothermal energy. The well may be subsea, as is the case with many wells for the production of oil and gas.

A camera assembly 6 is shown deployed in the well by means of a cable 8 controlled from a suitable station 10 at the surface. It will be appreciated that, in the case of a well extending subsea, the station 10 is typically located at the surface of the water, for example on a rigid or floating platform or vessel.

The cable 8 supports the camera assembly 6, allowing it to be lowered into the well for visual logging of the wellbore and later recovered to the surface. In addition, the cable 8 provides a means for the transmission of data signals from the camera assembly 6 to the station 10 and, if appropriate, signals from the station 0 to the camera assembly 6. Such techniques are known in the art.

Turning to Figure 2, there is shown a camera assembly, generally indicated as 102, according to one preferred embodiment of the present invention. The camera assembly 02 comprises a generally tubular, elongate outer housing 104, having a generally cylindrical inner chamber 106. The outer housing 104 is a pressure resistant structure capable of withstanding the elevated pressures prevailing at depths within the wellbore. The outer housing may be formed from any suitable material. Metals, in particular steel, such as stainless steel, are particularly preferred. The dimensions of the outer housing 104 will be determined in part by the material of construction.

The outer housing 104 protects the components of the camera assembly from the high pressures prevailing at downhole locations within the well, as noted above. In addition, the outer housing 104 provides a limited protection against elevated temperatures at the downhole locations. However, the outer housing 104 is generally of a material having a thermal conductivity sufficiently high that heat will be transferred to the interior of the housing through the walls and ends of the housing. Accordingly, thermal protection for vulnerable components of the camera assembly is provided, as described in more detail hereinafter.

The outer housing 104 is provided at a first end 108 with a coupling 10 for connection to a cable 1 12. In use, with the camera assembly 102 deployed in the wellbore, the first end 108 is generally uppermost. The coupling 1 10 provides a connection between the camera assembly 102 and the cable 1 12, allowing the assembly to be supported within with the wellbore. The coupling 110 further provides an electrical connection between the components of the camera assembly 102 and the cable, allowing data signals to be passed between the assembly and the station 10 at the surface.

The outer housing 104 is further provided at its second end 114 with an optical window 1 16. The optical window 1 16 provides an optical path for light to enter the interior of the outer housing 104 from outside the camera assembly 102. The optical window 116 is formed from a transparent material, in particular glass. The window 116 may be of any suitable shape to allow light to enter the interior of the outer housing 104. For example, the optical window 116 may be planar, in particular a disc of transparent material, mounted in the second end 14 of the outer housing 104. More preferably, as shown in Figure 2, the optical window 116 is convex, to thereby provide a wide angle of view for the camera assembly.

In use, with the camera assembly 102 deployed in a downhole location within the well, the second end 4 of the outer housing is generally lowermost.

The camera assembly 102 further comprises an inner housing 120 disposed within the chamber 106 within the outer housing 104. The inner housing 120 is generally tubular in configuration having a first, closed end 122 adjacent the first end 108 of the outer housing 104 and a second, open end 124. The inner housing 120 defines a generally cylindrical inner chamber 126 therein. The inner housing 120 is formed from a material and constructed to provide a thermal barrier between the outer housing 104 and the inner chamber 126. In particular, the inner housing 120 is provided with an outer wall 28 and an inner wall 130, with an annular cavity 132 defined therebetween. The annular cavity 132 is substantially evacuated. The inner housing 120 thus thermally insulates the inner chamber 126 from the outer housing 104 and the remainder of the chamber 106. Suitable inner housing assemblies are known in the art and are commercially available, for example ex. Dewar.

A first lens assembly 1 0 is disposed within the chamber 106 in the outer housing 104 outside the inner housing 120 and in the region of the second end 114 of the outer housing 104 and the optical window 116. The first lens assembly 0 is of known configuration and comprises one or more lenses for collecting and focussing the incident light entering the outer housing 104 through the optical window 11 . Suitable lens assemblies are known in the art.

As can be seen in Figure 2, the first lens assembly 40 is disposed within the chamber 106 in the outer housing 04, but outside the inner housing 120. In this way, the first lens assembly 140 may be positioned to most efficiently receive light entering through the optical window 116 and provide the camera assembly with a wide angle of view, The first lens assembly 0 is not thermally insulated from the chamber 106, the outer housing 104 and the optical window 1 16.

The camera assembly 102 is provided with an optical sensing assembly 142 disposed in the inner chamber 126 within the inner housing 120, which thermally insulates the optical sensing assembly from heat within the chamber 106 and the outer housing 104. The optical sensing assembly 142 is disposed within the inner chamber 126 adjacent the first end 122 of the inner housing 120. The optical sensing assembly 142 may be any suitable optical sensor, including CMOS and CCD devices, which are known in the art and are commercially available.

Data signals generated by the optical sensing assembly 142 are transmitted through the coupling 110 to the cable 1 12 and from within the wellbore to the surface station 10, as shown in Figure 1.

A second lens assembly 1 4 is disposed adjacent the optical sensing assembly 142 to receive light entering the open end 124 of the inner housing 120 and focus the incident light on the light sensitive components of the optical sensing assembly 142. The second lens assembly 144 may comprise one or more lenses and suitable components and configurations are known in the art and commercially available.

A path for light between the first lens assembly 140 and the second lens assembly 144 is provided by a gradient index lens relay 146 extending from the first lens assembly through the open second end 124 of the inner housing 120 to the second lens assembly in the_, inner chamber 126. The gradient index lens relay 146 provides a path for light to the optical sensing assembly 1 2, but with a low thermal conductivity. To increase the thermal isolation of the inner chamber 126 and the components therein, an insulating packing 148 is provided between the tubular conduit 146 and the inner housing 120 within the inner chamber 126 in the region of the open second end 124 of the inner housing 120. Turning to Figure 3, there is shown, in perspective view, a logging tool, generally indicated as 202, comprising a camera assembly of a second embodiment of the present invention. The logging tool 202 comprises a tool body 204 having a first end 206, disposed uppermost when in use, and a second end 208, disposed lowermost when in use. The second end 208 of the tool 202 comprises a camera assembly, generally indicated as 210 and described in more detail below.

The tool 202 comprises a physical and electrical interface 212 at its first end, for connecting the tool to an adjacent tool or controller in a tool string, in known manner. The tool 202 is further provided with first and second centralisers 214, 216, again of known configuration. The centralisers 214, 216 act to keep the tool centrally positioned within the wellbore when the tool is deployed.

The tool 202 of Figure 3 is shown in perspective cross-section in Figure 4, with the portion V of the camera assembly 210 of Figure 4 shown enlarged in Figure 5 and the portion VI of the camera assembly 210 of Figure 4 shown enlarged in Figure 6.

Referring to Figure 5, the distal end of the camera assembly 202 is shown and comprises a generally cylindrical, pressure resistant housing 220 having a convex quartz optical window 222 disposed in one end thereof. The housing 220 is provided with a cylindrical quartz window 224 disposed centrally along its length. A light assembly 226 is disposed within the housing 220 adjacent the window 224 and comprises a plurality of bulbs 228. In use, the light assembly 226 is activated to provide light emitted through the window 224 to illuminate the wellbore in which the assembly 202 is deployed.

A lens assembly 230 is disposed within the housing 220 inwards of the optical window 222 to receive light passing through the window into the housing. The lens assembly 230 comprises a fish-eye lens to provide a wide field of view from within the housing.

A gradient index lens relay 232 extends from the lens assembly 230 axially through the housing 220 and out from the end of the housing opposite the optical window 222. A steel tube 234, extending from the housing 220, encases the gradient index lens relay 232 to provide rigidity and protection for the relay. In addition, the steel tube 234 supports the centraliser assembly 216, as shown in Figure 5. Referring to Figure 6, a portion of the tool body 204 is shown and comprises a generally cylindrical, pressure resistant housing 240, within which is mounted an inner housing 242 formed as described above with reference to Figure 2, to provide a vacuum heat shield for an optical sensor assembly 244 mounted within. As can be seen in Figure 6, the gradient index lens relay 232 extends into the housing 240, extending axially into the inner housing 242 to provide a path for light to reach the optical sensor assembly 244. A packing of insulating material 246 is provided around the gradient index lens relay 232 within the inner housing, to provide insulation for the interior of the inner housing and prevent the ingress of heat axially along the assembly from the distal end.

The tool 202 is provided with a processor assembly within the tool body 204 for receiving and processing image signals from the optical sensor assembly 244 and generating data signals for transmission via the interface 212 to other components of the tool string and/or to the control station at the surface.

Claims

1. A camera assembly for use in a subterranean well, the camera assembly ^' comprising:

2. The camera assembly according to claim 1 , wherein the interior of the housing is provided with thermal insulation to thermally insulate the said portion of the chamber.

3. The camera assembly according to claim 2, wherein the thermal insulation comprises a heat shield. 4. The camera assembly according to claim 3, wherein the heat shield comprises a vacuum heat shield comprising an outer wall and an inner wall, having an annular cavity defined therebetween, the annular cavity being at least partially evacuated, the inner wall defining an insulated chamber therein, the optical sensor being disposed within the insulated chamber.

^■ 5. The camera assembly according to claim 4, wherein a layer of thermal insulation is disposed between the heat shield and the housing.

6. The camera assembly according to any preceding claim, wherein the optical window is planar or convex.

7. The camera assembly according to any preceding claim, wherein the optical window is disposed in the distal end of the assembly.

8. The camera assembly according to any preceding claim, wherein the lens assembly comprises a plurality of lenses. 9. The camera assembly according to any preceding claim, wherein the lens assembly comprises a wide angle lens.

10. The camera assembly according to any preceding claim, wherein the gradient index lens relay comprises a generally cylindrical glass lens.

11. The camera assembly according to claim 10, wherein the glass has been subjected to an ion exchange treatment.

12. The camera assembly according to any preceding claim, wherein the gradient index lens relay has a generally cylindrical lens having a diameter of from 2 to 20 mm. 3. The camera assembly according to any preceding claim, wherein the gradient index lens relay has a generally cylindrical lens having a length of from 25 to 150 cm.

14. The camera assembly according to any preceding claim, wherein the gradient index lens relay comprises a single generally cylindrical lens.

15. The camera assembly according to any of claims 1 to 13, wherein the gradient index lens relay comprises a plurality of generally parallel cylindrical lens.

16. The camera assembly according to any preceding claim, wherein the gradient index lens relay comprises a plurality of cylindrical lenses arranged end to end.

17. The camera assembly according to any preceding claim, comprising a further lens assembly disposed between the gradient index lens relay and the optical sensor. 18. The camera assembly according to any preceding claim, wherein the optical sensor, lens assembly and gradient index lens relay are disposed within the same housing.

19. The camera assembly according to any of claims 1 to 17, wherein the optical sensor is disposed in a first housing and the lens assembly is disposed in a second housing, the gradient index relay extending between the first and second housings.

20. The camera assembly according to any preceding claim, wherein the gradient index lens relay is disposed within a conduit.

21. The camera assembly according to any preceding claim, further comprising means for emitting light from the assembly.

22. The camera assembly according to claim 21, wherein the light emitting means are disposed within a housing of the assembly, the housing being provided with an optical window through which emitted light may leave the housing.

23. The camera assembly according to either of claims 21 or 22, wherein the light emitting means comprises one or light emitting diodes (LEDs).

24. A logging tool for use in a wellbore comprising a camera assembly according to any preceding claim.

25. The use of a gradient index lens as an optical relay for transmitting light from an optical window to the optical sensor of a downhole camera assembly.