Optical cap for a wellbore inspection assembly

An optical cap that protects a camera lens of the inspection assembly is disclosed herein. The disclosed optical cap for an inspection assembly may include an optically clear dome-shaped window element and a metal collar attached to the window element, the collar including means for securing the optical cap to said inspection assembly, wherein the collar is bonded to the window element by means of brazing or welding.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National phase entry under 35 U.S.C. § 371 of International Application No. PCT/GB2017/050136, filed on Jan. 19, 2017, which claims priority to Great Britain Patent Application 1601452.4, filed on Jan. 26, 2016. Each of these patent applications is incorporated by reference herein in its entirety.

BACKGROUND

a. Field of the Invention

This invention relates to an optical cap for an inspection assembly. In particular this invention relates to the provision of an optical cap that protects a camera lens of the inspection assembly. This invention further relates to a method of manufacturing an optical cap and to an inspection assembly including an optical cap. The invention is particularly suited to inspection assemblies and camera systems that operate in high temperature and high pressure environments, such as those that operate downhole.

b. Related Art

Systems and assemblies for inspecting internal spaces such as interior walls of pipelines or similar are known. When these systems are used downhole, for example in offshore environments, an inspection assembly comprising a source of illumination and a camera are lowered through the pipeline or conduit and the camera is configured to capture images of the internal surfaces of the pipeline. In this way the inspection system may be used to visualise the condition of the pipeline to determine if remedial action is required.

Pipelines or wellbores can reach depths of hundreds or thousands of metres and inspection assemblies may be required to withstand significant temperatures and pressures. Pressures at depth in a wellbore can reach around 150 MPa and temperatures may exceed 100° C.

In some inspection systems the camera and in particular the camera lens is located in a nose region of the assembly and is forward facing. In this way, the camera is able to capture images of the interior of the pipeline ahead of the inspection assembly as it is lowered or moved through the pipeline. In these systems it is necessary to provide a suitable cover and/or sealing arrangement to protect the inspection system from the environment of the pipeline and, in particular, to protect the vulnerable camera lens.

In order to provide even illumination of the field of view of the camera, the light sources are often located behind the camera lens and are angled in a direction towards the internal wall of the pipeline ahead of the inspection assembly. In this way the walls of the pipeline are illuminated at a distance from the front of the inspection assembly.

In some systems it is desirable to use a wide angle lens, such as a fish-eye lens. When existing systems are retrofitted with such a wide angle lens, however, the configuration of the light sources may be such that there is inadequate illumination of the entire field of view. In particular the periphery of the image may be under exposed and the central portion of the image may be over exposed.

It is, therefore, an object of the present invention to provide an assembly that overcomes at least some of the disadvantages of prior art assemblies, whether referred to herein or otherwise.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided an optical cap for a wellbore inspection assembly comprising a main body having a longitudinal axis and a forward end, a lens located at the forward end, and a light source disposed rearward of the lens and positioned to illuminate an area forward of the lens, the optical cap comprising:an optically clear window element comprising a domed portion and an attachment portion including an end face; anda metal collar including means for securing the optical cap to said inspection assembly such that, in use, light entering the lens passes through the window element of the optical cap, the collar being bonded to the window element by means of brazing, welding or fusing and at least a part of the collar surrounding the attachment portion of the window element such that, in use, a part of the collar blocks light that is emitted by the light source and that would otherwise be incident on the end face of the window element from entering the window element.

Preferably the material from which the window element is made has substantially the same coefficient of thermal expansion as the metal from which the collar is made.

The collar may be bonded to the window element by means of energy beam welding, solid state welding and/or brazing.

The window element is preferably made of sapphire, quartz or diamond. The collar is preferably made of titanium.

The collar may be bonded to a base edge of the window element. Alternatively or additionally the collar may be bonded to an external surface of the window element.

Typically the collar is substantially tubular and an external diameter of the collar is preferably between 25 mm and 35 mm.

In preferred embodiments the collar comprises a ring element and a sleeve element. The sleeve element preferably includes the means for securing the optical cap to the inspection assembly. The ring element is preferably bonded to the window element and the sleeve element is preferably bonded to the ring element. Advantageously an outer surface of the ring element is continuous with an outer surface of the sleeve element.

The ring element may include a radially inwardly extending rib. In these embodiments the window element is preferably in contact with a first side of the rib and the sleeve element is preferably in contact with an opposite second side of the rib. Alternatively or additionally, an internal surface of a first portion of the ring element may be in contact with an external surface of the window element and an internal surface of a second portion of the ring element may be in contact with an external surface of the sleeve element.

Preferably a first end of the ring element extends beyond a first end of the sleeve element, and the window element extends beyond the first end of the ring element.

The means for securing the optical cap to said inspection assembly preferably comprises a screw thread. The screw thread is preferably provided on an internal surface of the sleeve element in embodiments in which this is provided.

In particularly preferred embodiment the collar comprises a sleeve element having first and second ends defining an axis of the collar, the window element being located proximate the first end, and a reflection surface at the second end of the sleeve element, an angle between the reflection surface and the axis of the collar being between 10° and 70°. The reflection surface may be an unpolished surface of the collar.

According to a second aspect of the present invention there is provided a wellbore inspection assembly comprising:a main body having a longitudinal axis and a forward end;a lens located at the forward end of the main body;a light source disposed rearward of the lens and arranged to illuminate an area forward of the lens; andan optical cap comprising an optically clear window element and a metal collar, the window element comprising a domed portion and an attachment portion including an end face, and the collar being bonded to the window element by brazing, welding or fusing,the optical cap being secured to the main body such that the window element extends over the lens and light entering the lens passes through the window element of the optical cap,and wherein a part of the collar blocks light that is emitted by the light source and that would otherwise be incident on the end face of the window element from entering the window element.

Preferably the lens is a wide angle lens or a fish-eye lens.

The inspection assembly preferably comprises a plurality of light sources arranged around the main body and radially outward of the lens. In these embodiments the optical cap preferably comprises a sleeve element having first and second ends, the window element being located proximate the first end and a reflection surface being provided at the second end. The reflection surface is, therefore, located between the light sources and the lens.

The location of the reflection surface causes a part of a light beam emitted from a light source to be deflected such that an angle between the direction of travel of the deflected light beam and the longitudinal axis of the assembly is greater than the angle between a direction of travel of a non-deflected light beam and the longitudinal axis.

When the inspection assembly is located in a pipeline or conduit, the fraction of the emitted light that is deflected or reflected, therefore, illuminates a region of the interior walls of the pipeline closer to the inspection assembly. This creates a more even illumination of the field of view if a wide angle lens is used in the inspection assembly. In order to still provide adequate illumination of the central region of the field of view, however, it is preferable if the fraction of the emitted light that is deflected or reflected is less than 50% of the total emitted light.

Furthermore, when present, the reflection surface is located such that the emitted light that is incident on the reflection surface is reflected in a direction substantially away from the window element. As such, the likelihood of light directly entering the window element and being internally reflected or refracted is significantly reduced.

The inspection assembly preferably further comprises an image sensor arranged to capture an image of a field of view through the lens. The inspection assembly may additionally include a memory for storing the captured image data or a transmitter for transmitting the image data to a remote receiver in real time.

DETAILED DESCRIPTION

Inspection assemblies or camera systems used to inspect passageways such as pipelines and wellbores typically include a camera and one or more light sources arranged to light the field of view of the camera. Often these are housed in a first, distal end region of an elongate cylindrical housing which is lowered down the wellbore by cables or a shaft attached at a second end. In most cases, the camera systems will also include a viewport or window at or near the distal end of the camera housing that serves to protect the camera.

In use, when an inspection assembly is deployed along a passageway, the distal end of the assembly will be a front end with respect to a direction of travel of the assembly. Accordingly, in the following description the terms front end, forward facing or similar will be used to describe or refer to elements that are located at or near the first, distal end of the assembly or that face in a direction towards the distal end. Similarly, the terms rear end, rearward facing or similar denote elements that are located at or near the second, proximal end of the assembly or that face in a direction towards the second end.

A preferred embodiment of an inspection assembly10according to the present invention is illustrated inFIGS. 1 to 4. The inspection assembly10includes an elongate main body12having a first, distal end14and a second, proximal end16. The first and second ends14,16define a longitudinal axis18of the inspection assembly10.

An end region20of the main body12at the distal end14comprises a light emitting portion22, a light guide portion24and a nose portion26. The nose portion26includes a distal end face28of the main body12. The end region20is generally tapered such that an external diameter of the main body12at the light emitting portion22is greater than the external diameter of the nose portion26.

A decrease in diameter of the light emitting portion22creates a shoulder30having a generally forward facing surface32. A plurality of apertures34are formed in the shoulder30. The apertures34are sealed by transparent windows or viewports36. The apertures34are preferably in a substantially circular or annular arrangement around the shoulder30.

A bore38extends longitudinally through the end region20and terminates at an aperture40in the distal end face28. A lens42is mounted in the aperture40. The lens42is preferably an ultra wide angle lens such as a fish-eye lens. The fish-eye lens will typically have an angle of view (α) of about 185°, compared to a standard lens having an angle of view (β) of about 74°, as illustrated inFIG. 2. In this embodiment, including a fish-eye lens42, a part of the lens42projects forward of the distal end face28so that the angle of view or field of view is not obstructed by the end face28of the main body12.

The inspection assembly10further comprises a camera including an image sensor arranged to capture an image of the field of view through the lens42. Accordingly, the camera captures an image of a region substantially ahead or in front of the distal end14of the inspection assembly10. It will be appreciated that if an ultra wide angle lens42is used, having an angle of view of greater than 180°, the periphery of the image may include a region located substantially parallel with or a small distance behind the distal end face28of the inspection assembly10.

To protect the lens42, the inspection assembly10includes an optical cap44, shown most clearly inFIG. 4. The cap44comprises a hemi-spherical or dome-shaped window portion46and a tubular attachment portion48. At least the window portion46is optically transparent. Typically the cap44will be a unitary piece such that both the window portion and the attachment portion are made of the same transparent material. In this embodiment the cap44is made of a suitable acrylic material.

The attachment portion48includes a female securing feature in the form of a screw thread50on an internal surface52of the attachment portion48. A corresponding male securing feature in the form of a screw thread54is provided on an external surface56of the nose portion26of the main body12. The cap44is, therefore, secured to the main body12by engaging the complementary screw threads50,54. Once engaged, the attachment portion48of the cap44extends around the nose portion26of the main body12. Sealing elements such as o-rings55may be provided to form a seal between the external surface56of the nose portion26and the internal surface52of the cap44.

With the cap44secured to the main body12the window portion46extends beyond the distal end face28of the nose portion26. In particular the domed window portion46extends over the lens42such that there is a gap57between a front face43of the lens42and an internal surface31of the window portion46of the cap44.

The inspection assembly10further comprises a plurality of light sources58mounted in the light emitting portion22of the main body12. The light sources58are preferably light emitting diodes (LEDs). Each of the light sources58is arranged to emit a beam of light through a corresponding one of the apertures34. As such, the light sources58are substantially forward facing and the light emitted by the light sources58travels in a direction that illuminates an area ahead of or in front of the distal end14of the inspection assembly10.

The light guide portion24of the end region20comprises a plurality of radially extending webs or ribs60. Light guide channels are defined between neighbouring ribs60. Each channel is aligned with one of the apertures34.

As shown inFIG. 2, each light source58emits a diverging beam of light62. A direction of the emitted light is defined by a centre line64of the light beam62. The beam divergence angle is preferably between 10° and 30°, and most preferably about 20°.

A reflection collar66is located over and around the attachment portion48of the cap44. As shown inFIGS. 5 to 7, the collar66comprises a sleeve portion68and retaining means in the form of a retaining flange70. The sleeve portion68is substantially tubular and extends between first and second ends72,74. A bore76of the sleeve portion68extends along an axis78of the collar66. The retaining flange70projects radially inwardly from the second end74of the sleeve portion68.

In a preferred embodiment the collar66has a circular cross-sectional shape. An internal diameter of the sleeve portion68is constant along the length of the sleeve portion68and is sized to receive the attachment portion48of the cap44. An external surface80of the collar66at the first end72is tapered.

The external surface80of the collar66is also tapered at the second end74. This tapered portion of the surface80provides a reflection surface82. An angle between the reflection surface82and the axis78of the collar66is preferably greater than 10° and less than 70°. The angle between the reflection surface82and the axis78may be more than 20° or more than 30°. The angle between the reflection surface82and the axis78may be less than 60°, less than 50° or less than 40°. Most preferably the angle is between 30° and 40° and will typically be about 36°.

The collar66is preferably made from a metallic material, and will typically be made from a suitable grade of stainless steel. The reflection surface82is preferably unpolished. This causes the light that is reflected from the surface82to be diffused, as illustrated inFIG. 3.

To attach the reflection collar66to the main body12of the inspection assembly10, the collar66is fitted over the nose portion26of the main body12with the second end74of the collar66nearest the light sources44. The collar66is prevented from moving further along the end region20of the main body12by an abutment surface75of the main body12.

The reflection surface82of the collar66is, therefore, located between the light sources58and the lens42in a longitudinal direction. The reflection surface82is substantially rear facing so that a fraction of the light that is emitted by the light sources58is incident on the reflection surface82.

The cap44is screwed onto the nose portion26of the main body12such that the attachment portion48is located between the sleeve portion68of the collar66and the nose portion26. The cap44is screwed onto the nose portion26until an end49of the attachment portion48contacts the flange70of the collar66and the flange70of the collar66is in contact with the abutment surface75. In this way, with the collar66and cap44fully attached to the main body12, the flange70is clamped between the abutment surface75of the main body12and the end49of the cap44, thereby retaining the collar66on the main body12. Furthermore, in this position the flange70extends over and covers the end49of the cap44. In this way, the flange70blocks light emitted by the light sources58that would otherwise be incident on the end49of the cap44.

The length of the collar66, between the first and second ends72,74, is such that the first end72of the collar66does not extend beyond the front face43of the lens42. In this way the collar66does not block the field of view of the lens42. The collar66does, however, fully surround at least a part of the attachment portion48of the cap44thereby protecting this part of the cap44from damage.

The light sources58are arranged such that the centre lines64of the light beams62fall on a circle having a diameter greater than the external diameter of the collar66. In this way, at least 50% of the light emitted by the light sources58passes around the collar66without being reflected or deflected by the reflection surface82.

A fraction of the light emitted by each of the light sources58is incident on the reflection surface82. The angle of the reflection surface82causes the light to be reflected in a direction away from the axis18of the inspection assembly10. In particular, a fraction of the light beam62located between the main body12of the inspection assembly10and the centre line64of the light beam62is reflected by the reflection surface82.

This is illustrated inFIG. 8which shows the illumination pattern resulting from an annular arrangement of five light sources emitting divergent beams of light62.

The centre line64of each of the beams of light62lies on a circle84having a diameter greater than the external diameter86of the collar. The central shaded region88inFIG. 8denotes the part of each of the light beams62that is incident on a part of the inspection assembly10and does not reach the field of view of the lens42. The hatched region90denotes the fraction of each of the light beams62that strikes the reflection surface82and is reflected outwardly to a peripheral region of the field of view.

It can be seen that the result of reflecting a radially inner portion90of each of the light beams62is that the overall intensity of the light in a central region of the field of view is decreased while the overall intensity of the light in a peripheral region of the field of view is increased. In this way the field of view is more evenly illuminated decreasing the likelihood that regions of an image captured by the camera will be underexposed or overexposed.

In other embodiments the light sources may be arranged such that centre lines164of light beams162emitted by the light sources fall on a circle having a diameter smaller than the external diameter of the collar. This is illustrated inFIG. 9which shows the illumination pattern resulting from an annular arrangement of five light sources emitting divergent beams of light162. The centre line164of each of the beams of light162lies on a circle184having a diameter smaller than the external diameter186of the collar. The central shaded region188inFIG. 9denotes the part of each of the light beams162that is incident on a part of the inspection assembly10and does not reach the field of view of the lens42. The hatched region190denotes the fraction of each of the light beams162that strikes the reflection surface82and is reflected outwardly to a peripheral region of the field of view. In some of these embodiments at least 50% of the light emitted by the light sources58passes around the collar66without being reflected or deflected by the reflection surface82. In one particular embodiment the diameter of the circle184on which the centre line164of each of the beams of light162lies is approximately 28 mm and the external diameter186of the collar is approximately 30 mm.

It will be appreciated that although the reflection surface82has been described as being part of an illumination collar66that is separate from the main body12of the inspection assembly10, in other embodiments the reflection surface82may be provided on the main body12or may be provided by another component of the inspection assembly10. The reflection surface may be provided on the optical cap. Furthermore, in some embodiments, the collar66may be attached or secured directly to the main body12rather than being secured by means of the cap44as described above. Accordingly, in these embodiments the collar66may include means for securing the collar66to the main body12, for example by means of screw threads.

FIG. 10shows another embodiment of an inspection assembly210. Many of the features of this embodiment are the same as or similar to features of the previous embodiment and like features are indicated by reference numerals incremented by 200.

As described above, an end region220of a main body212of the inspection assembly210at a distal end214comprises a light emitting portion222, including a plurality of light sources258, a light guide portion224and a nose portion226.

A lens242is mounted in an aperture240in a distal end face228of the nose portion226. The lens242is preferably a wide angle lens and it is advantageous if the lens242projects forward of the distal end face228so that the angle of view of the lens242is not obstructed by the end face228of the main body212.

To protect the lens242, the inspection assembly210includes an optical cap244attached to the nose portion226. Additional views of the optical cap244are provided inFIGS. 11 and 12.

The optical cap244includes an optically transparent window element292and a collar266. In this embodiment the collar266comprises a sleeve element268and a ring element296. The window element292is made of a suitable optically transparent material that is able to withstand the high temperatures, high pressures and other harsh environments that may be encountered in use, for example in a downhole environment. In preferred embodiments the window element292is made of sapphire, quartz or diamond. Both the sleeve element268and the ring element296are made of a suitable metal material. In a preferred embodiment the sleeve element268and the ring element296are made of titanium. Importantly the materials from which the window element292and the collar266(the sleeve element268and/or the ring element296) are made should have substantially the same coefficient of thermal expansion. This means that the difference between the coefficient of thermal expansion of the material of the window element292and the coefficient of thermal expansion of the material of the collar266should be no more than 10×106(° C.)−1, preferably no more than 5×106(° C.)−1, and most preferably no more than 2×106(° C.)−1.

The window element292includes a domed portion293and an attachment portion295. The attachment portion295is integral with the domed portion293. The attachment portion295is annular and extends from the domed portion293to provide a base end face297of the window element292furthest from the apex or crown294of the domed portion293. Preferably the domed portion293of the window element292is hemispherical. In some embodiments, and as illustrated inFIG. 11, the radial thickness of the attachment portion295may be less than the radial thickness of the domed portion293such that an inner radius of the attachment portion295is greater than an inner radius of the domed portion293and an outer radius of the attachment portion295is smaller than an outer radius of the domed portion293.

The sleeve element268is tubular, and has a circular cross-sectional shape. A central bore276extends through the sleeve element268from a first end272to a second end274, thereby defining a longitudinal axis278of the sleeve element268. The sleeve element268includes means for securing the sleeve element268, and therefore the optical cap244, to the main body212of the inspection assembly210. In this embodiment the means comprises a screw thread250formed on an internal surface252of the sleeve element268proximate the first end272of the sleeve element268. The screw thread250does not extend for the full length of the sleeve element268and, in this example, the diameter of the threaded region is smaller than the diameter of a non-threaded section of the bore276proximate the second end274of the sleeve element268.

An outer surface280of the sleeve element268includes a step298such that an outer diameter of a first section301of the sleeve element268on a first side of the step298proximate the first end272of the sleeve element268is smaller than an outer diameter of a second section303of the sleeve element268on a second side of the step298proximate the second end274of the sleeve element268.

The step298, therefore, provides an abutment surface305, which in this embodiment is annular and is substantially perpendicular to the axis278of the sleeve element268.

The outer surface280of the sleeve element268is chamfered at its second end274forming a reflection surface282as described above. Preferably the angle between the reflection surface282and the axis278of the collar266is between 10° and 70° and more preferably between 30° and 40°. The angle between the reflection surface282and the axis278may be more than 20° or more than 30°. The angle between the reflection surface282and the axis278may be less than 60°, less than 50° or less than 40°.

As shown most clearly inFIG. 11, in this embodiment of the sleeve element268a second step307is formed in the outer surface280of the first section301of the sleeve element268. This second step307creates a further decrease in the outer diameter of the sleeve element268proximate the first end272. A ledge309having a radially outer surface is, therefore, created extending between the first and second steps298,307.

The ring element296is tubular and has a circular cross-sectional shape. An outer surface311of the ring element296at a first end313is tapered. An annular rib315extends radially inwardly from an internal surface317of the ring element296. The rib315is located nearer the first end313of the ring element296than a second end319such that a first section325of the ring element296is defined between the rib315and the first end313and a second section327of the ring element296is defined between the rib315and the second end319. The rib315comprises a first surface321facing generally towards the first end313of the ring element296and an opposite second surface323facing generally towards the second end319of the ring element296. The internal diameter of the first section325of the ring element296may be smaller than the internal diameter of the second section327of the ring element296.

The attachment portion295of the window element292is received in the first end313of the ring element296. As such the outer diameter of the attachment portion295of the window element292is substantially equal to the internal diameter of the first section325of the ring element296. The base end face297of the window element292is in contact with the first surface321of the rib315of the ring element296. The window element292is bonded to the ring element296by brazing, welding or fusing. Preferably the window element292is bonded to the ring element296by brazing, electron beam welding or diffusion bonding.

An end face329at the second end319of the ring element296seats on the abutment surface305of the sleeve element268. In this embodiment a part of the internal surface of the ring element296at the second end319contacts the outer surface of the ledge309of the sleeve element268. In this position, the outer surface311of the ring element296at the second end319is preferably continuous or contiguous with the outer surface280of the second section303of the sleeve element268. The ring element296is bonded to the sleeve element268by brazing, welding or fusing. Preferably the ring element296is bonded to the sleeve element268by brazing, electron beam welding or diffusion bonding.

In a particularly preferred embodiment the ring element296and the sleeve element268are both made from Grade 5 titanium and the window element292is made from sapphire. The sapphire is bonded to the titanium ring element296by brazing and the ring element296and the sleeve element268are joined by electron beam welding.

Returning toFIG. 10a screw thread254is provided on an external surface of the nose portion226of the main body212. The optical cap244is secured to the main body212by engaging the complementary screw threads250,254. Once engaged, the collar266, and in particular the sleeve element268, of the cap244extends around the nose portion226of the main body212. Sealing elements such as o-rings255may be provided to form a seal between the external surface of the nose portion26and the internal surface252of the sleeve element268.

The optical cap244is screwed onto the nose portion226until the second end274of the sleeve element268contacts an abutment surface275of the nose portion226. The length of the collar266, between the first end313of the ring element296and the second end274of the sleeve element268, is such that the first end313of the ring element296does not extend beyond the front face243of the lens242. In this way the collar266does not block the field of view of the lens242.

With the cap244secured to the main body212the window element292extends beyond the distal end face228of the nose portion226. In particular the lens242is located in the attachment portion295of the window element292and the domed portion293of the window element292extends over the lens242such that there is a gap257between a front face243of the lens242and an internal surface231of the domed portion293.

The reflection surface282of the collar266is located between the light sources258and the lens242in a longitudinal direction. The reflection surface282is substantially rear facing so that a fraction of the light that is emitted by the light sources258is incident on the reflection surface282. The angle of the reflection surface282causes the light to be reflected in a direction away from the axis of the inspection assembly210, as described above.

In other embodiments of the optical cap the collar may comprise a washer or sealing element located between the window element and the sleeve element or the ring element. The window element may be brazed or welded to one part of the sealing element and the sleeve element or the ring element may be brazed or welded to another part of the sealing element. In this way the sealing element may be chosen or designed to reduce the effects of any mismatch in coefficients of thermal expansion of the materials of the window element and the sleeve element or the ring element.

In the embodiment shown inFIGS. 10 and 11the collar266includes a ring element296that surrounds a part of the outer surface of the window element292and to which the window element292is bonded. In other embodiments the window element may be directly bonded to the sleeve element. For example a base end face of the window element may be directly bonded to an end face at the first end of the sleeve element by diffusion bonding.

In a further embodiment the collar may comprise a metal washer element located between a base end face of the window element and an end face at the first end of the sleeve element. The window element may be diffusion bonded to the washer element, and the washer element may be electron beam welded to the sleeve element.

The present invention therefore provides an optical cap that extends over and protects a lens of an inspection assembly and is suitable for operation in downhole environments.