Abstract:
The present invention relates to an optical element for use in a camera system for the inspection of passageways, a camera system for the inspection of passageways and a method of illuminating a passageway during inspection with a camera. An optical element for use in a camera system for the inspection of passageways comprises a first optical portion arranged to transmit light into a camera, a second optical portion arranged to transmit light emitted from a light source, the second optical portion located adjacent the first optical portion, and barrier means arranged to prevent light being transmitted from the second optical portion into the first optical portion.

Description:
BACKGROUND 
       [0001]    a. Field of the Invention 
         [0002]    The present invention relates to an optical element for use in a camera system for the inspection of passageways, a camera system for the inspection of passageways and a method of illuminating a passageway during inspection with a camera. In particular the invention relates to an optical element for protecting the video camera and the light source of a wellbore inspection system while permitting good illumination of the field of view of the camera. 
         [0003]    b. Related Art 
         [0004]    In oil and gas wells, the wellbore may be open or may be clad with a well casing. Visual inspection of the wellbore is important to check the integrity of the wellbore, and to investigate any downhole problems that may delay or prevent use of the well. For example, it is important to regularly inspect the casings for corrosion and wear. 
         [0005]    Although visual inspection of the wellbore is important, the conditions typically found in a wellbore tend to hinder the ability to use many camera systems. Wellbores can have diameters in the range 10 centimeters to 1 meter and can reach depths of hundreds or thousands of meters. In order to inspect these bores, therefore, it is not only necessary to provide a camera system that can operate at these depths, but also to provide the lighting required to be able to capture still images or video in this confined environment. 
         [0006]    Furthermore, any camera system must be able to withstand the pressures and temperatures encountered at depth in a borehole. Pressures at these depths can be very large and can reach around 150 MPa, and in addition, temperatures may exceed 100° C. 
         [0007]    Typically, downhole camera systems comprise a camera and light source contained in a protective steel sheath. These camera systems are lowered into the wellbore on an electrical cable or a shaft, with the images from the camera being relayed back to the surface where they are displayed and recorded. 
         [0008]    The confined environment of the wellbore causes problems in designing a camera and lighting arrangement that is small enough while still delivering high enough light levels to capture the required images. 
         [0009]    Several camera systems use a backlight system in which the light source is mounted at a distance behind the camera. The light is then directed into the field of view of the camera by means of a reflector mounted adjacent to the camera. However, this approach is less successful in narrower passageways as the size of the camera becomes too large compared to the diameter of the bore to allow sufficient light to be reflected. 
         [0010]    It is also known to provide an array of light emitting diodes (LEDs) as the light source due to their relatively low power consumption and small size. These LEDs are typically mounted around the outside of the camera approximately level with the camera lens. The LEDs therefore directly illuminate the field of view of the camera. 
         [0011]    In order to protect the camera and the light source from the harsh environment of the wellbore, a cover or window is typically placed over the distal end of the camera system. Any light emitted from the light source, therefore, must pass through this window before it illuminates the wellbore. 
         [0012]    This has a disadvantage, however, because some of the light that travels through the window is internally reflected and does not pass through the window. Furthermore, some of the internally reflected light is directed back towards the lens of the camera, leading to poor images. 
         [0013]    It is an object of the present invention to provide an improved window for a subsea camera system that overcomes these problems. 
       SUMMARY OF THE INVENTION 
       [0014]    According to the invention, there is provided an optical element for use in a camera system for the inspection of passageways, the element comprising:
       a first optical portion arranged to transmit light into a camera;   a second optical portion arranged to transmit light emitted from a light source, the second optical portion located adjacent the first optical portion; and   barrier means arranged to prevent light being transmitted from the second optical portion into the first optical portion.       
 
         [0018]    Also according to the invention, there is provided a camera system for use in the inspection of passageways, the system comprising:
       a housing having opposing first and second ends;   a camera mounted in the housing, the camera positioned proximate the first end of the housing;   a light source arranged to direct emitted light out of the first end of the housing; and   an optical element mounted at the first end of the housing, the element comprising:   a first optical portion arranged to transmit light into the camera;   a second optical portion arranged to transmit light emitted from the light source, the second optical portion located adjacent the first optical portion; and   barrier means arranged to prevent light being transmitted from the second optical portion into the first optical portion.       
 
         [0026]    Also according to the invention, there is provided a method of illuminating a passageway during inspection with a camera system, the camera system being according to the invention, and the method comprising the steps of:
       illuminating the light source to provide emitted light;   transmitting the emitted light through the second optical portion in a first direction to illuminate an object; and   transmitting light through the first optical portion in a second direction, substantially opposite to the first direction, into the camera so that the camera captures the image of the object;       
 
         [0030]    wherein, in use, the emitted light is prevented from being transmitted directly into the first optical portion from the second optical portion by said barrier means. 
         [0031]    Preferably, the barrier means comprises reflecting means to reflect light in the second optical portion and to prevent light from the second optical portion being transmitted into the first optical portion. The reflecting means may comprise a reflecting surface, which may comprise a peripheral surface of the first optical portion and/or the second optical portion. 
         [0032]    In a preferred embodiment the barrier means comprises an interface between the first optical portion and the second optical portion. The interface may be formed by an unpolished surface of at least one of the first and second optical portions. 
         [0033]    In other embodiments, the barrier means comprises a gap between the first optical portion and the second optical portion. Preferably the gap is filled with silicone. 
         [0034]    Preferably, the second optical portion surrounds the first optical portion. The first and second optical portions may be concentric. Preferably, the first optical portion is cylindrical and the second optical portion is annular and surrounds the first optical portion. 
         [0035]    Preferably, the first and second optical portions are made of sapphire. However, the first and second optical portions may be made of any other suitable materials. 
         [0036]    Preferably the optical portions are made of a ceramic material. More preferably the optical portions are made of quartz, diamond or crystal. 
         [0037]    The optical element may be disc-shaped having parallel opposing first and second end faces and the barrier means may be substantially perpendicular to the first and second end faces. 
         [0038]    In preferred embodiments, the optical element further comprises a base plate attached to the second end face. Preferably, the base plate is made of titanium and the first and second optical portions are bonded to the base plate by diffusion bonding. 
         [0039]    When the optical element is mounted in a camera system, preferably the first end face of the optical element is closer to the first end of the housing than the second end face, and the camera and the light source are located adjacent to the second end face. 
         [0040]    Preferably the light source is arranged, in use, to illuminate an object, the image of which is being captured by the camera. 
         [0041]    Preferably, the camera system comprises a plurality of light sources. The plurality of light sources may comprise light emitting diodes. 
         [0042]    Preferably, the plurality of light sources are arranged in a circle around the camera. 
         [0043]    In embodiments in which the optical element comprises a base plate in contact with the second end face, preferably the base plate includes at least two apertures, and the camera and the light source are arranged so that at least a part of each of the camera and the light source are located within an aperture. 
         [0044]    Preferably the second optical portion is arranged to transmit light from the light source in a first direction through the optical element. Preferably the first optical portion is arranged to transmit light into the camera in a second direction through the optical element. Preferably the first direction is the opposite direction to the second direction. 
         [0045]    The barrier means may prevent light from the second optical portion travelling in the second direction being transmitted into the first optical portion. 
         [0046]    Preferably the reflection means substantially maintains the light from the light source within the second optical portion as the light is transmitted from a second end of the second optical portion to a first end of the second optical portion. 
         [0047]    Preferably the second optical portion extends from a first end face of the optical element to a second end face of the optical element and transmits light from the second end to the first end. Preferably the first optical portion extends from a first end face of the optical element to a second end face of the optical element and the camera receives light entering from the first end and which is transmitted to the second end of the optical element. 
         [0048]    Preferably, the barrier means reflects light in the second optical portion and prevent light from the second optical portion being transmitted into the first optical portion. The barrier means may comprise a shroud. The shroud may locate around an outer peripheral surface of the first optical portion and/or an inner peripheral surface of the second optical portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0049]    The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: 
           [0050]      FIG. 1  is a perspective view of an optical element for use in a camera system according to a first embodiment of the invention; 
           [0051]      FIG. 2   a  is a schematic diagram illustrating light reflection by an interface present in the optical element of  FIG. 1 ; 
           [0052]      FIG. 2   b  is a schematic diagram illustrating internal light reflection by a front surface of an optical element when an interface is not present; 
           [0053]      FIG. 3  is a perspective view of an optical element for use in a camera system according to a second preferred embodiment of the invention; 
           [0054]      FIG. 4  is a sectional view of the optical element of  FIG. 3 ; 
           [0055]      FIG. 5  is a rear view of the optical element of  FIG. 3  showing the arrangement of apertures in the base plate; 
           [0056]      FIG. 6  is a cross-sectional view of the optical element of  FIG. 3  with the gap between the first and second optical portions exaggerated; 
           [0057]      FIG. 7  is a cross-sectional view of a camera system including the optical element of  FIG. 3 ; and 
           [0058]      FIG. 8  is an enlarged view of the front end of the camera system of  FIG. 7 , showing the arrangement of the camera lens, light sources and optical element. 
       
    
    
     DETAILED DESCRIPTION 
       [0059]      FIG. 1  shows a window or optical element  1  for use in a camera system that may be used to inspect wellbores or other passageways. These camera systems typically include a camera and one or more light sources arranged to light the field of view of the camera. Typically these are housed in a front, 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 optical element at the front end of the camera housing that serves to protect the camera, in the harsh environmental of a wellbore for example. 
         [0060]    In this embodiment the optical element  1  of the present invention comprises an optical layer  2  which includes an interface  4  which prevents light emitted from a light source being internally reflected within the optical element  1  back towards the camera. 
         [0061]    The optical element  1  comprises a disc-shaped optical layer  2 , which has a first, inner optical portion  6  and a second, outer optical portion  8 . The inner portion  6  is cylindrical, and the ring-shaped outer portion  8  surrounds it so that an inner surface  10  of the outer portion  8  is substantially in contact with the outer surface  12  of the inner portion  6  thereby forming a cylindrical interface  4  between the inner and outer portions  6 ,  8 . 
         [0062]    The thickness of the inner and outer portions  6 ,  8  is the same so that the front and rear faces  14 ,  16  of the inner portion  6  are co-planar with the respective front and rear faces  14 ′,  16 ′ of the outer portion  8 . 
         [0063]    Preferably, both the inner and outer portions  6 ,  8  of the optical layer  2  are made of sapphire, however, the optical layer  2  may be made of quartz, diamond, crystal or any other suitable material. The material of the optical layer  2  must be optically clear, for example transparent or translucent, and must also be able to withstand the harsh conditions within a wellbore. For example, the optical layer must be able to withstand high pressures of over 100 MPa as well as high temperatures of up to around 200° C. The material should also be able to withstand any corrosive chemicals that are encountered in the wellbore. 
         [0064]    In a simplest embodiment the cylindrical interface  4  extends for the full thickness of the optical layer  2  and the plane of the interface  4  is substantially perpendicular to the front and rear faces  14 ,  16  of the layer  2 . The inner and outer surfaces  10 ,  12  are unpolished so as to create a more optically reflective interface. When the optical element  1  is installed within a camera system as described above, light entering a camera  20  is transmitted predominantly through the inner optical portion  6 , and the light emitted by light sources  22  is transmitted substantially through the outer optical portion  8 . Due to the nature of the interface  4 , emitted light travelling in a range of angles towards the central axis  18  of the apparatus is reflected by the interface  4  and is directed outwards, away from the central axis  18 . This is shown most clearly in  FIG. 2   a . If the interface  4  was not present, then emitted light travelling in the same direction, as shown in  FIG. 2   b , would be reflected from the front surface  14  of the optical element  1  back towards the camera. 
         [0065]    The presence of the interface  4 , therefore, has two important advantages. Emitted light that would otherwise be internally reflected towards the camera is now reflected outwards through the front face  14  of outer portion  8  of the optical element  1 . This means that, firstly, more light is available to illuminate the field of view of the camera, and in particular the walls of the wellbore passageway, and secondly emitted light is prevented from being internally reflected into the camera which would otherwise adversely affect picture quality. 
         [0066]      FIG. 3  shows a second preferred embodiment of an optical element  100 . In this example, the optical layer  102  is mounted on a base layer or base plate  30 . The base plate  30  is disc-shaped and has an outer diameter equal to the outer diameter of the optical layer  102 . The thickness of the base plate  30  is significantly less than the thickness of the optical layer  102 , and in this embodiment the base plate  30  is about one quarter of the thickness of the optical layer  102 . 
         [0067]    The base plate  30  supports the optical layer  102  and includes a plurality of apertures  32 , 34  for receiving other parts of the camera system, as will be described in more detail below. In this example, the base plate  30  is made of titanium, however, the base plate may be made of any other suitable metallic material. Of importance in the selection of material for the base plate  30  is the matching of the coefficients of thermal expansion of the materials of the base plate  30  and the optical layer  102 . This is important as the optical element will be subjected to a large range of temperatures in use, for example −40° C. to 200° C., and a mismatch of coefficients of thermal expansion may lead to cracking or at least de-bonding of the optical layer  102 . 
         [0068]    The base plate  30  and the optical layer  102  are bonded together so that the rear face  116  of the optical layer  102  is in intimate contact with a front face  36  of the base plate  30 . In particular, in a preferred embodiment, a sapphire optical layer  102  is bonded to a titanium base plate  30  by a process known as diffusion bonding. This process uses high compressive forces and heat to bond the two materials at an atomic level. Preferably, a layer of aluminium  38  is introduced between the optical layer  102  and the base plate  30  to act as a ‘glue’ and aid in the diffusion bonding process. Other soft metals may be used to form the bond layer, however, the bond layer must be compliant. 
         [0069]    The base plate  30  includes a larger central aperture  32  and several smaller apertures  34  arranged in a circle around the central aperture  32 , as shown most clearly in  FIG. 5 . The smaller apertures  34  are spaced equidistantly around the circle and in this example there are ten apertures  34 . The central aperture  32  is sized to receive a lens of a camera that is mounted behind the base plate  30  when the optical element is installed in a camera system, and the smaller apertures  34  are designed to each house a single one of a number of light sources that are arranged to emit light to illuminate the field of view of the camera. 
         [0070]    The dimensions of the inner and outer portions  106 ,  108  of the optical layer  102  are such that the central aperture  32  is aligned with the inner portion  106  and the outer apertures  34  are aligned with the outer portion  108  so that the interface  104  between the portions lies between the central aperture  32  and the outer circle of apertures  34 , as shown most clearly in  FIG. 4 . 
         [0071]    As shown in  FIG. 6 , in another preferred embodiment, the interface  204  is in the form of a tapered annular gap  204  between the inner and outer optical portions  206 ,  208 . This tapered gap  204  is such that the outer surface  212  of the inner portion  206  and the inner surface  210  of the outer portion  208  are in contact at the rear face  216  of the optical layer  202 , but are spaced apart at the front face  214 . The size of the gap  204  shown in  FIG. 6  is exaggerated and typically the gap is minimal and primarily due to manufacturing tolerances between the inner and outer portions  206 ,  208  of the optical layer  202 . 
         [0072]    The gap  204  is filled with silicone which is preferably aerospace grade. In other embodiments other fillers may be used such as other grades of silicone, epoxies, rubbers or adhesives. Typically the choice of filler will be dependent on the environment in which the optical element will be used. The gap  204  must be filled to prevent contamination reaching the bond between the optical layer  202  and the base plate  230 . This is particularly important when aluminium is used to aid the bonding process due to the relatively reactive nature of aluminium with many different chemicals. 
         [0073]    Further, in a preferred embodiment, the inner and outer surfaces  210 ,  212  forming the interface  204  include a vapour deposition surface coating. This roughens the surfaces, further increasing the reflective nature of the interface  204 . 
         [0074]    In other embodiments, the inner and outer surfaces  210 ,  212  forming the interface  204  may be processed or treated in some other way to increase the reflective nature of the interface  204 . For example, one or both of the surfaces  210 ,  212  may be painted, or the surfaces may be textured by a process other than vapour deposition. 
         [0075]      FIGS. 7 and 8  show the optical element  100  in place in the distal end  42  of a camera system  40 . The camera system  40  comprises a cylindrical housing  44  which is typically made of stainless steel to withstand the operating environment at depth in a wellbore. In addition to the camera  120  and light sources  122 , the camera system  40  may also include a power supply, data transmitters and receivers, and controllers for controlling the camera  120  and light sources  122 . 
         [0076]    Connectors  46  are located at one end of the cylindrical camera system  40  for connecting to cables or a shaft used to lower the camera  40  down a wellbore and also for permitting electrical connections to be made to transmit data back up to the surface. 
         [0077]    The optical element  100  is located in a recess  48  in the distal end  42  of the housing  44  at the opposite end to the connectors  46 . 
         [0078]    The camera is mounted directly behind the base plate  30  of the optical element  100  such that the lens of the camera  120  is aligned with the central aperture  32  in the base plate  30 . The light sources  122 , which in this embodiment are light emitting diodes (LEDs)  122 , protrude through the smaller apertures  34  such that at least a front portion of the LEDs  122  are within the base plate  30 , as shown most clearly in  FIG. 8 . 
         [0079]    An O-ring  50  is used to form a seal between the optical layer  102  of the optical element  100  and the internal surface of the housing  44 . The use of a single optical element  100  having distinct inner and outer portions within an optical layer bonded to a unitary base plate means that only a single high pressure seal is required to seal the entire optical element  100  in the end of the camera system  40 . If the two optical portions were provided by two separate optical elements, or if the optical layer was not securely bonded to the base plate, then a number of high pressure seals would be required within the camera system to provide effective seals around each of the components. This would take up valuable space within the camera system and would decrease the available field of view of the camera. 
         [0080]    Although in the above-described embodiments the optical layer is disc-shaped and comprises concentric inner and outer optical portions the optical layer may be of any suitable shape for use within a camera system. Furthermore, the second optical portion may not surround the first optical portion but, instead, the first and second optical portions may be located side by side or in any other relative positions depending on the corresponding relative positions of the camera and light sources in the camera system. 
         [0081]    The optical element of the present invention, therefore, provides an improvement over existing camera system viewports by preventing unwanted internal reflections while maximising the illumination provided by the light sources and maximising the available field of view of the camera.