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DESCRIPTION OF THE DRAWINGS 
       [0001]      FIG. 1  is a perspective view of an embodiment of the invention; 
         [0002]      FIG. 2  is a front view of the cylindrical downhole camera comprising the embodiment of  FIG. 1 ; 
         [0003]      FIGS. 3   a  and  3   b  are front and side views, respectively, illustrating the tilting characteristics of the downhole camera assembly of  FIG. 2 ; 
         [0004]      FIG. 4  is a perspective view illustrating the downhole viewing coverage obtained by tilting the camera of  FIG. 2 ; 
         [0005]      FIG. 5  is a perspective view illustrating the semi-spherical field of view of the downhole imaging tool of the invention obtained by both tilting and rotating the camera&#39;s antenna; 
         [0006]      FIG. 6  is a block diagram illustrating the functional operation of the camera of  FIG. 2 ; 
         [0007]      FIG. 7  is a block diagram illustrating the functional operation of the overall downhole tool comprising the embodiment of  FIG. 1 ; 
         [0008]      FIG. 8  is a perspective view illustrating the downhole imaging tool of  FIG. 1  used to detect and inspect damaged or stuck tools in a downhole well casing; 
         [0009]      FIG. 9  is a perspective view illustrating the downhole imaging tool of  FIG. 1  used to detect and inspect slots, slits, frac holes, cracks, pipe collars, protrusions and other obstructions in a downhole well casing; 
         [0010]      FIG. 10  is a perspective view illustrating the downhole imaging tool of  FIG. 1  used to detect and inspect stuck pipes, tools, and other structures in a downhole open well bore; and 
         [0011]      FIG. 11  is a block diagram of the above ground equipment for the downhole inspection system of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION 
       [0012]    Referring to the drawings, and particularly to  FIGS. 1-11 , an embodiment of a downhole imaging tool and its method of use incorporating the invention is shown and generally designated by the reference numeral  10 . 
         [0013]    In  FIG. 1 , a new and improved downhole inspection tool  10  comprising an embodiment of the invention. The downhole inspection tool  10  is self contained and is comprised of a downhole camera assembly  18 , an antenna  20 , a data and control electronics assembly and memory  16 , a downhole tool power supply  14 , a backup battery module  15 , and a downhole centralizing unit  12 . The downhole camera assembly  18  may utilize millimeter wave imaging technology, typically operating in the frequency range from about 20 to about 300 GHz, however the tool is likewise capable of utilizing other imaging technologies including but not limited to of RF devices, microwave devices, infra-red devices, ultrasonic devices, acoustical devices, and optical devices. An appropriate antenna  20  is incorporated on the bottom end of the camera assembly  18  for directing the imaging source downward in a well bore onto a subject and for receiving images reflected therefrom. A data and control electronics assembly  16  is comprised of a microcontroller and a memory for storing programs, image data, and tool status data. The electronics assembly  16  further comprises means for two-way communication to above ground equipment via either wire or fiber optics or both. A downhole power supply  14 , which receives electric current at between about 200 volts and about 600 volts from an above ground AC or DC source, is used to develop required tool operating voltages ranging from between about plus and about minus 5 to 40 volts for use in powering the downhole tool. Optionally, the tool further comprises a backup battery module  15  as a secondary means of powering the camera and additional tool functions. The downhole inspection tool  10  is further comprised of a means for stabilizing itself inside a well tubing or casing through the utilization of devices comprised of one or more centralizing unit(s)  12 , and/or stabilizer locking feet. Finally, the downhole imaging tool further comprises a temperature sensor, a pressure sensor, a pressure safety relief valve, and other sensors as required. 
         [0014]    The downhole inspection tool  10  is used for various inspection functions in a well bore. Such inspections include, but are not limited to locating other downhole tools that may be stuck or otherwise impaired, observing how best to loosen and retrieve, stuck or impaired tools, and assisting in attaching other retrieval devices to stuck or impaired tools for removal from the well bore. The downhole inspection tool is further useful in locating other areas of interest in a well bore, such as, locating frac holes in well casings, slots in well casings, cracks or fractures in casings or tubing, obstructions in casings or tubing, and protruding structures inside casings or tubing. 
         [0015]      FIG. 2  is a more detailed description of the downhole camera assembly  18  of  FIG. 1 . The camera assembly  18  houses the imaging module  26 , which includes the high frequency millimeter wave or other imaging components and associated electronics. A rotation motor  22 , located near the top of the camera assembly  18 , has a rotating shaft  24  extending from the bottom end and attaching to the top portion of the imaging module  26 . The rotating shaft  24  is limited to rotating the imaging module  26  in azimuth through 360 degrees in steps as small as 0.8 degrees or multiples thereof. Furthermore, an antenna tilting device  28  is attached between the bottom end of the imaging module  26  and the antenna  20  and is used to tilt the antenna through 180 degrees in elevation. 
         [0016]      FIGS. 3   a  and  3   b  illustrate one configuration of the tilting device  28  for the camera assembly&#39;s antenna  20 . The tilting device  28  rotates a pin  32 , which is attached to a rotating antenna mounting plate  30 , so that when the pin  32  rotates the antenna  20  rotates through a 180 degree arc. In another embodiment a servo controlled swivel rotates the antenna  20  through a 180 degree arc. 
         [0017]      FIG. 4  illustrates tilting the camera antenna  20  over a 180 degree arc to illuminate a circular field of interest  36 . The camera antenna  20  is shown positioned at 0 degrees  35  looking directly into the wall of a well casing  34 , at 90 degrees  36  straight down the well bore casing, and at 135 degrees  37 , respectively. 
         [0018]      FIG. 5  illustrates the semi-hemispherical field of view  38  capability of the inspection tool  10  which is achieved by coupling the 360 degree rotation of the imaging module  26  with the 180 degree tilting characteristics of the tilting device  28 . The combination of rotating the imaging module  26 , which has the tilting device  28  and the antenna  20  attached at the bottom end thereof, through up to 360 degrees and tilting the antenna using the tilting device  28  through an angle up to 180 degrees allows the antenna to be focused  40  at any desired location within a hemispherical field of view  38 . In another embodiment the antenna is positioned by a servo controlled swivel. 
         [0019]      FIG. 6  is block diagram for the milli-meter wave camera assembly  18  utilized in the downhole inspection tool  10  which, in one embodiment of the invention operates in the frequency range of between about 20 and about 300 GHz. The basic components of the camera assembly  18  comprise a voltage controlled oscillator  42  coupled to a pre-amplifier  43 , which drives the input of feedback control circuitry  44 . The output of the feedback control circuitry  44  connects both to the antenna  20  and a low noise amplifier  45 , which couples to a signal output takeoff  46  and back into the feedback circuit  44 . A low noise intermediate frequency (IF) output signal is then taken from the output takeoff  46 . 
         [0020]      FIG. 7  is a block diagram illustrating the functional operation of a downhole inspection tool comprising an embodiment of the invention. A microcontroller unit (MCU)  50 , which communicates with an above ground control console by means of a transceiver  49  and tool interface  48 , provides master control of a downhole inspection tool comprising an embodiment of the invention. The MCU  50  controls the camera controller  54 , the data acquisition unit  58 , the imaging and control data memory bank  60 , the motor controller  52 , and antenna position controller  56  of the downhole inspection tool. The MCU  50  also tracks and communicates tool status to an above ground control console by means of the transceiver  49 . 
         [0021]      FIG. 8  is a perspective view illustrating an embodiment of the downhole inspection tool  10  used to detect and inspect damaged or stuck tools in a downhole well casing. The camera of the downhole inspection tool  10  focuses the circular field-of-view  36  from the antenna  20  on a broken drill bit  62  that is lodged sideways in a well casing  34 . The picture from the camera assembles of the downhole inspection tool is displayed on an above ground computer monitor for viewing by personnel of the tool retrieval crew to aid in more efficiently removing the broken drill bit. 
         [0022]      FIG. 9  is a perspective view illustrating an embodiment of the downhole inspection tool  10  used to inspect the conditions in a well bore casing  34 . This illustrates the use of the tool for locating and inspecting such features as casing slots  64  and smaller slits  66 , casing frac holes  68 , casing cracks  70 , casing pipe joint collars  72 , casing wall protrusions  74 , and other unwanted obstructions within a downhole well bore. In  FIG. 9  the camera&#39;s antenna  20  is shown focused at 0 degrees  35  on a slot  64  in a well casing  34 . 
         [0023]      FIG. 10  is a perspective view illustrating an embodiment of the downhole inspection tool  10  used to inspect the conditions in an open well bore  76 . This illustrates the use of the tool in which the tool&#39;s antenna  20  is focused  36  on a broken pipe  78  being lodge crosswise in an open well bore, thereby blocking access to the well bore for other tools and/or equipment to be placed therein. 
         [0024]      FIG. 11  is a block diagram of the above ground equipment control console for operating embodiments of the downhole inspection tool  10 . The above ground equipment control console is comprised of a controller  80  and computer/display  82  for controlling the overall operation of the system and displaying operational, status, and image data, a memory bank  84  for storing system and image information, an image processor  86  for processing image data, a transmitter/receiver (transceiver)  88  for communicating through a slip-ring interface  92  and downhole cable  94 , and a power supply  90  for supplying power to both the downhole tool power supply  14  and above ground equipment. 
         [0025]    Embodiments of the downhole inspection tool  10  can be operated in either wireline or slickline modes of operation. In the slickline mode there is no electrical connection with above ground equipment. In this mode the system operates from onboard battery power and stores image and status data in an onboard data storage memory bank. In this mode of operation, the tool is automatically turned on by onboard means, such as a timer, pressure sensor, or temperature sensor and takes downhole pictures based on a stored onboard operational program. The image data is then stored in the onboard data storage memory bank for above ground viewing later. 
         [0026]    Various embodiments of a downhole inspection tool and method have been described in detail herein. It will be appreciated, however, that the invention provides applicable inventive concepts that can be embodied in a wide variety of contexts. For example, while the description has included embodiments of the tool used in downhole oil and gas well applications, it can provide inspective functions in many other applications and especially so where high pressure and/or high temperature environments are involved. 
         [0027]    Although the invention has been described with reference to an illustrative embodiment, the foregoing description is not intended to limit the scope of the invention. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims incorporate any such modifications or embodiments.

Summary:
A downhole inspection tool for observing conditions in the harsh environment of a well bore. An embodiment of the tool comprises a high frequency camera, which operates in the millimeter wave frequency range with the capability of seeing through opaque environments. In use, the tool system provides pictures of conditions downhole for use by operators attempting to repair and/or remove broken downhole equipment by being able to observe the actual downhole conditions that exist. Furthermore, the system can be used to inspect the inside of a well casing or tubing for the presence of cracks, frac holes, slots, slits, protruding structures, stuck hardware, environmental conditions, etc.