Television – Special applications – Hazardous or inaccessible
Reexamination Certificate
2000-07-18
2003-06-17
Britton, Howard (Department: 2613)
Television
Special applications
Hazardous or inaccessible
C356S241100, C396S028000
Reexamination Certificate
active
06580449
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed generally towards the inspection of boreholes and other limited access passageways, and more particularly, to an inspection instrument having a low voltage, low power light-head and camera arrangement for capturing video images.
In drilling oil and gas wells it is often necessary to obtain information concerning conditions within the borehole. Where the borehole has casings and fittings, as is typical of production oil wells, there is a continuing need to inspect the casings and fittings for corrosion. The early detection of the onset of corrosion in borehole casings allows for the application of anti-corrosive compounds to the well. Early treatment of corrosive well conditions may prevent the need for expensive casing replacement procedures. Where the borehole may contain oil, natural gas, or water, it often proves convenient to verify the presence of these substances through visual examination.
There may also be a need to determine the entry points of fluids into a well. Where water is infiltrating an oil well, it is necessary to determine the point of entry so that steps may be taken to stop the infiltration. If a visual examination of a well bore reveals oil at one location and a mixture of oil and water at another location, it can be concluded that the infiltration of water is occurring at some point in between. By gradually moving a camera between the two locations, the point of infiltration may be located and consequently the flow of water may be blocked through subsequent action.
Although visual examination of well bores is highly desirable, the environmental conditions typical of oil and gas wells pose special problems that tend to hinder camera operation. Well bores range in depth from several hundred to several thousand feet. Consequently, hydrostatic pressure within a deep bore, in addition to high well head pressures caused by gas production, can be quite large and can reach and often exceed 70 mPa (10,000 pounds per square inch). Ambient well temperatures on the order of 135 degrees Celsius (275 degrees Fahrenheit) are not uncommon. In addition, oil wells typically contain highly corrosive hydrogen sulfide and carbon dioxide gases. These harsh environmental conditions dictate that cameras and associated lighting equipment must be enclosed within protective housings. Fluids collected in well bores further complicate the visualization problem. Collected fluids are generally dark, cloudy, and often contain mineral particulates in suspension. One effect most fluids found in well bores have is to reduce light transmission. For this reason, high intensity lights are generally required to illuminate a well bore sufficiently to obtain an adequate video image.
Prior devices for visually examining boreholes typically include a camera and a high intensity light source enclosed in a protective housing. The devices are generally attached to an armored cable that supports the device and provides electrical power and communication signals to the device. The cable is typically lowered and raised within the borehole by means of reel located at a surface station proximate the entrance to the borehole. The surface station further includes a power source and control apparatus for operation of the inspection device.
One constant problem facing down hole instrument designers is the need to make the instruments small enough to be usable in very narrow passageways, including those that have restrictions, such as small diameter pipes or casings but at the same time have the ability to provide high quality images, either in real time or stored for viewing later. Casings having internal restrictions, such as tubing, safety valves, or other devices, that result in an internal effective diameter of 44 millimeters (1¾ inches) are not uncommon. The need to provide both a camera and an associated light source can make the instrument too large to fit in such small diameter passageways.
Another problem faced by designers of borehole inspection devices is the effect of heat upon camera operation. Camera electronics possess a limited capacity to withstand heat and the combination of high ambient borehole temperatures and the heat generated by high intensity lighting systems may produce a temporary or permanent failure of the camera. Such failures can be quite expensive and time consuming as the instrument must either be raised until it cools down enough to once again come on line, or must be extracted from the borehole and replaced.
An example of an early borehole inspection device is one that includes a cylindrical housing into which is mounted a television camera and a light source in the form of a donut-shaped lamp that surrounds the television camera. The device also includes a coolant jacket and coolant that surrounds the heat sensitive camera electronics. Since the donut-shaped lamp surrounds the camera, heat developed by the lamp reaches the camera and will add to the heat environment the camera will experience. As discussed above, a level of heat that is too high will result in camera failure. The use of a cooling system in a down hole instrument is undesirable due to the added equipment that would be necessary, thereby increasing the size of the instrument, as well as the reliability considerations. The more equipment that is used, the more likely a failure will occur. Adding heat from a light source used to illuminate the field of view of the camera is also undesirable. Also, placing the lamp around the camera increases the diameter of the device thereby making it unusable in very restricted passageways. Approaches have been devised to longitudinally and physically separate the light source from the camera so that any heat developed by the light source will be generated at a distance from the camera. Once such approach is to mount the light source in front of the camera facing the field of view of the camera but separated from the camera by mounting arms. In this arrangement, the light source blocks a portion of the field of view of the camera, yet this approach has proven to be successful. In some applications however, is would be desirable to have a clear field of view for the camera.
A more modern borehole inspection device uses a back-lighted camera where the camera is suspended in front of a high intensity lamp and is axially separated from the lamp a sufficient distance to provide significant thermal isolation of the camera from the lamp. Light is directed into the camera's field of view by means of a reflector located behind the camera. By isolating the camera from the light source heat, a significant improvement in the art has been provided and this approach has proven successful. A back-light arrangement separates the heat generated by the light source from the camera resulting in cooler temperatures for the camera.
However, because back-lighting is used, a brighter light source is needed with an accompanying higher power requirement. More electrical energy must be provided to the light source so that enough light reaches the camera's field of view. Such increased power requirements either require a larger battery in the instrument, which can result in a larger and often impractical instrument, or power provided to the instrument through the cable which results in a larger cable. Additionally in this arrangement, the light source is exposed to the environment and must be sealed against contaminants, which is not a minor task. Further, the camera is extended from the light source by arms, which can be bent during operation. Bent arms can result in off-center view angles for the camera and if severe enough, the instrument must be withdrawn from the borehole and corrected.
Despite the above, the back-light approach has proven to be highly successful in large diameter tubular passageways. Better lighting is provided resulting in significantly better images. However, the back-light approach relies on the reflection of light from the walls of the passageway. In very small diameter passageways, the camera of
Britton Howard
DHV International, Inc.
Fulwider Patton Lee & Utecht LLP
LandOfFree
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