Video logging system having remote power source

Abstract: An instrument probe (12) contains a camera (38) and light source (28) which is positioned in front of the camera for illuminating the passage (14) being inspected, such as a bore or a casing. The power source for the instrument probe is located at the surface. A support cable (16) contains an optical fiber (50) for conducting camera signals to the surface and electrical conductors (54, 60) for conducting power from the surface to the instrument probe. Outer electrical conductors (60) in the cable are alternating with and in electrical contact with strength member strands (58). The cable is enclosed in a stainless steel outer sheath (62). The support cable is coupled to the instrument probe by three fluid seals (64, 73, 76). The first (64) seals the outer sheath in the probe. The second (73) seals at the breakaway connection and the third (76) seals at the probe bulkhead (74).

Description: BACKGROUND The invention is related generally to the remote viewing of well bores and other limited access areas, and more particularly, to an apparatus having a camera for remotely viewing the condition of such limited access areas. There has long been a need in the field of well boring to visually examine the bore hole to examine geological formations or for other reasons. Where those well bores have casings and fittings, there is a continuing need to inspect the casings and fittings for corrosion and other conditions. By means of visual inspection, the locations of leaks and points of infiltration can be more easily identified. One existing method of accomplishing this is to insert an instrument probe containing a camera, such as a closed circuit television camera, in the bore hole and move it through the area to be inspected. Typically, a compact, rugged instrument containing the camera and a light source is provided as an instrument probe. A cable is attached between the instrument probe and the surface station to communicate camera signals to the surface from the instrument probe. In one technique, the communication link comprises optical fibers. Where the bore is vertical, gravity can be used to pull the instrument probe through the bore hole. The support cable contains strength members which preserve the integrity of the cable as it and the instrument probe are being pulled from the bore hole. Optical fibers offer certain advantages in communication systems. They are relatively immune to electromagnetic interference, they have relatively low cable weight, they have a large bandwidth, high frequency video signals can be transmitted over long lengths of cable with minimum attenuation and they have lower cost. Thus they are desirable in a remote logging instrument probe such as that used to view bore holes. However, optical fibers are sensitive to point stresses and bending. The fiber may impart significant attenuation to its conducted signal when bent. The cable system of a well logging instrument is repeatably pulled around at least one sheave and wound on and off a winch drum as it is lowered into and lifted out of bore holes. The cable must withstand repeated bending and tensions of thousands of pounds. Stretching the cable can stretch the optical fibers thereby increasing their stress and aggravating their attenuation. High pressures and high temperatures in the well holes may assist moisture in invading the cable and the optical fibers. Moisture invading the optical fiber through micro-cracks can increase its attenuation and reduce its strength. Thus, the cable connecting the instrument probe with the remote controller must protect the optical fibers as well as be strong enough to withstand repeated bending about sheaves and a winch drum, withstand stretching forces and the high temperatures and pressures in the bore hole (see GB-A-2 173 034). A logging instrument probe for well holes must be tugged to withstand the sometimes harsh conditions encountered in typical operation. For example, hydrostatic well pressures in excess of 4.2 x 10 6 kilograms per square meter (6,000 pounds per square inch) and ambient wall temperatures of up to and above 190°C (375°F) are not uncommon. The point where the support cable enters the instrument probe must have effective seals to deflect such high pressure/temperature fluids from entering. The main purpose of such seals is to protect the camera, the optical fibers and the electrical connections from the fluids present in the bore hole. Such seals have been difficult to manufacture on a repeatable basis and make the instrument probe very expensive as well as unreliable. Thus, it would be desirable to provide an effective seal arrangement which can be manufactured on a repeatable basis and which uses standard parts readily available thereby lowering the cost of the seal. Another common condition in bore holes is turbidity in the form of gases, mud, oil, and other fluids under high pressure. In prior techniques, high intensity lighting such as that provided by quartz lamps or halogen lamps, is provided to give bright light in the visible range for use with conventional television cameras. Depending upon the amount of turbidity, higher intensity light from the lamps may be required to provide dear images. In order to provide power for such lamps and for the camera and other equipment, well bore inspection instruments carry a self-contained power supply, typically battery packs. In addition to adding weight and bulk to the instrument probe, these battery packs have a limited life which is directly dependent upon the intensity of the lights. As an example, many battery packs of the size which can fit in a bore hole logging instrument probe can provide power for only 3 to 3½ hours when used with halogen lamps. Upon dissipation of the stored energy, the battery packs must be removed and replaced with charged batteries or a charging process must occur which may take many hours. This usually requires that the instrument probe be removed from the well hole, dis-assembled and re-assembled. This can be a time consuming process which subjects the support cable of the instrument probe to the added stresses of being pulled over the sheave and wound on the drum an additional time. To the inventor's knowledge, remotely locating a power source has up until this time not been practical in an application where a small diameter optical fiber is employed in the support cable having the extremely long lengths required for deep well holes. The power source has been included in the instrument probe itself. This co-location of power source with instrument probe was caused by the long lengths of cable required for use in deep well bores. In prior cables, the steel strength members of the cable were used as part of the electrically conductive path. Typically, the strength members are made of steel which has a relatively high specific resistance, and therefore a low resistive loop circuit was not available to carry the required current at an acceptable working voltage. The diameter of the strength members was increased to result in less resistance; however, even with this technique, the loop resistance was relatively high and the increased size of the strength members resulted in a large cable with the associated disadvantages of high weight and bulk. Additionally, such strength members were used to form the outer surface of the cable, thus making it rough and more difficult to handle. Hence, it would be desirable to provide an improved power arrangement so that the power source for the well logging instrument probe could be remotely located from the probe, such as at the surface, yet impracticably large voltages would not be required in order to get the required power over the typically long distances between the surface and the probe. Additionally, it would be desirable to provide a smaller support cable and a support cable having a smooth outer surface to facilitate handling, yet one having the required strength. Additionally, those concerned with instrument probes for use in viewing bore holes and casing have recognized the need for an improved sealing system to keep fluids from entering the probe. SUMMARY OF THE INVENTION According to this invention there is provided a down-hole inspection system as claimed in claim 1 herein the preamble of which is based on US-A-2,912,495. In order to prevent fluids from entering the instrument probe along the support cable entry point, a multiple seal arrangement is provided. The sealing arrangement preferably comprises three seals. Because the power source is located at the surface, no battery packs are needed in the instrument probe and it can be used for much greater time periods for observation of the conditions of the bore hole, the casing and the fittings. The support cable provides not only the optical fiber support an strength members but also the power transmission means necessary to operate the camera and lights and other equipment in the instrument probe. The triple seal of the cable in the instrument probe assures protection of the instrument probe equipment and is easily and relatively inexpensively provided. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an over all block diagram of a well logging system according to the present invention; FIG. 2 is a side view of an instrument probe which is in place in a well bore showing a part of the support cable, cable head, camera section and the light section; FIG. 3 is a partial cross-sectional side view of the part of the camera section of the probe showing the camera, cabling, power distribution section, fiber optic transmitter section, lens and mounting points of the support legs used to hold the light section in front of the lens of the camera; FIG. 4 is a partial cross-sectional view of the light section of the instrument probe showing a halogen lamp and the legs and mountings; and FIG. 5 is a cross-sectional view of a preferred support cable. DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description, like reference numerals will be used to refer to like or corresponding elements in the different figures of the drawings. Referring now to the drawings with more particularity, in FIG. 1 there is shown a well logging system 10 comprising a well bore instrument probe 12 which has been lowered into a well bore 14, a support cable 16, a sheave 18, a rotatable winch drum 30, a surface controller 22, a controller enclosure 23 and a transportable platform 24 which in this case is a skid unit. One end of the support cable 16 is wound on the drum 20 which supports the cable 16 for raising and lowering it into the bore 14 as the drum is rotated. The surface controller 22 controls the operation of the winch and the probe 12 and receives and processes information provide by the probe 12. The control enclosure 23 may include a recorder, such a video tape recorder, for recording the information provided by the probe 12. Referring now to FIG. 2, an instrument probe 12 is shown in greater detail and is presently disposed in a bore 14. The support cable 16 is connected to the probe 12. The probe 12 has three sections a cable head 25, a camera head 26 and a light head 28. The light head 28 is attached to the camera head 26 through three legs 30, two of which are shown. Legs of different lengths may be used depending upon the inner diameter of the bore 14 or casing. The larger the inner diameter, the longer the legs should be so as to not interfere with the camera viewing angle. Referring now to Fig. 3, the camera head 26 part of the instrument probe 12 is presented. Section 32 of the cable 16 is coupled to the optical transmitter section 34. At this component, electrical signals from the camera representing camera images are converted into optical signals and coupled to an optical fiber disposed within the cable. The optical fiber is used for the transmission of the images to the surface. Electrical/optical converters are well known in the art as well as couplers for coupling the converter to the optical fiber and no further details are given herein. The next section in the camera head 26 is the electrical section 36. The electrical power brought into the instrument probe 12 by the cable 16 is coupled to this section where the electrical power is converted into the voltages needed by the camera, the light and the electrical/optical converter. For example, the voltage supplied by the cable 16 may be 100 Vdc while the camera operates on 12 Vdc and the light on 50 Vdc. The electrical/optical converter may requir 12 Vdc. Such converter boards are well known in the art, for example, Model SWA175-4300 by Power-One, Inc., Cammarillo, California. The next section in the camera head 26 is the camera 38 itself. In one embodiment, the camera was a charge coupled device (CCD) type television camera which is capable of providing high speed, high resolution images in relatively dim light. One camera found to be usable in an embodiment is the CCD Video Camera Module having a model number XC 37 made by Sony Corporation. Coupled to the camera is a lens 40 which in one embodiment was a fisheye lens, and a quartz window 42. The window 42 seals the camera head 26 at its bottom end and protects the lens 40 against the high pressure/high temperature fluids which may exist in the well bore. Its angle is selected so as to not obstruct the viewing angle of the lens 40. Also shown in FIG. 3 is part of the legs 30 which are welded to the camera head 26 in this embodiment and which hold the light head 28 in position in front of the lens 40. Electrical conductors 48 are separately routed through the legs to the light head. In the embodiment shown, three legs were used although only two legs are shown in this figure. Referring now to FIG. 4, the light head 28 is shown having a halogen lamp 46. The light head 28 is attached to the camera section by legs 30 which are also welded into the light head 28 in this embodiment. The length of the legs is selected based on the inner diameter of the bore or casing. Where the camera must see further because of a larger inner diameter of the casing, the legs 30 are made longer so that the light head will not obstruct the view of the lens. Where the inner diameter is small, the legs may be shorter so that more light is placed within the camera viewing angle. Thus, several different light heads with varying lengths of legs may be required. Electrical power conductors 48 which provide electrical power to the light traverse one or more of the legs 30. Other light sources may be used such as incandescent lamps. Additionally, light other than visible light may be used, for example, infrared and ultraviolet. In accordance with the invention, power for the instrument probe 12 resides at the surface at the controller 22. In one embodiment, the power sources at the controller 22 is transmitted to the support cable 16 via slip rings at the drum 20 in accordance with techniques known to those skilled in the art. In order to conduct the necessary power over the long distances commonly experienced by video logging systems, a multi-layer cable is provided. Referring now to FIG. 5, a cross-sectional view of a preferred cable is presented. Disposed at the center is the optical fiber 50 and immediately around it is a buffer layer 52. Although only a single optical fiber is shown in this embodiment, multiple fibers may be used to comprise a fiber optic cable The buffer layer 52 provides mechanical isolation. Surrounding the buffer layer 52 and coaxial therewith is an inner layer of electrically conductive strands 54 which in one embodiment are formed of copper. These strands form a power conductor which conducts power from the controller 22 to the instrument probe components. Surrounding the power conductor 54 is a layer of insulation 56 and surrounding the insulation is a layer comprising strength member strands 58 alternating with outer, electrically conductive strands 60. In this embodiment, one outer conductive strand 60 is interspaced with two strength member strands 58. To balance the resistance of the power conductors 54 with the resistance of the strength members 58 which also serve as one leg of the resistive loop, ten outer electrically conductive strands which in one embodiment are formed of copper, are alternately interspaced in the total of thirty strands in the layer. The power conductor resistance when formed of copper strands is 6.1 ohms per 305 meters (1000 feet). The twenty steel and the ten copper resistive loop strands have a resistance of 18.1 ohms per 30 m (1000 ft). Thus, the loop resistance is 24.2 ohms per 305 m (1000 ft). Because of this arrangement of alternately interspaced copper and steel strands, the loop resistance is lowered. The diameter of the strength members then may be selected to satisfy only strength concerns rather than both strength and electrical conductivity concerns. It has been found that in the preferred cable, the strength members are significantly smaller thus resulting in a much smaller and lighter support cable yet one with loop resistance low enough so that a manageable voltage may be used at the surface. In one embodiment, the optical fiber used was 50/125/245 multi-mode fiber with a buffer formed of Hytrel which is available from Dupont in Wilmington, Delaware. The optical fiber has a 0.050 mm core with 0.125 mm cladding. The Hytrel buffer was 0.18 mm (0.0007 in.) in average thickness. The power conductors were 0.38 mm (0.015 in.) in diameter and were formed of copper HDBC, the insulator was 0.48 mm (0.019 in.) in thickness, and each strength member and resistive loop conductor was 0.25 mm (0.010 in.) in diameter. The insulation was compounded Hytrel and the strength strands were formed of improved plow steel. Surrounding all of the above members is an outer sheath 62 which in one embodiment, is made of stainless steel sheet having a thickness of 0.20 mm (0.0008 in.). In one embodiment, the stainless steel sheet was formed into a tube shape and welded lengthwise to form the outer sheath. The stainless steel is strong and fluid resistive thus protecting the internal components. It was found that forming the outer sheath of stainless steel provides a smooth outer surface thus facilitating its movement in pressure sealing glands and around sheaves and drums. Because it is relatively thin, it can be rolled on the sheaves and drums as necessary. Because of the commonly-experienced high pressures of fluids found in bores, the cable entry point in the instrument probe 12 must be sufficiently sealed to protect against the entry of extraneous fluids. Preferably a series of three fluid seals is provided. Each seal is formed of commonly available parts thus being economical to provide. Thus by use of three seals, the connection of the support cable with the instrument probe 12 is made fluid tight for use in high pressure environment. Thus, the preferred inspection system is provided having the power source for the instrument probe located at the surface rather than in the instrument probe itself. The design of the support cable results in lower loop resistance thus allowing a smaller cable and a more manageable supply voltage at the surface. Additionally, a smooth yet strong outer sheath on the cable makes it easier to handle yet it provides protection for the internal cable components.

Claims: A down-hole well bore inspection system (10) for the remove visual inspection of the condition of a well bore (14), the well bore of a kind oriented other than horizontal to the earth's surface and possibly containing harsh conditions including high temperatures and high pressures, comprising a down-hole instrument (12) for placement in the well bore for performing the visual inspection of said well bore, said instrument comprising a first end and a non-articulated body being sealed against the entry of pressurized external fluid into the instrument and configured so that gravitational forces are required to move the instrument downwardly through the well bore, a support cable (16) having a first end and a second end, the first and connected to the first end of the down-hole instrument so as to support the entire weight of the instrument, and surface equipment (20, 22, 23, 24) located outside the well bore, a television camera (38) for rendering the visual imagery of the well bore into corresponding electrical image signals representative of that visual imagery, the camera being of the type configured to withstand harsh conditions of a well bore; characterised in that said surface equipment includes a controllable actuator (20) coupled to the second and of the support cable to control the position of the support cable and to oppose the gravitational forces acting on the instrument thereby controlling the position of the instrument in the well bore; and wherein the instrument body comprises: an electrical-to-optical transducer (34) for converting the electrical image signals into optical image signals; the support cable (16) comprises an optical fiber (50) and electrical conductors (54), the optical fibre (50) being located substantially at the centre of the support cable (16) and being operative to receive the optical image signals from the electrical-to-optical transducer (34) and conduct said optical image signals to the surface equipment, the electrical conductors (54) forming a layer connected between a power source in the surface equipment and the downhole instrument (12), a second layer of electrical conductors (60) separated from the first layer, and strength members (58) which are in electrical contact with and are alternating with the electrical conductors (60) of the second layer, the second layer of conductors (60) and the strength members (58) also being connected between the surface equipment and the down hole instrument; and a process (22) coupled to the optical fiber at the surface equipment to receive the optical image signals, the processor having an optical-to-electrical transducer for converting the optical image signals from the optical fiber into corresponding electrical image signals. The system of claim 1, characterized in that the surface equipment further comprises a display device for receiving the electrical image signals provided by the optical-to-electrical transducer and converting them into a visual display for presentation to an operator. The system of claim 1 or 2, characterized in that the surface equipment further comprises a recording device for receiving the electrical image signals provided by the optical-to-electrical transducer and recording those signals. The system of claim 1, 2 or 3, characterized in that the surface equipment further comprises a video tape recorder for receiving the electrical image signals provided by the optical-to-electrical transducer and recording the video imagery represented by those signals for later analysis and inspection. The system of any preceding claim, characterized in that the surface equipment further comprises a printing device for receiving the electrical image signals provided by the optical-to-electrical transducer and printing the images represented. The system of any preceding claim, characterized in that the television camera (38) comprises a charge coupled device television camera which is capable of providing high speed, high resolution images in relatively dim light. The system of any preceding claim, characterized by a light source (28) positioned so as to illuminate the field of view of the television camera. The system of claim 7, characterized in that the light source (28) is positioned within the field of view of the camera. The system of any preceding claim, characterized in that the light source (28) and the television camera (38) are held in relation to each other by means of at least one leg (30) mounted on the unitary body of the down-hole instrument. The system of claim 9, characterized in that the length of the at least one leg (30) is selected in dependence on the portion of the field of view of the camera (38) to be illuminated.

Inventors: RIORDAN MATHEW B, RIORDAN, MATHEW B.
Applicants: DHV INT INC, DHV INTERNATIONAL, INC.
Application year: 1991
Main classification: E21B47
IPC codes: E21B47, G02B6