Patent Application
20100266248
1. Technical Field
The present invention relates in general to power cables and, in particular, to an improved system, method and apparatus for an electrical power transmission cable having an optical fiber cable for an electrical submersible pump or other downhole tools in subterranean applications.
2. Description of the Related Art
Many types of electrical tools are used in subterranean applications. For example, electrical submersible pumps (ESP) are used to pump fluids from beneath the earth to the surface. Applications for ESPs and other types of downhole tools include geothermal exploration and development, carbon sequestration operations, and oil and gas wells. Such tools are typically powered by transmission cables that extend a long distance from the surface down into the subterranean borehole where the tool is located.
Power may be transmitted to an ESP by banding a specially constructed, three phase electric power cable to the production tubing. The cable is small in diameter, well protected from mechanical abuse and impervious to deterioration of its physical and electrical properties by the hot, aggressive well environments. Cables are available in a wide range of conductor sizes that permit efficient matching to motor requirements. Such cables can be manufactured in either round or flat configurations, using galvanized steel, stainless steel, or monel armor capable of withstanding the hostile environments of an oil well or water well. Solid or stranded electrical conductor construction may be used.
As described herein, the power cables contain several electrical conductors and, in some applications, also contain a smaller fiber optic cable for communications purposes. However, subterranean environments present extreme operational conditions, including certain types of highly corrosive chemicals and gasses that readily destroy the physical integrity and effectiveness of the fiber optic elements. An improved system, method and apparatus for power transmission cables having optical fiber cables for downhole tools in subterranean applications would be desirable.
Embodiments of a system, method, and apparatus for a power cable having electrical conductors for downhole tools and fiber optics for communications in subterranean applications are disclosed. In some embodiments, the invention provides means for installing fiber optic filaments in an electrical submersible pump (ESP) assembly that prevents them from being damaged during ESP cable handling and service.
In one embodiment, a buffered fiber optic filament, i.e., a fiber optic filament encased in a tube of protective material such as PEA, MEA, PEEK or FEP, is placed inside the insulation of one or more of the electrical conductors of the power cable. This design has the advantage of protecting the optical fiber and assuring that it is automatically disposed in a helical configuration when the conductor is placed in a round cable.
In another embodiment, the buffered fiber optic filament is placed beneath a lead sheath and on top of the insulation of a single insulated conductor in one or more of the electrical conductors of the power cable. In some embodiments, the buffered fiber is deployed under the lead sheath in a helix by wrapping it around the insulated conductor prior to applying the lead sheath. The buffered optical fiber also may be configured in a reversing helix, first going in one direction around the insulated conductor, and then in the opposite direction. This design insures that the buffered optical fiber is never placed in excessive tension when the conductor is bent, and facilitates applying the buffered optical fiber in a continuous manner directly behind the lead extruder during manufacturing. In yet another embodiment, the buffered optical fiber may be placed in a similar manner directly over the metal conductor and under the insulation prior to applying the insulating layer.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings.
So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.
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In additional embodiments, the optical fiber 7 may be helical in configuration and wrapped around the electrical insulation 5 of the one or more electrical conductors 4. Alternatively, the buffered optical fiber 7 may be configured in a reversing helix, first going in one direction around the electrical insulation 5, and then in the opposite direction. In still another alternate embodiment (see, e.g.,
The protection provided by the invention is required for at least two reasons. First, it is known that hydrogen invades the glass used in the optical fibers, which lowers their light transmission properties and thereby degrades the fiber optic capabilities. H2S and other gasses under the high pressures and high temperatures of a subterranean environment rapidly degrade the optical fibers in this manner. By surrounding the fiber optics with an impermeable lead sheath this degrading mechanism is eliminated.
Second, the pressures in subterranean environments change rapidly and dramatically, such as when pumps are turned on, or valves are opened. These changes result in rapid reductions in pressure that are generally referred to as decompression. Gasses dissolved inside glass fibers expand during decompression causing fractures in the glass which severely degrades its properties. For example, strong fiber glass tapes are placed around power cables and located underground during operation. Upon retrieval to the surface, the glass is often completely broken in very fine pieces due to the decompression mechanism. Again, by placing the fibers under the lead sheath, this decompression damage is prevented.
While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, different combinations of the various elements of the embodiments described herein may be joined together to form additional alternate embodiments of the invention.
