Abstract:
A system, method and apparatus for incorporating a fiber optic cable into a power cable for an electrical submersible pump is disclosed. The fiber optic components are protected from damage during handling of the cable with pump cable components, such as lead sheaths and jacketing materials. The optical fibers are protected from damage due to corrosive oil well chemicals and gasses, as well as protected from decompression damage.

Description:
BACKGROUND OF THE INVENTION 
     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. 
     SUMMARY OF THE INVENTION 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE 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. 
         FIGS. 1-4  are sectional end views of various embodiments of cables constructed in accordance with the invention; and 
         FIG. 5  is schematic diagram of one embodiment of a subterranean application for cables constructed in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1-5 , embodiments of a system, method and apparatus for a power cable having fiber optics for an electrical submersible pump (ESP) or other downhole tools in subterranean applications are disclosed. The invention comprises a power cable that is designed to operate in a pressurized subterranean environment that may contain H 2 S, methane and/or other corrosive gasses. A buffered fiber optic filament is isolated from exposure to these gasses by placing the buffered fiber optic under a hermetically sealed lead sheath. The sheath simultaneously provides protection to the buffered fiber optic filament and the insulation surrounding the electrical conductors from exposure to the environment. 
     In the embodiment of  FIG. 1 , a power cable  1  comprises an outer armor layer  2  having a longitudinal axis and an axial length extending along the longitudinal axis. The armor layer  2  may comprise armor that is formed from metallic or other protective materials. A jacket filling material  3  also is located within an interior of the armor layer  2 . The power cable  1  further contains a plurality of electrical conductors  4  that extend through the outer armor layer  2  along and throughout the axial length and are cabled about each other in a helical configuration. Each of the electrical conductors  4  is covered with an electrical insulation  5 , such that the electrical conductors  4  are electrically insulated from each other. The conductor insulation  5  may be covered with other protective tapes and braids or extruded layers  6 . 
     In the illustrated embodiment of  FIG. 1 , the power cable  1  additionally contains a buffered optical fiber  7  located inside the electrical insulation  5  of at least one of the electrical conductors  4 . 
     In  FIG. 2 , still another embodiment of the invention further comprises a lead sheath  8  that is located over the cable insulation  5  and extends throughout the lengths of the conductor  4 . The buffered optical fiber  7  is located radially under the lead sheath  8 . The lead sheath  8  is located around only one of the electrical conductors  4 , such that the buffered optical fiber cable  7  is positioned between the lead sheath  8  and the electrical insulation  5  of one or more of the electrical conductors  4 . 
     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.,  FIG. 3 ), the buffered optical fiber cable  7  may be located directly adjacent and in contact with one or more of the electrical conductors  4 , and under the electrical insulation  5  of the electrical conductors  4 . Multiple ones of these single conductor assemblies can be configured as a flat cable (see, e.g.,  FIG. 4 ) or round multi-conductor cable as shown in  FIG. 1 . 
     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. H 2 S 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. 
       FIG. 5  depicts one embodiment of a subterranean application for the invention. For example, in the illustrated embodiment, a well installation  130  has a number of components located at a surface  138  thereof. A power source  119  provides electrical power to a transformer  120  and then to a control system  133 . A power cable  132 , such as the numerous embodiments described herein, transmits the power downhole to a tool, such as subterranean equipment. The tool may comprise, for example, a pump  122 , seal section  124  and motor  126 . The pump  122  pumps fluids to other equipment at the surface  138  as is known by those of ordinary skill in the art. 
     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.