Abstract:
An electrical submersible pump cable having an integral capacitor. The electrical submersible pump cable has a primary conductor with an insulator surrounding the primary conductor. A coaxial conductive layer surrounds the insulator, wherein the insulator serves as a dielectric between the primary conductor and the coaxial conductive layer. An outer insulating sleeve is provided on an outer surface of the coaxial conductive layer. An inner cable armor surrounds the insulating sleeve, wherein the outer insulating sleeve provides electrical isolation between adjacent wires. An outer cable armor surrounds the inner cable armor. The coaxial conductive layer and primary conductor enables the coupling of data information onto or off of the cable.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to cables, in particular, to cables for electrical submersible pumps that are manufactured with electrically conductive layers formed coaxially around one or more of the primary conductor insulators to produce one or more capacitors integral to the cable.  
         BACKGROUND ART  
         [0002]    Electrical submersible pump cables typically consist of a plurality of conductors wrapped with armor. Such cables have been used to transmit signals to equipment downhole. In some applications, armor around the cable has been used as a return path for a signal conductor. However, this method is not effective for use with very high frequency signals because the armor offers a high skin resistance as a return path. As a solution, an armored cable described in U.S. Pat. No. 3,916,685 has been implemented. However, the &#39;685 cable is not readily adaptable to tools designed for multiconductor cables. U.S. Pat. No. 4,028,660 teaches an armored multiconductor coaxial well logging cable for both high frequency signal and low frequency signal transmission in which a plurality of conductors form a shield for an inner conductor. The plurality of conductors are capacitively coupled so that each conductor group may carry a different low frequency signal or direct current voltage. The &#39;660 cable utilizes a coaxial conductor group, wherein each of the conductors within the group are separated from each other by an insulating material. A plurality of capacitors are connected between conductors within a coaxial conductor group. The multi-layer concentric conductors of the &#39;660 patent travel the full length of the cable on high voltage conductors. A signal is transmitted down an inner conductor and power is transmitted down an outer conductor.  
           [0003]    Power cables for electrical submersible pumps have been used having an insulated conductor lead shield and wrapped with armor. Lead shields are not electrically insulated from armor or each other. The purpose of the lead shield is is to exclude hydrogen sulfide gas from contact with insulation of conductors.  
         SUMMARY OF THE INVENTION  
         [0004]    The invention includes a specially modified electrical submersible pump cable or specially modified motor lead extension on the cable. The specially modified cable or section has a primary conductor and an insulator that surrounds the primary conductor. A coaxial conductive layer surrounds the insulator. The insulator serves as a dielectric between the primary conductor and the coaxial conductive layer. An outer insulating sleeve is provided on an outer surface of the coaxial conductive layer. An inner cable armor surrounds the insulating sleeve. The outer insulating sleeve provides electrical isolation between adjacent wires. An outer cable armor surrounds the inner cable armor.  
           [0005]    The apparatus of the invention enables the coupling of data information onto or off of the primary conductor. Additionally, the invention enables coupling of data information onto or off of the coaxial conductive layer that surrounds the primary conductor. In a preferred embodiment, a motor lead extension is used to provide the capacitance necessary to couple the signal. The motor lead extension is typically 25-35 feet in length, although sufficient capacitance may be obtained in as little as twenty feet of the motor lead extension. The motor lead extension preferably has three conductors of copper surrounded by an insulation. The insulation is preferably Teflon™ for preventing shorting out between the conductors. Wires are inserted into the lead and into downhole instrumentation to transmit high frequency signals to the surface. A current modulator is used downhole to modulate the signal and to send data to the surface. Equipment at the surface monitors high and low frequencies to extract information from the signal. The signal may be routed up two or three phases of the cable. The information can be provided as a differential between two or three phases. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a schematic view of the ESP receiving power from a cable having integral capacitors.  
         [0007]    [0007]FIG. 2 is a cut-away view of the cable of the invention.  
         [0008]    [0008]FIG. 3 is a cross-sectional view of a typical round cable. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]    Referring now to FIG. 1, shown is an electrical schematic of an electrical submersible pump motor (ESP) designated generally  10  in a well  12 . The electrical submersible pump motor  10  receives power from a pump cable  13  having a motor lead extension  18  on a lower end thereof. FIG. 3 is a cross-sectional view of a typical round pump cable  13 . Pump cable  13  has three conductors  14  surrounded by insulation  15 . Conductors  14  and insulation  15 ,is surrounded by jacket  16 , which is surrounded by armor  17 .  
         [0010]    Typically, a motor lead extension  18  is 25-35 feet long. Motor lead extension  18  is spliced onto cable  13  and is typically constructed of high quality materials to withstand heat from motor  10 . It is preferable to specially construct motor lead extension  18  to act as a capacitor rather than to specially construct the entire cable  13  so that a regular cable may be used, thereby reducing cost. Motor lead extension  18  extends upwards from ESP motor  10  and splices into cable  13 . Cable  13  extends upwards to the surface  19 , which may be thousands of feet from motor  10 . Normally cable  13  will be several thousand feet long.  
         [0011]    At surface  19 , cable  13  is connected to a three-phase power source  20  and a high frequency carrier source. A differential data detector or surface instrumentation  22  on the surface communicates with cable  13 . Preferably, filters  23 , shown as a capacitor and inductor, are used to filter out all except high frequency signals generated by surface instrumentation  22 . A high frequency carrier receiver and differential modulator or downhole instrumentation  24  is located near motor  10  and is connected via wires  26  to the motor lead extension  18 . Downhole instrumentation  24  is in communication with the wires  26  for modulating a signal and for sending data to the surface  19 . Additionally, sensor  28  may be provided to deliver information to downhole instrumentation  24 . For example, sensor  28  may sense pressure and/or temperature in well  12 . Preferably, filters  29  are used to filter out all except high frequency signals generated by surface instrumentation  22 . Surface instrumentation  22  monitors high and low frequencies to process the data. Information can be transmitted by creating a differential in the current flowing between phases of pump cable  13 .  
         [0012]    Referring now to FIG. 2, a cut away view of a motor lead extension  18  is shown. Three primary conductors  30 ,  32  and  34  are made of a conductive material, such as copper. Typically, #4 copper is used, which has a resistance of 0.2485 ohms per 1000′ at 20° C. The primary conductors  30 ,  32  and  34  are preferably coated with insulating material  36 ,  38  and  40 , which is preferably formed of an elastomeric material, such as extruded EPDM, to prevent shorting out between the conductors  36 ,  38  and  40 . A typical thickness of the insulating material  36 ,  38  and  40  is 45 mil for a cable rated at 4 KV and 55 mil for cable rated at 5 KV. A coaxial conductive layer  46 ,  48  or  50  surrounds insulators  36 , or  40 . One or more of primary conductors  30 ,  32  and  34  may be surrounded by a coaxial conductive layer  46 ,  48  or  50 . However, it is preferred to use at least coaxial conductive layers  46 ,  48  and/or  50 . Coaxial conductive layers  46 ,  48  and are preferably formed of lead and are surrounded by insulators  52 ,  54  and  56 , which are made of high temperature thermoplastic or thermoset electrical insulation, such as an extruded Fluorinated Ethylene Propylene (FEP) layer, sold under the name Teflon. The extruded FEP layer is preferably 20 mils in thickness. Coaxial conductive layer  46 ,  48  and  50  have a resistance of approximately 3 ohms per 1000′ at 20° C. Insulators  52 ,  54  and  56  prevent electrical contact of conductive layers  46 ,  48  and  50  with each other. Insulating layers  36 ,  38 , and  40  serve as a dielectric between primary conductors  30 ,  32 , and  34  and coaxial conductive layer  46 ,  48  and  50 . Coaxial conductive layers  46 ,  48  and  50  act as a capacitor plate.  
         [0013]    It is preferred to provide just the motor lead extension  18  with coaxial conductive layers  46 ,  48  and/or  50  and insulators  52 ,  54  and  56 , rather than the entire cable  13 . By providing only motor lead extension  18  with the extra co-axial conductive layers  46 ,  48  and/or  50 , regular ESP cable  13  may be used, thereby reducing cost. Regular ESP cable  13  does not have coaxial combination layers. However, special ESP cable  13  may be used to facilitate capacitance if desired. Preferably, motor lead extension  18  is provided with inner cable armor  58 ,  60  and that surrounds insulators  52 ,  54  and  56 . Inner cable armor  58 ,  60  and  62  is preferably constructed of a non-conductive braid such as Nylon, Polyvinylidene Flouride sold under the name Kynar, or Polyphenylene Sulfide sold under the name Ryton, which offers fairly high resistance to electricity. An outer cable armor  64  surrounds inner cable armor  58 ,  60  and  62  to bundle the individual conductors  30 , and  34  together and to protect the bundle. Outer jacket or outer cable armor  64  is preferably a helical wrap of bands of steel. However, other materials may be used for outer jacket  64 , including an extruded material such as a high density polyethylene.  
         [0014]    In practice, three-phase power is supplied to ESP  10  by power source  20 , typically at a frequency of 50/60 Hz. Data from sensor  28  of downhole instrumentation  24  is coupled onto motor lead extension  18 . By using the downhole instrumentation  24 , the use of large and expensive downhole high voltage capacitors can be avoided. It has been found that capacitance can be obtained in specially modified cable of lengths as short as 12 to 20 feet, therefore, coaxial conductive layers  46 ,  48  and/or  50  may be provided on just the motor lead extension  18 . The electrical submersible pump cable  13  may be used to transmit data information from surface instrumentation  22  to an electrical submersible pump motor  10  by coupling with a capacitor at the surface high frequency data information onto and off of coaxial conductive layers  46 ,  48  and  50 , which surround primary conductors  30 ,  32  and  34 . The preferred frequency range of the data information is 2 KHz to 200 KHz. Filters  23  pass only high frequency signals to the cable  13 . High frequency carrier receiver or downhole instrumentation  28  extracts the signal from the motor lead extension  18  via wires  26 . The signal is filtered again by filters  29  before reaching downhole instrumentation  24 . Information may be passed up motor lead extension  18  and cable  13  by modulating current on selected phases of the cable  13 . Surface instrumentation  22  detects differential data from the current modulations.  
         [0015]    The invention has several advantages. The advantages include the ability to couple high frequency data information onto or off of the ESP power cable, rather than providing capacitors downhole, which are large and can be difficult and expensive to deploy.  
         [0016]    While the invention has been shown in only one 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.