Abstract:
An electrical submersible pumping system (ESP) for use in pumping fluids from a wellbore. The ESP includes fins on an outer portion of the ESP that transfer heat from a motor in the ESP to fluid flowing past the fins. A self removing material is provided over the fins when the ESP is deployed into the wellbore to protect the fins against being damaged when the ESP contacts a wall of the wellbore. The material can corrode, erode, melt, dissolve, disintegrate, or otherwise automatically decouple from the fins when the ESP is disposed in the wellbore.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The present disclosure relates to electrical submersible pumping (ESP) systems submersible in well bore fluids. More specifically, the present disclosure concerns a method of protecting motor cooling fins during deployment of an ESP. 
         [0003]    2. Description of Prior Art 
         [0004]    Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the well bore to the surface. These fluids are generally liquids and include produced liquid hydrocarbon as well as water. One type of system used in this application employs an electrical submersible pump (ESP). ESP&#39;s are typically disposed at the end of a length of production tubing and have an electrically powered motor. Often, electrical power may be supplied to the pump motor via an electrical cable. Typically, the pumping unit is disposed within the well bore above where perforations are made into a hydrocarbon producing zone. This placement thereby allows the produced fluids to flow past the outer surface of the pumping motor and provide a cooling effect. The motor may become overheated without the cooling effect by the transfer of heat. The prospect of overheating, even while heat is being transferred to fluid flowing adjacent the motor, limits the pumping ability of an ESP. 
       SUMMARY OF INVENTION 
       [0005]    The present disclosure describes an electrical submersible pumping system (ESP) with an improved cooling system and a method of cooling an ESP. In an example embodiment, disclosed is a method of cooling an ESP that involves adding fins to an outer surface of the ESP. The fins are shielded from damage by covering or potting them with a protective layer(s) that is removed after the ESP is deployed within a wellbore. While the ESP is being lowered downhole and inadvertently contacts a wall of the wellbore, the protective layer(s) safeguards the fins from damage. In an example embodiment, the potting or shielding material disintegrates when disposed in a wellbore and the fins conduct heat from within the ESP to fluid in the wellbore. The material can be made from wax, aluminum, zinc, beryllium, magnesium, alloys thereof, and combinations thereof. Optionally, the covering can be a protective packing encapsulated with an outer layer. Where in this example, the protective packing can be particulate material, sand, plaster, wax, and combinations thereof and the outer layer can be aluminum, zinc, beryllium, magnesium, alloys thereof, or combinations thereof. In an example embodiment, the fins are disposed on a motor section of the ESP that contains a motor for driving a pump in the ESP. After deploying the ESP with the protected fins, the motor can be started to drive the pump, and fluid can be pumped from the wellbore into production tubing attached to the pump. 
         [0006]    Also disclosed herein is an electrical submersible pumping system (ESP) that in one example embodiment includes a motor section having a motor, a seal section in pressure communication with the motor, a pump section having a pump coupled with the motor, fins on an outer surface of the motor section, and a cover over the fins for shielding the fins from damage as the ESP is lowered into a wellbore. The cover is made from a material that detaches from the fins when the ESP is disposed in a designated location in the wellbore. In one example embodiment the cover is made of wax, aluminum, zinc, beryllium, magnesium, alloys thereof, or combinations thereof. The cover can be a single layer or multiple layers. Optionally, the cover is made of a protective packing encapsulated in a protective layer; where the protective packing is a substance such as particulate material, dissolvable powders, low melting point metals and polymers or other hydrocarbon materials, such as lead, tin, bismuth, lithium, or alloys of, foams, particulates, sand, plaster, wax, or combinations thereof. In this embodiment, the outer layer is aluminum, zinc, beryllium, magnesium, alloys thereof, and combinations thereof. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0008]      FIG. 1  is a side partial sectional view of an example embodiment of an electrical submersible pumping system (ESP) having cooling fins and disposed in a wellbore. 
           [0009]      FIG. 2  is an axial sectional view of the ESP of  FIG. 1  showing a protective layer over the fins. 
           [0010]      FIG. 3  is an axial sectional view of the ESP of  FIG. 1  having an alternative protective covering over the fins that is encapsulated with an outer layer. 
           [0011]      FIG. 4  is a side partial sectional view of the ESP of  FIG. 1  having a protective covering over the fin area and being lowered into a wellbore. 
       
    
    
       [0012]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0013]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be through and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
         [0014]      FIG. 1  illustrates an example embodiment of an electrical submersible pumping system (ESP)  10  disposed in a subterranean wellbore  12 ; the ESP is used for pumping fluid  14  from the wellbore  12 . The fluid  14  resides as connate fluid within a formation  16  shown adjacent the wellbore  12 ; the fluid  14  enters the wellbore  12  through perforations  18  in a casing string  20  that lines the wellbore  12 . The ESP  10  includes a motor section  22  on its lower end having heat cooling fins  24  on its outer surface and extending generally axially along the length of the motor section  22 . The fins  24  provide for an increased heat transfer surface area from a motor  23  within the motor section  22  to fluid  14  that flows over the housing of the motor section  22  from the perforations  18  and upward to a pump inlet  25 . Also included with the ESP  10  is a seal section  26  provided on an upper end of the motor section  22 . The seal section  26  localizes pressure within the ESP  10  with the pressure ambient to the ESP  10 . In one example, the seal section  26  includes an internal bladder (not shown) that on one side is exposed to the ambient pressure and on the other side is dielectric fluid that makes its way between the seal section  26  and motor section  22 . Also included with the ESP  10  is a pump section  28  on which the pump inlets  25  are located as well as a pump  29  that receives the fluid  14  after flowing through the pump inlets  25 . The pump  29  is driven by the motor  23  by a shaft  30  coupled between the motor  23  and pump  29 . After becoming pressurized by the pump  29 , the fluid  14  exits the upper end of the pump section  28  where it is then pumped to the surface through attached production tubing  32 . 
         [0015]    In one embodiment, the fins  24  are relatively thin and easily damaged even by slight impact by the ESP  10  against the casing  20 . This is exacerbated in deviated portions of the well. Shown in  FIG. 2  is a sectional view of the motor section  22 A illustrating an embodiment where the fins  24  are provided on an annular sleeve  34  shown circumscribing the motor  23 . In this embodiment, the sleeve  34  with fins  24  provides housing for the motor  23  and is in contact with the cylindrical motor stators (not shown) inside the motor  23 . Optionally, a thermal grease or filler  36  can be provided in the annular space between the motor  23  and inner surface of the sleeve  34 . Further illustrated in  FIG. 2  is a covering over the fins  24  that is a protective packing  40  that extends from the spaces between each of the adjacent fins  24  and past the outer terminal end of each fin  24  to protect against direct collisions. The protective packing  40  also provides support between the fins  24  thereby enhancing integrity of the fins  24 . 
         [0016]    The protective packing  40  can be applied over the fins  24  prior to deploying the ESP  10  within the wellbore  12  to guard the fins  24  from damage due to collisions or other contact between the ESP  10  and casing  12 . The protective packing  40  can be made from a material that self-removes over time, such as through disintegration or dissolving when in the wellbore. Example self-removal times range from a few hours to 2-3 days. The disintegrating material may be one that quickly corrodes and may contain aluminum, zinc, beryllium, magnesium, alloys of these materials, and combinations thereof. Optionally, the protective packing  40  may be a single or multi-layered structured material, such as aluminum with a less active material coupled directly to the fins  24 , such as steel, or a more active alloy or pure layer, such as magnesium coupled with the aluminum. Additionally, the sleeve  34  can be formed by an extrusion process to facilitate manufacturing. 
         [0017]    Referring now to  FIG. 3 , illustrated is a side sectional view of an alternate embodiment of a motor section  22 B. In this example, the sleeve  34  with fins  24  is shown on the outer surface of the motor  23  along with the layer of thermal grease or filler  36  between the motor  23  and sleeve  34 . However, an alternate protective covering over the fins  24  includes a protective packing  40 A that is in contact with the fins and extending from between adjacent fins and up above or past the terminal ends of the fins  24 . Over the protective packing  40 A is a protective layer  42  that encapsulates the protective packing  40 A in place over the fins  24 . In an alternative, the protective packing  40 A is between the adjacent fins  24  and the protective layer  42  contacts the terminal ends of the fins  24 . In one example, the protective packing  40 A may include plaster, sand, or some other particulate matter. Once the protective layer  42  is removed, the protective packing  40 A can fall away or erode, such as from the fluid  14  flowing past the fins  24 . Additionally, the packing  40 A and/or layer  42  can be dissolved or disintegrated such as by a chemical reaction or corrosion. Chemical and/or electrical current application can accelerate the chemical reaction or corrosion. The protective layer  42  may be formed from a dissolving or disintegrating material such as that described above in reference to the protective layer  40  of  FIG. 2 . 
         [0018]      FIG. 4  illustrates in a side partial sectional view an example of the ESP  10 A being lowered within a wellbore  12 . In this example, the ESP  10 A includes a protective packing  40  or optionally having a protective layer  42  over the motor section  22 A. As previously discussed, the presence of the protective packing  40  and/or protective layer  42  guards against damage or other degradation to the fins  24  while the ESP  10  is being lowered within the wellbore  12 . When at a designated location in the wellbore  12 , wellbore conditions and/or the flow of fluid  14  removes the protective packing and/or protective layer  42 . By lowering the ESP  10  in the wellbore  12  without damaging the fins  24 , effective heat transfer may occur during pumping operations thereby cooling the motor  29  once the protective packing  40  and/or protective layer  42  is removed from the ESP  10 A. Also, the protective layer may allow for thinner fins which may be more economical to produce. In an alternative embodiment, the ESP  10  may be activated before the packing  40  or layer  42  is removed. In an example, fluid flow from the ESP  10  may be used for removing the packing  40  and/or layer  42 . 
         [0019]    It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. For example, the packing  40  and layer  42  can be made of a single layer or multiple layers. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.