Abstract:
An electrical submersible pumping system (ESP) having a stator lamination stack that is anchored to prevent the stack from spinning. The ESP includes a motor section having a housing with an axial bore. A groove circumscribes an inner surface of the housing and a snap ring is set in the groove. A portion of the snap ring projects into the bore and exerts an axial compression force onto the lamination stack The snap ring includes a gap that aligns with a bead of material that is set in the groove; engagement between the bead and gap prevents the snap ring from spinning in the groove. The bead, that in an embodiment is a weld, can extend across all or a portion of the groove and can also provide coupling between the lamination stack and the housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of U.S. Provisional application No. 61/222,412 filed Jul. 1, 2009, the full disclosure of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field of Invention 
     The present disclosure relates to downhole pumping systems submersible in well bore fluids. More specifically, the present disclosure concerns preventing rotation of stators in an electrical submersible pump with mechanical anchoring. 
     2. Description of Prior Art 
     Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the wellbore 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). ESPs 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 a power cable. ESPs usually are made up of a pump motor at its lowermost section with a seal section adjacent the pump motor. The seal section is used for equalizing pump system internal pressure with ambient to minimize the pressure differential across the pump system seals. 
     Motors for electrical submersible pump systems are typically formed by stacking a series of annular stator laminations inside a pump motor housing. Grooves are normally formed within the housing at the top and bottom terminal ends of a lamination stack. The grooves are configured to receive a snap ring, where the snap ring inner diameter extends into the pump motor from the housing inner diameter. Forming the motor typically comprises inserting the snap ring located at the bottom of the housing, then adding the lamination stack within the housing. The laminations are then compressed, with a press or some other mechanical device; while the laminations are still under compression the top snap ring is inserted. After the pressure on the lamination stack is released, the stack will slightly spring back and exert an axial force on both top and bottom snap rings, where the opposing force is in opposite directions. This force on the snap rings will slightly stretch the housing along its length to create an axial force intended to prevent lamination spin during motor operation. 
     The ESP pump motors also comprise a rotor attached to a pump motor shaft. The rotor also consists of corresponding rotor laminations usually coaxially within. The stator lamination stack and the rotor lamination stack include openings that axially run along the length of the motor, wherein the openings contain wires, or other electrical conducting elements that form corresponding coils in each of the rotor and stator lamination stack. Typically the coil in the stator lamination stack is energized to form an electrical field that through electromagnetic forces produces a rotation in the rotor stack and thus correspondingly rotates the pump motor shaft. 
     SUMMARY 
     Disclosed herein is a motor for an electrical submersible pumping system. In an example embodiment the motor includes a housing having a bore formed along its axis. The housing includes a groove on an inner surface that circumscribes the bore. A curved snap ring with a gap is in the groove; a portion of the ring extends inward into the bore. A stator is set in the housing, with an end contacting the portion of the ring in the bore. The stator is made of a stack of thin laminations. The snap ring is oriented so that material adhered to the housing and in the groove projects radially inward into the gap. Optionally, the material is a weld that is welded to the stack of laminations. In an alternative embodiment, the motor can have a second groove, snap ring, gap, and adhered material set in the housing at the other end of the stator stack. The stack of laminations can then be compressed between the two snap rings. The material can extend partially, or fully, across the groove in a direction parallel with an axis of the housing. The end of the stack of laminations and along an outer periphery of the stack of laminations can have a recess formed for receiving the snap ring Alternatively, the material can be provided partially or fully from the opening of the groove to the bottom of the groove. 
     Another embodiment of an electrical submersible pumping system includes a motor section with a housing having a bore along its axis. A groove is formed inside the motor housing around the bore and a snap ring is in the groove. A portion of the snap ring sticks into the bore. The snap ring is an elongated member that is curved so that the ends of the snap ring are spaced apart to define a gap between the ends. Inside the housing is a stack of laminations that form a stator. The stack is axially compressed against the snap ring. The snap ring is oriented so the gap aligns with a weld in the groove. The weld extends from within the groove to an end of one of the laminations. A rotor is inserted in the stack of laminations. The assembly also includes pump section and a pump shaft connected between the rotor and the pump section. Optionally, the weld adheres to an upper side and an outer side of the groove and protrudes inward into the bore of the housing or can extends across a radial depth in the groove. Alternatively, the weld extends an axial depth of the groove. The weld can be in non-adhering contact with the snap ring. The pumping system can include an annular recess on the end of one of the laminations configured to fit with the snap ring. A second, and similar, groove, snap ring, gap, and weld can be included on the opposite end of the stator so that the stack of laminations is compressed between the first and second snap rings. 
     Also disclosed herein is a method of forming a motor for an electrical submersible pumping system. In an example embodiment, the method includes providing an annular motor housing with an axial bore and a groove formed in an inner surface of the housing circumscribing the bore. The method also includes providing a motor stator and a snap ring. The snap ring is a member curved to have a circumference less than 360° so that a gap is between the ends. The method also includes setting the snap ring in the groove so that an inner diameter of the snap ring is in the bore and inserting the stator into the housing. An end of the stator contacts against the inner diameter of the snap ring in the bore. Also included in the method is adhering a bead of material in the groove and aligned with the gap. In an example embodiment, the bead of material is a weld; the weld can extend partially along a portion of the groove aligned with a path perpendicular to an axis of the housing; or can extend across the portion of the groove aligned with a path perpendicular to an axis of the housing; and can also extend across the portion of the groove aligned with a path parallel to an axis of the housing. The stator can be a stack of laminations with a winding through the stack of laminations. In an alternative embodiment, the method can also include inserting an electrically responsive cylindrical rotor that is attached to an end of a shaft that couples to a pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side partial sectional view of an electrical submersible pumping system (ESP) in accordance with the present disclosure disposed in a wellbore. 
         FIG. 2  is a sectional view of a portion of a motor assembly, in accordance with an embodiment of the invention. 
         FIG. 3  is a side perspective view of an embodiment of the snap ring of  FIG. 2 . 
         FIG. 4  is a top view of the motor assembly of  FIG. 2 . 
         FIG. 5  is a sectional view of a portion of the motor taken along line  5 - 5  of  FIG. 2 . 
         FIG. 6  is a sectional view of a portion of the motor of taken along line  6 - 6  of  FIG. 5 . 
         FIG. 7  is sectional view of an alternative embodiment of the embodiment of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Shown in a side partial sectional view in  FIG. 1  is a wellbore  2  capped with a wellhead  3  and production tubing  4  depending from the wellhead  3  into the wellbore  2 . An electrical submersible pumping system (ESP)  5  is shown attached on a lower end of the production tubing  4 . In the example embodiment of  FIG. 1 , the ESP  5  includes a motor section  6  for pumping fluids from the wellbore  2  into the production tubing  4  and to the wellhead  3 . Fluid (not shown) in the wellbore  2  flows into the pump section  6  through an inlet  7  shown formed on an outer surface of the pump section  6 . On a lower end of the pump section  6  is a seal section  8  for equalizing pressure within the ESP  5  to ambient conditions. A motor section  10  is shown on a lower end of the seal section  8  that includes a motor (not shown) for driving impellers (not shown) in the pump section  6 . 
     Referring to  FIG. 2 , a portion of the motor section  10  of the ESP  5  is illustrated in a side sectional view. The motor section  10  shown includes a cylindrical housing  12  having an inner surface  14 . Coaxially disposed within the housing  12  is a stack of thin ring-like laminations  32  that when assembled as shown provide an inner bore circumscribing the motor axis A x . The stack of laminations  32  are supported within the housing  12  by a thicker and lowermost lamination  20 . The stack of laminations  32  forms an annular stator  30  within the motor section  10 . A lower circumferential groove  16  is formed on the inner surface  14  of the housing  12 . A lower retainer ring or snap ring  18  is shown set within the groove  16 . The lower snap ring  18  of  FIG. 2  is a generally annular member with a gap  19  along a portion of its circumference ( FIG. 2 ). In one example the gap  19  is approximately ⅝ of an inch wide but can vary. The lower snap ring  18  protrudes radially inward from the groove  16  and into a recess  21  provided along the periphery of lamination  20  and on a lower surface. 
     Retention at the upper end of stack of laminations  32  is provided by an upper lamination  44 , shown coaxially coupled within the housing  12  by a ring like snap ring  42  ( FIG. 3 ). The snap ring  42  is shown set in a groove  40  provided on the inner surface  14  of the housing  12  above the stack of laminations  32 . The snap ring  42  extends radially inward from the groove  40  into a recess  41  formed along the outer circumference on the lamination  44  and on an upper surface. As shown in perspective view in  FIG. 3 , snap rings  42  includes a gap  43  similar to the gap  19  of snap ring  18 . 
     Referring back to  FIG. 2 , in an example embodiment, the stator  30  is fabricated by setting the lower snap ring  18  into the groove  16  and inserting the stack of laminations  32  into the housing  12  where they are supported on the lower snap ring  18 . Using a ram (not shown), the stack of laminations  32  with the lower thick end lamination  20  are compressed against the lower snap ring  18 . The upper snap ring  42  is set within the upper groove  40  and the ram is released. Releasing the ram creates a spring-like effect in the stator laminations  32 , with the previously compressed stator laminations  32  tending to push outward against the lower and upper end thick laminations  20 ,  44  secured by the snap rings  18 ,  42 . The stator  30  is thus rigidly mounted within housing  12 . 
     Shown in the axial cutaway view of  FIG. 4  are slots  22  formed through the lower thick end lamination  20  and stator laminations  32  that form passages axially through the stack of laminations. In an embodiment the disks or laminations  32  of the stator  30  comprise magnetic steel and may be insulated from each other by conventional coatings. The lower and upper thick end laminations  20 ,  44  can also be made of magnetic steel. Wires  33  extend through the passages that are wound in a conventional manner and into which epoxy can be introduced. The wound wires  33  form windings that can be energized by a supply of electrical current to create an alternating electromagnetic field. A rotor  24  is shown coaxially inserted within the stack of laminations  32  that connects to and circumscribes an elongated shaft  26 . In an example embodiment, the rotor  24  includes a series of stacked laminations and made from a material that is responsive to an electromagnetic field, such as a magnetic steel. In an example embodiment, motor section  10  operation includes energizing the windings to rotate the rotor  24  and shaft  26 . The shaft  26  drives impellers (not shown) in the pump section  6  for drawing fluid into the ESP  5  and pumping the fluid from a borehole. 
     During start-up, the rotor torque experienced by the motor is approximately 3.5 times more than running torque. The outward force of the stator laminations  32  against the thick end laminations  20 ,  44  is generally sufficient to prevent the stack of laminations  30  from spinning. However, slight differences between the fabrication of one motor to the next can inadvertently lower the outward force generated by the lamination stack  32 . If the outward force of the lamination stack  32  is sufficiently lowered, the stator  30  can spin within the housing  12  and cause failure in the motor section  10 . Typically, spinning occurs during start up and is between the snap ring  18  and a thick end lamination  20 . 
     In an embodiment of the motor section  10  described herein, spinning of the stator  30  can be mitigated by adding material in the gap  19  of the lower snap ring  18 . Optionally, the material can be set in the gap  43  of the upper snap ring  42 , or be set in both gaps  19 ,  43 . Illustrated in the example embodiment of  FIG. 2 , the material is made up of welds  50 ,  52  shown provided within the grooves  16 ,  40  adjacent the lower and upper end laminations  20 ,  44 . The welds  50 ,  52  can be made after releasing the ram that compresses the stack laminations  32 . The gaps  19 ,  42  on the snap ring  18  provide a space within the grooves  16 ,  40  for the welds  50 ,  52 . 
     Referring now to  FIG. 5  both welds  50 ,  52  are shown for simplicity. The welds  50 ,  52  are illustrating adhering to the lower and upper thick end lamination  20 ,  44  and to the housing  12 , thereby coupling the lower and upper end laminations  20 ,  44  to the housing  12 . The snap rings  18 ,  42  may contact the welds  50 ,  52 , be spaced apart from the welds  50 ,  52 , or be adhered to the welds  50 ,  52 . 
     As shown in  FIG. 6 , each weld  50 ,  52  can be in each respective groove  16 ,  40  oriented along a path perpendicular to the axis A x  of the motor  10 . However, in the example embodiment of  FIG. 6 , the height of each weld  50 ,  52  is less than the height of the grooves  16 ,  40 . In an alternate embodiment illustrated in side sectional view in  FIG. 7 , each weld  50 ,  52  is shown extending the entire height of each groove  16 ,  40 , and the upper and lower surfaces of the grooves  16 ,  40  along a path perpendicular to the axis A x  of the motor  10  Rotating the snap rings  18 ,  42  is prevented by contact between ends of the snap rings  18 ,  42  and the welds  50 ,  52 . Because the thick end laminations  20 ,  44  are coupled to the housing  12  by the welds  50 ,  52 , the thick end laminations  20 ,  44  also cannot rotate or spin. Preventing the stator  30  and individual stator laminations  32  from spinning thus can advantageously prevents premature failure of the ESP motor during operations, including at start-up. In example embodiments of  FIGS. 6 and 7 , the area of the welds  50 ,  52  is less than the area of the snap rings  18 ,  42 . 
     By welding the end laminations  20 ,  44  to the inner portion of the housing  14 , the possibility of the stator stack  30  spinning is dramatically reduced because spinning tends to occur at the interface of the snap rings  18 ,  42  with the end laminations  20 ,  44 . Further, welding the end laminations  20 ,  44  does not adversely affect the integrity of the individual stator laminations  32  as the epoxy and windings in the stator slots  22  are sufficiently strong to prevent the individual stator laminations  32  from spinning under start-up conditions. 
     In an example embodiment, the welds  50 ,  52  are formed using a metal inert gas (MIG) welder. For housings  12  formed of carbon steel, a 7018 electrode or 7018 MIG wire. The 7018 electrode or 7018 MIG wire can also be used for housings  12  having chrome; however, the housing  12  should be heated to around 350 F prior to welding. Excess weld material or slag can be removed by grinding or a chisel. 
     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.