Patent Publication Number: US-2019186245-A1

Title: Lubricant Circulating Pump For Electrical Submersible Pump Motor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to provisional application Ser. No. 62/608,043, filed Dec. 20, 2017. 
    
    
     FIELD OF INVENTION 
     The present disclosure relates to an electrical submersible pump motor. More particularly, the disclosure relates to a lubricant circulating pump that forms a part of a radial bearing for the motor. 
     BACKGROUND 
     Electrical submersible pumps (ESP) are commonly used to pump well fluid from hydrocarbon producing wells. A typical ESP includes a motor that rotates a shaft to drive a pump. The motor is normally a three-phase electrical motor having a non-rotating stator that has a stator bore. The shaft extends through the stator bore and has rotor sections spaced apart from each other along the length of the shaft. The stator has windings that when powered will interact with the rotor sections to cause rotation of the shaft. 
     The motors can be 30 feet or more in length. Radial bearings are located in the spaces between the rotor sections to provide radial support for the shaft. The bearings are immersed in a dielectric lubricant in the stator bore for lubrication. The bearings may be of various types and normally include an inner sleeve keyed to the shaft for rotation and a bearing carrier with an outer diameter that fits closely in the stator bore. An anti-rotation member on the outer diameter of the bearing carrier engages the stator bore to prevent rotation of the bearing carrier. 
     These types of ESPs work well. However, the lubricant in the stator bore can stagnate at and around the radial bearings. Stagnation can cause the temperature of the bearings to rise significantly. The heating will cause the lubricant viscosity to decrease, resulting in localized heating and thermal expansion. The localized heating can accelerate bearing degradation and in severe cases, bearing and motor failure. The heating can cause the rotating sleeve to lock with the non-rotating bearing carrier. Various proposals have been made for lubricant pumps to enhance lubricant circulation in motors. 
     SUMMARY 
     An electrical submersible pump assembly comprises a motor having a stator with a bore extending along a longitudinal axis. A shaft extends longitudinally through the bore. Rotor sections are mounted to the shaft for rotation in unison, the rotor sections being axially spaced apart from each other. At least one lubricant pump within the bore is mounted to the shaft for rotation therewith for circulating motor lubricant within the bore. A bearing carrier has an inner diameter in sliding engagement with an outer diameter of the lubricant pump. An anti-rotation member on an outer diameter of the bearing carrier is in engagement with the bore of the stator to prevent rotation of the bearing carrier. 
     The lubricant pump may have at least one curved blade. More particularly, the lubricant pump may have a plurality of curved blades spaced around the shaft, defining flow passages between the blades. 
     In the embodiment shown, the lubricant pump is located between adjacent ones of the rotor sections. The motor may have a plurality of lubricant pumps, each of the lubricant pumps being located in a space between adjacent rotor sections. 
     In the embodiment shown, the lubricant pump includes an inner sleeve mounted to the shaft for rotation in unison. An outer sleeve surrounds the inner sleeve, the outer sleeve having a greater inner diameter than an outer diameter of the inner sleeve, defining an annular space between. At least one curved blade is within the annular space and joined to the inner diameter of the outer sleeve and the outer diameter of the inner sleeve for rotation in unison with the inner sleeve and the outer sleeve. The inner sleeve, the outer sleeve, and the curved blade may be a monolithic single-piece member. 
     A port may extend from an inner diameter to the outer diameter of the lubricant pump to divert to the outer diameter of the lubricant pump a portion of the lubricant flowing through the lubricant pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of an electrical submersible pump assembly having a motor in accordance with this disclosure. 
         FIG. 2  is a partial axial sectional view of the motor of  FIG. 1 . 
         FIG. 3  is transverse sectional view of the motor of  FIG. 2 , taken along the line  3 - 3  of  FIG. 2  with the motor housing removed, illustrating a combined lubricant pump and bearing. 
         FIG. 4  is an enlarged transverse sectional view of a lubricant pump portion of the combined pump and bearing shown in  FIG. 3 . 
         FIG. 5  is an axial sectional view of the combined lubricant pump and bearing of  FIG. 3 , taken along the line  5 - 5  of  FIG. 3  with the adjacent rotor sections removed. 
         FIG. 6  is an enlarged axial sectional view of the lubricant pump portion of the combined lubricant pump and bearing of  FIG. 3 . 
         FIG. 7  is an isometric view of the lubricant pump portion of the combined lubricant pump and bearing of  FIG. 3 , shown removed from the motor. 
     
    
    
     DETAILED DESCRIPTION 
     The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be 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 thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude. 
     It is to be further understood that the scope of the present disclosure 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 and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
       FIG. 1  illustrates a cased well  11  extends downward from a wellhead (not shown). Cased well  11  contains an electrical submersible pump assembly (ESP)  13  for pumping well fluid flowing into cased well  11 . ESP  13  has a pump  15  suspended on a string of production tubing  17 . Pump  15  may be a centrifugal pump having a large number of stages, each stage having an impeller and a diffuser. Alternately, pump  15  could other types, such as a progressing cavity pump. Pump  15  has a well fluid intake  19  and is driven by a motor  21 , normally a three-phase electrical motor. 
     A seal section  23  connects to motor  21  and has features to reduce a pressure differential between a dielectric lubricant in motor  21  and the hydrostatic pressure of the well fluid. In this example, the pressure equalizing features of seal section  23  locate between motor  21  and pump intake  19 , but the pressure equalizing components could be mounted to a lower end of motor  21 . ESP  13  may also include other components, such as a gas separator (not shown) and another motor connected in tandem with motor  21 . If a gas separator is employed, intake  19  would be at a lower end of the gas separator. 
     Although  FIG. 1  shows ESP  13  oriented vertically, ESP  13  could be within an inclined or horizontal portion of cased well  13 . The terms “upper”, “lower” and the like are used only for convenience herein and not in a limiting manner because ESP  13  is not always operated vertically. 
       FIG. 2  shows more details of motor  21 . Motor  21  has a cylindrical housing  25  containing a stator  27 . Stator  27  is made up of a large number of thin laminations or disks in a stack in housing  25 , the stack being affixed to housing  25  to prevent rotation of stator  27 . Each disk has a central opening, defining a bore  29  in stator  27 . Electrical motor wire windings (not shown) wind through stator  27 . A shaft  31  extends through bore  29  along a longitudinal axis  32 . 
     Shaft  31  extends through a number of rotor sections  33 , which connect to shaft  31  with a key and slot arrangement to cause shaft  31  to rotate in unison with rotor sections  33 . Each rotor section  33  is made up of a large number of thin laminations or disks. Copper rods (not shown) are spaced around axis  32  parallel to axis  32 . The copper rods extend through the laminations of each rotor section  33  to end rings  35  located at the upper and lower ends of each rotor section  33 . Rotor sections  33  are axially spaced apart from each other. An electromagnetic field generated by supplying three-phase power to the windings of stator  27  causes rotor sections  33  to rotate shaft  31 . 
     Motor  21  may be lengthy, such as  30  feet or more. A combined radial bearing and lubricant pump  37  locates in at least some of the spaces between adjacent rotor sections  33  provide radial stabilization for shaft  31 . A dielectric lubricant fills stator bore  29  and immerses the combined radial bearings and lubricant pumps  37  for lubrication. 
       FIG. 3  illustrates stator slots  39  in stator  27  for receiving windings (not shown).  FIG. 3  also shows that the lubricant pump  40  of the combined bearing and lubricant pump  37  may comprise an inducer or screw pump  40 . Screw pump  40  has a cylindrical inner sleeve  41  having an inner diameter that closely receives shaft  31 . Inner sleeve  41  mounts to shaft  31  for rotation in unison, such as by a key  43  that fits in a longitudinally extending slot in shaft  31  and a mating slot  44  ( FIG. 4 ) in the inner diameter of inner sleeve  41 . Screw pump  40  also includes a cylindrical outer sleeve  45  that surrounds inner sleeve  41 . Outer sleeve  45  has an inner diameter larger than an outer diameter of inner sleeve  41 , defining an annular space  47  between them. 
     Referring also to  FIGS. 4 and 6 , annular space  47  of screw pump  40  contains at least one vane or curved blade  49  that has an inner edge joined to the outer diameter of inner sleeve  41  and an outer edge joined to the inner diameter of outer sleeve  45 . In the example of  FIGS. 3 and 4 , there are several blades  49 , each extending helically from an open lower end to an open upper of annular space  47  and curving at least partly around the inner sleeve  41 . Adjacent ones of the helical blades  49  create helical flow passages  50  between them that extend from the lower to the upper end of the inner and outer sleeves  41 ,  45 . Helical blades  49  are oriented to cause an upward flow of lubricant through flow passage  50  in this example, but the direction of flow alternately could be downward. 
     Referring also to  FIG. 7 , at least one port  51  (two shown) extends from the inner diameter to the outer diameter of outer sleeve  45 . Each port  51  may be located in a mid-section of outer sleeve  45  between upper and lower ends of screw pump  40 . Each port  51  leads from one of the flow passages  50  to the outer diameter of outer sleeve  45 . Each port  51  diverts a portion of the lubricant flowing through one of the passage  50  to the outer diameter of outer sleeve  45 . 
     Inner sleeve  41 , outer sleeve  45  and helical blades  49  may be integrally formed together as a monolithic single-piece rigid metal structure by additive manufacturing techniques. All of the radial bearings within motor  21  could include one of the screw pumps  40  or only some of them. 
     Referring to  FIGS. 3 and 5 , each combined bearing and lubricant pump  37  also includes a bearing carrier  53 . In this example, carrier  53  is a cylindrical member having an inner diameter that closely receives outer sleeve  45  in sliding, rotational engagement. Carrier  53  has an outer diameter that is in close reception with a side wall of stator bore  29 . An anti-rotation member prevents carrier  53  from rotating within stator bore  29 . In this example, the anti-rotation member comprises a key  55  that fits within mating axially extending slots  57 ,  59  in the side wall of stator bore  29  and the outer diameter of carrier  53 . Alternately, the anti-rotation member could comprise one or more resilient rings encircling the outer diameter of carrier  53  and compressed against the inner diameter or side wall of stator bore  29 . 
     In this example, carrier  53  is a single-piece member. Alternately, carrier  53  could include an insert sleeve between an inner portion of the carrier and the outer sleeve to attenuate vibration being transferred from shaft  31  through combined bearing and lubricant pump  37  to stator  27 . Carrier  53  does not need any axial flow passages for lubricant flow because the lubricant flows through flow passages  50  of screw pump  40 . 
     During operation, an electromagnetic interaction of rotor sections  33  with stator  27  causes shaft  31  to rotate. Screw pump  40  rotates with shaft  31 , inducing the flow of lubricant from a lower to an upper side of combined bearing and lubricant pump  37 , or vice-versa. The combined bearing and lubricant pump  37  provides radial stabilization of shaft  31  through the engagement of carrier  53  with stator bore  29  and the engagement of screw pump  40  with shaft  31 . Screw pump  40  and bearing carrier  53  resist any radial movement of shaft  31  by transferring radial forces from shaft  31  to the side wall of stator bore  29 . Outer sleeve  45  will perform like a standard bearing sleeve inside bearing carrier  53  with a lubricant wedge supporting it. Ports  51  divert a portion of the lubricant in some of the flow passages  50  to the dynamic interface between outer sleeve  45  and carrier  53 . Differences in thermal growth may cause slight axial movement between shaft  31 , screw pump  40  and carrier  53 . 
     The circulation of lubricant by screw pump  40  mitigates the occurrence of stagnant lubricant around combined bearing and lubricant pump  37 , which otherwise could undergo significant heating and thermal expansion. The present disclosure described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims. For example, the screw pump could be another type, such as an impeller style. Further, instead of the screw pump being integrated into bearing sleeve, it could also be integrated into the rotor end rings.