Patent Publication Number: US-10323641-B2

Title: Below motor equalizer of electrical submersible pump and method for filling

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to provisional application Ser. No. 62/002,259, filed May 23, 2014. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates in general to submersible well pump assemblies and in particular to a below motor pressure equalizer and method of filling the equalizer and motor with lubricant. 
     BACKGROUND 
     Many hydrocarbon wells are produced by electrical submersible well pump assemblies (ESP). A typical ESP includes a centrifugal pump having a large number of stages, each stage having an impeller and a diffuser. An electrical motor couples to the pump for rotating the impellers. A pressure equalizer or seal section connects to the motor to reduce a pressure differential between lubricant in the motor and the hydrostatic pressure of the well fluid. The pressure equalizer has a motor lubricant passage leading from a flexible barrier such as a bag or bellows into the interior of the motor. The motor lubricant passage is always open to communicate well fluid pressure applied in the pressure equalizer to the flexible barrier to the motor lubricant in the motor. 
     With most prior art ESP&#39;s, the pressure equalizer or seal section is located between the motor and the pump. In others, the pressure equalizer is mounted below the motor. During a prior art installation using a below motor pressure equalizer, the pressure equalizer may be initially filled with lubricant and suspended vertically from a rig at the well site. The motor is then lowered onto the equalizer and secured. Then motor lubricant may be pumped in from the lower end of the motor and upward through the motor. Alternately, the motor may be evacuated by a vacuum pump, then filled from the top. 
     The weight of the motor lubricant filled into the motor while the assembly is suspended above the well would act hydrostatically on the bellows of the pre-filled pressure equalizer, possibly causing the bellows to become fully extended. If fully extended before lowering into the well, and if the motor is completely full of lubricant, the bellows would not be able to further extend due to an increase in temperature, requiring some of the lubricant to be expelled through a check valve. The combined equalizer and motor would thus be over-filled with lubricant before the assembly is lowered into the well. The preferred position of the bellows prior to lowering the assembly into a well provides adequate expansion capacity of the bellows in cases of low pressure and high temperature while also maintaining adequate contraction capacity in cases of high pressure and low temperature. 
     Also, if multiple motors are in tandem, the assembly can be quite lengthy, more than 100 feet. The total length, including the pressure equalizer, could be greater than the distance from the blocks of the rig to the wellhead. If the lower end of the assembly is lowered into the wellhead in order to accommodate the length of the assembly during motor lubricant filling, the procedure becomes difficult if lubricant is pumped from the lower end, which would require access to the lower end of the assembly. 
     SUMMARY 
     An electrical submersible pump has a pump and a motor with a rotatable shaft extending along a longitudinal axis and operatively coupled to the pomp for driving the pump. A pressure equalizer is coupled to an end of the motor, the equalizer having a movable element for communicating well fluid pressure exterior of the pressure equalizer to motor lubricant in the motor. An adapter connects the equalizer to the motor, the adapter having a motor lubricant passage through which lubricant in the motor communicates with motor lubricant in the equalizing element. A valve located in the motor lubricant passage selectively opens and closes the motor lubricant passage. 
     Preferably, the valve is remotely actuable between open and closed positions. In the preferred embodiment, an end portion of the shaft is in engagement with, the valve while the valve is in a closed position. The valve is movable from the closed position to an open position in response to rotation of the shaft. A locking feature retains the valve in the closed position. In the preferred embodiment, a technician engages an upper end of the motor and manually rotates the shaft to release the locking feature. 
     In the embodiment shown, the valve is axially movable from the closed position to an open position out of engagement with the shaft in response to manual rotation of the shaft. A spring urges the valve toward the open position. 
     In the preferred embodiment, the locking feature comprises a set of internal threads in the motor lubricant passage that engage a set of external threads on the valve element to retain the valve element is in a closed position. A seal between the exterior of the valve element and the motor lubricant passage adjacent the internal and external threads seals the valve element in the motor lubricant passage while the valve element is in the closed position. A drive member on an end of the valve element engages a drive member on end of the shaft, the drive members having mating torque drive surfaces. 
     The drive members may comprise a socket on an end of the valve element that receives an end of the motor shaft, the socket and the end of the shaft having mating torque drive surfaces. Rotation of the motor shaft in a selected direction rotates the valve element and releases the locking feature, causing the valve element to move axially from the closed position to the open position and the socket to disengage from the end of the motor shaft. 
     The lubricant passage may have a bypass area of larger diameter joining a seal area. A spring support may be mounted in the lubricant passage at a point joining the bypass area. The spring support has a central bore and at least one flow-through passage laterally spaced from the central bore. The valve element seals to the seal area while the valve element is in a closed position. The valve element has a cylindrical exterior having a diameter smaller than a diameter of the bypass area, enabling lubricant to flow around the valve element and through the flow-through passage while the valve element is in an open position. 
     In the embodiment shown, a pin protrudes axially from the valve element through the central bore of the spring support. A spring surrounds the pin and is located within the central bore. The spring urges the valve element axially toward the open position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features, advantages and objects of the disclosure, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the disclosure briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the disclosure and is therefore not to be considered limiting of its scope as the disclosure may admit to other equally effective embodiments. 
         FIG. 1  is a side view of an electrical submersible pump assembly in accordance with this disclosure. 
         FIG. 2  is a schematic sectional view of the pressure equalizer of the pump assembly of  FIG. 1 , shown with the equalizer filled with motor lubricant. 
         FIG. 3  is a schematic sectional view of the pressure equalizer of  FIG. 2  mounted to a lower end of the motor of the pump assembly of  FIG. 1 , and prior to communicating lubricant in the motor with the lubricant in the equalizer. 
         FIG. 4  is a schematic sectional view of the pressure equalizer and motor of  FIGS. 2 and 3 , with a thrust bearing unit of the pump assembly of  FIG. 1  attached, and prior to communicating the lubricant in the motor with the lubricant in the equalizer. 
         FIG. 5  is a transverse sectional and more detailed view of a portion of the equalizer of  FIG. 5 . 
         FIG. 6  is a sectional view of the equalizer of  FIG. 5 , taken along the line  6 - 6  of  FIG. 5  and shown with the valve in a closed position. 
         FIG. 7  is a sectional view of the equalizer of  FIG. 5 , taken along the line  6 - 6  of  FIG. 5  and shown with the valve in an open position. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The methods and systems of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The methods and systems 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. 
     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. 
     Referring to  FIG. 1 , an electrical submersible pump (ESP)  11  typically includes an electrical motor  13 . Motor  13  is normally a three-phase AC motor and may be connected in tandem to other motors. An upper seal section or thrust bearing unit  15  is illustrated at an upper end of motor  13 . The terms “upper” and “lower” are used, only for convenience and not in a limiting manner. A pressure equalizer or lower seal section  17  is shown connected to a lower end of motor  13 . Pressure equalizer  17  has features to reduce a pressure differential between a dielectric motor lubricant in motor  13  and the exterior well fluid hydrostatic pressure. An instrument module  19  to measure various motor and well fluid parameters optionally may be mounted to the lower end of pressure equalizer  17 . 
     A rotary pomp  21  connects to the upper end of thrust bearing unit  15  in this example. Pump  21  could be a centrifugal pump with a large number of stages, each stage having an impeller and a diffuser. Alternately, pump  21  could be another type, such as a progressing cavity pump. Pump  21  has an intake  23  for admitting well fluid. A string of production tubing  25  secures to the upper end of pump  21  and supports ESP  11  in a well. Production tubing string  25  may be sections of tubing with threaded ends secured together, or it could be continuous coiled tubing. A wellhead assembly  27  at the upper end of the well supports production tubing string  25  and controls the flow of well fluid. 
     Referring to the schematic representation of  FIG. 2 , pressure equalizer  17  has a tubular housing  29 . An upper adapter  31  secures to the upper end of housing  29 , such as by threads. A lower adapter  33  secures to the lower end of housing  37 , and if an instrument module  19  ( FIG. 1 ) is employed, it will secure to lower adapter  33 . A flexible element, such as a bellows  35 , mounts within housing  29  to the lower side of upper adapter  31  in this example. Bellows  35  may be metal and has an interior that is filled with motor lubricant  37  employed for lubricating the rotating components of motor  13  ( FIG. 13 ). The exterior of bellows  35  may be immersed in well fluid that flows in from a port in housing  29 , bellows  35  may be immersed in an intermediate liquid that is separated from well fluid by an additional flexible element (not shown). In either case, when ESP  11  ( FIG. 1 ) is installed in a well, the hydrostatic pressure of well fluid on the exterior of ESP  11  is communicated to the interior of housing  29  in the chamber surrounding bellows  35 . The interior of bellows  35  is sealed from the liquid in housing  29  surrounding bellows  35 . 
     A plug or valve  39  in adapter  31 , when closed, seals the motor lubricant  37  within bellows  35  and isolates the motor lubricant  37  within bellows  35  from motor lubricant in motor  13  ( FIG. 1 ). As explained subsequently, valve  39  is remotely actuated from the closed to an open position, placing the motor lubricant  37  in bellows  35  in fluid communication with the motor lubricant in motor  13 . Motor lubricant  37  in bellows  35  may be filled to a precise level at a service facility, a manufacturing facility, or at a well site prior to connecting pressure equalizer  17  to motor  13 . As mentioned, motor  13  may be connected in tandem to other motors, and the motor lubricant  37  in each motor will be in fluid communication with that in the other motors. During operation of ESP  11 , motor lubricant  37  in motor  13  will in fluid communication with motor lubricant  37  in pressure equalizer  17 . 
     Valve  39  is closed initially to prevent the hydrostatic weight of the lubricant in motor  13  from acting on the motor lubricant  37  in bellows  35  after motor  13  is coupled to the upper end of equalizer  17  while motor  13  is being filled. Pressure equalizer  17  can thus be precisely filled with bellows  35  in a desired position between fully extended and fully contracted. Referring to  FIG. 3 , motor  13 , which may comprise a number of motors in tandem, is lowered onto and connected to pressure equalizer  17  after pressure equalizer  17  has been pre-filled precisely with motor lubricant  37  and valve  39  closed. In one method, motor lubricant  37  will not yet have been introduced into motor  13  when motor  13  is lowered onto and connected to pre-filled equalizer  17 . 
     Motor  13  has a tabular housing  41  with an upper adapter  43  at the upper end and a lower adapter  45  at the lower end. Upper adapter  31  of pressure equalizer  17  secures to lower adapter  45  of motor  13 , such as by bolting. A stator  47  extends most of the length of housing  41 . Stator  47  comprises thin metal discs or laminations with windings extending through holes in the laminations. A rotor  49  mounts within central bore of stator  47 . Rotor  49  is also made up of laminations and has copper rods extending longitudinally through holes in the laminations. Rotor  49  mounts to a drive shaft  51  and is made up in rotor sections separated by radial bearings  52 . Shaft  51  has an upper splined end  53  and a lower splined end  57 . Upper splined end  53  is within upper adapter  43  and lower splined end  57  is within lower adapter  45 . In this example, lower splined end  57  comprises a drive member that engages a mating drive member of valve  39  once equalizer  17  is connected to motor  13 , but lower splined end  57  does not move valve  39  to the open position, yet. 
     In one method, the operator introduces motor lubricant  37  into motor  13  after motor  13  has been connected to equalizer  17  and valve  39  remains closed. The filling procedure may proceed by pumping motor lubricant  37  into a lower port (not shown) in lower adapter  45 . The operator may employ a vacuum pump to evacuate air horn motor  13  prior to pumping lubricant  37 . The lubricant  37  flows up the spaces in motor housing  41  between upper and lower adapters  43 ,  45  and between rotor  49  and stator  47 . Motor lubricant  37  in motor  13  is initially not in fluid communication with motor lubricant  37  in bellows  35  because valve  39  is closed. If vertical space for the entire assembly is needed, pressure equalizer  17  could be lowered into wellhead  27  ( FIG. 1 ) before the filling procedure for motor  13  begins. 
       FIG. 4  illustrates thrust bearing unit  15  attached to the upper end of motor  13 , which in this example, occurs after motor  13  is filled with motor lubricant  37 . In this example, prior to mounting thrust bearing unit  15  to motor  13 , and after filing motor  13  with motor lubricant  37 , the operator would lower the assembled equalizer  17  and motor  13  into wellhead  27  ( FIG. 1 ) so as to facilitate connecting thrust bearing unit  15  to motor  13 . Motor lubricant  37  is also contained in thrust bearing unit  15 , and thrust bearing unit  15  could be filled with motor lubricant  37  after it has been connected to motor  13 . If vertical space of the rig permits, thrust bearing unit  15  could be mounted to motor  13  before motor  13  is filled with lubricant. 
     Thrust bearing unit  15  has a housing  61  with an upper adapter  63  and a lower adapter  65  for connecting to pump  21  ( FIG. 1 ) and motor  13  respectively. A thrust bearing unit shaft  67  extends through upper adapter  63  and lower adapter  65 . A splined coupling  69  connects the lower end of thrust bearing unit shaft  67  to the splined upper end  53  of motor shaft  51 ; thus thrust bearing unit shaft  67  may be considered to be a part of motor shaft  51 . Thrust bearing unit shaft  67  has an upper splined end  71  accessible from upper adapter  63 . A thrust bearing runner  73  rotates with thrust bearing unit shaft  67  and rotatably engages a thrust bearing pad  74 . A mechanical shaft seal  75  seals between thrust bearing shaft  67  and upper adapter  63 , sealing well fluid from entering housing  61 . 
     Referring to  FIG. 5 , equalizer upper adapter  31  has means, such as a bolt hole pattern  77  or a rotatable threaded collar (not shown), for securing equalizer  17  to motor  13  ( FIG. 1 ). As shown in  FIGS. 6 and 7 , a motor lubricant passage having an axial bore  79  extends through upper adapter  63 . Bore  79  has an upper enlarged portion  79   a  extending downward to a reduced diameter threaded portion  79   b . A seal area or portion  79   c  of slightly greater diameter extends below threaded portion  79   b . Bore  79  has lower portions  79   d  of several successively larger diameters extending below seal portion  79   c.    
     Valve  39  has a valve element or body  81  located within bore upper portion  79   a . Body  81  has an upward-facing splined receptacle or drive member  83  that is engaged by motor shaft lower splined end or drive member  57  ( FIG. 3 ) when equalizer  17  is connected to motor  13 . Valve body  81  has an externally threaded section  85  that engages bore threaded portion  79   c  while valve  39  is in the closed position of  FIG. 6 . Internal threaded section  79   b  and external threaded section  85  serve as a locking feature to releasably retain body  81  in the upper closed position. A seal  87  on valve body  81  seals to bore seal portion  79   c  while valve  39  is in the closed position. The portion of body  81  containing seal  87  is smaller in diameter than bore portion  79   d , which serves as a bypass area to allow flow ground body  81  while body  81  is in the lower open position of  FIG. 7 . 
     Valve body  81  has a smaller diameter cylindrical portion or pin  89  extending downward. Pin  89  extends through a central aperture or bore  92  in a spring support  91 . Spring support  91  is a cylindrical element secured in bore lower portion  79   c , such as by a snap ring  94 . A coil spring  93  secured in central aperture  92  has an upper end bearing against a downward facing shoulder and a lower end bearing against a retainer  95 . Spring support  91  has flow-through passages  97  extending axially through and spaced around central aperture  92 . 
     Threads  79   b  on upper adapter  31  and mating threads  85  on valve body  81  retain valve body  81  in an upper closed position, compressing spring  93 . Rotating valve body  81  relative to upper adapter  31  releases threads  85  from threads  79   b , allowing spring  93  to extend and push valve body  81  downward to the open, position of  FIG. 6 . While in the open position, motor lubricant  37  in motor  13  ( FIG. 4 ) is free to flow downward through flow-by passages  97  into bellows  35 . Motor shaft  51  does not move downward with valve body  81 , thus lower splined end  57  disengages from receptacle  83  when body  81  moves downward. Bellows  35  is attached and sealed to the lower end of upper adapter  31  below valve  39  by a retainer (not shown). 
     In one method of operation, the operator will pre-fill bellows  35  of pressure equalizer  17  with motor lubricant  37 , as shown in  FIG. 2 , to a level placing bellows  35  in a desired position. Valve  39  will be closed. The operator supports pressure equalizer  17  axially at the well site, then, lowers and connects motor  13  to pressure equalizer  17 . The operator then completely fills motor  13  with motor lubricant  37  while valve  39  remains closed, as shown in  FIG. 3 . The operator lowers a lower portion of the assembly into the well and attaches thrust bearing unit  15  to motor  13 , as shown in  FIG. 4 . Using a manual tool (not shown), an operator engages upper splined end  71  and rotates thrust bearing unit shah  67  and motor shaft  51 . Referring to  FIGS. 6 and 7 , this rotation causes valve body  81  to unscrew from bore threads  79   b . Spring  89 , gravity, and the weight of motor lubricant  37  in motor  13  push valve body  81  to the lower open position of  FIG. 7 . 
     In the open lower position, motor lubricant  37  in motor  13  is free to communicate with bellows  35 . The hydrostatic weight of the motor lubricant  37  in motor  13  may cause some of the motor lubricant  37  in motor  13  to flow downward into bellows  35  and cause bellows  35  to extend from the initial position. The amount of motor lubricant  37  flowing downward into bellows  35  leaves an equal volume of space at the upper end of thrust chamber  15  that is free of motor lubricant. 
     The operator then connects pump  21  to thrust bearing unit  15  and lowers ESP  11  into the well. As ESP  11  is lowered into the well, hydrostatic well fluid pressure acts on bellows  35 , causing it to contract. When bellows  35  is contracted back into the initial position, the displaced motor lubricant  37  is pushed back into the free space at the upper portion of thrust chamber  15 . An increase in well fluid temperature may cause the motor lubricant  37  to expand. If so, the excess volume of the motor lubricant  37  will flow into bellows  35 . Check valves, such as used in the prior art to expel lubricant due to lubricant thermal expansion, may not be needed. 
     While the disclosure has been shown in only one of its forms, it should be apparent to those skilled in the art that various changes may be made.