Abstract:
A submersible pump assembly has modules, including a rotary pump, an electrical motor, and a seal section located between the motor and the pump. The seal section has a tubular housing with a lower adapter secured to the housing and joining the seal section with the motor. An upper adapter is secured to the housing and joins the seal section with another one of the modules. An inlet port in the upper adapter admits well fluid into the housing. A tubular, flexible compensator element has an upper end sealed to the upper adapter and a lower end sealed to the lower adapter. A communication passage in the lower adapter admits lubricant from the motor into the compensator element. A cap is mounted around the upper end of the compensator element. The cap has a skirt extending radially outward to limit upward expansion of the compensator element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to provisional application 61/756,298, filed Jan. 24, 2013. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates in general to electrical submersible well pumps and in particular to a cap located within a seal section adjacent a flexible compensator element to limit expansion of the compensator element in one direction. 
     BACKGROUND 
     Electrical submersible well pumps are commonly used for pumping well fluid from wells producing oil, water and possibly gas. A typical submersible pump assembly has a rotary pump driven by an electrical motor. A seal section locates between the motor and the pump. The seal section has a flexible compensator element that reduces a pressure differential between lubricant in the motor and the surrounding hydrostatic well fluid pressure. The compensator element may be a tubular elastomeric bag, with an interior in communication with motor lubricant and an exterior in communication with well fluid. The upper end of the bag is secured by a bag clamp to an adapter on the upper end of the seal section. 
     The motor lubricant will expand with temperature. At the typical depths, the well fluid in most wells will be at a higher temperature than the temperature of the air surrounding the wellhead. Also, when the motor begins to operate, the lubricant temperature increases. Consequently, the compensator element will normally expand from its initial state. 
     Seal sections have check valves to expel excess lubricant if the interior pressure becomes too much greater than the hydrostatic well fluid pressure. However, even if the check valves are pre-set to a relatively low differential pressure, there still may be enough pressure in the bags due to thermal lubricant expansion to expand the bags up and over the bag clamp. When the bags are expanded around the bag clamp, it causes excessive stress in the area where the edge of the clamp contacts the bag. 
     SUMMARY 
     The submersible pump assembly disclosed herein has a cap mounted around a first end of the compensator element. The cap has a skirt extending radially outward relative to an axis of the shaft to limit expansion of the compensator element in a first direction. 
     In the embodiment shown, the skirt of the cap is conical with a diameter increasing in a direction away from the first end of the compensator element. Also, the cap has a cylindrical neck. The skirt joins the neck and flares radially outward from the neck in a direction away from the first end. The skirt of the cap has an outer edge spaced radially inward from an inner sidewall of the seal section. 
     The first end of the compensator element comprises a cylindrical compensator neck. A conical compensator shoulder may join the compensator neck and extends in a direction away from the first end at a diverging angle. The cylindrical cap neck circumscribes the compensator neck. The skirt joins the cap neck and extends conically around the compensator shoulder and away from the first end at the same diverging angle. The cylindrical cap neck may be radially spaced from the compensator neck, defining an annulus between the cap neck and the compensator neck. 
     The seal section includes an adapter secured to a first end of the housing, the adapter having an axial passage through which the shaft extends. A tubular retainer is mounted in the axial passage and extends from the adapter in a direction away from the first end of the housing. The first end of the compensator element may be secured or clamped around the retainer. The cap may have a rim that is secured around the tubular retainer. 
     The skirt of the cap has a first side surface facing toward a first end of the seal section and a second side surface facing away from the first end of the seal section. A vent port may be in the cap to vent any trapped well fluid from the first side surface to the second side surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present technology will be better understood on reading the following detailed description of nonlimiting embodiments thereof, and on examining the accompanying drawings, in which: 
         FIG. 1  is a side view of an electric submersible pump assembly (ESP) according to an embodiment of the present technology; 
         FIG. 2A  is a side cross-sectional view of an upper portion of the sealing chamber of the ESP of  FIG. 1 ; 
         FIG. 2B  is a side cross-sectional view of a lower portion of the sealing chamber of the ESP of  FIG. 1 ; 
         FIG. 3  is a side cross-sectional view of a bladder stress reducer cap according to an embodiment of the present technology; and 
         FIG. 4  is an enlarged cross-sectional view of the area identified as area  4  in  FIG. 2A . 
     
    
    
     DETAILED DESCRIPTION 
     The foregoing aspects, features, and advantages of the present technology will be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing the preferred embodiments of the technology illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, it is to be understood that the specific terminology is not limiting, and that each specific term includes equivalents that operate in a similar manner to accomplish a similar purpose. 
     Referring to  FIG. 1 , there is shown an electric submersible pump assembly  10  (ESP) installed within casing  12  in a well. ESP  10  is suspended on a string of tubing  14 , and may discharge well fluid up tubing  14 . ESP  10  has a plurality of modules, including a motor  16 , which is connected to a seal section  18 , which is in turn connected to a pump  20 . Motor  16  is filled with a lubricant, and seal section  18  is configured to equalize the lubricant pressure with the hydrostatic pressure of the well fluid on the exterior. Pump  20  may be a rotary pump, such as a centrifugal pump or progressing cavity pump, and has an intake  22  on its lower end that draws well fluid into the pump  20 . The ESP assembly  10  herein described is one possible embodiment of the present technology. For example, ESP assembly  10  could include other modules, such as a gas separator. If so, intake  22  would be in the gas separator rather than the pump  20 . 
     Referring to  FIGS. 2A and 2B , seal section  18  has a lower adapter  24  for securing to motor  16  ( FIG. 1 ). Lower adapter  24  typically has a flange  26  that receives bolts that bolt to a mating flange of motor  16 . An upper adapter  28  ( FIG. 2A ) connects seal section  18  to pump  20  ( FIG. 1 ). Upper adapter  28  has threaded holes  30  for receiving bolts from a lower adapter of pump  20 . Seal section  18  has a housing  32  that comprises a cylindrical sleeve secured to lower and upper adapters  24 ,  28 . Housing  32  may be a single integral member. 
     A shaft  34  extends through seal section  18  for transmitting rotary motion from motor  16  to pump  20 . Shaft  34  has an upper splined end  36  that optionally may have a latch member  38 . Latch member  38  latches to the shaft (not shown) of pump  20  so as to transmit tension. Shaft  34  has lower splined end  40  that engages the shaft of motor  16  (not shown). 
     A conventional thrust bearing  42  is located in seal section  18 , as illustrated in  FIG. 2B . Thrust bearing  42  comprises a rotary thrust member or runner  44  that is secured to shaft  34 . Runner  44  rotatably engages a stationary downthrust member or base  46  that is mounted to the upper side of lower adapter  24 . Runner  44  also engages a stationary upthrust member  48  while in upthrust. Upthrust member  48  is supported within housing  32  against upward movement by a retainer ring  50 , which may be a snap ring. 
     A lower radial bearing support  52  is supported in housing  32  against downward movement by retainer ring  50 . Lower radial bearing support  52  has a bushing  54  that is slidingly engaged by shaft  34 . Bushing  54  does not form a seal on shaft  34  and may have passages or channels through it to freely allow the passage of motor lubricant. Lower radial bearing support  52  has seals  56  on its exterior that sealingly engage the inner diameter of housing  32 . A lower isolation tube  58  extends sealingly into a counterbore in lower radial bearing support  52  at the upper end of bushing  54 . Lower isolation tube  58  has an inner diameter that is larger than the outer diameter of shaft  34 , creating an annular passage for the flow of motor lubricant. Motor lubricant is free to flow between the area surrounding thrust bearing  42  and the annular clearance within lower isolation tube  58 . 
     The upper end of lower isolation tube  58  extends into sealing engagement with a counterbore in a central radial bearing support  60 . Central radial bearing support  60  has seals  62  on its exterior that seal against the inner diameter of housing  32 . Central radial bearing support also has a bushing  64  that slidingly engages shaft  34  but does not seal against the flow of lubricant. A lower chamber  66  is defined by the annular space between radial bearing supports  52  and  60  and surrounding lower isolation tube  58 . A passage  68  extends through central radial bearing support  60  from its lower end to its upper end. 
     Still referring to  FIGS. 2A and 2B , an upper isolation tube  70  has its lower end sealingly engaged in a counterbore in central radial bearing support  60  above bushing  64 . The upper end of upper isolation tube  70  extends to upper adapter  28 , defining an annular upper chamber  72  within housing  32 . 
     A tubular elastomeric compensator element, bag or bladder  74  is located within upper chamber  72 . Bladder  74  has a lower end  76  that fits sealingly around an upper neck portion of central radial bearing support  60 . Bladder  74  has a neck  78  on its upper end that is sealingly secured or clamped to a bladder retainer  80 , as shown in  FIG. 2A . Bladder retainer  80  is a tubular member that may be secured by threads to the upper end of upper isolation tube  70 . Bladder retainer  80  has an upper portion that may sealingly engage a counterbore formed in the lower end of upper adapter  28 . Bladder  74  has a cylindrical sidewall  79  in this example. A conical shoulder  81  joins bladder neck  78  with bladder cylindrical sidewall  79 . 
     Referring to  FIG. 4 , there is shown a port  82  located in the sidewall of upper isolation tube  70  near its upper end. Port  82  communicates the annular clearance within upper isolation tube  70  with the interior of bladder  74 , providing a communication passage for admitting motor lubricant to the interior of bladder  74 . In addition, a labyrinth tube  84  has its upper end secured to a port  85  located adjacent port  82 . Port  85  is shown below port  82 , but it could be located at the same level or even above port  82 . Labyrinth tube  84  is a small diameter tube that extends from port  85  downward alongside upper isolation tube  70  sealingly into the upper end of passage  68  ( FIG. 2B ) in central radial bearing support  60 . Lubricant within lower chamber  66  can thus communicate with lubricant in the annular clearance around shaft  34  within isolation tubes  58  and  70  via labyrinth tube  84 . 
     A bladder stress reducer cap  86  is positioned adjacent bladder retainer  80 . Bladder stress reducer cap  86  is configured to prevent an upper end of the bladder  74  from extending upward toward upper adapter  28 . 
     Referring to  FIG. 4 , a threaded plug receptacle  88  is located in upper adapter  28 . Plug receptacle  88  will normally contain a plug (not shown) during operation, but it is removed during the lubricant filling procedure. A radially extending passage  90  joins an inner end of plug receptacle  88  and extends inward to an axial passage  92  through which shaft  34  extends. A bushing  94  is located within passage  92  for slidingly engaging and radially supporting shaft  34 . Bushing  94  does not provide a seal against the flow of lubricant and may have flow passages through it as indicated by the dotted lines  96  in  FIG. 4 . One or more check valves  98  are located within a vent port  100  in upper adapter  28 . Vent port  100  extends upward from the lower end of upper adapter  28  into an intersection with radial passage  90  inward from plug receptacle  88 . Check valve  98  will allow downward flow of fluid into upper chamber  64  but not allow upward flow. A well fluid port  102  extends from the lower end of upper adapter  28  to a cavity  104  formed in the upper end of upper adapter  28 . Cavity  104  is in fluid communication with well fluid on the exterior of seal section  18  via intake  22  ( FIG. 1 ) of pump  20 . Well fluid port  102  alternately could extend through an exterior sidewall of upper adapter  28 . 
     A mechanical seal assembly  106  is located at the upper end of shaft  34  for sealing against the encroachment of well fluid from cavity  104  into motor  16  ( FIG. 1 ). In this embodiment, mechanical seal assembly  106  includes a rotary seal member  108  that rotates with shaft  34  and is biased by a coiled spring  110  against a stationary seal base  112 . A secondary shaft seal  114  may optionally be located below seal base  112 . Secondary shaft seal  114  may optionally be a conventional shaft oil seal. A lubricant may be located between secondary shaft seal  114  and seal assembly  106 , and that lubricant may differ from the motor lubricant. 
     As mentioned above, bladder stress reducer cap  86  is positioned adjacent the bladder retainer  80 , and configured to prevent an upper end of the bladder  74  from extending upward toward the upper adapter  28 . An enlarged view of the bladder stress reducer cap  86  is shown in  FIG. 3 . As shown, the bladder stress reducer cap  86  is a generally cup shaped member having an upper rim  116 , a central neck  118 , and a lower fluted, conical skirt  120 . Cap  86  is a rigid member formed of a metal, composite, or hard plastic so that it will not deflect upward when bladder  74  expands upward. Cap  86  is on the exterior of bladder  74 , thus during use, will be immersed in well fluid in seal section housing  32 . 
     Skirt  120  flares outward in a downward direction and has an outer diameter less than an inner diameter of seal section housing  32  ( FIG. 4 ). The outer diameter of skirt  120  is at least equal and preferably slightly greater than the outer diameter of bladder cylindrical portion  79 , when bladder  74  is in a natural, unexpanded condition. The diverging angle of skirt  120  is the same as the diverging angle of bladder conical shoulder  81 . Skirt  120  overlies and is in contact with bladder shoulder  81 . 
     Cap neck  118  of the bladder stress reducer cap  86  connects cap rim  116  to the lower skirt  120 , and spans the length of neck  78  at the upper end of bladder  74 . In the embodiment shown, the inner diameter of cap neck  118  is greater than the outer diameter of bladder neck  78 , creating an annulus  121  between them. Annulus  121  is in fluid communication with the well fluid in seal section housing  32 . Annulus  121  may be advantageous because it allows for the use of the bladder stress reducer cap  86  with ESPs  10  having shafts  34  of different diameters, thereby making the bladder stress reducer cap  86  more universal and adaptable to ESPs  10  other than that specifically described herein. 
     In practice, rim  116  is configured to engage an outer surface of bladder retainer  80 . This may be accomplished by any appropriate means. For example, in the embodiment of  FIG. 3 , rim  116  includes stepped ridges  122 . These stepped ridges  122  generally correspond to a protrusion  124  on bladder retainer  80 , so that when bladder stress reducer cap  86  is in place, stepped ridges  122  contact protrusion  124  of bladder retainer  80 . In the embodiments shown, a portion of upper adapter  28  may extend toward bladder  74  until a bottom surface of upper adapter  28  is adjacent to bladder stress reducer cap  86 , thereby restricting the ability of bladder stress reducer cap  86  from moving axially away from bladder  74 . 
     Skirt  120  of bladder stress reducer cap  86  tapers radially outward from cap neck  118  toward the lower end of seal section  18 . The junction between skirt  120  and cap neck  118  may be positioned adjacent the bottom of bladder neck  78  at the upper end of bladder  74 . Skirt  120  is designed so that as bladder  74  expands, the top of bladder  74  is restrained by skirt  120  from extending upwardly around bladder retainer  80 . One advantage to this is that bladder  74  will not expand around bladder retainer  80  and experience excessive stress in the area where the edge of bladder retainer  80  contacts bladder  74 . 
     At least one vent  126  may extend through bladder stress reducer cap  86  to allow fluids to pass from above to below bladder stress reducer cap  86 , and vice versa. One reason for such vents  126  is that as bladder  74  expands, it may seal against lower skirt  120  of bladder stress reducer cap  86  and trap well fluid. However, in most instances, a space will remain above such a seal, between neck  78  of the bladder  74  and cap neck  118  of bladder stress reducer cap  86 . Provision of the vents  126  allows the pressure within this space to equalize with the pressure in the upper chamber  72 , thereby preventing damage to bladder  74  or any other components. 
     During filling, lubricant flows upward through the spaces around thrust bearing  42  ( FIG. 2B ) and the annular clearance around shaft  34  in lower isolation tube  58 . The lubricant flows up through the annular clearance in upper isolation tube  70  and down into bladder  74  via port  82  ( FIG. 2A ). Lubricant also flows into lower chamber  66  via labyrinth tube  84  and passage  68 . Once lower chamber  66  and the interior of bladder  74  are filled, the lubricant will flow up into the spaces around shaft  34  in upper adapter  28 , at least up to secondary shaft seal  114 , if utilized. 
     After filling, a plug is installed in receptacle  88  and ESP  10  is lowered into the well. As ESP  10  is lowered into the well, well fluid enters upper chamber  72  via cavity  104  and passage  102 . The hydrostatic pressure of the well fluid is exerted via bladder  74  to the lubricant within bladder  74  and motor  16 . When at the desired depth, the operator supplies power to motor  16 , causing pump  20  to draw well fluid in through intake  22  and discharge the well fluid through tubing  14  to the surface. 
     During operation, bladder  74  will tend to expand or contract depending on the relative pressures of the lubricant within bladder  74 , and the fluids outside bladder  74 . For example, in some instances the hydrostatic pressure of the fluids outside bladder  74  will be higher than the pressure of the lubricant within bladder  74 , thereby causing the bladder to contract. However, during operation of motor  16 , the lubricant within motor  16  and bladder  74  will heat. As the lubricant heats, it will expand, thereby expanding bladder  74 . Because the bladder is elastomeric, it can expand or contract, thereby allowing the pressure of the lubricant to equalize with the pressure outside the bladder. Furthermore, as the bladder expands, it is restrained by bladder stress reducer cap  86  from expanding upwardly around bladder retainer  80 , as described above. 
     Although the technology herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present technology. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present technology.