Abstract:
A seal section for a submersible well pump assembly has a housing for connection between a pump and a motor. A central radial bearing support rotatably supports a drive shaft and defines upper and lower chambers in the housing. A well fluid passageway leads from an exterior portion of the housing to the upper chamber. Upper and lower isolation tubes extend around the shaft within the upper and lower chambers, defining an annular passage for fluid communication with lubricant contained in the motor. A bladder surrounds the upper isolation tube for separating lubricant from well fluid in the upper chamber. A labyrinth tube within the bladder has an upper end in fluid communication with a labyrinth port leading through the upper isolation tube and a lower end in fluid communication with the lower chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to provisional patent application Ser. No. 60/810,115, filed May 31, 2006. 
     
     FIELD OF THE INVENTION 
       [0002]    This invention relates in general to electrical submersible well pumps and in particular to a seal section that locates between the pump motor and the pump for equalizing lubricant pressure contained within the motor with hydrostatic pressure on the exterior. 
       BACKGROUND OF THE INVENTION 
       [0003]    Electrical submersible pumps are often used for pumping a mixture of oil and water from a well. Normally the pump assembly has an electrical motor and a rotary pump, which may be centrifugal or other types. The motor is filled with a dielectric lubricant, and a seal section between the motor and the pump serves to equalize the internal pressure of the lubricant with the hydrostatic pressure on the exterior of the pump assembly. 
         [0004]    A typical seal section, also called a pressure equalizer, has a tubular housing through which a drive shaft extends for transmitting rotation of the motor to the pump. A thrust bearing assembly is often located in the seal section for absorbing downthrust created by the pump. The lubricant in the pump also lubricates the thrust bearing. 
         [0005]    Various means are employed to equalize lubricant pressure with the well fluid. A tubular elastomeric bladder may be mounted in the seal section, the bladder having an interior in fluid communication with the lubricant in the motor. A well fluid passageway allows well fluid to enter the seal section on the exterior of the bladder. Labyrinth tubes are also employed, either alone or in a separate chamber from the bladder. The water of the well fluid is normally denser than the oil. Generally, the labyrinth tubes are mounted with an upper inlet and a lower outlet, so that water flowing downward through the tube cannot flow back upward through the outlet in a manner so as to migrate into the motor. 
         [0006]    The seal section also has features to accommodate expansion of the lubricant in the motor, which occurs as the motor gets hotter. A check valve may be employed to expel excess lubricant without allowing the entry of well fluid. 
         [0007]    Most seal sections have multiple chambers, usually two to four, for housing the bladder and labyrinth tubes. Normally, each chamber is a cylindrical sleeve secured at its upper and lower ends by threads to adapters and shaft support members. The additional threaded sleeves add to the cost of a seal section. 
       SUMMARY 
       [0008]    The seal section of this invention has a number of desirable features. A labyrinth tube is located within the bladder for expelling air during filling. The labyrinth tube has a lower end that connects to a separate oil-filled chamber. 
         [0009]    The seal section has upper and lower adapters for securing the seal section between a pump and motor. The housing is a single cylindrical sleeve connected between the upper and lower adapters. A thrust bearing assembly is located in the housing above the lower adapter. Lower and central radial bearing supports fit within the housing for radially supporting the shaft. Isolation tubes enclose the shaft and connect between the lower and central radial bearing supports and the central radial bearing support and the upper adapter. The lower and central radial bearing supports, the isolation tubes, and the bag can be assembled as a unit and inserted into one end of the housing. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIGS. 1A and 1B  comprise a vertical sectional view of a seal section for an electrical submersible well pump assembly in accordance with this invention. 
           [0011]      FIG. 2  is an enlarged sectional view of an upper portion of the seal section of  FIG. 1 , 
           [0012]      FIG. 3  is a schematic sectional view of an electrical submersible pump assembly in accordance with this invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring to  FIG. 3 , an electrical submersible pump assembly  11  (“ESP”) is shown installed within casing  13  in a well. ESP  11 I is suspended on a string of tubing  15 , and in this embodiment, discharges well fluid up tubing  15 . ESP  11  has a motor  17 , typically a three-phase AC motor. Motor  17  is connected to a seal section  19 , which in turn is connected to a pump  21 . Motor  17  is filled with a lubricant, and seal section  19  equalizes the lubricant pressure with the hydrostatic pressure of the well fluid on the exterior. Pump  21  is a rotary pump, such as a centrifugal pump having a large number of stages, each stage having an impeller and a diffuser. Pump  21  has an intake  23  on its lower end that draws well fluid in. 
         [0014]    Referring to  FIGS. 1A and 1B , seal section  19  has a lower adapter  25  for securing to motor  17  ( FIG. 3 ). Lower adapter  25  typically has a flange  27  that receives bolts that bolt to a mating flange of motor  17 . An upper adapter  29  ( FIG. 1A ) connects seal section  19  to pump  21  ( FIG. 3 ). Upper adapter  29  has threaded holes  31  for receiving bolts from a lower adapter of pump  21 . Seal section  19  has a housing  33  that comprises a cylindrical sleeve secured to lower and upper adapters  25 ,  29 , preferably by threads. Housing  33  is preferably a single integral member. 
         [0015]    A shaft  35  extends through seal section  19  for transmitting rotary motion from motor  17  ( FIG. 3 ) to pump  21 . Shaft  35  has an upper splined end  37  that optionally may have a latch member  39 . Latch member  39  latches to the shaft (not shown) of pump  21  ( FIG. 3 ) so as to transmit tension. Shaft  35  has lower splined end  41  that engages the shaft of motor  17  (not shown). 
         [0016]    A conventional thrust bearing  42  is located in seal section  19 , as illustrated in  FIG. 11B . Thrust bearing  42  comprises a rotary thrust member or runner  43  that is secured to shaft  35 . Runner  43  rotatably engages a stationary downthrust member or base  45  that is mounted to the upper side of lower adapter  25 . Runner  43  also engages a stationary upthrust member  47  while in upthrust. Upthrust member  47  is supported within housing  33  against upward movement by a retainer ring  48 , which may be a snap ring. 
         [0017]    A lower radial bearing support  49  is supported in housing  33  against downward movement by retainer ring  48 . Lower radial bearing support  49  has a bushing  51  that is slidably engaged by shaft  35 . Bushing  51  does not form a seal on shaft  35  and may have passages or channels through it to freely allow the passage of motor lubricant. Lower radial bearing support  49  has seals on its exterior that sealingly engage the inner diameter of housing  33 . A lower isolation tube  53  extends sealingly into a counterbore in lower radial bearing support  49  at the upper end of bushing  51 . Lower isolation tube  53  has an inner diameter that is larger than the outer diameter of shaft  35 , 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  53 . 
         [0018]    The upper end of lower isolation tube  53  extends into sealing engagement with a counterbore in a central radial bearing support  55 . Central radial bearing support  55  has seals on its exterior that seal against the inner diameter of housing  33 . Central radial bearing support also has a bushing  57  that slidingly engages shaft  35  but does not seal against the flow of lubricant. A lower chamber  59  is defined by the annular space between radial bearing supports  49  and  55  and surrounding lower isolation tube  53 . A passage  61  extends through central radial bearing support  55  from its lower end to its upper end. 
         [0019]    Referring to  FIGS. 1A and 1B , an upper isolation tube  63  has its lower end sealingly engaged in a counterbore in central radial bearing support  55  above bushing  57 . The upper end of upper isolation tube  63  extends to upper adapter  29 , defining an annular upper chamber  64  within housing  33 . A tubular elastomeric bladder  65  is located within upper chamber  64 . Bladder  65  has a lower end  67  that fits sealingly around an upper neck portion of central radial bearing support  55 . Bladder  65  has a neck  69  on its upper end that is sealingly secured to a bladder retainer  71 , as shown in  FIG. 2 . Bladder retainer  71  is a tubular member that is secured by threads to the upper end of upper isolation tube  63 . Bladder retainer  71  has an upper portion that sealingly engages a counterbore  70  formed in the lower end of upper adapter  29 . 
         [0020]    Referring again to  FIGS. 1A and 1B , a port  72  is located in the sidewall of upper isolation tube  63  near its upper end. Port  72  communicates the annular clearance within upper isolation tube  63  with the interior of bladder  65 . In addition, a labyrinth tube  73  has its upper end secured to a port  75  located adjacent port  72 . Port  75  is shown below port  72 , but it could be located at the same level or even above port  72 . Isolation tube  73  is a small diameter tube that extends from port  75  downward alongside upper isolation tube  63  sealingly into the upper end of passage  61  ( FIG. 1B ) in central radial bearing support  55 . Lubricant within lower chamber  59  thus communicates with lubricant in the annular clearance around shaft  35  within isolation tubes  53  and  63  via labyrinth tube  73 . 
         [0021]    Referring to  FIG. 2 , a threaded plug receptacle  77  is located in upper adapter  29 . Plug receptacle  77  will normally contain a plug (not shown) during operation, but it is removed during the lubricant filling procedure. A radially extending passage  79  joins an inner end of plug receptacle  77  and extends inward to an axial passage  81  through which shaft  35  extends. A bushing  83  is located within passage  81  for slidingly engaging and radially supporting shaft  35 . Bushing  83  does not provide a seal against the flow of lubricant. One or more check valves  85  are located within a vent port  87  in upper adapter  29 . Vent port  87  extends upward from the lower end of upper adapter  29  into an intersection with radial passage  79  inward from plug receptacle  77 . Check valve  85  will allow downward flow of fluid into upper chamber  64  but not allow upward flow, as indicated by the arrow in  FIG. 2 . A well fluid port  89  extends from the lower end of upper adapter  29  to a cavity  91  formed in the upper end of upper adapter  29 . Cavity  91  is in fluid communication with well fluid on the exterior of seal section  19  via intake  23  ( FIG. 3 ) of pump  21 . Well fluid port  89  alternately could extend through an exterior side wall of upper adapter  29 . 
         [0022]    A mechanical seal assembly  92  is located at the upper end of shaft  35  for sealing against the encroachment of well fluid from cavity  91  into motor  17  ( FIG. 3 ) In this embodiment, mechanical seal assembly  92  includes a rotary seal member  93  that rotates with shaft  35  and is biased by a coiled spring  95  against a stationary seal base  97 . A secondary shaft seal  99  may optionally be located below seal base  97 . Lubricant seal  99  is shown to be a conventional shaft oil seal. Preferably a lubricant is located between oil seal  99  and seal assembly  92 , and that lubricant may differ from the motor lubricant. 
         [0023]    To assemble seal section  19 , the internal components of sleeve or housing  33  are pre-assembled and pushed into housing  33  from one end. For example, the user may first install lower adapter  25 , thrust bearing  42  and shaft  35  in housing  33 . The user then would preassemble upper and lower isolation tubes  63 ,  53  with radial bearing support members  49  and  55  and bladder  65 . The user then would push this subassembly over shaft  35  and into housing  33 . The user then would secure upper adapter  29  to housing  33 . Counterbore  70  slides sealingly over bladder retainer  71  to make up the engagement while the threads on upper adapter  29  engage the threads within housing  33 . 
         [0024]    Prior to operation, motor  17  and seal section  19  are filled with a motor lubricant, and various methods can be employed. In one technique, motor  17  is initially filled with lubricant at a manufacturing or service facility. At the well site, seal section  19  is secured to the upper end of motor  17 , and the lubricant is pumped in from a fill port (not shown) at the upper end of motor  17 . The plug for receptacle  77  ( FIG. 2 ) is removed prior to pumping the lubricant into motor  17  ( FIG. 3 ). The operator can pump lubricant from the fill port upward in seal section  19  until lubricant begins to flow out plug receptacle  77 , Air in seal section  19  would be displaced out port  77  during that procedure. 
         [0025]    During filling, lubricant flows upward through the spaces around thrust bearing  42  ( FIG. 1B ) and the annular clearance around shaft  35  in lower isolation tube  53 . The lubricant flows up through the annular clearance in upper isolation tube  63  and down into bladder  65  via port  72  ( FIG. 1A ). Lubricant also flows into lower chamber  59  via labyrinth tube  73  and passage  61 . Once lower chamber  59  and the interior of bladder  65  are filled, the lubricant will flow up into the spaces around shaft  35  in upper adapter  29 , at least up to oil seal  99 , if utilized. 
         [0026]    After filling, a plug is installed in receptacle  77  and ESP  11  ( FIG. 3 ) is lowered into the well. As ESP  11  is lowered into the well, well fluid enters upper chamber  64  via cavity  91  and passage  89 . The hydrostatic pressure of the well fluid is exerted via bladder  65  to the lubricant within bladder  65  and motor  17 . When at the desired depth, the operator supplies power to motor  17 , causing pump  21  to draw well fluid in through intake  23  and discharge the well fluid through tubing  15  to the surface. 
         [0027]    Motor  17  will begin to heat up, which causes the lubricant to expand. Due to the expansion, excess lubricant may vent through ports  79 ,  87  and check valves  85  into upper chamber  64 . The lubricant is normally less dense than the well fluid, which often contains a high percentage of salt water, thus the vented lubricant in upper chamber  64  will typically gravitate upward through passage  89  and into cavity  91  where it would be pumped to the surface by pump  21  ( FIG. 3 ). 
         [0028]    Over time, some leakage of well fluid past mechanical seal  92  and oil seal  99  may occur. If so, this well fluid will gravitate downward past bushing  83  and into the annular clearance surrounding upper isolation tube  63 . Some of the well fluid will flow out port  72  into bladder  65 . Some of the well fluid will flow down labyrinth tube  73  into lower chamber  59 . Any well fluid that enters bladder  65  will collect at the lower end and would not be able to reenter port  72  located near the upper end of bladder  65 . Also, any well fluid that may collect in lower chamber  59  would not be able to flow upward into ports  72  or  75 . 
         [0029]    The invention has significant advantages. The single cylindrical sleeve of the housing reduces cost over multiple sleeve housings. Because the lower and central radial bearing supports slide into the housing, the seal section can have more volume for oil expansion than a prior art seal section having the same overall length. The labyrinth tube allows bleeding of trapped air and provides an additional barrier for well fluid in the event of leakage. The oil seal serves as backup seal to reduce entry of well fluid into contact with the lubricant. Filling and servicing are more easily performed. 
         [0030]    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.