Abstract:
An electrical submersible pumping (ESP) system for use in a wellbore having a pressure equalization system that employs modules with a bellows. The bellows axially expands and contracts in response to pressure fluctuations encountered in the wellbore. The modules are attachable in series on a lower end of a motor of the ESP to form the string, where the string can range from a single module to a multiplicity of modules, depending on the application. The bellows has a conduit axially inserted through the bellows that includes an umbilical and has an end in pressure communication with the motor.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/331,555, filed May 5 th , 2010, the full disclosure of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    This invention relates in general to oil and gas production, and in particular to a pressure equalization system for an electrical submersible pumping (ESP) system. 
         [0004]    2. Description of Prior Art 
         [0005]    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 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 cable. The pumping unit is usually disposed within the well bore just above where perforations are made into a hydrocarbon producing zone. This placement thereby allows the produced fluids to flow past the outer surface of the pumping motor and provide a cooling effect. 
         [0006]    ESPs are generally elongate so they can be inserted within a producing wellbore where the motor usually is on the lowermost end of the ESP assembly. The motor is typically protected by dielectric fluid housed in the ESP motor. A seal section, which also contains dielectric fluid, usually provides pressure equalization between the dielectric fluid and conditions ambient to the ESP. As the ESP is lowered within a wellbore, fluid static head increases well above atmospheric pressure. Without equalizing pressure between the dielectric fluid and ambient, a pressure gradient could be generated sufficient to breach pressure seals in the ESP assembly. 
       SUMMARY OF INVENTION 
       [0007]    Disclosed is an embodiment of an electrical submersible pumping (ESP) system that when inserted in a wellbore is useful for pumping fluid from the wellbore. In an example embodiment the ESP is made up of a pump that is driven by a pump motor and a pressure equalizer for equalizing pressure between the wellbore and inside of the motor. The pressure equalizer is mounted to an end of the pump motor distal from the pump, and can be removed from the pump motor when needed or desired. Bellows are provided with the pressure equalizer, where the bellows have an inside in pressure communication with the pump motor. The bellows also have an outer surface in pressure communication with the wellbore. The pressure equalizer includes a fitting on its end opposite where it attaches to the pump motor; an additional pressure equalizer with bellows can be mounted onto the fitting. A conduit is set axially within the bellows that provides pressure communication between the motor and the fitting. In an alternate embodiment, a second pressure equalizer is included that mounts to the fitting on the first pressure equalizer. The second pressure equalizer has bellows with insides that are in pressure communication with the pump motor, and also has an outer surface that is in pressure communication with the wellbore. In an alternate embodiment, a fitting is set on an end of the second pressure equalizer opposite from its attachment to the first pressure equalizer. The fitting can be used to attach a third pressure equalizer that also has bellows. In an alternate embodiment, a sensor is attached to the fitting on the end of the pressure equalizer. In an alternate embodiment, an umbilical is inserted through the conduit for transmitting data from the sensor to the surface. In an alternate embodiment, the sensor is mounted on the fitting on the end of the second pressure equalizer. In an alternate embodiment, the bellows is an annular member with folds in its side wall that fold and unfold to allow the annular member to stretch or compress as the pressure differential changes between the inside of the bellows and the outer surface of the bellows. In an alternate embodiment, the pressure equalizer is made up of a housing that is around the bellows. An upper end of the bellows can attach within the housing so that a plenum is defined in the space between side walls of the annular member and the lower end. The housing can have a flanged fitting for attaching the pressure equalizer to the motor and for communicating pressure between the inside of the bellows and the motor, and can also have a fluid inlet formed through the housing for providing fluid communication between the wellbore and the outer surface of the bellows. In an alternate embodiment, a thrust assembly is disposed between the pump motor and the pump. In an alternate embodiment, the bellows has a portion with a diameter greater than the diameter of another portion of the bellows. 
         [0008]    Also provided herein is a submersible pump assembly for lifting fluids from a wellbore. In an example embodiment the submersible pump assembly includes a pump motor mounted below a pump with a string of pressure equalizers attached on a lower end of the pump motor. The pressure equalizers, which are in series, each have an annular bellows member configured so that an inside of each bellows member is in pressure communication with the pump motor and an outer surface of each bellows member is in pressure communication with the wellbore. Also included in this embodiment is a conduit extending axially through a bellows member. An upper end of the conduit is in pressure communication with the motor and a lower end of the conduit is in pressure communication with a lower bellows member. In an alternate embodiment, each bellows member has an annular member arranged with folds in a side wall of the annular member for selective axially lengthening or shortening of the annular member in response to a pressure differential between the inside of each bellows member and the outer surface of each bellows member. In an alternate embodiment, a housing is provided over each bellows member, wherein each housing is equipped with lower fitting and an upper flange selectively attachable to one of a lower flange on a lower end of the motor and a lower fitting on another housing. In an alternate embodiment, a sensor mounts to the lower fitting on a housing of a lowermost bellows member in the string and an umbilical for communication between the sensor and surface, wherein the umbilical is routed through the conduit 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  is a side sectional view of a submersible pumping system disposed in a wellbore. 
           [0011]      FIG. 2  is a side schematic partial sectional view of the ESP of  FIG. 1 . 
           [0012]      FIG. 3  is a side schematic view of an alternate ESP in a wellbore. 
           [0013]      FIG. 4  is a side partial sectional view of a bellows portion of an ESP. 
       
    
    
       [0014]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied 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 the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
         [0016]    Referring now to  FIG. 1 , a side schematic view of an ESP system  20  is illustrated disposed in a wellbore  22  and suspended on production tubing  24  from a wellhead assembly  26 . In the embodiment of  FIG. 1 , the ESP system  20  includes a pump  28  on its upper end for pressuring production fluid from within the wellbore  22 . The pressurized fluid exits the pump  28  into the production tubing  24  for delivery to the wellhead assembly  26 . Production fluid may enter into the pump  28  via an inlet  32  shown formed on the pump  28  and through an outer housing of the pump  28 . A fluid inlet  32  is shown provided on the pump  28  through which fluid from the wellbore  22  flows through the pump  28  to be pressurized. A thrust assembly  32  is shown coaxially provided within the ESP system  20  and mounted below the pump  28 . A pump motor  34  attaches to a lower end of the thrust assembly  32  distal from the end where the thrust assembly  32  connects with the pump  28 . In the embodiment of  FIG. 1 , the motor  34  couples to the pump  28  via a shaft (not shown) and thrust assembly  32  for providing rotational energy to the pump  28 . A modular pressure equalizer  36  is illustrated attached to the lower end of the motor  34 . The pressure equalizer  36  equalizes pressure ambient within the wellbore  22  to fluids within the ESP system  20 ; such as dielectric fluid within the motor  34 , and alleviates mechanical loading on pressure seals within the ESP system  20 . 
         [0017]    An optional gauge  37  is shown attached to the pressure equalizer  36 . In an example embodiment, the gauge  37  is coupled with the umbilical  45  for measuring conditions downhole and providing data signals representing the measured signals through the umbilical  45  to a monitoring system (not shown). Embodiments exist wherein the umbilical  45  connects to windings (not shown) in the motor  34  so the signals travel through the windings and a power cable energizing the motor  34 . Optionally, a dedicated line can connect between the umbilical  45  and monitoring system. Examples of measured conditions include temperature, pressure, and fluid properties. The gauge  37  may be attached to an end of the pressure equalizer  36  distal the end of attachment to the motor  34  or another upwardly disposed pressure equalizer. The motor  34  can generate heat to an already heated area, thus an advantage of setting the gauge  37  away from the motor  34  is an easing of environmental conditions experienced by the gauge  37  potentially prolonging the useful life of the gauge  37 . 
         [0018]    Referring now to  FIG. 2 , provided is a side partial sectional view of a portion of the ESP  20  of  FIG. 1  that illustrates in more detail an embodiment of the pressure equalizer  36 . In this example embodiment the pressure equalizer  36  is shown having an outer annular rigid housing  38  bolted to a lower end of the motor  34  by an adapter flanged head  40 . A bellows  42  is illustrated concentrically provided within the housing  38 . An inner annulus in the flanged head  40  provides fluid communication from within the motor  34  to the inside of the bellows  42 . An elongated tubular conduit  44  is provided within the motor  34  and having an umbilical  45  within. The conduit  44  and umbilical  45  extend from within the motor  34 , through the annulus of the flanged head  40 , into the bellows  42 , and exit a lower lateral wall of the bellows  42 . 
         [0019]    A plenum  47  is defined in the space between the outer periphery of the bellows  42  and inner surface of the housing  38 . Fluid inlets  48  are shown formed through a wall of the housing  38 , thereby providing communication between the plenum  47  and within the wellbore  22 . The radial wall of the bellows  42  is formed of a number of folds  49  that are accordion shaped to allow expansion and/or contraction of the bellows  42 . The bellows  42  can lengthen and extend when expanding and shorten when contracting. Fluid F B  is provided within the bellows  42  and fluid F M  is provided within the motor  34 , fluids F B  and F M  are in pressure communication with one another via the annulus of the adapter flanged head  40 . Pressure in the plenum  47  will be substantially at pressure within the wellbore  22  due to pressure communication through the fluid inlets  48  in the housing  38 . Pressure differentials between the plenum  47  and bellows fluid F B  produce a resultant force on the bellows  42  causing expansion or contraction of the folds  49  to equalize pressure inside the bellows F B  to the pressure inside the plenum  47 , which is substantially the same as pressure in the wellbore  22 . Pressure communication between the bellows fluid F B  and motor fluid F M  through the flanged head  40 , thereby equalizes pressure within the motor  34  and pressure in the wellbore  22 . As noted above, minimizing the pressure differential of within the motor  34  and the wellbore  22  in turn minimizes loading on seals (not shown) within the ESP  20  the sidewalls of the ESP  20 . 
         [0020]    Schematically illustrated in  FIG. 3  is an alternative embodiment of an ESP system  20 A disposed in a wellbore  22  and having a series of pressure equalizers  36   1 - 36   n . In this example, multiple modules  36   1 - 36   n  are shown mounted on a lower end of the motor  34 . The multiple modules  36   1 - 36   n  may be required to provide an amount of fluid capacity to ensure a sufficient amount of equalizing fluid is included with the ESP system  20 A. In an example embodiment, each module  36   i  mounts to an upper module  36   i-1  by bolting the flanged fitting  40 , to the flanged mounting  46   i-1  on a lower end of the upper module  36   i-1 . 
         [0021]    Shown in a side sectional view in  FIG. 4  is an alternative embodiment of a pressure equalizer  36 A and having a segmented bellows  42 . In this example, one portion of the segmented bellows  42  has a greater outer circumference than an adjoining portion of the segmented bellows  42 A. Shown provided along an axis A X  of the segmented bellows  42  is conduit  44  having umbilical  45  coaxially disposed therein. Optionally shown on the lower end of the pressure equalizer  36 A of  FIG. 4  is a adapter base  50  on which the flanged mounting  46  is provided for connection of the gauge  37 , another pressure equalizer  36  ( FIG. 3 ), or some other device or attachment. In the example embodiment, the base  50  is a disk like member mounted transverse to the axis A X . In another example embodiment, the bellows  42  can be capped or completed by a plug (not shown) if required. 
         [0022]    Example materials for the bellows include metal alloys, that in one optional embodiment are resistant to high temperatures and compounds in the wellbore (either connate or injected from surface) that are corrosive and/or aggressive. The metallic bellows material enables an equalization assembly to have a low elastomeric content. Although shown as a flange and bolt arrangement, the attachment for pressure equalizer  36  may include threads or welds for coupling to the motor  34  or other pressure equalizers  36 . It should be pointed out that in the example of  FIG. 3 , in embodiments using bellows  42  within the pressure equalizers, the size of the bellows within each individual pressure equalizer may be different or have a different configuration, such as that of  FIG. 4 . 
         [0023]    The present invention 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. For example, modular pressure equalizers may comprise elastomeric membranes in combination with the bellows  42 . Optionally, the membranes can be included in one or more of the pressure equalizers in place of the bellows  42 . 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.