Abstract:
A floating ring bearing for an electric submersible pump (ESP) assembly disposable within a cased wellbore and a method to assemble the same are disclosed. The ESP assembly includes a motor, a pump, and a shaft coupling the pump to the pump motor. One or more floating ring bearings are disposed within the motor and the pump, each floating ring bearing circumscribing the shaft to radially support the shaft. A floating ring is disposed within each floating ring bearing. The floating ring circumscribes the shaft so that the floating ring rotates about the shaft in response to rotation of the shaft.

Description:
[0001]    This application claims priority to and the benefit of co-pending U.S. Provisional Application No. 61/448,470, by Forsberg, filed on Mar. 2, 2011, entitled “ELECTRIC SUBMERSIBLE PUMP FLOATING RING BEARING,” which application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates in general to bearings supporting a rotating member and, in particular, to bearings supporting rotating shafts of an electric submersible pump and a method to assemble the same. 
       BRIEF DESCRIPTION OF RELATED ART 
       [0003]    Wells may use an artificial lift system, such as an electric submersible pump (ESP) to lift well fluids to the surface. Where ESPs are used, the ESP may be deployed by connecting the ESP to a downhole end of a tubing string and then run into the well on the end of the tubing string. The ESP may be connected to the tubing string by any suitable manner. In some examples, the ESP connects to the tubing string with a threaded connection so that an uphole end or discharge of the ESP threads onto the downhole end of the tubing string. 
         [0004]    ESPs generally include a pump portion and a motor portion. Generally, the motor portion is downhole from the pump portion, and a rotatable shaft connects the motor and the pump. The rotatable shaft is usually one or more shafts operationally coupled together. The motor rotates the shaft that, in turn, rotates components within the pump to lift fluid through a production tubing string to the surface. ESP assemblies may also include one or more seal sections coupled to the shaft between the motor and pump. In some embodiments, the seal section connects the motor shaft to the pump intake shaft. Some ESP assemblies include one or more gas separators. The gas separators couple to the shaft at the pump intake and separate gas from the wellbore fluid prior to the entry of the fluid into the pump. 
         [0005]    The pump portion includes a stack of impellers and diffusers. The impellers and diffusers are alternatingly positioned in the stack so that fluid leaving an impeller will flow into an adjacent diffuser and so on. Generally, the diffusers direct fluid from a radially outward location of the pump back toward the shaft, while the impellers accelerate fluid from an area proximate to the shaft to the radially outward location of the pump. Each impeller and diffuser may be referred to as a pump stage. The shaft couples to the impeller to rotate the impeller within the non-rotating diffuser. In this manner, the stage may pressurize the fluid to lift the fluid through the tubing string to the surface. 
         [0006]    The rotating shaft of the ESP may be supported on rotary bearings such as journal or plain bearings, sleeve bearings, or the like. These bearing assemblies include a sleeve surrounding and mounted to the rotating shaft, for example with a key, so that the sleeve rotates with the shaft. The sleeve is supported by an insert, for example a bushing, and a lubricant film between the sleeve and the insert. The sleeve and shaft rotate within the insert that is held in place by a race, in turn mounted to a pump housing or pump body through a T-ring that prevents rotation of the bearing relative to the pump housing or body. These types of bearings face problems in environments where high vibration may occur, for example in an eccentrically loaded shaft of an ESP or an imbalanced rotating shaft of the ESP. In addition, due to the relatively thin lubrication layer between the sleeve and the insert, the bearing may be subject to a high degree of wear at the high rotational operating speeds experienced by ESPs. This leads to a significantly shorter life that may necessitate frequent replacement of the bearings. Replacing rotary bearings in an ESP may be extremely costly, particularly where the ESP is positioned within increasingly deep wellbores. Therefore, there is a need for a bearing that may accommodate high vibration of a rotating member in an ESP while having increased wear resistance. 
       SUMMARY OF THE INVENTION 
       [0007]    These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention that provide an electric submersible pump floating ring bearing and a method to assemble the same. 
         [0008]    In accordance with an embodiment of the present invention, an electric submersible pump (ESP) assembly disposable within a cased wellbore is disclosed. The ESP assembly includes a motor, a pump, and a shaft coupled between the pump and the motor. The ESP further includes an outer bearing surface circumscribing the shaft and fluid between the shaft and the bearing surface. An annular ring floats in the fluid and is rotatable with respect to the shaft and the outer bearing surface. 
         [0009]    In accordance with another embodiment of the present invention, an electric submersible pump (ESP) assembly disposable within a cased wellbore is disclosed. The ESP assembly includes a motor, a pump, and a shaft coupled between the pump and the motor. A stationary journal defines a bore through which the shaft extends and fluid circumscribes the shaft in the stationary journal. An annular ring floats in the fluid coaxial with an axis of the shaft and rotatable with respect to the shaft to reduce the rotational inertia of the fluid resulting from rotation of the shaft, the annular ring rotating at a slower speed than the shaft so that fluid between the ring and the shaft has a higher rotational inertia than the fluid between the ring and the stationary journal. 
         [0010]    In accordance with yet another embodiment of the present invention, a method to assemble a floating ring bearing for use in an electric submersible pump (ESP) to radially support one or more rotating shafts coupling a motor of the ESP to a pump portion of the ESP is disclosed. The method provides providing a stationary journal defining a bore having an axis. The journal is secured to a non-rotating member of the electric submersible pump. The method positions the shaft within the journal coaxial with the bore so that the shaft is rotatable relative to the journal. The method positions a floating ring coaxial with the bore between the journal and the shaft. The floating ring defines an outer annular cavity between the floating ring and the journal and an inner annular cavity between the floating ring and the shaft. The method fills the inner and outer cavities with a fluid freely flowing through the ESP to transfer rotational inertia of the shaft to the floating ring when the shaft rotates, thereby allowing the floating ring to rotate within the journal. 
         [0011]    The disclosed embodiments provide a bearing that can offer improved damping and vibration characteristics. In addition, this bearing type may be used in a system with high vibration to improve the energy dissipation of the rotating shaft and, consequently, the vibration characteristics. Furthermore, the disclosed embodiments will experience reduced wear, such as abrasive wear, compared to similarly situated bearings. This is because the effective velocity between the shaft and the ring, and the ring and the journal is lower. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained, and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings that form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
           [0013]      FIG. 1  is a schematic representation of an electric submersible pump coupled inline to a tubing string and suspended within a casing string in accordance with an embodiment of the present invention. 
           [0014]      FIG. 2  is a sectional view of a floating ring bearing of  FIG. 1 , taken along line  2 - 2  in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings which illustrate embodiments of the invention. 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, and the prime notation, if used, indicates similar elements in alternative embodiments. 
         [0016]    In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. Additionally, for the most part, details concerning drilling rig operation, electric submersible pump construction and operation, and the like have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the skills of persons skilled in the relevant art. 
         [0017]    With reference now to  FIG. 1  an example of an electrical submersible pump (ESP) system  11  is shown in a side partial sectional view. ESP  11  is disposed in a wellbore  29  that is lined with casing  12 . In the embodiment shown, ESP  11  includes a motor  15 , a seal section  19  attached on the upper end of the motor  15 , and a pump  13  above seal  19 . Fluid inlets  23  shown on the outer housing of pump  13  provide an inlet for wellbore fluid  31  in wellbore  29  to enter into pump section  13 . A gas separator (not shown) could be mounted between seal section  19  and pump section  13 . 
         [0018]    In an example of operation, pump motor  15  is energized via a power cable  17  and rotates an attached shaft assembly  35  (shown in dashed outline). Although shaft  35  is illustrated as a single member, it should be pointed out that shaft  35  may comprise multiple shaft segments. Shaft assembly  35  extends from motor  15  through seal section  19  to pump section  13 . Impellers  25  (also shown in dashed outline) within pump section  13  are coupled to an upper end of shaft  35  and rotate in response to shaft  35  rotation. Impellers  25  can be a vertical stack of individual members alternatingly interspaced between static diffusers (not shown). Wellbore fluid  31 , which may include liquid hydrocarbon, gas hydrocarbon, and/or water, enters wellbore  29  through perforations  33  formed through casing  12 . Wellbore fluid  31  is drawn into pump  13  from inlets  23  and is pressurized as rotating impellers  25  urge wellbore fluid  31  through a helical labyrinth upward through pump  13 . The pressurized fluid is directed to the surface via production tubing  27  attached to the upper end of pump  13 . 
         [0019]    Shaft  35  is radially supported within ESP  11  by bearings, such as floating ring bearings  37 . A person skilled in the art will understand that any number of floating ring bearings  37  may be used to support shaft  35  as necessary. Similarly, a person skilled in the art will understand that floating ring bearings  37  may be placed within any portion of ESP  11 , such as motor  15 , seal section  19 , or pump  13  so that each component of ESP  11  may radially support shaft  35  at one or more locations. 
         [0020]    Referring to  FIG. 2 , shown is an example of a floating ring bearing  37  that includes a journal  39 , and a floating ring  41 . Journal  39  may be a stationary component. In the illustrated embodiment, journal  39  may be an outer housing element of floating ring bearing  37  suitably mounted to a pump housing, shaft support, or shaft alignment member. A person skilled in the art will recognize that journal  39  may mount to the appropriate member in any suitable manner such that floating ring bearing  37  may support shaft  39  as disclosed herein. In other embodiments, journal  39  may be the pump housing, shaft support, or shaft alignment member adapted to function as described herein with respect to journal  39 . In an example, journal  39  is a tubular member having a curved inner surface that defines a bore  43  having an axis  45 . An inner diameter of bore  43  will be sufficient to accommodate placement of both shaft  35  and floating ring  41  as described in more detail below. Shaft  35  resides within bore  43  and is coaxial with axis  45 . Floating ring  41  also resides within bore  43  and is coaxial with axis  45 . Floating ring  41  has an outer diameter  42  smaller than the inner diameter of journal  39  so that an outer annular cavity  47  is formed between floating ring  41  and journal  39 . Outer annular cavity  47  extends radially outward from the outer diameter  42  of floating ring  41  to the inner diameter of journal  39 . Floating ring  41  has an inner diameter  44  larger than the outer diameter of shaft  35  to form an inner annular cavity  49  between shaft  35  and floating ring  41 . Inner annular cavity  49  extends from the outer diameter of shaft  35  to inner diameter  44  of floating ring  41 . Both outer and inner annular cavities  47 ,  49  may be respectively filled with a non-compressible fluid F 1 , F 2 , such as a lubricating oil, grease, gas, or a fluid within ESP  11 . Inner and outer annular cavities  47 ,  49  allow shaft  35  and floating ring  41  to move radially relative to one another, and relative to journal  39 . Floating ring  41  is not secured to shaft  35  for rotation therewith. 
         [0021]    A person skilled in the art will understand that floating ring  41  has a length as needed to provide sufficient radial support of shaft  35 . Similarly, outer and inner annular cavities  47 ,  49  may be defined in part by the length of floating ring  41 . The length of floating ring  41  may vary based on the dimensional and material properties of shaft  35 , the load carrying capacity of shaft  35  and floating ring bearing  37 , and they dynamic characteristics of the rotation of shaft  35 . A person skilled in the art will further understand that floating ring  41  may move axially relative to shaft  35  and journal  39 . However, axial movement of floating ring  41  may be constrained by adjacent components of ESP  11 . In some embodiments, a limiter pin (not shown), annular shoulder on journal  39  (not shown), or similar feature may be used axially above and axially below floating ring  41  to limit the overall axial movement of floating ring  41 , provided floating ring  41  may still rotate relative to both journal  39  and shaft  35 . Floating ring  41  may also have a width sufficient to maintain the ring-like shape of floating ring  41  when subjected to the pressure profile of the ESP  11  application of floating ring bearing  37  and the particular geometry of the ESP  11  component, i.e. pump  13 , motor  15 , seal section  19 , etc., in which floating ring bearing  37  is used. 
         [0022]    Shaft  35  may selectively rotate in response to operation of motor  15  ( FIG. 1 ). As shaft  35  rotates with a rotational velocity w 1 , frictional forces between the exterior surface of shaft  35  and the surrounding fluid F 2  in inner annular cavity  49  will cause shaft  35  to impart rotational energy to the fluid F 2  in inner annular cavity  49  between shaft  35  and floating ring  41 , causing that fluid F 2  to rotate in the same direction as shaft  35 . In turn, the rotational motion of the fluid F 2  in cavity  49  will impart rotational energy to floating ring  41  causing floating ring  41  to rotate with a rotational velocity w 2  in the same direction as shaft  35 . In the exemplary embodiment, w 2  is approximately ⅓w 1  to ¼w 1 . Similarly, frictional forces between floating ring  41  and the fluid F 1  in cavity  47  impart rotational energy from floating ring  41  to the fluid F 1 , causing the fluid F 1  to rotate, although at a lower velocity than floating ring  41 , the fluid F 2  in cavity  49 , or shaft  35 . Thus, shaft  35  may rotate within journal  39  with reduced wear between shaft  35  and journal  39 . In addition, the reaction forces necessary to prevent rotation of journal  39  may be significantly decreased as the total energy that may be exerted on journal  39  is reduced through the successive energy transfers between shaft  35 , fluid F 1 , floating ring  41 , and fluid F 2 . 
         [0023]    In the illustrated embodiment, the fluid F 1 , F 2  in cavities  47 ,  49  is not sealed from the working fluid that is pumped up through pump  13  or the dielectric fluid that may fill seal section  19  and motor  15 . As shown, floating ring bearing  37  is a hydrodynamic bearing lubricated with the working fluid or dielectric fluid of the component in which floating ring bearing  37  is positioned. In an exemplary embodiment, shaft  35  may rotate at slower rotational speeds during operation of ESP  11 , for example at approximately 3500 revolutions per minute. These operating speeds permit use of the working fluid or dielectric fluid of ESP  11  to lubricate floating ring bearing  37  and provide the fluid films maintaining separation between shaft  35 , floating ring  41 , and journal  39 . In these exemplary embodiments, no additional pressurization system or specialized sealing system is needed to provide fluid F 2  or Fluid F 1  to outer and inner annular cavities  47 ,  49 , respectively. A person skilled in the art will understand that alternative embodiments may seal the fluid in outer and inner annular cavities  47 ,  49  from the working fluid or dielectric fluid in use in ESP  11 . 
         [0024]    Outer annular cavity  47  has a width  51  between journal  39  and floating ring  41 . Similarly, outer annular cavity  49  has a width  53  between shaft  35  and floating ring  41 . Widths  51 ,  53  are selected based on the design parameters of the particular ESP  11  into which floating ring bearing  37  is placed. For example, to decrease wear between shaft  35  and journal  39 , widths  51 ,  53  may be larger to allow for a larger decrease in the rotational velocity of w 2  relative to w 1 . However, a person skilled in the art will understand that knowledge of the particular ESP  11  application to which floating ring bearing  37  will be applied, including knowledge of the load and operational speed requirements of ESP  11 , is necessary to accurately size widths  51 ,  53 . A person skilled in the art will further understand that widths  51 ,  53  will be limited by the overall size of the ESP component. 
         [0025]    A person skilled in the art will recognize that floating ring bearing  37  may be used in any suitable component of ESP  11 . For example, floating ring bearings  37  may be used in pump  13 , motor  15 , and seal section  19 . In addition, floating ring bearings  37  may be used in optional equipment such as gas separators, sand separators, and the like. A person skilled in the art will further understand that each floating ring bearing  37  used in individual components of ESP  11  may be sized according to the particular component of ESP  11  in which floating ring bearing  37  is used, provided that the particular floating ring bearing  37  may operate as described herein. 
         [0026]    Accordingly, the disclosed embodiments provide numerous advantages. For example, the disclosed embodiments provide a bearing that can offer improved damping and vibration characteristics. In addition, this bearing type may be used in a system with high vibration to improve the energy dissipation of the rotating shaft and, consequently, the vibration characteristics. Furthermore, the disclosed embodiments will experience reduced wear, such as abrasive wear, compared to similarly situated bearings. This is because the effective velocity between the shaft and the ring, and the ring and the journal is lower. 
         [0027]    This application claims priority to and the benefit of co-pending U.S. Provisional Application No. 61/448,470, by Forsberg, filed on Mar. 2, 2011, entitled “ELECTRIC SUBMERSIBLE PUMP FLOATING RING BEARING,” which application is incorporated herein by reference. 
         [0028]    It is understood that the present invention may take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or scope of the invention. Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.