Abstract:
A centrifugal pumping system having a stack of impellers and diffusers for pressurizing fluid. The impellers are rotated by a motor for pressurizing and lifting fluid from within a wellbore. Undulating profiles are provided on leading edges of the impellers for inducing turbulence in the fluid being pumped. Increasing turbulence better homogenizes the fluid, so that choked flow is avoided when different density components are present in the fluid. Reducing the possibility of choked flow increases pump efficiency and lift capacity.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/557,448, filed Nov. 9, 2011, the full disclosure of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates in general to electric submersible pumps (ESPs) and, in particular, to an impeller vane with a leading edge profiled to increase turbulence in fluid contacting the leading edge. 
         [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. 
         [0006]    Centrifugal submersible pumps typically employ a stack of rotatable impellers and stationary diffusers, where the impellers and diffusers alternate in the stack and are arranged coaxial with one another. Passages provided through both the impellers and diffusers define a flow path through which fluid is forced while being pressurized in the pump. Changes in density of the fluid being pumped, such as gas or emulsions in the fluid, can choke flow through the pump thereby decreasing pump efficiency and capacity. 
       SUMMARY OF INVENTION 
       [0007]    Disclosed herein is an example of an electric submersible pump (ESP) that has an increased efficiency, especially when fluid is being pumped that has a non-uniform density. In one example the ESP is made up of a motor, a shaft coupled to and selectively rotated by the motor, and a pump. In this example, pump includes a plurality of the impellers having a fluid inlet, an annular hub coupled to the shaft, flow passages extending radially and or axially between the hub and an outer periphery of the impeller, and a vane between the flow passages that extends radially between the hub and an outer periphery of the impeller. An undulating profile is provided on an end of the vane that faces the hub, where the profile defines a leading edge. Thus when fluid from the fluid inlet contacts the leading edge, turbulence is increased in the fluid to mix the fluid and homogenize the fluid and prevent any choked flow. The vane can have a cross section with an elongate side, and wherein the undulating profile extends along the elongate side. The pump can further include an upper shroud and a lower shroud, where the shrouds extend radially outward from the hub to the outer periphery of the impeller and are respectively set on upper and lower surfaces of the vane. In an example, the fluid inlet is formed axially through the lower shroud, and the leading edge is proximate the fluid inlet. Alternatively, the undulating profile is made of undulations that each have about the same height and length, or the undulations that each have a different height and length. An outer surface of the vane between the leading edge and outer periphery of the impeller can be substantially planar. In an optional embodiment, the undulating profile has two undulations, but may alternatively have more than two undulations. The thickness of the vane can decrease proximate the leading edge. 
         [0008]    Also disclosed herein is an example of an electric submersible pump (ESP) system for use in a wellbore that includes a motor section having a motor, a pump section, a shaft coupled to and selectively rotated by the motor, and a stack of impellers in the pump section. In this example each impeller has an annular hub coupled to the shaft that is rotatable with rotation of the shaft, vanes that project radially between the hub and an outer periphery of the impeller and that are spaced apart to define flow passages between adjacent vanes, fluid inlets to each flow passage disposed adjacent the hub, a fluid flow path in each flow passage extending from each fluid inlet, in each passage along vanes adjacent each passage, and towards the outer periphery of each impeller, and an undulating profile on an end of each vane proximate the hub that defines a leading edge and that is in a fluid flow path. The undulating profile perturbs flow, so that when fluid flows along the fluid flow path and against the leading edge, turbulence is increased in the flowing fluid to mix the fluid. The ESP can further include diffusers in the pump section coaxially disposed between each adjacent impeller. Each undulating profile on the vane can be disposed along a path adjacent an interface between the vane and an adjacent flow passage. In one embodiment, each vane has a cross section with an elongate side, and wherein the undulating profile extends along the elongate side. Optionally, each undulating profile comprises undulations of about the same size or have a different size. An upper shroud can be included with each impeller that extends from the hub radially outward to the outer periphery of the impeller and covers a lateral side of each vane, and a lower shroud with each impeller that extends from the hub radially outward to the outer periphery of the impeller and covers a lateral side of each vane distal from the upper shroud. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    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. 
           [0010]      FIG. 1  is a schematic view of an electric submersible pump assembly disposed within a wellbore. 
           [0011]      FIG. 2  is a perspective representation of an impeller of the electric submersible pump assembly of  FIG. 1 . 
           [0012]      FIG. 3  is a partial perspective view of a vane of the impeller of  FIG. 2 . 
           [0013]      FIG. 4  is a top perspective view of the vane of  FIG. 3 . 
           [0014]      FIG. 5  is a front perspective view of the vane of  FIG. 3 . 
           [0015]      FIG. 6  is a side sectional view of an alternate embodiment of an impeller. 
           [0016]      FIG. 7  is a sectional view of an alternate embodiment of a leading edge of an impeller. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    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. 
         [0018]    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 ESP operation, construction, 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. 
         [0019]    With reference now to  FIG. 1  an example of an electrical submersible pumping (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 pump  13  on an upper portion that is driven by a motor  15 . Pump motor  15  is energized via a power cable  17  that connects to an electrical source (not shown). A seal section  19  is further shown attached on the upper end of the motor  15  and between pump  13 . Fluid inlets  23  shown on the outer housing of pump  13  provide communication from outside of the pump  13  to an impeller stack  25  shown in dashed outline in the pump  13 . Fluid  31  flows from a formation surrounding the casing  12 , through perforations  33  in the casing  12 , up the wellbore  29 , and to inlets  23  for wellbore fluid  31  in wellbore  29 . Through the inlets  23 , fluid  31  enters into pump section  13  where it is directed to the impeller stack  25 . Wellbore fluid  31  can include liquid hydrocarbon, gas hydrocarbon, and/or water; a gas separator and a fluid intake (not shown) may be mounted between seal section  19  and pump section  13 . 
         [0020]    Motor  15  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  where it connects to and drives impeller stack  25 , thus stack  25  and rotates in response to shaft  35  rotation. Impeller/diffuser stack  25  includes a vertical stack of individual impellers  37  alternatingly interspaced between static diffusers  38 . Wellbore fluid  31  drawn into pump  13  from inlets  23  is pressurized as the stack of 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 . 
         [0021]    In an exemplary embodiment, impeller stack  25  includes one or more impellers  37  illustrated in  FIG. 2 . Impeller  37  is a rotating pump member that accelerates fluid  31  ( FIG. 1 ) by imparting kinetic energy to fluid  31  through rotation of impeller  37 . Impeller  37  has a central bore defined by the inner diameter of impeller hub  39 . Shaft  35  ( FIG. 1 ) passes through the central bore of impeller hub  39 . Impeller  37  may engage shaft  35  by any means including, for example, splines (not shown) or keyways  41  that cause impeller  37  to rotate with shaft  35  ( FIG. 1 ). 
         [0022]    As shown in example of  FIG. 2 , impeller  37  includes a plurality of vanes  43 . Vanes  43  project radially through impeller  37  between an interior of impeller  37  proximate to hub  39  and an impeller edge  49  distal from hub  39 . Impeller vanes  43  follow a curved path between hub  39  and edge  49 , and may be attached to or integrally formed with impeller hub  39 . Vanes  43  may extend radially from impeller hub  39  and may be normal to shaft  35 , or may extend at an angle. In the illustrated embodiment, vanes  43  are curved as they extend from impeller hub  39  so that a convex portion of each vane  43  extends in the direction of rotation. Passages  45  are formed between surfaces of vanes  43 . Impeller  37  may rotate on shaft  35  ( FIG. 1 ) about axis  57  passing through hub  39  in the direction indicated by arrow  59 . As impeller  37  rotates, fluid may be directed into passages  45  through an impeller inlet  51  that communicates with a lower surface of impeller  37 . Fluid accelerated by rotating impeller  37  in vane  43  flows towards high pressure surface  55  and then is directed out of the associated passage  45 . High pressure surface  55  may be a surface of vane  43  that contacts and pressurizes fluid as described in more detail below. Each vane  43  also has a low pressure surface  56  on an opposite side of vane  43  from high pressure surface  55 . 
         [0023]    A lower shroud  47  forms an outer edge of impeller  37  and may be attached to or join an edge of each vane  43 . Lower shroud  47  defines a planar surface intersected by axis  57  and adjacent a lower lateral side of impeller  37 . In some embodiments, lower shroud  47  is attached to impeller hub  39 , either directly or via vanes  43 . In some embodiments, impeller hub  39 , vanes  43 , and lower shroud  47  are all cast or manufactured as a single piece of material. Lower shroud  47  may have a lower lip for engaging an impeller eye washer on a diffuser. The lower lip may be formed on the bottom surface of lower shroud  47 . Lower shroud  47  defines impeller inlet  51  on a lower side of lower shroud  47 . Impeller inlet  51  allows fluid flow from below impeller  37  into passages  45  defined by vanes  43 . 
         [0024]    Each impeller  37  includes impeller edge  49  that is a surface on an outer radial portion of impeller  37 . In an exemplary embodiment, impeller edge  49  is the outermost portion of lower shroud  47 . Impeller edge  49  need not be the outermost portion of impeller  37 . The diameter of impeller edge  49  is slightly smaller than an inner diameter of a diffuser in which impeller  37  is positioned. 
         [0025]    Further in the example of  FIG. 2 , impeller  37  includes an upper shroud  53  located opposite lower shroud  47  and joins an upper lateral edge of each vane  43 . Upper shroud  53  generally defines an upper boundary of passages  45  between vanes  43 . Upper shroud  53  may seal against an upthrust washer (not shown) of a diffuser  38  ( FIG. 1 ) disposed above impeller  37 . A downthrust washer (not shown) may be located between a downward facing surface of impeller  37  and an upward facing surface of a diffuser  38  disposed below impeller  37 . 
         [0026]    Within a single pump housing, one or more of the plurality of impellers  37  may have a different design than one or more of the other impellers  37 , such as, for example, impeller vanes  43  having a different pitch. A plurality of impellers  37  may be installed on shaft  35  ( FIG. 1 ). Diffusers  38  are installed, alternatingly, between impellers  37 . The assembly having shaft  35 , impellers  37 , and diffusers  38  are installed in pump  13 . 
         [0027]    Referring to  FIGS. 3-5 , an exemplary portion of vane  43  is shown in a side perspective view and with high pressure surface  55  on its outer radial periphery. As shown in  FIG. 2 , high pressure surface  55  may extend between lower shroud  47  and upper shroud  53 . High pressure surface  55  of  FIG. 3  may also be proximate to inlet  51  ( FIG. 2 ). As shown in  FIG. 3 , each vane  43  includes a curvilinear leading edge  63  formed on a portion of vane  43  proximate to hub  39  ( FIG. 2 ). In an example, leading edge  63  extends a height  65  of vane  43  from upper shroud  53  to lower shroud  47 . Leading edge  63  has an undulating profile in a direction along height  65 . In an example, leading edge  63  defines an edge joining high pressure surface  55  and low pressure surface  56 , and as shown in  FIG. 4  has a thickness that decreases proximate its terminal end. The undulating profile of leading edge  63  defines depressions  67  and extensions  69 ; wherein depressions  67  depend inwardly toward vane  43  from a line  71  encompassing apexes of extensions  69 , and extensions  69  depend outwardly away from vane  43  from a line  73  encompassing low points of depressions  67 . Line  71  and line  73  may be separated by an amplitude or distance  75  of extensions  69 . High pressure surface  55  may have a uniform surface extending from line  73  to a trailing edge or surface  77  as shown in  FIG. 4 . High pressure surface  55  and low pressure surface  56  tapers from a depth  79  to leading edge  63  at a rate such that high pressure surface  55  and low pressure surface  56  are substantially smooth across leading edge  63  as shown in  FIGS. 4 and 5 . 
         [0028]    In an example of operation, impeller  37  rotates in the direction indicated by arrow  59  of  FIG. 2 , and fluid passing through inlet  51  flows across leading edge  63  and is pressurized and accelerated along high pressure surface  55 . Depressions  67  and extensions  69  increase the turbidity of the flow across high pressure surface  55  by inducing vortices in the fluid as it flows across extensions  69  and depressions  67 . These vortices can increase the rate of mixing of fluid flowing through passage  45  ( FIG. 2 ) and, consequently, increase fluid flow through passage  45 . By increasing the rate of mixing in passage  45 , gas may not build up along low pressure surface  56  as in the prior art; thus, the disclosed embodiments decrease instances of gas lock and choking of ESP  11  ( FIG. 1 ). 
         [0029]    A person skilled in the art will recognize that there may be significant variation in the contour of leading edge  63 . For example, distance  75  may be varied as needed to accommodate the type of flow and the type of impeller in which vane  43  is positioned. Similarly, while extensions  69  and depressions  67  are shown evenly spaced across leading edge  63  in  FIG. 3 , a person skilled in the art will recognize that extensions  69  and depressions  67  may be unevenly spaced, have different distances  75  from an apex of an extension  69  to a nadir of a depression  67  from adjacent extensions  69  and depressions  67 . There also may be more or fewer extensions  69  and depressions  67  between upper shroud  53  and lower shroud  47 . Leading edge  63  may also comprise a surface having a depth between high pressure surface  55  and low pressure surface  56 . In still other embodiments, trailing edge or surface  77  may include extensions and depressions similar to leading edge  63 . 
         [0030]    An alternate embodiment of an impeller  37 A is shown in a side sectional view in  FIG. 6 . In this example, a leading edge  67 A of vane  43 A extends along a path generally oblique to axis  57 A of impeller  37 A and in the path of fluid, represented by arrows A, flowing from inlet  51 A into passage  45 A. Leading edge  63 A of  FIG. 6  is formed to have a generally discontinuous surface, that sufficiently perturbs fluid flowing from inlet  51 A to passage  45 A to increase turbulence of the fluid. In an example, a discontinuous surface describes a surface having a portion that disposed outside of a plane that intersects adjacent portions. Examples include surfaces with projections or depressions formed thereon. Thus as the fluid flows over a discontinuous surface, velocity changes in the fluid that contacts or otherwise encounters the discontinuities, 
         [0031]    Shown in side sectional view in  FIG. 7  is an example of a leading edge  63 B of a vane  43 B having discontinuities for perturbing fluid flow to increase turbulence. The discontinuities include a depression  81  formed into the surface  63 B, a rounded projected  83  that extends away from the surface of the leading edge  63 B. Also shown are peaked projections  85  that can have varying widths and heights. Thus example leading edges  63 B can include multiple depressions  81 , rounded projections  83 , peaked projections  85 , as well as combinations of these elements. The discontinuities on the surface  63 B are not limited to those illustrated, but can include any symmetric or asymmetric shape or configuration, including generally rectangular shapes. 
         [0032]    Accordingly, the disclosed embodiments provide numerous advantages. For example, the disclosed embodiments will improve pump performance and operating range. In addition, the disclosed embodiments will increase turbulence in the pump that will break any choking or stagnation within the impeller and limit gas collection, thereby increasing lift. Still further, the disclosed embodiments may accomplish this without any substantial change in drag forces within the impeller. 
         [0033]    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. For example, considered with the present disclosure are embodiments of an ESP  11  that include a gas separator equipped with the examples of the impellers described herein. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.