Abstract:
An electrical submersible pump having a pump section with a stack diffusers and a stack of impellers mounted on a rotatable shaft. Flow paths extends through the pump section directed axially and radially within the impellers and diffusers. Vanes define the flow path through each impeller that provide fluid communication with an upstream side of each impeller and an outer circumference. An annular flow diverting hub is provided on a downstream side of each impeller. The hub has an outer surface that curves radially inward, and having a minimum radius proximate its middle portion. The diffusers are annular members coaxially mounted in a housing of the pump section. Passages define the flow path through each diffuser that extend axially along the pump section and radially between an outer and inner circumference of each diffuser. The outer surface of each hub makes up a portion of an associated passage.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to impellers and diffusers for use in electrical submersible pump (ESP) applications, and in particular to an ESP having an impeller with a bearing hub and a diffuser coupled with the impeller. 
       BACKGROUND OF THE INVENTION 
       [0002]    In oil wells and other similar applications in which the production of fluids is desired, a variety of fluid lifting systems have been used to pump the fluids to surface holding and processing facilities. It is common to employ various types of downhole pumping systems to pump the subterranean formation fluids to surface collection equipment for transport to processing locations. One such conventional pumping system is a submersible pumping assembly which is immersed in the fluids in the wellbore. The submersible pumping assembly includes a pump and a motor to drive the pump to pressurize and pass the fluid through production tubing to a surface location. A typical electric submersible pump assembly (“ESP”) includes a submersible pump, an electric motor and a seal section interdisposed between the pump and the motor. 
         [0003]    Centrifugal well pumps are commonly used as the submersible pump in an ESP application to pump oil and water from oil wells. Centrifugal pumps typically have a large number of stages, each stage having a stationary diffuser and a rotating impeller driven by a shaft. The rotating impellers exert a downward thrust as the fluid moves upward. Also, particularly at startup and when the fluid flow is non-uniform, the impellers may exert upward thrust. It is most common for the impellers to float freely on the shaft so that each impeller transfers downward thrust to an adjacently located diffuser. Thrust washers or bearings are often located between each impeller and the upstream diffuser to accommodate the axially directed upward and/or downward thrusts. 
       SUMMARY 
       [0004]    Disclosed herein is an electrical submersible pump (ESP), in one example embodiment the ESP is made up of an annular diffuser having passages that extend axially and radially throughout. Also included is an impeller coaxial to the diffuser and-having an upstream and a downstream side. A rotatable shaft connects to the impeller, and when rotated the impeller is also rotated. Also included is an annular flow diverter coaxially mounted on a downstream side of the impeller having vanes that project radially through the impeller. The impeller vanes are in fluid communication with the flow diverter through the passages. Further included is a fluid flow path extending through the vanes to an outer circumference of the impeller, into the diffuser directed radially toward an axis of the pump, and along an outer surface of the flow diverter. 
         [0005]    In an alternative embodiment, disclosed is an electrical submersible pumping system that is made of a stack of impellers mounted on a rotatable shaft; where each impeller has an upstream side and a downstream side. Included is an annular flow diverter coaxially provided on the downstream side of each impeller. Vanes disposed in each impeller have an entrance on the upstream side. Diffusers circumscribe each impeller and flow diverter and define a stack of diffusers. Passages are provided that extend radially and axially in each diffuser and having a portion of which defined by an outer surface of the flow diverter circumscribed by the diffuser. A fluid flow path through the stack of impellers and stack of diffusers is defined by the passages and vanes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1A and 1B  are exploded views of a stack of impellers and diffusers in accordance with the present disclosure. 
           [0007]      FIG. 2  is a side section view of a portion of submersible pump in accordance with the present disclosure. 
           [0008]      FIG. 3  is a side partial sectional view of an electrical submersible pumping system set in a wellbore. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    Shown in an exploded view in  FIGS. 1A and 1B  are stacks  28  made up of diffusers  30 , diffuser wear plates  31 , and impellers  32 . The diffusers  30 , diffuser wear plates  31 , and impellers  32  are each generally planar disk like elements that when coaxially assembled form generally cylindrical stacks  28  that are used in a pump for pumping fluids ( FIG. 3 ).  FIGS. 1A and 1B  respectively provide perspective views of upper and lower surfaces of the diffusers  30 , diffuser wear plates  31 , and impellers  32 . For the purposes of reference, each impeller  32  is depicted with a designated downstream side  33  shown facing an adjacent diffuser wear plate  31  and an upstream side  35  shown directed towards an adjacent diffuser  30 . An annular bearing hub  34  is provided on the downstream side  33  of each impeller  32 . 
         [0010]    As described in more detail below, the bearing hub  34  defines a portion of a fluid flow path that winds through the stack  28 . The bearing hub  34  may be hydro-isostatic press formed, welded or threadingly attached to the impeller  32 ; or optionally it may be integral with the impeller  32 . An example of forming an impeller  32  with an integral bearing hub  34  can include a casting process or other manufacturing process as well as one that sinters powdered metal particles. Example metals used in manufacturing the impeller  32  and diffuser  30  include alloys of tungsten carbide, such as a tungsten carbide cobalt alloy. Optionally, the impeller  32  may be forged from metals such as aluminum, titanium, steel, alloys, combinations thereof, and the like. Alternately, base impeller, diffuser, and wear plate materials prior mentioned permits use of line-of sight hard coatings, hard facings, and/or other coatings harder than the base material that otherwise would not be permitted with previous designs. 
         [0011]    Each diffuser  30  also includes a downstream side  36  and an upstream side  38 . In the embodiment of  FIGS. 1A and 1B , the downstream side  36  is facing the upstream side  35  of an adjacent impeller  32 . Each diffuser  30  includes a sidewall  40  along its outer periphery that projects axially from the downstream side  36  and defines a space for receiving an adjacent and downstream impeller  32 . As further illustrated in  FIGS. 1A and 1B , the diffuser wear plate  31  also has a downstream side  42  shown facing an adjacent diffuser  30  and upstream side  44  opposite the downstream side  42  facing the downstream side  33  of an adjacent impeller  32 . Passages  46  are shown formed through the body of the wear plate  31  and along sections that are adjacent the outer periphery of the wear plate  31 . A bearing carrier  48  is also illustrated in  FIGS. 1A and 1B  and on an upstream side  38  of one of the diffusers  30 . The bearing carrier  48  of  FIGS. 1A and 1B  is made up of an outer tubular body  49  and annular midsection  50  mounted within the body  49 . The bearing carrier  48  of  FIGS. 1A and 1B  further includes a sleeve-like bearing insert  51  coaxially mounted within the midsection  50 . Passages  52  are formed axially through the bearing carrier  48  and between the midsection  52  and body  49 . 
         [0012]    Referring now to  FIG. 2 , the diffusers, impellers, and wear plates are shown coaxially combined end to end to form a stack  28 A. For reference purposes, subscripts are included to identify the relative position of the diffusers, impellers, and wear plates in the stack with respect to the bearing carrier  48 . With a plurality of stacks and bearing carriers throughout the pump and equally or not equally spaced bearing carriers providing radially stability to the impellers at intervals throughout the pump. More specifically, a diffuser  30   i  is shown coaxially mounted on the downstream side  54  of the bearing carrier  48 . The upstream side  38  of the diffuser  30   i  is set facing the bearing carrier  48 . Each of the bearing hubs  34  includes an axial bore so that when the impellers  32   i - 32   2  are stacked as shown in  FIG. 2 , an axial passage is formed therethrough and a drive shaft  58  is inserted therein. Axial keyways  59  shown along the inner surface of each bearing hub  34  are configured to receive a key (not shown) that also fits within the shaft  58  and thereby coupling the impellers with the shaft  58 . 
         [0013]    The stack  28 A of  FIG. 2  forms part of a pump; in an example of use, fluid flows through a winding passage in the stack  28 A as illustrated by arrows F. In an embodiment, rotating the shaft  58  thereby rotates the impellers  32  that then draws fluid from below the bearing carrier  48 , into the passage  52 , from the upstream side  56 . The fluid exits the passage  52  at the downstream side  54  of the bearing carrier  48  and enters diffuser flow passages  60 . The flow passages  60  follow a curved path from the outer diameter towards a midsection of the diffuser  38 . The flow passages  60  are formed by diffuser vanes  62  shown provided on the upstream side  38  of the diffusers  30  and arranged along a circular pattern on the outer portion of the upstream side  38 . In the embodiment of  FIG. 2 , the fluid enters the passages  60  proximate the outer periphery of the diffusers  30  and is directed radially inwards toward the axis A X  of the stack  28 A. The flow is directed axially through the diffusers  30  within a bore  63  formed along the diffuser axis. 
         [0014]    An annular shroud  64  circumscribes the diffuser bore  63  and serves to direct the flow from the upstream side  38  of the diffusers into an impeller throat  66  that is coaxially around the axis A X  and within the impeller  32 . Impeller flow passages  68  are depicted on the upstream side  34  of the impeller  32  that are generally curved and have an increasing width with proximity to the outer periphery of the impeller  32  ( FIG. 1B ). A series of curved impeller blades  70  are set on the upstream side  35  of the impeller  32 , the passages  68  are defined in the spaces between adjacent impeller blades  70 . Proximate the axis of each impeller  32  a notch  72  is formed within each impeller blade  70  so that the shroud  64  of the adjacent upstream diffuser may partially project into the impeller  70 . Thus, as the shaft  58  rotates the fluid enters into the impeller flow passages  68  proximate to the axis A X  and is directed radially outward. 
         [0015]    In the example embodiment of  FIG. 2 , the dimensions of the sidewall  40  of the diffuser exceed the height of the impeller blades  70 . When the fluid exits the impeller flow passages  68 , the fluid contacts an inner surface of the side wall  40  where it is then directed upward and towards a wear plate  31 . The wear plate  31  is shown set on a downstream side  33  of the impeller  32 . As noted above, each wear plate  31  includes passages  46  formed along the outer periphery of the wear plate  31 . The fluid exiting each of the impeller flow passages  68  of  FIG. 2 , enters the passages  46  and is directed into diffuser flow passages  60  of a downstream diffuser. In the example of  FIG. 2 , the diffuser downstream of the wear plate  31   i  is designated as  30   i+1 . After entering the flow passages  60  of diffuser  30   i+1 , the fluid is directed radially inward toward the axis and into contact with an outer surface of the bearing hub  34  mounted on the downstream side  33  of impeller  32   i . Fluid flows substantially axially along the outer surface of the bearing hub  34  and encounters a lip  74  on an end of the bearing hub  34  opposite where it attaches to the impeller  32   i . The lip  74  has an outer surface profiled to extend radially outward so that as the fluid flows past the bearing hub  34 , the fluid is directed radially outward. Thus, the fluid is flowing in a direction substantially aligned with impeller passages  68  provided within impeller  32   i+1 . The above-described flow path is repeated along the length of the stack  28 A and with increasing pressure along the length of the stack  28 A. 
         [0016]    Shown in a side partial sectional view in  FIG. 3  is a wellbore  76  capped with a wellhead  78  and production tubing  80  depending from the wellhead  78  into the wellbore  76 . An electrical submersible pumping system (ESP)  82  is shown attached on a lower end of the production tubing  80 . In the example embodiment of  FIG. 3 , the ESP  82  includes a pump section  86  for pumping fluids from the wellbore  76  into the production tubing  80  and to the wellhead  78 . Fluid (not shown) in the wellbore  76  flows into the pump section  86  through an inlet  60  shown formed on an outer surface of the pump section  86 . On a lower end of the pump section  86  is a seal section  88  for equalizing pressure within the ESP  82  to ambient conditions. A motor section  90  is shown on a lower end of the seal section  88  that includes a motor  92  (shown in phantom) coupled to an output shaft  58  (also shown in phantom). The output shaft  58  extends axially through the seal section  88  of the ESP  82  and into the pump section  86 . Shown within the pump section  86  is an example embodiment of the stack  28  of  FIGS. 1A ,  1 B, and  2 . The output shaft  58  rotates when the motor  92  is energized to rotate the impellers  32  within the pump section  86  and pump fluid from the wellbore  76  into the production tubing  80  for delivery to the wellhead  78 . 
         [0017]    The invention has significant advantages. It is to be understood that the invention is not limited to the exact details of the construction, operation, exact materials or embodiment shown and described, as obvious modifications and equivalents will be apparent to one skilled in the art.