Abstract:
A technique is provided to facilitate pumping of fluids in a well environment. A submersible pumping system having a submersible pump incorporates features that manage thrust loads resulting from rotating impellers. The thrust reducing features cooperate with the action of the impellers in one or more pump stages to reduce forces otherwise acting on certain pump related components.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 11/468,565, filed Aug. 30, 2006, which is a continuation of U.S. patent application Ser. No. 11/468,511, entitled “System and Method for Reducing Thrust Acting On Submersible Pumping Components”, filed Aug. 30, 2006, and is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     When pumping downhole fluids with an electric submersible pump, a variety of hydraulic forces act on various components. For example, impellers in centrifugal, submersible pumps tend to create large reaction forces that act in a direction opposite to the direction of fluid flow. The large reaction forces are resisted by, for example, a thrust washer in each stage of a floater style pump or by a motor protector thrust bearing in a compression style pump. 
     The thrust created by the impeller in each stage of a submersible pump can be problematic in a variety of submersible pump types, including pumps with mixed flow stages and pumps with radial flow stages. In some floater style designs, for example, a significant portion of power loss in the pump is due to thrust friction occurring at the outer thrust washer due to relatively high friction induced torque at this radially outlying position. If the outer thrust washer is removed from the floater style stage, however, the lack of any seal functionality increases leakage loss. 
     SUMMARY 
     In general, the present invention provides a technique for pumping fluids in a submerged environment. The technique is useful with submersible pumping systems, such as those used in wellbore applications for pumping downhole fluids. A submersible pumping system is designed to utilize thrust control features with the submersible pump to reduce certain thrust loads otherwise acting on submersible pump components. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
         FIG. 1  is an elevation view of an embodiment of an electric submersible pumping system deployed in a wellbore, according to an embodiment of the present invention; 
         FIG. 2  is a partial cross-sectional view of an embodiment of the submersible pump illustrated in  FIG. 1 , according to an embodiment of the present invention; 
         FIG. 3  is a partial cross-sectional view of another embodiment of the submersible pump illustrated in  FIG. 1 , according to an embodiment of the present invention; 
         FIG. 4  is a partial cross-sectional view of another embodiment of the submersible pump illustrated in  FIG. 1 , according to an embodiment of the present invention; 
         FIG. 5  is a partial cross-sectional view of another embodiment of the submersible pump illustrated in  FIG. 1 , according to an embodiment of the present invention; and 
         FIG. 6  is a partial cross-sectional view of another embodiment of the submersible pump illustrated in  FIG. 1 , according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
     The present invention relates to a system and methodology for reducing certain effects of thrust loads created while pumping fluids. For example, the system and methodology can be used in submersible pumping systems having centrifugal style, submersible pumps. One or more features are incorporated into the submersible pumping system to manage the hydraulic forces acting on external surfaces of the pump impellers that tend to create large reaction forces acting opposite to the flow direction of the pumped fluid. 
     Referring generally to  FIG. 1 , an embodiment of a submersible pumping system  20 , such as an electric submersible pumping system, is illustrated. Submersible pumping system  20  may comprise a variety of components depending on the particular application or environment in which it is used. Examples of components utilized in pumping system  20  comprise at least one submersible pump  22 , at least one submersible motor  24 , and one or more motor protectors  26  that are coupled together to form the submersible pumping system. 
     In the example illustrated, submersible pumping system  20  is designed for deployment in a well  28  within a geological formation  30  containing desirable production fluids, such as petroleum. A wellbore  32  is drilled into formation  30 , and, in at least some applications, is lined with a wellbore casing  34 . Perforations  36  are formed through wellbore casing  34  to enable flow of fluids between the surrounding formation  30  and the wellbore  32 . 
     Submersible pumping system  20  is deployed in wellbore  32  by a deployment system  38  that may have a variety of configurations. For example, deployment system  38  may comprise tubing  40 , such as coiled tubing or production tubing, connected to submersible pump  22  by a connector  42 . Power is provided to the at least one submersible motor  24  via a power cable  44 . The submersible motor  24 , in turn, powers submersible pump  22  which can be used to draw in production fluid through a pump intake  46 . Within submersible pump  22 , a plurality of impellers is rotated to pump or produce the production fluid through, for example, tubing  40  to a desired collection location which may be at a surface  48  of the Earth. 
     It should be noted the illustrated submersible pumping system  20  is only one example of many types of submersible pumping systems that can benefit from the features described herein. For example, other components can be added to the pumping system, and other deployment systems may be used. Additionally, the production fluids may be pumped to the collection location through tubing  40  or through the annulus around deployment system  38 . The submersible pump or pumps  22  also can utilize different types of stages, such as mixed flow stages or radial flow stages. 
     Referring generally to  FIG. 2 , a cross-sectional view is provided of a portion of one embodiment of submersible pump  22 . In this embodiment, submersible pump  22  comprises a plurality of stages  50 . Each stage  50  comprises an impeller  52  coupled to a shaft  54  rotatable about a central axis  56 . Rotation of shaft  54  by submersible motor  24  causes impellers  52  to rotate within an outer pump housing  58 . Each impeller  52  draws fluid in through an impeller or stage intake  60  and routes the fluid along an interior impeller passageway  62  before discharging the fluid through an impeller outlet  64  and into an axially adjacent diffuser  66 . The interior passageway  62  is defined by the shape of an impeller housing  68 , and housing  68  may be formed to create an impeller for a floater stage, as illustrated in  FIG. 2 , or for a compression stage (see  FIG. 6 ). Additionally, impeller housing  68  may be designed to create a mixed flow stage, a radial flow stage, or another suitable stage style for use in submersible pump  22 . 
     In the embodiment illustrated in  FIG. 2 , an inner thrust member  70 , such as an inner thrust washer, is positioned to resist thrust loads, e.g. downthrust loads, created by the rotating impeller  52 . In this embodiment, inner thrust washer  70  is positioned in an impeller feature  72 , such as a recess formed in an upper portion of impeller housing  68 . The inner thrust washer  70  is disposed between the impeller  52  and a radially inward portion  74  of the next adjacent upstream diffuser  66 . Instead of a conventional outer thrust washer, however, an axially compliant outer seal member  76  is used. In the embodiment of  FIG. 2 , seal member  76  comprises a radial seal  78  positioned in sealing engagement with a generally axially oriented section  80  of impeller housing  68 . Thus, the seal member  76  forms a sealing point with section  80  of impeller  52 , and the sealing point is translatable axially along section  80 . The radial seal  78  may be positioned within a recess  82  formed in a portion of the adjacent diffuser  66 , as illustrated. Accordingly, an outer seal is formed between the impeller and the adjacent diffuser without the creation of unwanted reaction forces on radially outward surfaces within submersible pump  22 . 
     An alternate embodiment of seal member  76  is illustrated in  FIG. 3 . In this embodiment, inner thrust member  70  is similarly positioned at a radially inward position. However, seal member  76  comprises a radially outlying member  84 , such as an outer washer, supported by an axially compliant member  86 . The axially compliant member  86  enables translation of seal member  76  in a generally axial direction by virtue of the compression and expansion of member  86 . By way of example, axially compliant member  86  may comprise a spring member or other type of compliant member made from a variety of materials, including metallic materials, elastomeric materials and composite materials. It should be noted the embodiment illustrated in  FIGS. 2 and 3  also can be used with compression stages to eliminate front seal leakage. 
     In another embodiment of the system for managing thrust loads, the net thrust load, e.g. net downthrust load, can be reduced by pressure balancing a thrust washer area so the impeller discharge pressure rather than the impeller inlet pressure acts on the thrust washer. In this embodiment, a flow passage is formed across a thrust member  88  to pressure balance the thrust member  88 . The flow passage can be routed, for example, between the thrust member  88  and the impeller  52  or between the thrust member  88  and a thrust pad of the adjacent diffuser. In one example, the thrust member  88 , e.g. a thrust washer, is held in a retaining feature  90  of impeller  52  at a position located radially outward of an eye  91  of the impeller, as illustrated in  FIG. 4 . The retaining feature  90  may comprise a groove  92  formed in a lower portion of the impeller  52 . A flow passage  94  is routed along a backside of thrust member  88  between thrust member  88  and impeller  52 , as illustrated by arrow  96  in  FIG. 4 . The flow path or passage  94  creates a flow of fluid during operation of submersible pump  22  which decreases the thrust load acting on the thrust member  88 . Alternatively, flow passage  94  can be formed between thrust member  88  and the adjacent diffuser  66  (see dashed lines in  FIG. 4 ). For example, flow can be directed along radial grooves formed across the thrust member  88  and/or the adjacent diffuser  66  to decrease the thrust load acting on thrust member  88 . 
     The flow passage  94  may be created by a variety of techniques, including spot facing impeller  52  at several locations in the retaining feature region to create the passage behind thrust member  88 . The thrust member  88  may be press fit into retaining feature  90  to secure the thrust member at a location that forms the desired flow passage  94 . In this embodiment, the net thrust reducing flow is directed from a radially outward region of thrust member  88 , along the backside of thrust member  88 , and out along a radially inward region of thrust member  88 . In some embodiments, the flow of fluid through flow passage  94  is expelled out through a gap between a washer bore and an outside diameter of an impeller front seal. It should be noted that the flow resistance of the balance flow passage  94  should be less than the flow resistance of the front seal gap in each stage. 
     Another embodiment of the system and methodology for pumping fluids and managing thrust loads is illustrated in  FIG. 5 . In this embodiment, the net downthrust load acting on a downthrust member  98  is reduced. Downthrust member  98  may comprise a downthrust pad or thrust washer and may be located at a radially inward position, as illustrated. The downthrust acting on member  98  is reduced by incorporating an upper thrust member  100 , such as an upper thrust pad or washer. Additionally, one or more balance holes  102  are positioned to allow leakage of fluid from interior passage  62  of impeller  52  and across upper thrust member  100 . In the embodiment illustrated, balance holes  102  are formed through an upper portion of impeller housing  68  above the interior passage  62 , and they are oriented in a generally axial direction. However, the positioning and orientation of balance holes  102  can be adjusted as desired for specific applications. 
     At start up of submersible pump  22 , the impeller  52  of each stage  50  rests on its downthrust member  98 . After startup, impellers  52  rotate and a leakage flow is induced by the discharge of each impeller  52  across upper the thrust member  100  and through balance hole(s)  102 . This leakage flow reduces the pressure in the cavity between thrust members  98  and  100 , causing the impeller  52  to shift upwardly and to contact the upper thrust member  100 . The face seal formed by the upper thrust member  100  also seals off leakage flow through the balance holes  102 . Accordingly, this configuration provides an improved axial balance because the top area of impeller  52  that is located radially inward of upper thrust member  100  is exposed to impeller inlet pressure rather than impeller discharge pressure. Also, the embodiment illustrated in  FIG. 5  may utilize seal member  76  to facilitate sealed, axial movement of impeller  52 . For example, seal member  76  may comprise radial seal  78  which allows axial translation of the impeller while maintaining a seal between the impeller and an adjacent diffuser. The embodiment illustrated in  FIG. 5  is particularly applicable to radial flow stages and enables the stages to have a compact stage height relative to conventional designs. 
     Referring generally to  FIG. 6 , another embodiment of the system and methodology for pumping fluids and managing thrust loads is illustrated. In this embodiment, submersible pump  22  of submersible pumping system  20  is formed with a plurality of stacked, compression stages  104  having impellers  52  rotated by shaft  54 . With compression stages  104 , the net thrust load, e.g. downthrust load, resulting from rotation of impellers  52  is resisted by a protector bearing  106  (illustrated schematically in dashed lines) located in motor protector  26 . The thrust load on protector bearing  106  is reduced by effectively porting pressure from an inlet  108  of a lower or upstream stage  104  to a balance chamber  110  of an upper or downstream stage  104 . In some embodiments, the upper/downstream stage  104  is the topmost stage, and the lower/upstream stage  104  is a lower or lowermost stage  104  in submersible pump  22 . In other embodiments, the system can be designed such that the inlet  108  is the inlet of the submersible pump. 
     The pressure may be ported by creating a pressure relief path or fluid passageway  112  from the selected stage inlet  108  to the selected balance chamber  110 . In one embodiment, passageway  112  is routed at least partially through shaft  54 , and the passageway may be routed generally along a central axis of shaft  54 . Additionally, an orifice  114  or other restrictor may be located in the passageway  112  to control the leakage flow rate from the upper/downstream stage  104  to the lower/upstream stage  104 . 
     Specific components used in submersible pumping system  20  can vary depending on the actual well application in which the system is used. The specific components, component size and component location for managing net thrust loads also can vary from one submersible pumping system to another and from one well application to another. The specific embodiment utilized for controlling the thrust loads acting on certain components within the submersible pumping system is selected based on a variety of factors, e.g. the number and arrangement of submersible pumps, submersible motors, and motor protectors as well as the specific well environment, well application and production requirements. Other components can be attached to, or formed as part of, the electric submersible pumping system. 
     Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.