Abstract:
An electrical submersible well pump assembly having a pump, a pump motor, and a seal section. The motor drives the pump via shafts rotatingly coupled with a coupling assembly. The coupling assembly maintains the shaft ends in coaxial alignment with an alignment device. The alignment device is profiled on opposite ends for mating engagement with the centering profiles on the shaft ends.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to electrical submersible well pumps, and in particular to couplings between splined shafts of an electrical submersible pump. 
       BACKGROUND OF THE INVENTION 
       [0002]    Electrical submersible pumps (ESP) are commonly used for hydrocarbon well production,  FIG. 1  provides an example of a submersible pumping system  10  disposed within a wellbore  5 . The wellbore  5  is lined with casing  4  and extends into a subterranean formation  6 . Perforations  9  extend from within the wellbore  5  through the casing  4  into the formation  6 . Hydrocarbon fluid flow, illustrated by the arrows A, exits the perforations  9  into the wellbore  5 , where it can either be pumped by the system  10  or migrate to a wellhead  12  disposed on top of the wellbore  5 . The wellhead  12  regulates and distributes the hydrocarbon fluid for processing or refining through an associated production line  7 . 
         [0003]    The pumping system  10  includes an electrical submersible pump (ESP)  14  with production tubing  24  attached to its upper end. The ESP  14  comprises a motor  16 , an equalizer or seal  18 , a separator  20 , and a pump  22 . A fluid inlet  26  is formed in the housing in the region of the ESP  14  proximate to the separator section  20 . The fluid inlet  26  provides a passage for the produced hydrocarbons within the wellbore  5  to enter the ESP  14  and flow to the pump  22 . Fluid pressurized by the pump  22  is conveyed through the production tubing  24  connecting the ESP  14  discharge to the wellhead  12 . The pump  22  and separator  20  are powered by the motor  16  via a shaft (not shown) that extends from the motor  16 . The shaft is typically coupled to respective shafts in each of the pump  22 , separator  20 , and seal  14 . 
         [0004]    Delivering the rotational torque generated by an ESP motor  16  typically involves coupling a motor shaft (i.e., a shaft connected to a motor or power source) to one end of a driven shaft, wherein the other end of the driven shaft is connected to and drives rotating machinery. Examples of rotating machinery include a pump, a separator, and tandem pumps. One type of coupling comprises adding splines on the respective ends of the shafts being coupled and inserting an annular collar over the splined ends, where the annular collar includes corresponding splines on its inner surface. The rotational force is well distributed over the splines, thereby reducing some problems of stress concentrations that may occur with keys, pins, or set screws. Examples of a spline cross-section include an involute and a square tooth. Typically, splines having an involute cross-section are smaller than square tooth splines thereby leaving more of the functional shaft diameter of a shaft to carry a rotational torque load. Additionally, involute spline shapes force the female spline to center its profile on the male spline, thus coaxially aligning the shafts in the coupling with limited vibration. Square tooth splines are made without specialized cutters on an ordinary mill. However square teeth spline couplings do not align like involute teeth unless the clearance is reduced or the male and female fittings are forced together. However, reducing clearance or force fitting square teeth splines prevents ready assembly or disassembly. 
       SUMMARY OF THE INVENTION 
       [0005]    Disclosed herein is a submersible pumping system for pumping wellbore fluid, comprising, a pump motor, a seal section, a motor shaft having an end rotatably affixed within an end of a shaft coupling, the motor shaft rotatable by the motor, a driven shaft having an end rotatably affixed within an end of the shaft coupling opposite to the motor shaft, the respective ends of the motor shaft and driven shaft being substantially coaxial within the shaft coupling, and an alignment element provided in the shaft coupling, the element coaxially engaging the respective terminal ends of the motor shaft and driven shaft within the shaft coupling. Optionally, the alignment element may be disposed on a shaft end. A first centering guide may be included on one side of the alignment element and a second centering guide on the alignment element opposite side, the first centering guide being substantially coaxial with the second centering guide. The first and second centering guides may be one of a protrusion on a side of the alignment element or a recess bored in the alignment element. A motor shaft tip alignment member may be included on the end of the motor shaft within the coupling and a driven shaft tip alignment member provided on the end of the driven shaft within the coupling. The tip alignment members may be a protrusion on the end of a shaft or a recess bored into the shaft. Square tooth splines may be formed on the motor shaft and driven shaft respective ends. An axial bore can be formed through the coupling where square tooth splines are formed on the bore inner diameter. In one embodiment, the driven shaft drives rotating machinery, where the machinery may be a pump, a tandem pump, and a separator. A resilient member may be included with the alignment element. The resilient member can be used to align the shafts with an opposing force in the absence of a shaft thrust load. 
         [0006]    Also disclosed herein is a method of using an electrical submersible pump (ESP) in a wellbore involving providing the ESP in the wellbore. The ESP may include a motor, a motor shaft rotatingly affixed to the motor; a rotating device, a driven shaft rotatingly affixed to the rotating device, and a coupling rotatingly affixing ends of the motor shaft and driven shaft. The method may further include energizing the motor thereby rotating the motor shaft, the coupling, and the driven shaft. Additionally, the present method includes substantially coaxially aligning the ends of the motor shaft and driven shaft during shaft rotation. The method optionally further comprises providing an alignment element in the coupling between the shaft ends, and coaxially mating the shaft ends with the alignment element. A resilient member may be includable with the alignment element. The shaft ends can be profiled for coaxial alignment. The shaft end profile might include a protrusion or a recess bored into the shaft end. The method can also include profiling a side of the alignment element to align with the shaft ends. Profiling can involve forming a protrusion on a side of the alignment element and forming a recess bored into a surface of the alignment element. 
         [0007]    The present disclosure also includes an electrical submersible pump (ESP) comprising a pump motor, a motor shaft mechanically affixed to the pump motor, a seal portion, a pump, a pump shaft mechanically affixed to the pump, a connector assembly rotatingly coupling respective terminal ends of the motor shaft and the pump shaft, and an aligning pin in the connector assembly axially engaged on one end with a terminal end of the pump shaft and axially engaged on another end with a terminal end of the motor shaft, wherein the pump shaft, motor shaft, and aligning pin axes are substantially aligned. A profile can be included on the aligning pin configured to engage the shaft ends, wherein the profile may be a protrusion or a recess. A resilient member may be included with the aligning pin. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a side view of a prior art submersible electrical pumping system in a wellbore. 
           [0009]      FIG. 2   a  is an exploded view of a shaft coupling for use with the system of  FIG. 1 . 
           [0010]      FIG. 2   b  is an assembled view of the shaft coupling of  FIG. 2   a.    
           [0011]      FIG. 3   a  is an exploded view of an alternative shaft coupling for use with the system of  FIG. 1 . 
           [0012]      FIG. 3   b  is an assembled view of the shaft coupling of  FIG. 3   a.    
           [0013]      FIG. 4   a  is an exploded view of an alternative shaft coupling for use with the system of  FIG. 1 . 
           [0014]      FIG. 4   b  is an assembled view of the shaft coupling of  FIG. 4   a.    
           [0015]      FIG. 5  is a side partial cut-away view of an alternative shaft coupling for use with the system of  FIG. 1 . 
           [0016]      FIG. 6  is a side partial cut-away view of an alternative shaft coupling for use with the system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    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. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
         [0018]    It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. 
         [0019]    The present disclosure includes a square tooth spline coupling with vibration control. The coupling disclosed herein provides sufficient clearance between the respective male and female splines providing ready assembly and disassembly. With reference now to  FIG. 2   a , an exploded side partial cutaway view of one embodiment of a coupling assembly and respective shafts is provided. As noted above, during operation of a pumping assembly, a motor shaft is powered by a pump motor, either directly or through a shaft coupling. The coupling assembly provides a manner of connecting the motor shaft to a driven shaft that drives rotating machinery. The coupling connection also transfers rotational energy between the motor and driven shaft, thus providing power for the rotating machinery. 
         [0020]    The coupling assembly  30  of  FIG. 2   a  comprises an annular collar  48  with a bore  50  formed lengthwise therein. Female splines  52  extend axially along the bore  50  inner surface. The bore  50  diameter transitions at a point to form a shoulder  56  that is substantially perpendicular to the collar  48  axis A X . An alignment element  54  is on the shoulder  56 . In the embodiment shown, the alignment element  54  has a disc-like midsection and disposed in the collar  48  with its midsection axis (not shown) largely aligned with or parallel to the collar axis A X . The alignment element  54  outer diameter exceeds the shoulder  56  inner diameter and its lower side butts on the shoulder  56 . The outer diameter fits closely in the bore  50 . An insert or sleeve  60  is coaxially received within the collar  48  in the portion of the bore  50  having an increased diameter. The insert  60  extends from the upper surface of the alignment member  54  terminating at the upper end of the collar  48 . The insert  60  is optionally threaded on its outer diameter to mate with corresponding threads provided on the collar  48  inner diameter. Female splines  52  are formed along the insert  60  inner diameter. Positioning the insert  60  against the alignment element  54  toward the shoulder  56 , retains the alignment element  54  within the collar  48 . 
         [0021]    Centering guides ( 62 ,  63 ) are shown extending from the upper and lower surface of the alignment element  54 . In this embodiment, the centering guides ( 62 ,  63 ) comprise conically shaped protusions. Above and below the coupling assembly  30  are an upper shaft  32  and lower shaft  40 . The upper shaft  32  lower end  36  is provided with male splines  34  configured for coupling engagement with the female splines  52  of the coupling assembly  30 . Similarly, the lower shaft  40  upper end  44  includes male splines  42  configured for coupling engagement with the female splines  52 . The shafts ( 32 ,  40 ) are profiled on their terminal ends for centering engagement with the centering guides ( 62 ,  63 ) of the alignment element  54 . In the embodiment shown, the profiling on the shafts comprises recesses or bores ( 38 ,  46 ) extending from the terminal mating tips of the shafts and substantially aligned with the respective axes (A SH , A SL ) of the upper or counterbore lower shafts ( 32 ,  40 ). Each recess ( 38 ,  46 ) has a conical entry way with a taper matching the centering guides ( 62 ,  63 ). The recess and protrusion provide examples of guide profiles formed on the shaft ends and alignment element for engaging the shaft ends to the alignment element. During pumping operations, impellers in the pump create an axial thrust force in the pump shaft forcing the shafts ( 32 ,  40 ) together and engaging the centering guides ( 62 ,  63 ) with the recesses ( 38 ,  46 ). 
         [0022]    Referring now to  FIG. 2   b , an example of an assembled shaft coupling is shown in side cross-sectional view. The male splines  34  on the lower end  36  of the upper shaft  32  engage the female splines  52  and the upper shaft  32  bore  38  mates with the centering guide  62  that extends from the alignment element  54 . Similarly, the male splines  42  on the upper end  44  of the lower shaft  40  are engaged with the female splines  52  of the collar  48  and the bore  46  on the upper terminal end of the shaft  40  mates with the centering guide  63  that extends from the opposite side of the alignment element  54 . The upper shaft  32  and lower shaft  40  are aligned along a common axis within the collar  48  thus preventing shaft vibration when one of the shafts energizes the other. 
         [0023]      FIG. 3   a  shows an alternative embodiment of a shaft coupling  30   a  for coupling an upper shaft  36   a  to a lower shaft  44   a . In this embodiment, the alignment element  54   a  has a largely disc-like cross-sectional area and is seated on the shoulder  56 . The insert  60  retains the element  54   a  within the collar  48 . The centering guides ( 62   a ,  63   a ) comprise a conical profile bored into the body of the alignment element  54   a . Similarly, the terminal tips of the upper shaft  36   a  and lower shaft  44   a  include conically profiled protrusions ( 39 ,  47 ) formed to engaged the bores of the centering guides ( 62   a ,  63   a ).  FIG. 3   b  illustrates the assembled shaft coupling  30   a  and engagement of the protrusions ( 39 ,  47 ) with the centering guides ( 62   a ,  63   a ). This configuration also control s shaft vibration during transmission of torque through the coupling  30   a . The profiles on the alignment elements and the terminal tips of the shafts are not limited to the figures described herein, but can include other shapes such as conical, concave, convex, spherical or other curved surfaces. Additionally, cylindrical profiles with may be employed and may include rounded tips on the cylinder end. 
         [0024]    Yet another embodiment of a shaft coupling  30   b  is provided in side cross-sectional view in  FIG. 4   a . In this embodiment, the centering guides  62   b  and centering guide  63   b  comprise a raised profile on the respective upper and lower sides of the alignment element  54   b . The alignment element  54   b  comprises an upper housing  64 , a lower housing  66 , and a resilient member housed within the upper and lower housings ( 64 ,  66 ). One example of a resilient member is a spring  68 . In this embodiment, the upper and lower housing ( 64 ,  66 ) both comprise a generally cup-like structure having a closed base that is largely perpendicular to the axis of the collar  48   a . The housings have sides extending from the base towards an open end, the sides lie generally concentric with the axis A X  of the collar  48   a . The upper housing  64  inner diameter is greater than the lower housing  66  outer diameter allowing insertion of the lower housing  66  into the upper housing  64  in telescoping relation. The spring  68  provides a resilient force for urging the upper and lower housing ( 64 ,  66 ) apart. 
         [0025]    As shown in  FIG. 4   b , in some embodiments, a vertical force may move the shaft ( 32 ,  40 ) toward one another and pushes on one of the upper or lower housing ( 64 ,  66 ), thereby compressing the spring  68  there between. One of the advantages of this embodiment is an axial force from one of the shafts ( 32 ,  40 ) is fully absorbed by the spring  68  and not transferred to the other or any other adjacent shaft within a pumping system. Moreover, the resilient nature of the spring  68  can force the housings ( 64 ,  66 ) apart upon absence of the vertical force while continuing axial alignment of the shafts ( 32 ,  40 ) during operation of the pumping system. Because rotational shafts in an ESP seal portion typically are not subjected to axial thrust, the resilient feature may be useful for these couplings. As shown, the housings ( 64 ,  66 ) have protrusions profiled on their respective outer surfaces formed to match recesses ( 38 ,  46 ) on the shafts ( 32 ,  40 ). However, the housings ( 64 ,  66 ) could be fashioned to include recesses and the shafts ( 32 ,  40 ) having corresponding protrusions. 
         [0026]    Another embodiment illustrating ESP shaft coupling is provided in a side partial cut-away view in  FIG. 5 . Here an upper shaft  36   b  and lower shaft  44   b  are aligned with a retaining pin  70  that extends from a bore  38   b  in the lower terminal end of the upper shaft  36   b  into a corresponding bore  46   b  in the upper terminal end of the lower shaft  44   b . The retaining pin  70  may include an annular shoulder  71  radially disposed around the body of the pin  70  approximately at its mid-section. To accommodate the retaining pin  70 , the bores ( 38   b ,  46   b ) are formed deeper into the shafts ( 36   b ,  44   b ) than the bores ( 38 ,  46 ) illustrated in  FIGS. 2   a  and  2   b.    
         [0027]    A coupling assembly is presented in side partial cross sectional view in  FIG. 6  that combines concepts described above. An upper shaft  36  with a bore  38  is disposed within a collar  48   b  into coaxial alignment with a corresponding lower shaft  44   b . A protrusion  47   a  extends from the lower shaft  44   b  upper terminal end into the bore  38  and is retained therein for coaxial alignment of the shafts ( 36 ,  44   b ). The protrusion  47   a  of  FIG. 6  is similar to the protrusion  47  of  FIGS. 3   a  and  3   b , but has increased dimensions, including an increased length, to ensure mating cooperation with the bore  38 . The collar  48   b  inner diameter is smaller at its upper end to match the upper shaft  36  outer diameter. The collar  48   b  can be machined or forged as a uni-body configuration, or reduced with an insert (not shown) similar to the collar  48  of  FIGS. 2   a - 3   b.    
         [0028]    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. 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. While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.