Patent Publication Number: US-8109746-B2

Title: Progressing cavity pump/motor

Description:
FIELD OF THE INVENTION 
     The present invention relates to a progressing cavity pump/motor of the type used in a downhole well to pump fluid to the surface or to convert hydraulic energy into mechanical energy to rotate a bit. More particularly, this invention relates to a progressing cavity pump/motor which has structurally separable upper and lower stator tubes. 
     BACKGROUND OF THE INVENTION 
     Progressing cavity pumps and motors have been used for decades in pumping applications and in hydraulic motor applications. A conventional progressing cavity pump consists of a rigid rotor having a contoured interior surface along an axial length thereof. The interior surface of the rotor mates with the exterior surface of a rotor which has a contoured exterior surface, with one additional lead on the interior of the stator. This lead difference forms cavities between the rotor and the stator which are continually progressing from one end of the stator to the other when the rotor is turning. Operation of a pump is achieved by mechanically turning the rotor, while operation of a motor is achieved by forcing fluid into one end of the stator to turn the rotor. An elastomeric or plastic material is conventionally bonded to the rigid stator tube, thereby providing a fluid tight seal between the elastomeric stator material and the outer tubular housing. 
     In some applications, a progressing cavity pump has an extremely long length, e.g., thirty feet or more, which makes transportation and handling of the stator difficult. During manufacturing, an elongate rotor in two or more pieces may be assembled end-to-end at the manufacturing plant using appropriate jigs. The end of one rotor section may thus be aligned with the adjacent end of another rotor section, so that rotor sections are rotationally aligned when welded together. Such direct alignment of a motor/pump housing is difficult to envision with the structural and functional requirements of a pump/motor. More specifically, the elongate stator of a pump/motor is preferably connected in the field, and does not require welding at the rig site or the use of specialized jigs. 
     The disadvantages of the prior art are overcome by the present invention, and an improved progressing cavity pump/motor with upper and lower stator sections and a coupling assembly for interconnecting these sections is hereinafter disclosed. 
     SUMMARY OF THE INVENTION 
     In one embodiment, a progressing cavity pump is provided for positioning along a tubular string in a well to pump fluids to the surface through the tubular string. In another embodiment, the same assembly may be used to create downhole mechanical energy from fluid transmitted downhole to the motor. The pump/motor includes an upper stator tube, a lower stator tube, and a rotor extending axially between the upper stator tube and the lower stator tube. The exterior of the rotor and the interior of the stator tubes have contoured surfaces. A coupling assembly interconnects the upper stator tube and the lower stator tube while maintaining the tubes in circumferential alignment for cooperation with the rotor. The coupling assembly includes an outer sleeve supported on one of the stator tubes and having a first stop surface thereon and external threads. An inner sleeve is supported on the other of the tubes, and circumferentially aligns the upper and lower tubes. The inner sleeve has a second stop surface for engagement with the first stop surface when the pump/motor is assembled, and a nut with internal threads for threaded engagement with the external threads on the outer sleeve. 
     According to another embodiment, a stator as discussed above is provided for a pump/motor, with a stator cooperating with a rotor having an external profile and rotatable within the stator, with a plurality of axially moving chambers between the rotor and the stator. 
     These and further features and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified view of a pump/motor according to the present invention. 
         FIG. 2  is an enlarged view illustrating a coupling assembly for interconnecting a lower end of one stator tube and an upper end of another stator tube. 
         FIG. 3  is an enlarged cross-sectional view illustrating the threaded connection of the outer sleeve with a nut and a shoulder between the outer sleeve and the inner sleeve. 
         FIG. 4  is an exploded view of the coupling generally shown in  FIG. 2 . 
         FIG. 5  is a cross-sectional view of an alternate embodiment of a stator coupling assembly. 
         FIG. 6  is a cross-sectional view of yet another embodiment of a stator coupling. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is a cross-sectional view of a progressing cavity pump/motor  10 , which is positionable along a tubular string in a well to either pump fluids to the surface through the tubular string or to create downhole mechanical energy from fluid transmitted downhole to the pump/motor, e.g., to rotate a bit. The pump/motor  10  includes an upper stator tube  12  having an upper contoured interior surface  14  along an axial length thereof, and a lower stator tube  16  having a lowered contoured interior surface  18  along the axial length thereof. The rotor  20  extends axially between the upper stator tube and the lower stator tube and, as shown in  FIG. 1 , frequently extends vertically above the upper end of the stator tube, and below a lower end of the stator tube. Rotor  20  has an exterior contoured surface  22  creating progressing cavities between the upper contoured interior surface and the contoured exterior surface, and between the lowered contoured interior surface and the contoured exterior surface when the rotor rotates with respect to both the upper stator tube and the lower stator tube.  FIG. 1  also illustrates a coupling assembly  30  for interconnecting the upper stator tube  12  and the lower stator tube  16  while maintaining the tubes circumferentially aligned for cooperation with the rotor. 
       FIG. 2  is a cross-sectional view of the coupling  30  shown in  FIG. 1 , with the elastomeric layer forming the contoured surfaces  14 ,  18  removed for clarity of the depicted components. Coupling assembly  30  includes a radially outer sleeve  32  supported at either the lower end of the upper stator tube or the upper end of the lower stator tube. In the  FIG. 2  embodiment, the outer sleeve  32  is fixed to the lower end of the upper stator tube  12  by weld  34  and has external threads  33  thereon. When the weld  34  is made at a manufacturing facility, the outer sleeve  32  may be circumferentially aligned with the tube  12  by various conventional means, so that both the circumferential and axial positioning of the outer sleeve  32  with respect to the tube  12  is known and fixed. Inner sleeve  36  is shown axially secured to ring member  40  by pins  44 , and ring member  40  is connected by welds  38  to the upper end of the lower stator tube  16 , and the inner sleeve  36 . More specifically, ring member  40  and through may be threaded at  42  to a lower end of the sleeve  36  with pins  44  each extending through the ring  40  and through the lower end of the inner sleeve  36 , with a pin head positioned within slot  46 , so that the axial and circumferential position of the inner sleeve  36  with respect to the lower housing  16  is known and fixed. 
     The inner sleeve  36  extends between the lower stator tube  16  and the upper stator tube  12 , and the upper end of the inner sleeve  36  has a plurality of elongate slots  48  each receiving a pin  50  therein. In this manner, the circumferential position of the upper stator tube  12  with respect to the upper end of the inner sleeve  36  is known, and similarly the circumferential position of the lower housing  16  with respect to the sleeve  36  is known. Sleeve  36  thus circumferentially aligns the upper stator tube and the lower stator tube as a function of the axial spacing between these tubes. The exact axial position between the tubes is achieved by engagement of stop surface  54  (see  FIG. 3 ) on the inner sleeve  36  with the stop surface  52  on the outer sleeve  32 . Preferably these surfaces are coplanar so that planar-to-planar contact is achieved. More particularly, the angle of each stop surface preferably is from 50° to 80° relative to the central axis of the coupling assembly, so that substantial surface area is available for transmitting high axial forces. 
       FIGS. 2 and 3  also depict a nut  60  having internal threads  62  for threaded engagement with the external threads  33  at the lower end of the outer sleeve  32 . The nut  60  includes a flange member  64  for engagement with the stop surface  66  on the inner sleeve, as shown in  FIG. 2 , so that tightening the nut  60  causes the flange member to engage the stop surface  66  while bringing the tapered surfaces  52  and  54  into mating engagement. 
       FIG. 4  is an exploded pictorial view of a coupling assembly  10 . Pins  50  pass through the outer sleeve  32 , with the pin heads fitting within a slot (not shown in  FIG. 4 , but shown in  FIG. 2 ) in the lower end of tube  14 . The outer sleeve includes threads  33  for mating engagement with threads  62  on the nut  60 . The inner sleeve  36  is shown with elongate slots  48  each for receiving one of the pins  50 . 
       FIG. 4  depicts ring  40  positioned with respect to lower end of sleeve  36 , so that pins  44  secure ring  40  to sleeve  36 . A portion of each pin  44  will be positioned within a respective slot  46  in the upper end of the lower tube  16  when the coupling is fully assembled. The ring  40  as shown in  FIG. 4  is engaging the bottom of nut  60 . 
     For the embodiment discussed above, the contoured interior surfaces along the length of both the upper stator tube and the lower stator tube are formed from an elastomeric material which is securely bonded to an outer tubular housing. In other embodiments, the outer housing itself may have a contoured interior surface, so that a uniform thickness elastomeric layer may be bonded to the outer contoured surface of this revised housing. In still other embodiments, no elastomeric layer is provided, and the interior contoured surface of the metal stator tube creates a progressing cavity when a rotor with an exterior contoured surfaces is rotated therein. 
     For the embodiment which utilizes elastomeric material, this material is preferably cut back several inches from all weld joints to prevent any rubber in the stator from becoming burned during the welding process. This break in engagement between the rotor and the stator is acceptable since production losses are small over the length where the elastomeric material is cut back. 
     A coupling as disclosed herein can be turned end-to-end, so that the outer sleeve is attached to the lower stator tube and the inner sleeve is affixed to the upper stator tube. The coupling as disclosed herein achieves a known and consistent orientation between both the upper and lower tube contoured interior surfaces and the exterior contoured surface of the rotor. Although only two alignment pins per stator tube are shown for purposes of clarity, a larger number of pins may be used to reduce the dimensional variance with regard to stator orientation. 
     For the embodiment as shown in  FIG. 5 , a nut is threaded to both the inner sleeve and the outer sleeve. The components in  FIG. 5  which are functionally the same as components in  FIG. 2  are provided the same reference numerals. In the  FIG. 5  embodiment, the radially outer sleeve  72  is provided with external left-hand threads  74 , while the radially inner sleeve  76  is provided with external right-hand threads  78 . Inner sleeve  72  is welded at  34  to the upper stator tube  14 , while the inner sleeve  76  is secured by pin  44  directly to the lower stator sleeve  16 , rather than to a ring  40  as shown in  FIG. 2 . The nut  80  has left-hand threads for mating with the left-hand threads  74  on the outer sleeve  72 , and right-hand threads for mating with threads  78  on the inner sleeve  76 . Rotation of the nut  80  thus brings inner sleeve  76  axially closer to the outer sleeve  72 , so that the planar surface  54  on the inner sleeve engages planar surface  52  on the outer sleeve, thereby bringing the coupling components into rigid and secured engagement. 
     In yet another embodiment as shown in  FIG. 6 , the nut  82  is threaded to the inner sleeve  84 , and a stop surface  86  on the nut engages the outer sleeve  88  such that rotation of the nut causes the stop surface  90  on the nut to engage a mating surface on the outer sleeve  88 , and thereby pull the outer sleeve axially toward the inner sleeve until the tapered surface  52 ,  54  are brought into rigid engagement. The radially inner sleeve  84  thus includes an elongate slot  48  as previously discussed, and the pins  44 ,  50  circumferentially align the inner and outer coupling sleeves as per the earlier embodiments. In the  FIG. 6  embodiment, the radial thickness of the externally threaded end  92  of the inner sleeve is increased, allowing the nut  82  to thread to the inner sleeve while pulling the radially outer sleeve  88  downward until the mating surfaces  52 ,  54  engage. 
     For each of the embodiments disclosed herein, the lower end of the upper stator tube and upper end of the lower stator tube are provided with slots, which cooperate with pins to maintain the upper and lower tubes in circumferential alignment. Such slots are well suited for accomplishing the purposes of the invention without significantly reducing the permissible loading on the coupling assembly. Alternative designs could use keys and keyways between the inner and outer sleeve and a respective stator tube. In other embodiments, the purpose of the slots may be satisfied by a splined rotational connection between the stator tube and a respective sleeve. In all cases, rotational alignment of the inner sleeve and the outer sleeve within a tolerance of 2° or less is particularly significant so that the efficiency of the pump/motor is maintained. 
     Although specific embodiments of the invention have been described herein in some detail, this has been done solely for the purposes of explaining the various aspects of the invention, and is not intended to limit the scope of the invention as defined in the claims which follow. Those skilled in the art will understand that the embodiment shown and described is exemplary, and various other substitutions, alterations and modifications, including but not limited to those design alternatives specifically discussed herein, may be made in the practice of the invention without departing from its scope.