Abstract:
A progressing cavity pump is located within a well and has a gas separator for separating gas before reaching the pump. The pump has a rotor that is driven by a string of rods extending to the surface. A drive shaft for the gas separator is coupled to the rotor during pumping operation both for axial as well as rotational movement. The rotor assembly, when lowered through the tubing, stabs into engagement with the drive shaft of the gas separator in one version. In another version, the gas separator drive shaft is lowered through the tubing with the rotor and stabs into a hub sleeve in the gas separator.

Description:
FIELD OF THE INVENTION 
   This invention relates in general to submersible well pumping assemblies, and in particular, to a rod-driven progressing cavity pump assembly with a gas separator. 
   BACKGROUND OF THE INVENTION 
   One use for a progressing cavity pump is as a well pump. A progressing cavity pump has a stator with an elastomeric liner in its interior. The liner has a passage through it that has a helical contour. A helical rotor, typically of metal, locates within the stator and is rotatable relative to it. Rotating the rotor causes the well fluid to pump through the stator. 
   In one type of installation, the stator is secured to the lower end of a string of tubing that is suspended in the well. The rotor is secured to a string of drive rods and lowered through the tubing into the stator. After reaching the lowermost point, the operator lifts the rods and rotor a short distance to properly align the rotor with the stator. The drive rods are driven by a drive source at the surface, typically a bearing box and electrical motor. As the well fluid fills the tubing, the rods will stretch to some extent due to the weight of the well fluid. The rotor will thus move downward a short distance relative to the stator. 
   Some wells produce a combination of liquid and gas. The gas entrained within the liquid is detrimental to the efficiency of the progressing pump. Gas separators have been utilized with electrical submersible well pumps for many years. One type of gas separator has a rotating member, typically a set of vanes that spins with the pump to impart centrifugal force to the well fluid. The centrifugal force results in the heavier components flowing to the outer portion and the lighter components are gas remaining in the center. A crossover member at the top diverts the gas out into the casing and directs the liquid component up into the pump. 
   The centrifugal pump is made up of a large number of stages of impellers and diffusers. A centrifugal pump is not driven by rods and does not experience any downward movement of the drive shaft as a result of the weight of liquid in the tubing. 
   Progressing cavity pumps with gas separators are known, both for rod-driven types as well as the type that utilizes a downhole submersible electrical motor to drive the rotor. However, provisions to accommodate the rod stretch for the rod-driven type are not known in the prior art. 
   SUMMARY OF THE INVENTION 
   In this invention, a gas separator is secured to the lower end of the stator of a progressing cavity pump assembly. The gas separator is of a rotary type, having a rotary member for imparting centrifugal force to the well fluid flowing into the gas separator. The gas separator has a drive shaft that is operably engaged by the rotor for causing rotation of the rotary member. 
   The rotor is axially movable a limited amount relative to the stator during operation of the pump as a result of stretch of the rods. The drive shaft is axially movable in unison with the rotor after it is in operative engagement with the stator. 
   In one embodiment of the invention, the drive shaft is fixed to the rotary member, and both the drive shaft and the rotary member are movable axially within the housing of the gas separator. The rotor has a flex shaft on its lower end with a splined end that stabs into engagement with a coupling on the upper end of the gas separator drive shaft. Once in engagement, the drive separator drive shaft and the rotor are axially movable as well as rotationally movable in unison with each other. 
   In another embodiment, the drive shaft is secured to the lower end of the rotor at the surface and lowered through the tubing with the drive rods. The drive shaft stabs into a bushing located in the rotary member of the gas separator. The bushing has splines that engage splines on the lower end of the drive shaft. The drive shaft is movable in unison with the rotor, both axially and rotationally, but the rotary member is only rotationally engaged with the drive shaft. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  comprise a side view, partially sectioned, of a well pump assembly constructed in accordance with this invention. 
       FIGS. 2A and 2B  comprise a sectional view of the pump and gas separator of  FIGS. 1A and 1B  and showing the drive shaft and rotary members in a lower position. 
       FIGS. 3A and 3B  comprise a sectional view of the pump and gas separator of  FIG. 1 , and showing the rotary members and drive shaft in an upper position. 
       FIG. 4  is a schematic sectional view illustrating a coupling between the rotor assembly and the gas separator drive shaft in accordance with this invention. 
       FIG. 5  is a view of the coupling of  FIG. 4 , but showing the rotor disengaged from the coupling. 
       FIG. 6  is a sectional view of an alternate embodiment of a pump and gas separator in accordance with this invention. 
       FIG. 7  is an exploded sectional view of a portion of a drive shaft and hub sleeve of the gas separator of  FIGS. 6A and 6B . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , progressing cavity pump  11  is conventional. Pump  11  has a stator  13  that has a tubular housing containing an elastomeric liner  15 . Liner  15  has a passage through it that has a double helical contour. Stator  13  is secured to the lower end of a string of production tubing  17  that extends into the well. Tubing  17  extends to the surface of the well for delivering well fluid. Tubing  17  may comprise sections of conventional well production tubing screwed together. Alternatively, tubing  17  could comprise a single continuous length of coiled tubing. 
   Pump  11  includes a rotor  19  that rotates within stator  13 . Rotor  19  is typically of metal and has a single helical contour. A string of drive rods  21  extends form the surface to rotor  19  for rotating rotor  19 . Drive rods  21  typically comprise sections of rods secured together by threads. 
   A bearing box  23  located at the surface is driven by a motor  25 , normally an electrical motor. Bearing box  23  engages the upper end of drive rods  21  for rotating drive rods  21  and rotor  19 . 
   Rotor  19  orbits or oscillates as it rotates, rather than remaining on a single concentric axis. A flex shaft  27  is secured to the lower end of rotor  19 , and for the purposes herein, may be considered to be a part of rotor  19 . Flex shaft  27  is typically a steel rod that has sufficient length to allow flexing. The lower end of flex shaft  27  is constrained about a single axis while the upper end of flex shaft  27  is free to orbit with the lower end of rotor  19 . Flex shaft  27  extends through a flex shaft housing  29  that contains bearings for supporting the lower end of flex shaft  27 . Flex shaft housing  29  does not have an elastomeric liner  15  within it, but could be integrally formed with the housing of stator  13  and may be considered a part of stator  13 . 
   A gas separator  31  is carried below flex shaft housing  29 . Gas separator  31  has a lower intake  35  for drawing well fluid into it and a gas discharge  37  near its upper end for discharging separated gas into the well. Gas separator  31  has a drive shaft  39  that is rotated by drive rods  29 , rotor  15  and flex shaft  27 . Referring to  FIGS. 2A and 2B , gas separator  31  may be of a variety of rotary types. In this embodiment, gas separator  31  has a set of vanes  41  that rotate with drive shaft  39  to impart centrifugal force to the well fluid. Vanes  41  comprise a plurality of flat blade-like members, each being in a plane that is perpendicular to the axis of drive shaft  39  in this embodiment. The centrifugal force imparted by vanes  41  causes the heavier components to flow radially outward while the lighter components of the well fluid remain in the central area. 
   An inducer  43  optionally may be incorporated with gas separator  31 . Inducer  43  is a type of pump for inducing the flow of well fluid into gas separator  31 . In this embodiment, inducer  43  has a helical vane, similar to an auger for forcing well fluid upward into vanes  41 . Inducer  43  has a key, like vanes  41 , that causes it to rotate in unison with gas separator drive shaft  39 . 
   A crossover  45  is located at the upper end of gas separator housing  33 . Crossover member  45  has an inner passage  47  that leads to gas discharge port  37 . Crossover member  45  has an outer passage  49  that leads upward into flex shaft housing  29 . Crossover member  45  has an annular skirt  51  that depends downward and divides inner passage  47  from outer passage  49  at the entrance. A base member  53  secures to the lower end of gas separator housing  33 . Base member  53  may be used to connect gas separator  31  to other equipment, or it may have a cap  55  at the lower end. Base member  53  has an extension section  57  that extends downward below intake  35 . Drive shaft  39  has a lower end that extends into the extended section and is retained herein by a retaining ring  59 . Drive shaft  39  is movable between a lower position shown in  FIG. 2B  and an upper position shown in  FIG. 3B . In the lower position, retaining ring  59  is located at the lower end of extension section  57 . In  FIG. 3B , retaining ring  59  abuts a bushing or bearing member  61  located at the upper end of extension section  57 . 
   In this embodiment, vanes  41  and inducer  43  are secured to drive shaft  39  for axial movement as well as rotational movement. The length of housing  33  is greater than the axial length of the rotary components made up of vanes  41  and inducer  43  to accommodate this axial movement. In  FIG. 2A , a substantial space exists between the upper edge of vanes  41  and skirt  51 . When in the upper position shown in  FIG. 3A , the upper edge of vanes  41  engages skirt  51 . Drive shaft  39  may have a protective sleeve  63  or bushing surrounding it both in the lower section from inducer  43  to retaining ring  59  as well as in the upper section above vanes  41 . 
   In the embodiment of  FIGS. 1-5 , drive shaft  39  is assembled with gas separator  31  at the surface and lowered into the well on tubing  17 . Rotor  19  and flex shaft  27  ( FIGS. 1A-1B ), are lowered through tubing  17  on drive rods  21 . A coupling  65  connects flex shaft  27  to drive shaft  39  when rotor  19  is fully inserted into stator  13 . Once engaged, coupling  65  will cause drive shaft  39  to rotate with flex shaft  27  and also will cause drive shaft  39  to move axially with flex shaft  27  and rotor  19 . Coupling  65  may be of a variety of types. In this embodiment, coupling  65  is secured to the upper end of drive shaft  39 , shown in  FIG. 4 . Coupling  65  has a receptacle  67  on its upper end for receiving the lower end of flex shaft  27 . Receptacle  67  has a plurality of internal splines  69 . A latch ring  71  is mounted within receptacle  67 . Latch ring  71  is a split ring that is by standard for engaging an annular groove  73  ( FIG. 5 ) located on flex shaft  27 . Flex shaft  27  has a lower splined end  75  which mates with splines  69 . 
   In the operation of the embodiment of  FIGS. 1-6 , the operator secures gas separator  31  to stator  13 . In this embodiment, this is accommodated by securing gas separator  33  to flex shaft housing  29 . Drive shaft  39  will be located within gas separator  33 . The operator lowers gas separator  33  on the string of tubing  17 . 
   The operator then connects flex shaft  27  to rotor  19  and lowers rotor  19  through tubing  17  on drive rods  21 . When rotor  19  reaches the lower end of stator  13 , flex shaft  27  will engage gas separator drive shaft  39 . Referring to  FIG. 5 , lower end  75  of flex shaft  27  stabs into receptacle  67 , and latch ring  71  engages groove  73 . At this point, drive shaft  39 , vanes  41  and inducer  43  will be in the lower position shown in  FIGS. 2A and 2B . 
   The operator then lifts drive rods  21  a measured distance to place rotor  19  with its upper end a selected distance above the upper end of stator liner  15 . Drive shaft  39  of gas separator  33  will move upward, bringing along with it vanes  41  and inducer  43 . This position will be located either at the uppermost position shown in  FIGS. 3A and 3B , or some slightly lower position. The position will be selected to account for the stretch of rods  21  when tubing  17  is filled with liquid, and the amount of stretch will depend upon the length of rods  21 . 
   The operator then actuates motor  25  to rotate rods  21 , which in turn rotates rotor  19  and gas separator drive shaft  39 . Inducer  43  rotates to assist in drawing well fluid in through intake  35 . The well fluid flows through the rotating vanes  41 , which through centrifugal force forces the liquid to the outer side relative to the gaseous components which remain in the central area. The liquid flows up outer passage  49  and into stator  13  ( FIG. 1A ). The liquid is pumped by rotor  19  up tubing  17  to the surface. The gas flows through inner passage  47  ( FIG. 2A ) out gas discharge  37  into the well. The liquid within tubing  17  will gradually cause rods  21  to stretch. As rotor  19  and flex shaft  27  move downward, rotor drive shaft  39  also moves downward along with vanes  41  and inducer  43 . The amount of downward movement is pre-calculated so as to avoid vanes  41  and inducer  43  reaching the lowermost position shown in  FIGS. 2A and 2B . 
   To retrieve rotor  19 , the operator exerts sufficient pull with drive rods  21  to over-pull latch ring  71  ( FIG. 4 ), causing it to release from coupling  65 , which remains downhole. In the embodiment of  FIGS. 6 and 7 , gas separator  77  also has a rotary member which comprises vanes  79  and an optional inducer  81 . Vanes  79  and inducer  81  are linked together by an elongated hub sleeve  83 . Hub sleeve  83  has internal splines  85  within it, either continuous or in sections as shown in  FIG. 7 . As shown in  FIG. 6 , hub sleeve  83  extends downward into a lower bearing support  87 . The upper end of hub sleeve  83  preferably extends above crossover member  88 . 
   Drive shaft  89  is carried by rotor  19  ( FIG. 1A ) as rotor  19  is lowered through tubing  17 . Drive shaft  89  may comprise a portion of a flex shaft, or may be coupled to a flex shaft such as flex shaft  27  in the first embodiment. Drive shaft  89  has a section containing splines  91  that will mate with splines  85  in hub sleeve  83 . Drive shaft  89  may also have a pointed tip  93 , shown in  FIG. 7 , to facilitate stabbing into hub sleeve  83 . 
   In the operation of the embodiment of  FIGS. 6 and 7 , gas separator  77  is secured to tubing  17  and lowered into place in the same manner as in  FIG. 1 , except that it does not contain a drive shaft. The operator then connects drive shaft  89  to the lower end of rotor  19  and lowers the assembly through tubing  17 . As rotor  19  reaches the lower end of stator  13 , drive shaft  89  will enter hub sleeve  83  and slide to the position shown in  FIG. 6B . After reaching the lowermost position, the operator picks up drive rods  21  a selected distance to accommodate for stretch of drive rods  21  as in the first embodiment. The second embodiment operates in the same manner as in the first embodiment except vanes  79  and inducer  81  are not axially movable within gas separator  77 . Rather, only drive shaft  89  is axially movable in unison with rotor  19  ( FIG. 1A ). 
   The invention has significant advantages. The floating drive shaft of the gas separator allows for expansion and contraction of the rod string driving the unit. The floating shaft gas separator can be designed with varying axial movable links. 
   While the invention has been shown in only two of its forms, it should be apparent to those skilled in the art that it is not so limited but susceptible to various changes without departing from the scope of the invention.