Patent Publication Number: US-2015078943-A1

Title: Tunable Progressive Cavity Pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to provisional application 61/878,367, filed Sep. 16, 2013. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates in general to progressive cavity pumps for wells and in particular to a system that changes the inner diameter of the stator in response to changes in operating conditions. 
     BACKGROUND 
     One type of well pump used in oil wells is a progressive cavity pump. The pump has a stator with an elastomeric inner portion. An axial cavity having an internal helical profile extends through the stator. A rotor with an external helical profile fits within the axial cavity. A motor causes the rotor to rotate, with the interaction of the helical profile on the rotor and the helical profile in the stator causing fluid to be pumped upward through the cavity. The rotation of the rotor also causes the rotor to orbit within the stator. 
     The interface between the rotor and axial cavity is sensitive and may change due to various conditions in the well. The stator may swell, causing the interference between the rotor and the helical profile of the axial cavity to create excessive friction, increasing the torque and creating a potential to lock or break of the rotor. On the other hand, if the stator shrinks, the cross-sectional area of the axial cavity increases, reducing the interference between the rotor and the axial cavity. Erosive wear may also increase the cross-sectional area of the axial cavity. If too large, the interface between the rotor and the stator may allow leakage of well fluid, reducing the efficiency of the pump. 
     The radial shrinkage or swelling of the stator depends on well fluids and environmental conditions. For example, the hydrocarbon content of the well fluid may cause the stator to swell, decreasing the cross-sectional area of the axial cavity while the pump is being lowered into the well. Consequently, manufacturers custom size the interference between the rotor and the axial cavity for a particular well. However, if the environmental conditions change, the axial cavity geometry may cause the pump to either become less efficient or cease to function. 
     SUMMARY 
     A well pump assembly includes a progressive cavity pump having a stator with an elastomeric inner portion. The stator has an axial cavity with an internal helical profile. A rotor with an external helical profile is positioned within the axial cavity. A motor operatively coupled to the progressive cavity pump rotates the rotor when supplied with power. At least one effector is cooperatively associated with the stator to selectively increase and decrease a stiffness of the stator. Preferably, a controller senses operating conditions of the progressive cavity pump assembly and controls the effector in response. The change in stiffness may be caused by the effector increasing and decreasing a cross sectional area of the axial cavity in the stator. 
     The effector may comprises a reservoir within the stator separate from the axial cavity and containing a pressure fluid. A reservoir pump for selectively increases and decreases a pressure of the pressure fluid in the reservoir. The reservoir may be elongated and extend along a length of the stator, separated from the axial cavity. 
     Alternately, the stator may contain a reservoir filled with a magneto-rheological fluid (MR fluid). A coil generates an electromagnetic field within the MR fluid to selectively increase and decrease a viscosity of the MR fluid. The MR fluid reservoir may have two portions axially spaced apart and connected by an orifice. A coil generates an electromagnetic field within the MR fluid at the orifice to selectively increase and decrease a viscosity of the MR fluid. 
     The pump assembly may have a plurality of separate effectors spaced along a length of the progressive cavity pump. Each of the effectors is separately controllable for varying a stiffness of the stator along the length of the progressive cavity pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present technology will be better understood on reading the following detailed description of nonlimiting embodiments thereof, and on examining the accompanying drawings, in which: 
         FIGS. 1A and 1B  are a sectioned side view, partially schematic, of a progressive cavity well pump assembly having a stator with tunable features in accordance with this disclosure. 
         FIG. 2  is an enlarged transverse cross-sectional view of an alternate embodiment of the pump of  FIG. 1A . 
         FIG. 3  is an enlarged axial cross-sectional view of the pump of  FIG. 1A  with the rotor not shown. 
         FIG. 4  is an axial cross-sectional view of an alternate embodiment of the pump of  FIG. 3 . 
         FIG. 5  is an enlarged axial cross-sectional view of another alternate embodiment of the pump of  FIG. 1A . 
         FIG. 6  is a schematic, perspective exploded view of the pump of  FIG. 5 . 
         FIG. 7  is a schematic, perspective exploded view of a portion of the effector of the pump of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1A , a cased well  11  has a wellhead assembly or production tree  13  mounted at its upper end. Production tree  13  is shown schematically and has a flow line  15  for discharging production fluid from well  11 . A valve  17  opens and closes flow line  15 . Preferably the surface equipment includes a flow meter  19  connected into flow line  15  for measuring the flow rate of the well fluid. Alternately, flow meter  19  could be located in the well. An electrical line  21  connects flow meter  19  to a controller  23  located on the surface adjacent production tree  13 . 
     Production tubing  25  has an upper end supported by a hanger (not shown) in production tree  13  and extends into cased well  11 . Tubing  25  may comprises joints of pipe secured by threads to each other. Alternately, tubing  25  could be continuous coiled tubing deployed from a reel. 
     A progressive cavity pump  27  secures to a lower end of tubing  25  to pump well fluid up to production tree  13 . Alternately, progressive cavity pump  27  could be deployed through tubing  25 . Pump  27  has a stator  31  within a cylindrical housing  29 , which may be considered to be part of stator  31 . Stator  31  is fixed against rotation in housing  29 , and at least an inner portion is formed of an incompressible but resilient elastomeric material. Stator  31  has an axial cavity  33  extending its length that is formed with a helical configuration. In  FIGS. 1A and 3 , axial cavity  33  has two helical lobes, creating a sinusoidal appearance, narrowing and widening with inward projecting lobes separated by outward extending valleys. Axial cavity  33  could have more than two helical lobes, such as stator  31 ′ in  FIG. 2 , which has an axial cavity  33 ′ with three helical lobes. 
     A rotor  35  rotatably extends through stator axial cavity  33 . Rotor  35  is normally of metal and has an exterior profile  37  that slidingly engages the profile of axial cavity  33 . Exterior profile  37  has a single helical configuration that is also sinusoidal in appearance. However, when viewed in cross-section, the lobes appear on one side of rotor  35  to be offset from the lobes on the opposite side, presenting a sinuous appearance. The transverse cross-sectional appearance of rotor  35  is illustrated by rotor  35 ′ in  FIG. 2 . 
     Exterior profile  37  and the profile of axial cavity  33  are well known and conventional. Because of exterior profile  37  and the profile of axial cavity  33 , when rotor  35  rotates, it orbits around axis  39  of pump housing  29 . As rotor  35  rotates, an interference fit with axial cavity  33  causes rotor  35  to deflect or deform elastomeric stator  31  inward and outward as well fluid is pushed upward into tubing  25 . 
     A gripping section  40  may be mounted to the upper end of rotor  35  to be engaged by a tool for retrieving rotor  35  from stator  31 . Normally, the upper end of rotor  35  extends above stator  31 , and the lower end of rotor  35  extends below stator  31 . 
     The interface between rotor  35  and axial cavity  33  is sensitive and may change due to various conditions in the well. Stator  31  may swell, causing the interference between rotor  35  and the profile of axial cavity  33  to create excessive friction, increasing the torque and creating a potential to lock or break of rotor  35 . On the other hand, if stator  31  shrinks, the cross-sectional area of axial cavity  33  increases, reducing the interference between rotor  35  and axial cavity  33 . Erosive wear may also increase the cross-sectional area of axial cavity  33 . If too large, the interface between rotor  35  and axial cavity  33  may allow leakage of well fluid, reducing the efficiency of pump  27 . 
     The radial shrinkage or swelling of stator  31  depends on well fluids and environmental conditions. For example, the hydrocarbon content of the well fluid may cause stator  31  to swell, decreasing the cross-sectional area of axial cavity  33  while pump  27  is being lowered into the well. Consequently, manufacturers custom size the interference between rotor  35  and axial cavity  33  for a particular well. However, if the environmental conditions change, the axial cavity geometry may cause the pump to either become less efficient or cease to function. 
     To avoid these problems, an effector is employed that selectively increases and decreases the stiffness of elastomeric stator  31  in response to changes in operating conditions. A change in stiffness also changes the interference between rotor  35  and axial cavity  33 . The effector may also reduce the cross-sectional area of the axial cavity, which in effect, changes the stiffness of stator  31 . 
     Referring to  FIG. 3 , in this example, an effector chamber or reservoir  41  within pump housing  29  is formed within or outside of stator  31 . In this example, reservoir  41  comprise several separate axially extending cavities, each formed within stator  31  and evenly spaced around axis  39 . Each reservoir  41  could have an axis parallel with axis  39 , or each reservoir could be helical and extend helically around axis  39 . Alternately, reservoir  41  could be annular, extending completely around an outer diameter of stator  31 . Effector reservoir  41  may be elongated, as shown, and could extend all or just part of the length of stator  31 . A pressure fluid  43  pumped by a reservoir pump or compressor  45  selectively increases and reduces fluid pressure within reservoirs  41 . Pressure fluid  43  may be incompressible, such as a hydraulic fluid. Pressure fluid  43  may alternately be a compressible fluid, such as air. Pressure fluid  43  within each reservoir  41  is isolated or blocked from fluid communication with well fluid in axial cavity  33 . 
     Reservoir pump  45  may be located adjacent to production tree  13  and controller  23  ( FIG. 1A ). Controller  23  ( FIG. 1A ) controls reservoir pump  45  based on torque sensed and the flow rate of well fluid being monitored by flow meter  19 . As an alternate to being mounted adjacent to production tree  13 , the portion of controller  23  that controls reservoir pump  45  could be mounted to progressive cavity pump  23  within the well. Reservoir pump  45  draws fluid  43  from a tank  47 . A valve  48  allows reservoir pump  45  to pump fluid  43  to reservoirs  41  and will hold the pressure when reservoir pump  45  is turned off. When actuated by controller  23 , valve  48  allows flow back of fluid  43  to tank  47 . 
     When the pressure of fluid  43  increases, reservoirs  41  expand and stiffen stator  31 . If rotor  35  is not present, as shown in  FIG. 3 , the increase in fluid pressure in reservoirs  41  causes the dimensions of axial cavity  33  to shrink, as indicated by the dotted lines  49 . The flow area of axial cavity  33  thus shrinks. The difference between the unaltered size of axial cavity  33  and the reduced size shown by the dotted lines may only be 0.20 inches or less, as an example. During operation, rotor  35  ( FIG. 1 ) will be present, and being metal, it does not change dimensions in response to increasing pressure in reservoirs  41 . Thus the interference between rotor  35  and axial cavity  33  increases in response to increasing fluid pressure within reservoirs  41 . 
     Referring to  FIG. 1A , rotor  35  may be driven in various conventional manners. In this example, a flex shaft  51  couples to a lower end of rotor  35  via a coupling  53  that allows rotor  35  to stab into engagement with flex shaft  51 . Flex shaft  51  rotates within a connector shaft housing  55  that has a well fluid intake  57  for admitting well fluid to axial cavity  33 . A concentric coupling  59  connects to and causes the lower end of flex shaft  51  to remain concentric on axis  39 . The upper end of flex shaft  51  and coupling  53  orbit. Flex shaft  51  is typically formed of a steel material. 
     A drive shaft  61  has an upper end that connects to concentric coupling  59 . Drive shaft  61  extends through a seal section  63 . In this example, a gear reducer  65  secures to the lower end of seal section  63  to reduce the rotational speed of drive shaft  61 . An electrical motor  67  couples to the lower end of gear reducer  65 . Motor  67  may be a three-phase type that rotates typically around 3600 rpm. Motor  67  has a drive shaft (not shown) that couples to gear reducer  65  for rotating drive shaft  61  at a lower rate of speed. A dielectric lubricant fills motor  67  and also part of seal section  63 . Seal section  63  reduces a pressure differential between well fluid on the exterior and the lubricant within motor  67 . Seal section  63  may be a conventional type having a communication port that admits well fluid to one side of a bag or bellows, the other side being in contact with the lubricant. A power cable  69  connects to motor  67  and extends alongside tubing  25  to the surface where it connects to controller  23 . Optionally, a sensing unit  71  may connect to motor  67 . Sensing unit  71  senses various parameters such as temperature and well fluid pressure. 
     Pump  27  may alternately be driven by a motor located adjacent production tree  13 . In that case, a drive rod (not shown) extends from the surface motor to pump  27 . 
     In operation, controller  23  supplies electrical power to motor  67 , which causes rotor  35  to rotate, pumping well fluid up tubing  25  to production tree  13 . Controller  23  monitors the flow rate with flow meter  19 . Controller  23  also monitors the torque required to rotate rotor  35 . Torque monitoring can be accomplished various ways. In one example, controller  23  monitors the electrical current supplied via power cable  69  to motor  67 . Controller  23  will actuate reservoir pump  45  to increase the pressure of fluid  43  in reservoirs  41  if the flow rate drops below an acceptable level. Controller  23  will stop reservoir pump  45  from increasing the fluid pressure in reservoirs  41 , and with valve  48 , hold the desired pressure once a desired flow rate is reached. Controller  23  will also control valve  48  to bleed off pressure in reservoirs  41  if the torque monitored is too high. 
     The initial interference between rotor  35  and stator axial cavity  33  could be sized loosely enough so that once pump  27  has been located in the well, the start up torque will not be excessive. That is, possible swelling of stator  31  could be accounted for in advance by making the dimensions of stator axial cavity  33  sufficiently large so that expected swelling would not cause too much interference between stator  31  and rotor  35 . When pump  27  is first installed, reservoir pump  45  would not be operating, and the pressure of fluid  43  in reservoirs  41  would be equal to the hydrostatic pressure of the well fluid in the well. After pump  27  operates for a selected duration, controller  23  may increase the stiffness of stator  31  by causing reservoir pump  45  to increase the pressure of fluid  43  in reservoirs  41 , thereby increasing the flow rate of well fluid. If the torque becomes too high, controller  23  actuates valve  48  to bleed off some of the pressure in reservoirs  41 . Controller  23  thus continually tunes pump  27  to operate with a desired stiffness of stator  31 . As an alternate to automatic control by controller  23  based on torque and flow rate, the operator could manually adjust the stiffness of stator  31  with manual controls on controller  23  to change the pressure within reservoirs  41 . 
     Referring to  FIG. 4 , progressive cavity pump  27 ′ has more than one stator portion, and three portions are shown by the numerals  31   a ,  31   b , and  31   c . Stator portions  31   a ,  31   b ,  31   c  are shown stacked coaxially on each other within a single housing  29 ′, however they could have separate housings secured to each other. Each stator portion  31   a ,  31   b , and  31   c  has one or more reservoirs  41   a ,  41   b  and  41   c , respectively. A separate flow line  74   a ,  74   b  and  74   c  leads from the reservoirs  41   a ,  41   b  and  41   c . A separate valve  48   a ,  48   b  and  48   c  is located in each flow line  74   a ,  74   b  and  74   c , respectively. In this example, a single reservoir pump  45  ( FIG. 3 ) supplies pressure fluid through the separate valves  48   a ,  48   b  and  48   c  to separate flow lines  74   a ,  74   b , and  74   c . Flow lines  74   a ,  74   b  and  74   c  are illustrated on the exterior of housing  29 ′, but they could extend upward through the stator portions  31   a ,  31   b  and  31   c  to an upper end of progressive cavity pump  27 ′. The pressure fluid in each reservoir  74   a ,  74   b  and  74   c  is isolated or not in fluid communication with the pressure fluid in the other reservoirs  74   a ,  74   b  and  74   c.    
     During operation of the embodiment of  FIG. 4 , the well fluid pressure within stator cavity  33 ′ caused by the rotation of the rotor (not shown) gradually increases from the bottom to the top of progressive cavity pump  27 ′. Because of the lower pressure within lower stator portion  31   a , the desired stiffness of lower stator portion  31   a  may be less than the desired stiffness in intermediate stator portion  31   b . Similarly, the optimum stiffness in intermediate stator portion  31   b  may be less than the optimum stiffness of upper stator portion  31   c . More interference and stiffness may be desirable in the portions of pump  27 ′ having higher fluid pressures. Controller  23  ( FIG. 1A ) can control pump  45  and valves  48   a ,  48   b  and  48   c  to provide a different reservoir fluid pressure in each reservoir  41   a ,  41   b  and  41   c . Alternately, an operator could manually control valves  48   a ,  48   b  and  48   c  to maintain different pressures in reservoirs  41   a ,  41   b  and  41   c.    
     Although three separate stator portions  31   a ,  31   b  and  31   c  are illustrated, pump  27 ′ could have more or fewer. Also, rather than separate stator portions, a single stator could have several zones along its length, each zone having a separate reservoir. 
     Referring to  FIGS. 5-7 , in this embodiment, two separate stator sections  73   a ,  73   b  are illustrated, but more could be employed. Stator sections  73   a ,  73   b  are axially aligned along a longitudinal axis  75  and spaced axially apart from each other a short distance. Referring more particularly to  FIG. 5 , each stator section  73   a ,  73   b  is of incompressible elastomeric material fixed for non rotation within a steel housing  77 . The ends of housings  77  may protrude past the ends of stator sections  73   a ,  73   b  and abut each other. Each stator section  73   a ,  73   b  has an axial cavity  79  for receiving a conventional rotor  80 , which is a single-piece member extending through both stator sections  73   a ,  73   b.    
     A stator stiffness effector  81  is mounted between opposing ends of stator sections  73   a ,  73   b . Effector  81  has a rigid tubular body  83  with one end abutting stator section  73   a  and the other end abutting stator section  73   b . Body  83  has an axial bore  85  that is cylindrical and has a diameter large enough so that rotor  80  does not contact it as rotor  80  rotates and orbits. Effector body  83  has at least one, and preferably several magneto rheological (MR) passages  87 . In this example, three MR passages  87  are shown in  FIG. 7 , spaced equally around axis  75 . Each MR passage  87  has a first or upper section  87   a  and a second or lower section  87   b . Each section  87   a ,  87   b  joins a central pocket  88  formed in effector body  83 . In this example, effector body  83  has three pockets  88 . 
     Mating MR fluid reservoirs  89  are formed within stator sections  73   a ,  73   b  to register with MR passages  87 . Each MR fluid reservoir  89  may have the same diameter as each MR passage  87 . Seals (not shown) seal the interface between MR passages  87  and MR fluid reservoirs  89 . Each MR fluid reservoir  89  extends parallel to axis  75  a selected distance and has a closed end opposite the end joining MR passages  87 . The axial length of each MR fluid reservoir  89  need not be as long as each stator section  73   a ,  73   b , but could be. MR fluid reservoirs  89   a  are located in stator section  73   a  and mate with MR passage sections  87   a . MR fluid reservoirs  89   b  are located in stator section  73   b  and mate with MR passage sections  87   b.    
     An orifice or tube  91  extends through each pocket  88  and connects each MR fluid passage  87   a  with the corresponding MR fluid passage  87   b . Orifice tube  91  seals to MR fluid passages  87   a ,  87   b  and has a flow area smaller than the flow areas of MR fluid passages  87   a ,  87   b , creating an orifice. 
     A magneto rheological (MR) fluid  93  is located in MR reservoirs  89 , MR fluid passages  87  and orifice tubes  91 . MR fluid  93  is a known liquid that will undergo a significant change in viscosity when an electromagnetic field passes through MR fluid  93 . One or more coils or electromagnets  95  are located within each pocket  88  adjacent to each orifice tube  91  to impose an electromagnetic field on MR fluid  93  contained in orifice tube  91 . In this example, two substantially flat electromagnets  95  are located in each pocket  88 , one or each side of orifice tube  91 . Electromagnets  95  are connected by wires (not shown) to a controller, such as controller  23  ( FIG. 1 ) to selectively supply electrical current. 
     Stator sections  73   a ,  73   b  may be secured together with effector  81  sandwiched between in various manners. If desired, effectors  81  could also be located at the upper end of stator section  73   a  and lower end of stator section  73   b . A collar or clamp  99  is schematically illustrated as enclosing effector  81  and joining stator housings  77 . Effector body  83  may have an outer diameter smaller than the inner diameter of housings  77 , as illustrated, and fits within the portions of housings  77  that extend beyond stators  73   a ,  73   b . Rather than a collar  99 , the abutting ends of housings  77  could be welded to each other or secured in other manners. 
     During operation of the embodiment of  FIGS. 5-7 , rotation of rotor  80  exerts radial outward forces on each stator section  73   a ,  73   b , causing lobes within axial cavity  79  to deflect radially back and forth. The deflection force transmits through stator sections  73   a ,  73   b  and acts radially on MR fluid reservoirs  89   a ,  89   b , alternately squeezing and relaxing reservoirs  89   a ,  89   b . This alternating force on MR fluid reservoirs  89   a ,  89   b  causes a pumping action of MR fluid  93 , causing it to flow in an oscillating manner through orifice tubes  91 . At the same time, the rotation of rotor  80  pumps well fluid through axial cavity  79  up from stator section  73   a.    
     If controller  23  ( FIG. 1A ) senses from flow meter  19  that the flow rate of well fluid is too low, it will send a signal to electromagnets  95 , which impose an electromagnetic field on MR fluid  93  flowing through orifice tube  91 . The viscosity of MR fluid  93  within each orifice tube  91  increases as a result, which slows the flow rate between MR fluid reservoirs  89   a ,  89   b . The fluid pressure within reservoirs  89   a ,  89   b  increases as the helical lobes of rotor  80  exert radial outward forces on stator sections  73   a ,  73   b . The increased pressure resists the outward deflection of stator sections  73   a ,  73   b , thereby increasing the stiffness of stator sections  73   a ,  73   b . The increased stiffness effectively increases the interference between rotor  80  and stator sections  73   a ,  73   b , thereby increasing the flow rate. 
     If controller  23  senses that the torque to rotate rotor  80  is too high, it will cut off the voltage supplied to electromagnets  95 . The viscosity of MR fluid  93  within orifice tubes  91  rapidly drops, lowering the pumping pressure within MR fluid reservoirs  89 . The stiffness of stator sections  73 ,  73   b  thus decreases to reduce the torque. Rather than automatically controlling the stiffness with controller  23  based on torque and well fluid flow, an operator could manually vary the stiffness with manual controls on controller  23  to supply voltage to electro magnets  95 . 
     The embodiment of  FIGS. 5-7  could also be incorporated into separate zones, in a manner similar to the embodiment shown in  FIG. 4 . Controller  23  ( FIG. 1A ) could supply voltages to electromagnets  95  in one or more of the zones to increase or decrease the viscosity and not to other of the zones. Also, the zones could be manually controlled. 
     The foregoing aspects, features, and advantages of the present technology will be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing the preferred embodiments of the technology illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, it is to be understood that the specific terminology is not limiting, and that each specific term includes equivalents that operate in a similar manner to accomplish a similar purpose. 
     For example, other effectors to increase and decrease the stiffness of the stator in response to changing conditions are feasible. Shape memory gel and shape memory alloys change shapes in response to voltage changes. Piezoelectric crystals, voice coils or any other media or elements that alter geometry in response to changing conditions sensed could also be used. 
     Although the technology herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present technology. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present technology.