Abstract:
A latching mechanism for selectively disengaging an upper pump from a motor in an ESP. The latching mechanism comprises barbs formed on an upper end of an upper shaft that are engaged by a tool to lift the upper shaft until a lower end of the upper shaft disengages from an upper end of a motor shaft. When the upper pump is disengaged from the motor shaft, only a lower pump is driven by the motor and flow of well fluid is circulated past the disengaged upper pump via a bypass line. The upper pump shaft may reengage the motor shaft if additional lift is required.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to provisional application 61/235,611, filed Aug. 20, 2009. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to the operation of electrical submersible pumps (ESPs), including Electrical Submersible Progressive Cavity Pumps (ESPCPs) and in particular to changing the pump size of an ESP or ESPCP in a well while ESP or ESPCP system is installed. 
     BACKGROUND OF THE INVENTION 
     Electrical submersible pumps (“ESP”) are used to pump wellbore fluids from the depths of the earth to the surface. A typical ESP has a motor, a seal section, and a pump. The motor rotates a shaft inside the seal section. The seal section shaft is connected to the pump. The ESP pump is typically an impeller pump having multiple stages. Each pump stage has an impeller and a diffuser through which wellbore fluid travel. In operation, wellbore fluids enter the first impeller and are accelerated by centrifugal force out of the impeller into the adjacent diffuser. The diffuser then reduces the velocity of the wellbore fluid, converts the high velocity to pressure, and directs the fluid into the next impeller. The pressure of the wellbore fluid is increased with each successive stage as described above, until the fluid is discharged from the pump into tubing that carries the fluid to the surface. 
     A central pump shaft is connected to the seal section shaft. As the motor rotates, it ultimately causes the central pump shaft to rotate. The central pump shaft passes through each impeller. Keys or splines on the shaft engage corresponding slots on each impeller so that the impellers rotate with the shaft. Spacers are frequently required between the impellers so that the impellers are properly spaced to engage the diffusers. 
     An electrical submersible progressive cavity pump (“ESPCP”) having a single stator and a rotor may also be used. A typical ESPCP has a motor, a seal section, and a pump. An optional gearbox may also be included. A PCP is a positive displacement pump in which the rotor and the stator have cavities that are filled with fluid. As the rotor is rotated by the motor, fluid is moved upward. For discussion purposes only, ESP is used throughout with the understanding that either an ESP or ESPCP can be used. 
     Multiple ESP pumps may be connected in series and used in a single well. The ESP pumps are typically driven by a single motor with the shaft running through each of the ESP&#39;s. During operation, multiple ESP pumps, or tandem pumps, arranged in this manner provide additional lift that may be necessary to lift the wellbore fluids to the surface. 
     In wells where tandem pumps are deployed, there may be times during the life of a well where a reduced number of stages or a single ESP pump may be required to lift the fluids. Running the additional ESP pump or increased number of stages is inefficient and expensive. However, to disengage the ESP pumps from the shaft, the ESP string typically requires the ESP system to be pulled out of the well. This is an expensive proposition because production must be stopped during this procedure and subsea replacement can cost millions of dollars. 
     It would be advantageous to selectively engage or disengage an ESP pump from a drive shaft without pulling the ESP assembly from the well. 
     SUMMARY OF THE INVENTION 
     In an embodiment of the present technique, a latching mechanism including a pump shaft adapted to latchingly engage a tool for disengaging the pump shaft of the upper pump from engagement with a second shaft of a lower pump, is shown. The lower pump shaft transfers torque produced by a motor to drive a pump shaft in the upper pump when they are engaged through coupling. This embodiment further includes a sleeve keyed to the pump shaft that is in sliding engagement with a stationary bushing connected to a bearing housing that is located within the pump. A spring retainer may be connected to the stationary bushing to allow for receiving and retaining of a protrusion keyed to the pump shaft. This allows the pump shaft to be maintained in a disengaged position, effectively changing the size and capacity of the ESP assembly. The invention described herein may also be used with progressive cavity pumps to change their size and capacity. 
     The latching mechanism may also include an adapter located at the upper end of the of the pump that has a cylindrical body. The adapter may have a bypass port and a sleeve that is in sliding engagement with the adapter. The sleeve slides between a closed position and open position to control well fluid flowing through the bypass port. A bypass line may also be used to communicate well fluid from a discharge of a pump driven by the motor to the bypass port of the adapter to thereby bypass the disengaged pump. Thus, the latching mechanism described above advantageously changes the pump size to prevent wasteful operation and without the need for pulling the ESP string to disengage the upper pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an ESP with multiple pumps and suspended from production tubing, in accordance with an embodiment of the invention. 
         FIG. 2  is a sectional view of an adapter for disconnecting the shaft of a pump, in accordance with an embodiment of the invention. 
         FIG. 3  is a sectional view of an adapter for disconnecting the shaft of a pump with a sleeve in a position to allow flow from a bypass, in accordance with an embodiment of the invention. 
         FIG. 4A  is an enlarged sectional view of an upper pump assembly, in accordance with an embodiment of the invention. 
         FIG. 4B  is an enlarged sectional view of a lower end of an upper pump assembly in accordance with an embodiment of the invention. 
         FIG. 4C  is an enlarged sectional view of a top end of a lower pump assembly in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , an embodiment of a well pump assembly  10  is shown in a sideview suspended in a well  12 . The pump assembly  10  of  FIG. 1  include a motor  11  at its base that is connected on its upper end to a seal section  13 . A lower pump  15 , is attached to the seal section  13  upper end that in turn connects to an upper pump  17 . Seal section  13  equalizes the pressure of lubricant in the interior of motor  11  with hydrostatic well fluid pressure. Motor  11  rotates a shaft (not shown) coupled to a shaft of lower pump  15 ; lower pump  15  shaft is coupled to a shaft of upper pump  17 . During normal operation, motor  11  drives both upper and lower pump  15 ,  17  shafts, and fluid discharged by lower pump  15  flows into the intake of upper pump  17 . Pumps  15 ,  17  provide the lift required to overcome the initial, high viscosity of the well fluid. In addition, because the head produced by a pump varies with the square of the speed of the motor  11 , running pumps  15 ,  17  together compensates for the initially low speed of the motor  11  at startup. However, as well fluid flow increases, fluid temperature also increases to decrease fluid viscosity. Further, lift from one pump is sufficient once higher motor speeds are achieved. Operating the two pumps  15 ,  17  can thus be wasteful and inefficient once sufficient lift can be generated by one pump. 
     In an embodiment of this invention, the upper pump  17  can be selectively disconnected from the lower pump  15  driven by motor  11  without pulling the pump assembly out of the well. Production would be stopped momentarily to disengage the shaft  29  ( FIGS. 2 and 3 ) of the upper pump  17 . After disconnection, the fluid from lower pump  15  could flow though upper pump  17 , and into production tubing  27  for flowing to the surface. The internal parts, such as the impeller, of the disconnected upper pump  17  would introduce a pressure drop that the connected lower pump  15  would have to overcome. Further, the fluid flowing through upper pump  17  rotates its impeller. 
     The embodiment of  FIG. 1  also includes a bypass line  19  connected on one end to a discharge of lower pump  15 . An adapter  21  (which will be described in more detail below) is shown disposed between the upper pump  17  and production tubing  23 . The end of the bypass line opposite the lower pump  15  connects to the adapter  21 . 
     Alternatively, as shown in  FIG. 1 , fluid flow can bypass the disconnected upper pump  17 . When upper pump  17  is disconnected from being driven by the motor shaft, the flow from lower pump  15  can flow through a port  50  ( FIG. 4C ) to the bypass  19  and into adapter  21 . The bypass line  19  registers with a port  20  at its upper end that is formed through the annular adapter wall. An embodiment shown in  FIGS. 2 and 3  illustrate one way fluid can selectively be directed through the bypass  19  and adapter  21  and into the production tubing  23  for flowing to the surface. An annular sliding sleeve  25  as shown can be coaxially located within adapter  21 . When upper pump  17  driven by the motor shaft, the sliding sleeve  25  covers the port  20 , thereby blocking flow exiting the bypass  19 . Seals  22  can prevent fluid flow between the sleeve  25  and adapter  21 . To shift sleeve  25  away from the bore  20  as shown in  FIG. 3 , a tool  27  shown in dashed outline, such as an overshot tool, can be lowered through tubing  23  ( FIG. 1 ) on wireline  32 . The tool  27  can be conventional, with outward facing, spring loaded lugs that can engage, for example, a shoulder (not shown) on the inner surface of the sleeve  25 . 
       FIGS. 4A and 4B , illustrate one embodiment for disengaging the shaft  29  of the upper pump  17  from the motor  11 . Although the adapter  21  is shown without the sliding sleeve  25  described above, the sleeve  25  can also be used as previously described. An annular bearing housing  30  located inside the upper pump  17  circumscribes and radially supports the shaft  29  at its upper end. A sleeve  31 , which supports a ball stop  33 , is coaxially mounted around and keyed to the shaft  29 . The ball stop  33  can be a ball with a passage drilled through it and a key formed within the passage that can engage a slot on the shaft  29 . Alternatively, a slot could be formed within the passage in the ball stop  33  that could receive a key or rib formed on the shaft  29 . A conventional split ring assembly (not shown) can be used to lock the ball stop  33  to a location on the shaft  29  or alternatively, retaining rings  38 ,  39  can be keyed to the shaft  29  on either side of the ball stop  33  to lock it into place. The ball stop  33  snaps into engagement with a spring retainer or grapple  35  to hold shaft  29  in the upper disengaged position after wireline tool  27  is retrieved. In this embodiment, the grapple  35  is supported from the bearing housing  30 . As shown, the grapple  35  includes cantilevered spring members  34  mounted to the annular bearing housing  30 . An annular bushing  36  connects to one end of the cantilevered spring members  34  and is disposed around the shaft  29 . The spring members  34  have a free end  40  depending downward towards the ball stop  33  and a mid-section  42  profiled similar to the ball stop  33  outer periphery. 
     During the disengagement operation, the shaft  29  of the upper pump  17  can be disengaged at the same time the tool  27  shifts the sliding sleeve  25  upward to open the bypass bore  20  ( FIG. 3 ). The tool  27  can latch onto the fishing neck  28  of shaft  29  ( FIG. 2 ). The tool  27  can have inward facing, spring loaded lugs that can latch onto the fishing neck  28 . Although the fishing neck  28  is shown with multiple recesses, a single recess can allow engagement with the tool  27 . Once the tool  27  latches onto the shaft  29  of upper pump  17 , it is pulled upward sufficiently to cause splines  44  ( FIG. 4B ) at the lower end of the shaft  29  to disengage from a coupling  54  ( FIG. 4C ) secured to a top end of a lower shaft  52  with a pin  60  and running through an axis of lower pump  15  as shown in  FIGS. 4B and 4C . This essentially disconnects the upper pump  17  from the lower pump  15 . An annular bushing  62  is disposed around the lower shaft  52  which surrounds a bushing  64 . The bushing  64  is keyed to the lower shaft  52  and is in contact with a sleeve  66  that may also be keyed to the shaft  52 . As in the upper pump  17 , the lower pump shaft  52  is radially supported at its top end to the annular bearing housing  70  of the lower pump  15 . 
     As shaft  29  moves upward, it also moves sleeve  31 , a bushing  37  keyed to the shaft  29 , and retaining ring  39  also keyed to the shaft  29 , upward relative to the grapple  35  and bushing  36 . The shaft  29  is pulled upward until the ball stop  33  snaps into engagement with the grapple  35  to hold shaft  29  in the upper disengaged position. Bushing  36  on grapple  35  and bushing  37  keyed to the shaft  29  slidingly and coaxially engage when the ball stop  33  snaps into engagement with the grapple  35 . A retaining ring  38  located below the ball stop  33  and keyed to the shaft supports the ball stop  33  and prevents it from moving if the shaft  29  is overpulled. As explained earlier, in this embodiment, the ball stop  33  can be locked into place on the shaft  29  by the retaining ring  38  located below the ball stop  33  and the retaining ring  39  located above bushing  37 . In addition to locking the ball stop  33  in place, in this embodiment the retaining rings  38 ,  39  also function to hold the portion of the sleeve  31  and bushing  37  between the retaining rings, in place. To retrieve the tool  27 , a shear pin (not shown) in the tool can be sheared to release from the fishing neck  28  barbs on the shaft  29 . The shaft  29  can be reconnected to lower pump shaft  52  ( FIG. 4C ) and thus the motor by landing a weight bar on the upper end of the shaft  29 . This disengages the ball stop  33  from the grapple  35 , thus allowing the splines  44  ( FIG. 4B ) at the lower end of shaft  29  to reengage the splines  56  and recesses  58  ( FIG. 4C ) on the coupling  54  at the upper end of the lower pump shaft  52 . 
     In an additional embodiment, shaft  29  and sliding sleeve  25  could be shifted upward by sending power to an electromechanical device permanently mounted to adapter  21 . The electromechanical device would thus disconnect the shaft  29  and open the bypass port  19 . The shaft  29  and sliding sleeve  25  could also be shifted upward by a hydraulically device permanently mounted to adapter  21 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. These embodiments are not intended to limit the scope of the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.