Tunable Progressive Cavity Pump

Abstract

A well pump assembly includes a progressive cavity pump having a stator with an elastomeric inner portion. The stator has an axial cavity with internal lobes; a rotor with external lobes positioned within the axial cavity. An effector selectively increases and decreases a stiffness of the stator by changing a cross sectional area of the axial cavity in the stator. The effector may include a reservoir within the stator containing a fluid. A reservoir pump selectively increases and decreases a pressure of the fluid in the reservoir in response to sensing the flow rate from the progressive cavity pump and the torque of the motor. Alternately, the reservoir may contain 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.

1 . A well pump assembly, comprising:
 a progressive cavity pump having a stator with an elastomeric inner portion, the stator having an axis, an axial cavity with an internal helical profile, and a rotor with an external helical profile positioned within the axial cavity;   a motor operatively coupled to the progressive cavity pump for rotating the rotor when supplied with power, and   at least one effector cooperatively associated with the stator that selectively increases and decreases a stiffness of the stator.   
     
     
         2 . The assembly according to  claim 1 , further comprising:
 a controller that senses operating conditions of the progressive cavity pump assembly and controls the effector in response.   
     
     
         3 . The assembly according to  claim 1 , wherein the effector selectively increases and decreases a cross sectional area of the axial cavity in the stator. 
     
     
         4 . The assembly according to  claim 1 , wherein the effector comprises:
 a reservoir within the stator separate from the axial cavity and containing a fluid; and   a reservoir pump for selectively increasing and decreasing a pressure of the fluid in the reservoir.   
     
     
         5 . The assembly according to  claim 1 , wherein the effector comprises:
 at least one elongated reservoir extending along a length of the stator, separated from the axial cavity and containing a fluid;   a reservoir pump located exterior of the progressive cavity pump that is connected to the reservoir by a fluid line;   a valve for opening and closing the fluid line; and   a controller that senses a flow rate from the progressive cavity pump and a torque from the motor and controls the valve and the reservoir pump in response.   
     
     
         6 . The assembly according to  claim 1 , wherein the effector comprises:
 at least one fluid reservoir within the stator separate from the axial cavity;   a magneto-rheological fluid (MR fluid) within the reservoir; and   a coil that generates an electromagnetic field within the MR fluid to selectively increase and decrease a viscosity of the MR fluid.   
     
     
         7 . The assembly according to  claim 1 , wherein the effector comprises:
 at least one reservoir within the stator having two portions axially spaced apart and connected by an orifice, the reservoir being separated from the axial cavity;   a magneto-rheological fluid (MR fluid) within the reservoir;   a coil that generates an electromagnetic field within the MR fluid at the orifice to selectively increase and decrease a viscosity of the MR fluid; wherein   rotation of the rotor deforms the internal helical profile, causing the MR fluid to flow through the orifice between the portions of the reservoir; and   increasing the viscosity of the MR fluid slows a flow rate of the MR fluid through the orifice and thereby stiffens the stator.   
     
     
         8 . The assembly according to  claim 1 , wherein the at least one effector comprises:
 a plurality of separate effectors spaced along a length of the progressive cavity pump, each of the effectors being separately controllable for varying a stiffness of the stator along the length of the progressive cavity pump.   
     
     
         9 . The assembly according to  claim 1 , wherein:
 the stator comprises a lower section, an intermediate section, and an upper section;   each of the lower, intermediate, and upper sections has a reservoir containing a pressure fluid that is isolated from fluid communication with well fluid in the axial cavity;   the pressure fluid in the reservoir in the lower section is isolated from fluid communication with the pressure fluid in the reservoir in the intermediate section and the pressure fluid in the reservoir in the upper section, and the pressure fluid in the reservoir in the intermediate section is isolated from fluid communication with the pressure fluid in the reservoir in the upper section;   a reservoir pump located exterior of the progressive cavity pump;   lower, intermediate and upper fluid lines, leading from the reservoir in the lower, intermediate and upper sections, respectively, to the reservoir pump, each of the fluid lines being blocked from fluid communication with each other,   lower, intermediate and upper valves in the lower, intermediate and upper fluid lines, respectively; and   a controller that senses a flow rate from the progressive cavity pump and a torque of the motor and controls the reservoir pump and the valves in response so as to be able to apply a different fluid pressure to the reservoir in the lower section from the reservoir in the intermediate section and from the reservoir in the upper section.   
     
     
         10 . A well pump assembly, comprising:
 a progressive cavity pump having a stator with an elastomeric inner portion, the stator having an axis, an axial cavity with an internal helical profile, and a rotor with an external helical profile positioned within the axial cavity;   a motor operatively coupled to the progressive cavity pump for rotating the rotor when supplied with power;   at least one elongated reservoir in and extending along a length of the stator containing a pressure fluid;   a reservoir pump located exterior of the progressive cavity pump for selectively increasing and decreasing a pressure of the pressure fluid in the reservoir; and   wherein increasing the pressure increases a cross sectional dimension of the axial cavity of the stator.   
     
     
         11 . The assembly according to  claim 10 , further comprising:
 a valve located in a fluid line between the reservoir pump and the reservoir; and   a controller that senses operating conditions of the well pump assembly and controls the valve and the reservoir pump in response.   
     
     
         12 . The assembly according to  claim 10 , further comprising:
 a valve located in a fluid line between the reservoir pump and the reservoir; and   a controller that senses a torque of the motor and a flow rate of the progressive cavity pump and controls the valve and the reservoir pump in response.   
     
     
         13 . The assembly according to  claim 10 , wherein the reservoir extends substantially an entire length of the stator. 
     
     
         14 . The assembly according to  claim 10 , wherein:
 the at least one reservoir comprises a lower and an upper reservoir, the pressure fluid in the lower reservoir being isolated from fluid communication with the pressure fluid in the upper reservoir;   a lower pressure fluid line leading from the lower reservoir to the reservoir pump;   an upper pressure fluid line leading from the upper reservoir to the reservoir pump;   a lower valve in the lower pressure fluid line, and an upper valve in the upper pressure fluid line, enabling the reservoir pump to apply a different pressure to the pressure fluid in the lower reservoir than the pressure of the pressure fluid in the upper reservoir.   
     
     
         15 . The assembly according to  claim 10 , wherein said at least one reservoir comprises at least two reservoirs spaced apart from each other on opposite sides of the axis. 
     
     
         16 . A method of pumping fluid from a well, comprising:
 (a) providing a progressive cavity pump assembly having a progressive cavity pump having a stator with an elastomeric inner portion, the stator having an axis, an axial cavity with an internal helical profile, a rotor with an external helical profile positioned within the axial cavity, and a motor operatively coupled to the progressive cavity pump;   (b) installing the pump assembly in a well and operating the motor to rotate the rotor, and   (c) while the pump assembly is operating, selectively increasing and decreasing a stiffness of the stator.   
     
     
         17 . The method according to  claim 16 , wherein step (c) comprises selectively increasing and decreasing a cross sectional area of the axial cavity in the stator. 
     
     
         18 . The method according to  claim 16 , wherein:
 step (a) comprises providing a reservoir in the stator containing a pressure fluid that is isolated from well fluid in the axial cavity; and   step (c) comprises selectively increasing and decreasing a pressure of the pressure fluid in the reservoir.   
     
     
         19 . The method according to  claim 16 , wherein step (c) comprises varying a stiffness of a lower portion of the stator relative to a stiffness of an upper portion of the stator. 
     
     
         20 . The method according to  claim 16 , wherein:
 step (a) comprises providing a reservoir within the stator, placing a magneto-rheological fluid (MR fluid) within the reservoir; and   step (c) comprises generating an electromagnetic field within the MR fluid to selectively increase and decrease a viscosity of the MR fluid.