Long-stroke pumping unit

1. A pumping unit to reciprocate a rod string for a downhole pump disposed in a well, the pumping unit comprising:

a tower extending from a base to a crown;

a counterweight assembly being movable along the tower;

a belt disposed on the tower, the belt being connected between the counterweight assembly and the rod string and passing over the crown of the tower;

an electric motor being configured to reciprocate the passing of the belt over the crown;

a variable speed driver in electrical communication with the electric motor;

a sensor configured to detect a first position associated with the rod string; and

a controller in data communication with the variable speed driver and the sensor and being configured to control the electric motor with the variable speed driver based on the detected first position associated with the rod string.

2. The pumping unit of claim 1 , wherein the sensor is configured to detect a second position of the counterweight assembly, the second position being related to the first position associated with the rod string, whereby the controller is configured to determine the first position of the rod string based on the second position of the counterweight assembly detected by the sensor.

3. The pumping unit of claim 1 , wherein the electric motor has a stator, a rotor, and a sprocket, the stator mounted at the crown of the tower, the rotor connected to the sprocket, the sprocket being meshed with the belt.

4. The pumping unit of claim 3 , further comprising a gear box torsionally connecting the rotor to the sprocket.

5. The pumping unit of claim 1 , wherein the belt comprises a body made from at least one of an elastomer and an elastomeric copolymer, the body having a length and a width and defining rows of sprocket holes, each row formed adjacent to and along a respective edge of the body; and wherein the belt comprises at least one of:

a mesh disposed in the body and extending along the length and across the width, each sprocket hole formed through the body and the mesh;

a ply of lateral cords and pairs of longitudinal ropes disposed in the body, each lateral cord extending across the width, each sprocket hole formed through the body and the ply, each longitudinal rope extending along the length, each pair straddling the sprocket holes; and

a ply of cords disposed in the body adjacent to an inner surface of the body, each cord extending along the length, alternating teeth and flats each formed across the inner surface of the body.

6. The pumping unit of claim 1 , wherein the sensor is selected from the group consisting of a laser rangefinder; an ultrasonic rangefinder; an ultrasonic rangefinder having a long-range transducer and a short-range transducer; a string potentiometer; a linear variable differential transformer (LVDT); or a linear variable differential transformer (LVDT) comprising: a string connected to the counterweight assembly and wound onto a spool, a screw shaft engaged with a thread of the spool, an LVDT core mounted to the screw shaft, and an LVDT body at least partially receiving the LVDT core.

7. The pumping unit of claim 1 , wherein the controller is further operable to monitor the sensor for failure of the rod string and instruct the variable speed driver to control descent of the counterweight assembly along the tower in response to detection of the failure.

8. The pumping unit of claim 1 , wherein the electric motor is an electric three-phase motor; and wherein the pumping unit further comprises:

a power converter in electrical communication with the variable speed driver; and

a battery in electrical communication with the power converter and being configured to store electrical power generated by the electric three-phase motor during a downstroke of the pumping unit.

9. The pumping unit of claim 1 , wherein the controller is further operable to monitor for failure or imminent failure of the pumping unit and to shut down the pumping unit in response to detection of the failure or imminent failure.

10. A pumping unit to reciprocate a rod string for a downhole pump disposed in a well, the pumping unit comprising:

a tower;

a counterweight assembly being movable along the tower;

a belt disposed on the tower and being connected between the counterweight assembly and the rod string;

a prime mover configured to reciprocate the belt on the tower;

a plurality of sensors configured to measure a plurality of sensor measurements, the senor measurements at least including a first position associated with the rod string, a measured force exerted on the rod string, and a measured vibration associated with the reciprocation of the rod string in the well; and

a controller connected to the prime mover and the sensors, the controller being configured to:

monitor for failure of at least one of the rod string and the belt based on at least one of the sensor measurements; and

control descent of the counterweight assembly along the tower in response to detection of the failure.

11. The pumping unit of claim 10 , wherein the controller is configured to:

determine a second position associated with the downhole pump based at least on the first position;

determine a load associated with the downhole pump based at least on the measured force; and

control an upstroke speed, a downstroke speed, a turnaround acceleration, and a turnaround deceleration for the prime mover based on the determined second position and the determined load.

12. The pumping unit of claim 11 , wherein the controller is configured to:

determine acceptability of two or more parameters of the pumping unit;

select a prime objective based on a hierarchy of the parameters and the acceptability of the parameters; and

determine the upstroke speed, the downstroke speed, the turnaround acceleration, and the turnaround deceleration for the prime objective.

13. The pumping unit of claim 12 , wherein the two or more parameters are selected from a group consisting of: production rate, efficiency, fillage of the downhole pump, fluid level of the downhole pump, static and dynamic stress of the rod string, torque and torque factor of the prime mover, vibration of the rod string, vibration of a production string, reciprocation speed of the rod string, fluid velocity in the production string, drag of production fluid on the rod string, and gas-oil ratio of the production fluid.

14. The pumping unit of claim 10 , wherein the sensors comprise:

a load cell configured to measure the measured force exerted on the rod string;

a position sensor configured to detect the first position associated with the rod string; and

an accelerometer configured to measure the measured vibration associated with reciprocation of the rod string.

15. The pumping unit of claim 14 ,

wherein the load cell comprises:

a tubular body disposed around a portion of the rod string, and

a strain gauge attached to the tubular body and configured to measure strain associated with the tubular body; and

wherein the controller is disposed in communication with the strain gauge of the load cell and is configured to:

determine, based on measured strain, a load on the rod string indicative of the measured force exerted on the rod string,

monitor for failure associated with at least one of the rod string and the belt based on the determined load, and

control the descent of the counterweight assembly along the tower in response to detection of the failure.

16. The pumping unit of claim 15 , wherein the load cell comprises the accelerometer disposed in communication with the controller, the accelerometer being disposed in a chamber of the load cell, the chamber being formed between a recess defined on an outer surface of the tubular body and a sleeve disposed on the tubular body around the recess.

17. The pumping unit of claim 16 , wherein at least one of:

the accelerometer is a dual axis microelectromechanical system;

the sleeve includes an arm attached thereto and extending toward a wire rope connected to the belt;

the load cell is disposed in the chamber; and

the chamber comprises an inert gas.

18. The pumping unit of claim 15 , wherein at least one of:

the load cell is torsionally arrested relative to the rod string;

the load cell includes a pair of washers supporting the tubular body around the portion of the rod string; and

the tubular body of the load cell is disposed between a hanger bar and an upper end of the rod string, the hanger bar being connected to the belt.

19. The pumping unit of claim 14 , wherein the position sensor is selected from the group consisting of: a laser rangefinder; an ultrasonic rangefinder; an ultrasonic rangefinder having a long-range transducer and a short-range transducer; a string potentiometer; a linear variable differential transformer (LVDT); or a linear variable differential transformer (LVDT) comprising: a string connected to the counterweight assembly and wound onto a spool, a screw shaft engaged with a thread of the spool, an LVDT core mounted to the screw shaft, and an LVDT body at least partially receiving the LVDT core.

20. The pumping unit of claim 10 , wherein the sensors further comprise a meter configured to measure power consumed by the prime mover.

21. The pumping unit of claim 10 , wherein the controller is further configured to monitor for failure of the pumping unit and is configured to at least one of:

shut down the pumping unit in response to detection of the failure; and

operate the pumping unit using an emergency hierarchy and emergency acceptability values in response to detection of the failure.

22. The pumping unit of claim 10 , wherein the prime mover is an electric three-phase motor, and wherein the controller further comprises a three-phase variable speed driver.