ELECTRIC MOTOR CONTROL FOR PUMPJACK PUMPING
A pumpjack is driven by an electric motor coupled to a gear box. A local drive controller controls the motor in accordance with a varying motor speed profile over a pumping cycle of the pumpjack. The drive controller determines, based on sensory feedback from the one or more sensors, a pumping cycle load profile, automatically determines, based on the pumping cycle load profile, a varying voltage profile, and controls the motor in accordance with the varying motor speed profile while applying the varying voltage profile to the motor.
This specification generally relates to controlling an electric motor to pump fluid in a pumpjack.
BACKGROUNDReciprocating oil pumps are traditionally provided in the form of a beam-balanced pumpjack unit. Conventional pumpjacks provide a sinusoidal characteristic of reciprocating pumping motion dictated by its geometry and the fixed speed of its prime mover. Other types of pumping units, such as long stroke or hydraulically actuated pumping units, operate at a first constant speed during upstroke motion and at a second constant speed during downstroke motion. Traditional pumping units employ a fixed speed electric motor as the prime mover and develop a desired speed profile by design of the mechanical linkage between motor and pump rod, while some modern units feature a variable frequency drive (VFD) that varies drive speeds for various portions of the pumping cycle to provide a desired pumping speed profile.
SUMMARYThis specification describes technologies related to systems and methods for pumpjack fluid pumping.
One aspect of the invention features a pumpjack motor system, including an electric motor coupled to a gear box of a pumpjack, one or more sensors mounted to monitor at least one operating condition of the pumpjack during operation of the motor, and a drive controller coupled to the motor and operable to control the motor in accordance with a varying motor speed profile over a pumping cycle of the pumpjack, while applying voltage to the motor. The drive controller is configured to determine, based on sensory feedback from the one or more sensors, a pumping cycle load profile, to automatically determine, based on the pumping cycle load profile, a varying voltage profile, and to control the motor in accordance with the varying motor speed profile while applying the varying voltage profile to the motor.
In some situations, the varying motor speed profile is an altered version of a stroke timing curve implemented during one or more previous pumping cycles of the pumpjack. In some cases, the varying motor speed profile includes a plurality of target motor speeds corresponding to each of a plurality of discrete control periods within the pumping cycle of the pump jack.
In some examples, the pumping cycle load profile includes a plurality of torque loads corresponding to each of the plurality of discrete control periods.
Preferably, the plurality of discrete control periods of the first pump stroke cycle includes at least 100 control periods. One or more of the plurality of discrete control periods of the first pump stroke cycle may have a time duration of between about 5 and 100 milliseconds.
In some examples, the drive controller is configured to determine the pumping cycle load profile as a mathematical prediction based on historical sensory feedback provided by the one or more sensors during one or more previous pumping cycles of the pumpjack, and/or adjustments between the varying motor speed profile and a stroke timing curve implemented during one or more previous pumping cycles of the pumpjack.
In some embodiments, at least one of the sensors is a load sensor, such as a load cell responsive to load of a polish rod of the pumpjack. In some examples, at least one of the sensors is a crank rotation sensor, or a motor shaft position sensor, or a motor current sensor.
Another aspect of the invention features a method of operating a pumpjack, including operating an electric motor driving the pumpjack according to a varying motor speed profile during a first pump stroke cycle of the pumpjack (the motor speed profile including a plurality of target motor speeds corresponding to each of a plurality of discrete control periods), receiving sensory feedback from one or more sensors mounted to monitor at least one operating condition of the pumpjack (the sensory feedback including data collected during the first pump stroke cycle), determining a pump cycle load profile based on the sensory feedback (the pump cycle load profile corresponding to a plurality of torque loads of the electric motor at each of the discrete control periods of the first pump stroke cycle), automatically determining, based on the pump cycle load profile, a varying voltage profile, and then operating the electric motor according to the varying motor speed profile and the varying voltage profile during a second pump stroke cycle of the pumpjack.
Various examples of the method according to this aspect of the invention include one or more features discussed above with respect to the first aspect.
Various examples of methods or systems corresponding to one or more of the described aspects of the invention discussed herein may advantageously provide improved fluid production rate of a pumpjack unit, and/or improved pumping efficiency, by implementing optimization techniques designed to increase the pumping rate, pump efficiency and/or pump stroke length by automatically adjusting the pumping speed throughout the pump stroke cycle, in response to local conditions. Further, the efficiency of the electric motor serving as the prime mover of the pumpjack can be improved by employing a voltage pattern commensurate with required torque levels of the adjusted/optimized motor speed pattern. These techniques may be implemented automatically (e.g., without user interaction) by a local controller, without employing computationally complex mathematical simulations. Speed adjustments may therefore be implemented in essentially real time (e.g., in response to changing downhole conditions) and without interruption of the pumping process.
The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.
Many of the features are exaggerated to better show the features, process steps, and results.
DETAILED DESCRIPTIONOne or more implementations of the present disclosure include pumpjacks and pumpjack motor systems, as well as techniques for operating the same, where the controller facilitates tuning and adaptation of the stroke timing by dynamically (e.g., on a stroke cycle interval basis) adjusting motor RPM to optimize a broad set of configurable parameters, including overall system efficiency and various stress conditions. In some examples, the controller can be implemented by a moderately capable local processor, so as to avoid exceedingly complex mathematical computations that may delay adjustment of the stroke timing. In some examples, the controller utilizes a combination of mathematically predictive and partially predictive empirical (e.g., Perturb-now and Observe-later) algorithms for dynamic stroke-timing modification.
Referring first to
The rod system (e.g., the polish rod 108 and the sucker rod 116) carries a continuously varying load due to the reciprocating motion of the horsehead 106 and the associated fluid movement of the pump 110. The maximum load occurs shortly after the beginning of the upstroke, when the riding valve closes. The polish rod 108 must carry the full weight of the fluids, the rod system, and the added inertial effects that occur as the motion of the rods is reversed. The minimum load occurs shortly after the beginning of the downstroke, as the riding valve opens. At that point, the rod system no longer carries the fluid load and the inertial effects are reversed, thereby reducing the total rod load below the weight of the rods and the produced fluids. The rod system continuously stretches and contracts in response to the varying load. In addition, because of the elasticity of the sucker rod 116, which is usually of substantial length (e.g., over 5,000 ft.), large stress waves run up and down the rod in response to the various applied forces (e.g., the above described loads, as well as mechanical and fluid friction). These stress waves may cause the sucker rod 116 to break if they become excessive.
The walking beam 104 is driven by powertrain assembly including a prime mover 118, a reduction gearbox 120, and a piloting shaft 122 (sometimes referred to as a “Pitman arm”). The prime mover 118 drives the gearbox 120 through a belt system (not shown). The gearbox 120 imparts rotary motion into the proximal end of the piloting shaft 122 via a rotating crank 123. The distal end of the piloting shaft 122 is coupled to a rear end of the walking beam 104, and rocks the walking beam 104 back and forth in a pivoting motion about the frame 102, thus moving the horsehead 106 up and down as described above. In this example, the free end of the rotating crank 123 carries a counterweight 124, which at least partially offsets the weight of the rods (e.g., the polish rod 108 and sucker rod 116) and fluid to assist the prime mover 118 during the upstroke of the pump 110, and provides substantial resistance against the prime mover 118 to inhibit freefall of the rod system and pump 110 during the downstroke.
In this example, the prime mover 118 is provided in the form of an electrical induction motor (e.g., a high efficiency Nema B motor) operated by a variable frequency drive (“VFD”) 126. The VFD 126 regulates the speed and torque output of the prime mover 118 by varying input frequency and voltage. In some embodiments, the VFD 126 includes appropriate hardware and circuitry (e.g., processors, memory, and I/O components) to regulate the speed and torque output based on one or more setpoint values. A controller 128 communicatively coupled to the VFD 126 includes appropriate hardware and circuitry (e.g., processors, memory, and I/O components) so as to achieve any of the control operations described herein. For example, the controller 128 may be configured to provide a target motor speed and/or a target motor torque setpoint to the VFD 126. In some implementations, the controller 128 may be implemented locally with the VFD 126 (e.g., fully or partially integrated therewith) or located at a remote location with communication between the components being conducted across a wired or wireless link (e.g., wired radio, the Internet, wireless cellular network, telephone network or satellite communication). In some examples, the prime mover 118 is further equipped with a regenerative drive provided for the dual purpose of providing a braking (or negative) torque to control the descent of the rod system and simultaneously converting the kinetic energy of the downward moving rod system into electrical power. Thus, the pumpjack is able to recapture at least a portion of its power draw from the grid as it operates according to the various tuning and monitoring techniques described in the present disclosure.
One or more aspects of the present disclosure are based on a realization that the timing of the stroke cycle of the pump 110 can be dynamically adjusted via the controller 128 without physically altering the pumpjack components discussed above (e.g., the gearbox 120, the piloting shaft 122, and the crank 123). For example, the controller 128 can provide a motor speed profile to the VFD 126 that includes a plurality of varying target motor speeds corresponding to each of a plurality of discrete control periods within a pump stroke cycle. In some embodiments, the motor speed profile may be determined by the controller 128 so as to improve the production of fluid from the pump 110. In some embodiments, the motor speed profile may be determined by the controller 128 so as to mitigate or decrease the risk of pump-off (a condition where the lower portion of the pump barrel is not filled with fluid during the upstroke, causing the plunger to pound into the fluid during the downstroke, which sends a damaging shockwave through the rod system), high stress or fatigue load limits in the rod system (e.g., the polish and sucker rods), and/or high torque in the gearbox.
In some embodiments, the controller 128 determines an appropriate motor speed profile in response to feedback received during a previous stroke cycle of the pump 110 from one or more sensors distributed across the pumpjack 100. In this example, the pumpjack 100 includes a load cell sensor 130, a crank rotation sensor 132, and a motor shaft position sensor 134 (each of which is depicted schematically in
As illustrated in the graph 200, the adjusted stroke timing curve 204 has the same duration as the default stroke timing curve 202. Thus, the adjusted stroke timing curve 204 provides an increase in pumping efficiency without affecting the overall “pumping rate” (by “pumping rate” we refer to the number of pump stroke cycles executed in a given time period—e.g., strokes per minute (SPM)). The increase in pump efficiency and pump stroke length combined with a constant pumping rate results in an increased fluid production rate. The fluid production rate is typically measured in units of barrels of fluid per day (BFPD). In some embodiments, such as described below, the downstroke time may be even further decreased to increase the pumping rate relative to the default stroke timing curve and further increase the fluid production rate.
Referring next to
In some embodiments, the RPM adjustment values are determined according to a pumpjack optimization algorithm implemented by the controller 128. The pumpjack optimization algorithm may include a tuning mode and a monitoring mode. While operating in the tuning mode, the algorithm may determine one or more RPM adjustment values that will improve fluid production. While operating in the monitoring mode, the algorithm may determine one or more RPM adjustment values that will relieve one or more detrimental operating conditions (e.g., the onset of pump-off, high stress on the rod system, and/or high torque at the gearbox) detected based on sensory feedback.
As discussed above with reference to
In some embodiments, one or more of the RPM adjustment values is determined based on sensory feedback, such as may be received by the controller 128 from the load cell sensor 130, the crank rotation sensor 132, and/or the motor shaft position sensor 134 can be used to determine suitable RPM adjustment values. As noted above, the feedback from the crank rotation sensor 132 and the motor shaft position sensor 134 can be used to determine the position of the polish rod 108, and feedback from the load cell sensor 130 is proportional to the load carried by the polish rod 108. This position and load data can be used to construct a synthetic surface dynamometer card (e.g., using techniques described in U.S. Pat. No. 4,490,094) representative of loading at the polish rod 108 during a stroke cycle. The surface dynamometer card can then be transformed using techniques known to those of skill in the art (such as described in U.S. Pat. No. 3,343,409) into a downhole pump card representative of loading at the pump 110 during a stroke cycle. The surface dynamometer card and the downhole pump card can be used to detect or predict the conditions that are detrimental to pumpjack fluid production, such as the onset of pump-off, high stress on the rod system, and high torque at the gearbox. Thus, in some examples, the pumpjack optimization algorithm may conduct this type of analysis and appropriately respond by deriving an appropriate motor speed adjustment table 304 to relieve the detrimental condition by: (1) implementing a limited increment amount of one or more RPM adjustment values; (2) implementing one or more null or zero RPM adjustment values; and/or (3) implementing a decrement for one or more RPM adjustment values.
The graph 400 of
The graph 500 of
The graph 600 of
The graph 700 of
In some embodiments, the tuning mode and/or the monitoring mode of the pumpjack optimization algorithm may include an iterative process for progressively improving pumpjack performance. In some examples, the iterative process may proceed continuously over a sequence of two or more adjacent pump stroke cycles. So, one or more of the above.. described techniques may be repeated through multiple iterations to gradually increase fluid production.
In some embodiments, iterative tuning of the pumpjack may take place over several stroke cycles. In some examples, RPM adjustments to the motor speed profile may be conducted in successive cycles of the tuning process, such as shown in the graph 800 of
The graphs of
This iterative tuning process, while demonstrated across two pump stroke cycles in this example, may be repeated any number of times to achieve an optimized motor speed profile. As noted above, such adjustments of the motor speed profile may be conducted across successive cycles or between one or more intervening cycles. The first and second motor speed adjustment curves 902 and 908 may be derived according to any suitable algorithm for improving fluid production, such as those described above involving increased pump efficiency, increased pumping rate, as well as preventing, relieving or mitigating detrimental operating conditions using sensory feedback. Furthermore, a similar process may be performed to adjust the motor speed profile during a monitoring mode. For example, the controller may detect one or more detrimental operating conditions based on sensory feedback and derive an appropriate motor speed adjustment curve to relieve the condition. In some embodiments, after a detrimental condition detected during the monitoring mode has been relieved, the pumpjack controller may re-enter the tuning mode in an attempt to improve fluid production.
According to the process 1000 of
According to the process 1100 or
According to the process 1200 of
As described in detail above, the prime mover of a pumpjack may be operated according to varying motor speed profile to improve fluid production and prevent or inhibit certain adverse operating conditions. The motor speed profile includes a plurality of target motor speeds corresponding to each of a plurality of discrete control periods within the stroke cycle. The VFD regulates the speed and torque output of the pumpjack motor by varying input frequency and voltage. In some embodiments, a controller coupled to the VFD can be configured (e.g., appropriately programmed) to implement a dynamic torque control technique where the torque of the motor is adapted to meet, but not exceed (at least beyond a predetermined safety margin), the load requirements for operation at the prescribed motor speed for each control period of the current stroke cycle. The voltage applied creates the potential for torque within the motor. Thus, the applied voltage may be reduced according to a reduction in torque required by the motor. In some examples, the voltage required may be accurately predicted and regulated based upon historical pump cycle data, allowing for prevention of stall conditions (i.e., where the motor is starved of torque) and optimization of the efficiency of the motor by applying only the voltage required to deliver that torque. Accordingly, decreased energy consumption may be achieved by using dynamic torque control. The graph 1300 of
According to the process 1400 of
The graph 1500 of
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the inventions.
Claims
1. A pumpjack motor system, comprising:
- an electric motor coupled to a gear box of a pumpjack;
- one or more sensors mounted to monitor at least one operating condition of the pumpjack during operation of the motor; and
- a drive controller coupled to the motor and operable to control the motor in accordance with a varying motor speed profile over a pumping cycle of the pumpjack, while applying voltage to the motor;
- wherein the drive controller is configured to determine, based on sensory feedback from the one or more sensors, a pumping cycle load profile; automatically determine, based on the pumping cycle load profile, a varying voltage profile; and to control the motor in accordance with the varying motor speed profile while applying the varying voltage profile to the motor.
2. The pumpjack motor system of claim 1, wherein the varying motor speed profile comprises an altered version of a stroke timing curve implemented during one or more previous pumping cycles of the pumpjack.
3. The pumpjack motor system of claim 1, wherein the varying motor speed profile comprises a plurality of target motor speeds corresponding to each of a plurality of discrete control periods within the pumping cycle of the pump jack.
4. The pumpjack motor system of claim 3, wherein the pumping cycle load profile comprises a plurality of torque loads corresponding to each of the plurality of discrete control periods.
5. The pumpjack motor system of claim 3, wherein the plurality of discrete control periods comprises at least 100 control periods.
6. The pumpjack motor system of claim 3, wherein one or more of the plurality of discrete control periods of the first pump stroke cycle has a time duration of between about 5 and 100 milliseconds.
7. The pumpjack motor system of claim 1, wherein the drive controller is configured to determine the pumping cycle load profile as a mathematical prediction based on:
- historical sensory feedback provided by the one or more sensors during one or more previous pumping cycles of the pumpjack; and/or
- adjustments between the varying motor speed profile and a stroke timing curve implemented during one or more previous pumping cycles of the pumpjack.
8. The pumpjack motor system of a claim 1, wherein at least one of the sensors comprises a load sensor.
9. The pumpjack motor system of claim 8, wherein the load sensor is responsive to load of a polish rod of the pumpjack.
10. The pumpjack motor system of claim 1, wherein at least one of the sensors comprises a crank rotation sensor.
11. The pumpjack motor system of claim 1, wherein at least one of the sensors comprises a motor shaft position sensor.
12. The pumpjack motor system of claim 1, wherein at least one of the sensors comprises a motor current sensor.
13. A method of operating a pumpjack, comprising:
- operating an electric motor driving the pumpjack according to a varying motor speed profile during a first pump stroke cycle of the pumpjack, the motor speed profile comprising a plurality of target motor speeds corresponding to each of a plurality of discrete control periods;
- receiving sensory feedback from one or more sensors mounted to monitor at least one operating condition of the pumpjack, the sensory feedback comprising data collected during the first pump stroke cycle;
- determining a pump cycle load profile based on the sensory feedback, the pump cycle load profile corresponding to a plurality of torque loads of the electric motor at each of the discrete control periods of the first pump stroke cycle;
- automatically determining, based on the pump cycle load profile, a varying voltage profile; and
- operating the electric motor according to the varying motor speed profile and the varying voltage profile during a second pump stroke cycle of the pumpjack.
14. The method of claim 13, wherein the varying motor speed profile comprises an altered version of a stroke timing curve implemented during one or more previous pumping cycles of the pumpjack.
15. The method of claim 13, wherein the plurality of discrete control periods comprises at least 100 control periods.
16. The method of claim 13, wherein at least one of the plurality of discrete control periods of the first pump stroke cycle has a time duration of between about 5 and 100 milliseconds.
17. The method of claim 13, wherein determining the pump cycle load profile comprises implementing a mathematical prediction algorithm based on:
- historical sensory feedback provided by the one or more sensors during one or more previous pumping cycles of the pumpjack; and/or
- adjustments between the varying motor speed profile and one or more stroke timing curves implemented during one or more previous pumping cycles of the pumpjack.
18. The method of claim 13, wherein at least one of the sensors comprises a load sensor.
19. The method of claim 18, wherein the load sensor is responsive to load of a polish rod of the pumpjack.
20. The method of claim 13, wherein at least one of the sensors comprises a crank rotation sensor.
21. The method of claim 13, wherein at least one of the sensors comprises a motor shaft position sensor.
22. The method of claim 13, wherein at least one of the sensors comprises a motor current sensor.
Type: Application
Filed: Jun 23, 2016
Publication Date: Jan 5, 2017
Inventors: Bertrand Jeffery Williams (Austin, TX), Victor Sauers, II (Cedar Park, TX)
Application Number: 15/191,136