SYSTEM AND METHOD FOR MONITORING ROD POSITION AND ROTATION

Abstract

A system and method for monitoring a rod string used in a pumpjack machine comprises a load-cell device including at least one sensor, a controller configured to receive a signal from the load-cell device and control a pump operation. The load-cell device is attached to a part of the pumpjack machine and wirelessly communicates with the controller to determine the pump operation of the pumpjack machine. The load-cell device is capable of generating a position marker to determine a location of the rod string during a cyclic event of the pumpjack machine. Further, at least one sensor of the load-cell device includes a RF transceiver configured to detect a RF transmission path between the load-cell device and the controller such that the controller is configured to monitor and use the detected RF transmission path to indicate a rotational position and/or a rotational rate of the rod string.

Description

FIELD

The present disclosure generally relates to a system and method for monitoring a rod of a pumpjack machine, and particularly relates to a system and method for monitoring the rod's position and rotation in the pumpjack machine.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

A pumpjack machine is a device that can be used to pump for oil on land. A hole can be drilled into the ground and cemented with a well casing, resulting in a vertical cavity. An assembled series of rods referred to a rod string, can be inserted into the vertical cavity and moved up and down using the rod pump. A plunger can be attached to the bottom of the well. On the downward stroke, the plunger can be filled with oil, and on the upward stroke the oil can be transported to the surface, where it can be extracted and put into barrels.

Unsatisfactory operation and performance results from defects in the pumpjack machine. These defects include gas interference, tubing movement, excessive fluid slippage, top and bottom pump tagging, plunger sticking or excessive friction (e.g., due to solids in between the plunger and the barrel), rod string's position deviation from the vertical axis of the well, among others. Thus, it can be desirable to monitor rod pumps in order to identify when unsatisfactory operation is occurring so that corrective maintenance and operation can be performed.

SUMMARY

The present disclosure provides a monitoring system having a wireless load-cell device used in a pumpjack machine having a gear box and a prime mover. Although depicted in a pumpjack machine, it should be understood that the system described in the present disclosure, is not limited to the pumpjack machine and could extend to other machines to sense a position and/or a rotation of a component used in other machines.

According to an exemplary form of the present disclosure, a system for monitoring a rod string used in a pumpjack machine having a gear box and a prime mover comprises a load-cell device including at least one sensor, and a controller configured to receive a signal from the load-cell device and control a pump operation of the pumpjack machine. The load-cell device is attached to a part of the pumpjack machine and wirelessly communicates with the controller to determine the pump operation of the pumpjack machine. Further, the load-cell device is capable of generating a position marker to determine a location of the rod string during a cyclic event of the pumpjack machine.

According to a further aspect of the present disclosure, the load-cell device is in communication with a base receiving unit of the controller to transmit the signal having the generated position marker. The controller is configured to detect an amount of slippage occurring between a motor output pulley of the prime mover and an input pulley of the gear box and determine a calculated position of the rod string based on the detected slippage. Further, the controller is configured to phase the calculated position of the rod string at the location of the rod string determined by the generated position marker.

According to a further aspect of the present disclosure, the load-cell device is securely placed on the rod string including a polished rod, which is connected to the top end of the rod string, and the load-cell device is wirelessly in communication with the controller of the pumpjack machine. Further, at least one sensor of the load-cell device includes an accelerometer, a magnetometer, a Radio-Frequency (RF) transceiver, a proximity sensor, or a strain gauge to generate a position marker of the rod string.

According to a further aspect of the present disclosure, the pumpjack machine further includes a polished rod connected to a top end of the rod string and a rod rotator installed at the polished rod. The load-cell device is securely attached to the polished rod (i.e., a part of the rod string) and placed above the rod rotator and beneath a rod retaining clamp. The load-cell device attached to the polished rod rotates together with the rod string such that the load-cell device is configured to index an angular position of the rod string during the pumpjack stroke.

According to a further aspect of the present disclosure, the at least one sensor of the load-cell device includes a RF transceiver configured to detect a RF transmission path between the load-cell device and a base receiving unit of the controller. The controller is configured to monitor and use the detected RF transmission path to indicate a rotational position and/or a rotational rate of the rod string for controlling the pump operation of the pumpjack machine.

According to another aspect of the present disclosure, a method for monitoring a rod string used in a pumpjack machine having a gear box and a prime mover includes the steps of providing a load-cell device having at least one sensor, providing a controller configured to receive a signal from the load-cell device and control a pump operation of the pumpjack machine, generating a position marker from the at least one sensor of the load-cell device, communication wirelessly between the load-cell device and the controller to transmit the generated position marker, and controlling the pump operation of the pumpjack machine based on the position marker generated from the load-cell device.

According to a further aspect of the present disclosure, the step of controlling the pump operation of the pumpjack machine includes the step of detecting an amount of slippage occurring between a motor output pulley of the prime mover and an input pulley of the gear box. The step of controlling the pump operation of the pumpjack machine further includes the steps of determining a calculated position of the rod string based on the detected slippage and phasing the calculated position of the rod string at the location of the rod string determined by the generated position marker.

According to another aspect of the present disclosure, a method for monitoring a rod string used in a pumpjack machine having a polished rod connected to a top end of the rod string and a rod rotator installed at the polished rod includes the steps of providing a load-cell device having at least one sensor, providing a controller configured to receive a signal from the load-cell device and control a pump operation of the pumpjack machine, detecting a RF transmission path between the load-cell device and a base receiving unit of the controller, and controlling the pump operation of the pumpjack machine based on the detected RF transmission path.

According to a further aspect of the present disclosure, the step of controlling the pump operation of the pumpjack machine includes the step of monitoring the RF transmission path to indicate a rotational position and/or a rotational rate of the rod string.

Further details and benefits will become apparent from the following detailed description of the appended drawings. The drawings are provided herewith purely for illustrative purposes and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a schematic view of a pump jack machine in accordance with an exemplary embodiment of the present disclosure;

FIG. 2 is a detailed view of a load-cell device placed on a rod string of the pumpjack machine of FIG. 1;

FIG. 3 is a diagram of the load-cell device used in the pumpjack machine of FIG. 2; and

FIGS. 4A-4C show a graph having rod load and RF signal strength of the pumpjack machine of FIG. 1.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

Oil well pumping units are being automated with controllers that enable the pump motor to be run at changing speed over time, varying speeds within a pumping cycle, or even deactivated for a period of time, based on the state of the fluid fill below the pump near the bottom of the well. The state of the fluid fill in the pumping volume near the bottom of the well is typically inferred by detecting changes in the weight of the rod string as fluid buoyancy forces change the apparent weight of the rod string as the pump submerges into and emerges from the fluid bath. If rod position is also known, a force-distance work diagram can be created in real time to determine the instantaneous pump work over each cyclical event of the pumpjack. The work diagram, commonly known, as a ‘surface card’, is a useful tool for determining the optimal operation speed of the pumpjack that maximizes fluid extraction while properly protecting pumpjack hardware from potentially damaging forces.

The surface card can be used to generate a second force-distance work diagram, known as a ‘downhole card’, which is a measure of the actual work being down by the pump at the pump-fluid interface near the bottom of the well. These two cards are linked together by accounting for the gravitational forces acting on the rod string (i.e., the rod string weight), inertial forces required to accelerate and decelerate the rod string and fluid volume above the pump, frictional forces acting on the rod string by the well bore, and dynamic elastic forces within the rod string created by the changing tensile forces acting on the rod string inertial resistance. By accounting for these body forces, an external force acting on the bottom face of the pump by the fluid pressure can be calculated, and together with a calculated pump face position, can be used to create a downhole card. The downhole card is an even more direct indication of the state of the fluid fill within the pump working volume and is a primary tool for making pumpjack control decisions.

Generation of the surface and downhole cards is contingent on having good position data for the rod string throughout the pumpjack cyclical event. The kinematics of the pumpjack are well known from its design, and the gearbox output speed is also known as the drive motor is being electronically controlled and the gear ratio is fixed. Thus, instantaneous position of the rod string throughout the cyclic event of the pumpjack may be calculated as a function of these knowns.

Position Sensing

In accordance with an exemplary embodiment of the present disclosure, FIG. 1 shows a pumpjack machine 10 that is generally illustrated in a typical vertical well. However, this should not be considered limiting. For instance, the pumpjack machine 10 may also be utilized in a horizontally drilled well. The pumpjack machine 10 includes a base 12 that supports a walking beam 14 where the walking beam 14 is pivotally attached to the base 12. The walking beam 14 has a distal end 16 and a proximal end 18. The pumpjack machine 10 further includes a horsehead 20 that is attached to the distal end 16 of the walking beam 14 and an optional equalizer (not shown) that may be secured to the proximal end 18 of the walking beam 14.

As shown in FIG. 1, the pumpjack machine 10 further includes a crank 22 having a first end 24 that is attached to the proximal end 18 of the walking beam 14 and a second end 26 that is attached to a crank arm 28 that engages a gear box 30 driven by a prime mover 32. The prime mover 32 is typically an electrically powered motor, such as with an alternating current (AC) or a direct current (DC) or with a suitable motor drive, including a gas or diesel engine used to power a generator that supplies electric power to the prime mover 32.

The prime mover 32 drives the gear box 30 which in turn moves the crank arm 28. As the crank arm 28 moves, the crank 24 moves upward in an eccentric path, which allows the horsehead 20 and a rod string 34 (i.e., a sucker rod) including a downhole pump assembly 36, which is attached to the horsehead 20 to move downward. As the crank 22 is moved downward, the horsehead 20 is raised along with the rod string 34 and the downhole pump assembly 36, which causes liquid to be pumped from the well. A counterweight 38 is attached to the crank 22 to aid in raising the horsehead 20.

In FIG. 1, further, a proximal end of at least one cable 40 is attached to the horsehead 20 and has sufficient flexibility to follow a cammed surface on the horsehead 20. The at least one cable 40 has sufficient strength to raise the downhole pump assembly 36 and the rod string 34 along a column of fluid within the well hole. A distal end of the at least one cable 40 is securely connected to a polished rod 42, which is the top-most rod in the rod string 34. Further, the rod string 34 has a downhole end 44 to which the downhole pump assembly 36 is attached, and an upper end 46 attached to the polished rod 42 that moves through a casing head and a stuffing box 48. A tolerance between the stuffing box 48 and the polished rod 42 is sufficiently small to prevent liquid from exiting through the interface between the stuffing box 48 and the polished rod 42.

As shown in FIG. 1, the pumpjack machine 10 includes a controller 50 that is in communication with the prime mover 32 to operate the pump units including the horsehead 20, the rod string 34, and the downhole pump assembly 36. During normal operation condition, the horsehead 20 is moved upward, the rod string 34 including the polished rod 42 and the downhole pump assembly 36 is moved upward, and as the horsehead 20 is moved downward, the rod string including the polished rod 42 and the downhole pump assembly 36 is moved downward. Accordingly, the pump units including the rod string 34 and the downhole pump assembly 36 are being automated with the controller 50 that enables pump motor to be run at changing speeds over time, varying speeds within a pumping cycle, or even deactivated for a period of time, based on the state of the fluid fill below the pump near the bottom of the well.

In a pumpjack machine 10, the controller 50 is configured to use the surface card for determining the optimal operation speed of the pumpjack and also the downhole card for measuring the actual work being done by the pump at the pump-fluid interface near the bottom of the well. In accordance with an exemplary embodiment of the present disclosure, the controller 50 is further configured to monitor the amount of slippage that has occurred between the motor output pulley of the prime mover 32 and the input pulley of the gear box 30 to operate the pumpjack machine 10. Thus, phasing the calculated rod string position for a given pump cycle with the actual rod string is achieved by indexing the calculated position to a specific marker event.

This marker event is typically generated by placing a Hall Effect sensor (not shown) at the output crank of the gearbox at a known position such as top or bottom of stroke. The controller is then informed as to which of these two positions is represented by the marker event. Once the marker is detected by the controller 50, the controller 50 may now phase a calculated position signature at the actual rod string marker location, and then use the corrected rod string position signature together with the measured load signature to create a surface and downhole card. It is important to generate a position marker that is accurate to within a few degrees of crank rotation as improper phasing of the force-position diagram can lead to improper assessment of the pump performance and significant error in determining cyclic pump work and power.

In accordance with an exemplary embodiment of the present disclosure, FIG. 2 shows a monitoring system 100 to generate an emulated position marker signal may be attached to the pumpjack machine 10. As shown in FIG. 2, the monitoring system 100 includes a load-cell device 102 that is in communication with the controller 50 to control the operation of the pumpjack machine 10. The load-cell device 102 of the monitoring system 100 is securely attached to the polished rod 42 of the rod string 34 and wirelessly communicates with the controller 50 of the pumpjack machine 10. As shown in FIG. 2, the use of the wireless load-cell 102 may reduce or obviate the cost and complexity of installing a conventional Hall Effect sensor. The wireless load-cell device 102 attached to the rod string 34 is configured to detect the rod top/bottom-of-stroke, rod load and rod rotation, which will be described later.

In the present disclosure, various techniques may be used to generate a position marker by integrating a variety of sensors into the wireless load-cell device 102. Further, as shown in FIG. 3, the load-cell device 102 may include an accelerometer 104 (having a three-axis accelerometer sensor), a magnetometer 106, a radio frequency (RF) transceiver 108, a proximity sensor 110, and/or a strain gauge 112. The various on-board sensors installed in the load-cell device 102 may provide valuable information for determining an accurate position marker during cyclical rod string travel of the pumpjack machine 10 of FIG. 1.

The accelerometer 104 is capable of detecting acceleration of the crank-slider mechanism where it tends to be highest during top and bottom stroke. Other high frequency signatures may overshadow the lower frequency motion signature, however, requiring data filtering techniques. In addition, the accelerometer 104 is configured to sense a circumferential acceleration of the pump rod (i.e., rod string). The magnetometer 106 is capable of detecting changes in the magnetic flux path as the exposed portion of the pump rod enters and exits the well head near bottom of the stroke, and approaches the walking beam 14 (for pumpjack configuration) near top of stroke. The onboard wireless RF transceiver 108 of the wireless load-cell 102 has a changing attenuation path throughout the entire stroke and could be used to detect rod string motion based on the reception strength/quality signal sent between paired transmitters and receivers. The proximity sensor 110 may be used to detect the approaching well head and/or walking beam to detect stroke reversal. Finally, the strain gauge signal obtained from the load cell itself has a unique change in measured load that occurs at stroke reversal. Each of these signals has advantageous and disadvantageous, and may require a combination of signals to provide an accurate stroke reversal signal that may be used to emulate a hall-effect signal.

Rod Rotation

Referring back to FIGS. 1 and 2, an oil well bore and pump rod string 34 may penetrate several miles into the earth's crust. The deviation in the bore hole from its initial axis depends on several factors including the local composition of the earth being drilled into as well as the quality and control capability of the drilling equipment. As shown in FIG. 2, further, pumping oil out of deviated well bores often requires installation of a rod rotator 52 at the top of the rod string 34 (i.e., at the polished rod) to slowly rotate the rod during pumping operations in order to promote even rod wear as the rod string rubs against the deviated well tubing. Rod rotation is typically not monitored remotely, but rather observed during pump serving, often times by attaching a zip tie to the rod string 34 and detecting rotary motion of the zip tie over several strokes of the pumpjack machine 10. The rod rotator device failure may cause the rod string 34 to prematurely wear out resulting in early, costly replacement of the damaged rod string.

In one approach, wired load cells (not shown), which are used to measure instantaneous rod loads for purposes of controlling the pumpjack speed, are typically installed beneath the rod rotator 52 to keep the load cell from rotating as a cable is attached to the load cell providing power and returning the load signal to the controller. According to an exemplary embodiment of FIG. 2 in the present disclosure, a wireless load-cell device 102 may be placed above the rod rotator 52 and beneath a rod retaining clamp 54, thus, rotating with the rod string 34 as the rod rotator top plate indexes the rod angular position during each pumpjack stroke.

As the load-cell device 102 rotates, the RF transmission path between the wireless load-cell 102 and a base receiving unit 51 of the pumpjack controller 50 changes resulting in a variation of the RF energy level and link quality. These parameters tend to remain fairly constant during the 180 degree portion of rotation that faces the pumpjack, and tend to follow a sinusoidal waveform on the back half of rotation with a minimum occurring when the load cell's RF emissions window is pointing exactly 180 degrees away from the pumpjack. (See FIGS. 4A-4C as examples of the sinusoidal waveform). Accordingly, monitoring this variation in RF transmission parameters may be used as a direct indicator of rod string's rotational position and rotational rate, and may be reported to the pumpjack controller 50 by the base receiving unit 51 via analog and/or digital means. The signal is useful in detecting potential failure of normal rod string rotation operation due to either a failure of the rod rotator mechanism and/or excessive angular load on the rod string downhole. In another approach, a gyroscope MEMS (not shown) is another mechanism by which angular portion could be determined, however, dc drift of the sensor would need to be accounted for. A magnetometer and/or compass MEMS (not shown) could be also used to determine changes in magnetic field strength and/or direction as the rod rotates.

When excessive downhole angular loads occur on the rod string 34, thus keeping the lower portion of the rod string 34 from rotating, the rod string 34 begins to store torsional energy as the rod rotator 52 continues to rotate the top of the rod string 34. This torsional energy continues to increase until it ultimately exceeds the downhole torsional load, thus resulting in a rapid release of the torsional energy in the rod string 34. This condition may create excessive static and dynamic loads on the top plate of the rod rotator 52 leading to degradation and/or failure of the rod rotator 52. The RF signal strength may not be able to observe this phenomenon as the top of the rod string continues to rotate.

Referring back to FIG. 3 of the present disclosure, the load-cell device 102 includes the accelerometer 104 having a three-axis accelerometer sensor to detect a rapid change in torsional rod string motion, however, by observing abnormal spikes in the tangential component of acceleration as found from the two radial axes of the accelerometer 104. Alternatively, a gyroscope MEMS (not shown) could similarly be used to detect a rapid change in angular position. As discussed above, the accelerometer 104 configured to sense the circumferential acceleration of the rod string 34 may be included. Thus, a circumferential accelerometer measurement (i.e., x-axis) near a bottom of a stroke of the rod string 34 (i.e., when a rod rotation indexer or rod rotator 52 is attempting to rotate the rod string 34) could potentially indicate a unique signature if the rod rotation indexer is properly functioning or not.

With a dual channel wireless load-cell, further, a second strain channel may be used to monitor torsional strain which is transmitted from the rod rotator plate through the load-cell body and into the rod string, and subsequently alert the controller when excessive torsional string occurs in order to take corrective actions to protect the rod string from a potentially damaging torsional energy storage and release event. These corrective actions may include a change in well operational speeds, a well shutdown, or deactivation of the rod rotation until torsional strain is relieved.

Since the monitoring system 100 has on-board ‘position’ integration from a Y-axis (i.e., along a length of the pump rod) accelerometer measurement, the potential to ‘time’ observation of rod rotation with instantaneous stroke position may be thereby provided, and thus only reading when needed after a bottom of the stroke is encountered and the rod rotator 52 has indexed. Due to the function of the load-cell device 102 of the present disclosure, the overall power consumption of the sensor used may be reduced. One advantage of the monitoring system 100 described herein is that a quantity of strokes required to achieve each rotation may be tracked and thus, provide an indicator of the variability and/or degradation of the performance of the rod rotator 52. In addition, the quantity of the stroke described above may be tracked in the controller 50 by monitoring total number of strokes in-between rotation pulses, and the system described herein provides this information independent of the ability of the controller to do so. Such information may, for example, be provided to a smart phone app in communication with the controller to give a well operator an indication of rotation performance.

The foregoing description of various forms of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications or variations are possible in light of the above teachings. The forms discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various forms and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

1. A system for monitoring a rod string used in a pumpjack machine having a gear box and a prime mover, the system comprising: a load-cell device including at least one sensor; anda controller configured to receive a signal from the load-cell device and control a pump operation of the pumpjack machine,wherein the load-cell device is attached to a part of the pumpjack machine and wirelessly communicates with the controller to determine the pump operation of the pumpjack machine.

2. The system of claim 1, wherein the load-cell device is capable of generating a position marker to determine a location of the rod string during a cyclic event of the pumpjack machine.

3. The system of claim 2, wherein the load-cell device is in communication with a base receiving unit of the controller to transmit the signal having the generated position marker.

4. The system of claim 3, wherein the controller is configured to detect an amount of slippage occurring between a motor output pulley of the prime mover and an input pulley of the gear box and determine a calculated position of the rod string based on the detected slippage.

5. The system of claim 4, wherein the controller is configured to phase the calculated position of the rod string at the location of the rod string determined by the generated position marker.

6. The system of claim 1, wherein the load-cell device is securely attached to the rod string and wirelessly in communication with the controller of the pumpjack machine.

7. The system of claim 1, wherein the at least one sensor of the load-cell device includes an accelerometer, a magnetometer, a Radio-Frequency (RF) transceiver, a proximity sensor, or a strain gauge to generate a position marker of the rod string.

8. The system of claim 1, wherein the pumpjack machine further includes a polished rod connected to a top end of the rod string and a rod rotator installed at the polished rod.

9. The system of claim 8, wherein the load-cell device is securely attached to the polished rod, and placed above the rod rotator and beneath a rod retaining clamp.

10. The system of claim 9, wherein the load-cell device attached to the polished rod rotates together with the rod string such that the load-cell device is configured to index an angular position of the rod string during the pumpjack stroke.

11. The system of claim 8, wherein the at least one sensor of the load-cell device includes a RF transceiver configured to detect a RF transmission path between the load-cell device and a base receiving unit of the controller.

12. The system of claim 11, wherein the controller is configured to monitor and use the detected RF transmission path to indicate a rotational position and/or a rotational rate of the rod string for controlling the pump operation of the pumpjack machine.

13. A method for monitoring a rod string used in a pumpjack machine having a gear box and a prime mover, the method includes the steps of: providing a load-cell device including at least one sensor;providing a controller configured to receive a signal from the load-cell device and control a pump operation of the pumpjack machine;generating a position marker from the at least one sensor of the load-cell device;communicating wirelessly between the load-cell device and the controller to transmit the generated position marker; andcontrolling the pump operation of the pumpjack machine based on the generated position marker generated from the load-cell device.

14. The method of claim 13, wherein the step of controlling the pump operation of the pumpjack machine includes the step of detecting an amount of slippage occurring between a motor output pulley of the prime mover and an input pulley of the gear box.

15. The method of claim 14, wherein the step of controlling the pump operation of the pumpjack machine includes the step of determining a calculated position of the rod string based on the detected slippage.

16. The method of claim 15, wherein the step of controlling the pump operation of the pumpjack machine includes the step of phasing the calculated position of the rod string at the location of the rod string determined by the generated position marker.

17. The method of claim 13, wherein the step of providing the load-cell device includes the step of placing the load-cell device on the rod string.

18. A method for monitoring a rod string used in a pumpjack machine having a polished rod connected to a top end of the rod string and a rod rotator installed at the polished rod, the method includes the steps of: providing a load-cell device including at least one sensor;providing a controller configured to receive a signal from the load-cell device and control a pump operation of the pumpjack machine;detecting a RF transmission path between the load-cell device and a base receiving unit of the controller; andcontrolling the pump operation of the pumpjack machine based on the detected RF transmission path.

19. The method of claim 18, wherein the step of controlling the pump operation of the pumpjack machine includes the step of monitoring the RF transmission path to indicate a rotational position and/or a rotational rate of the rod string.

20. The method of claim 18, wherein the step of providing the load-cell device of the pumpjack machine includes the steps of attaching the load-cell device to the polished rod, and placing above the rod rotator and beneath a rod retaining clamp.