CA2309523A1 - Wireless pump jack dynamometer - Google Patents

Abstract

A sucker rod pump dynamometer has a movable signal device secured to and movable with the polish rod and which transmits a first signal and receives wireless signals. A fixed signal source receives the first signal and returns a wireless return signal. A controller directs the movable signal device to send the first signal and measures the elapsed time between its transmission and the receipt of the wireless return signal, be it a reflection of the first signal or an independent signal emitted by the fixed signal source. Preferably, the first signal is an infrared signal which instantaneously triggers the second signal device to return an ultrasound return signal; the reverse also being a preferred embodiment. If both the first and return signals are ultrasonic, then the second device introduces a built in delay to permit spurious reflections to dissipate. The controller calculates the polish rod position based upon the elapsed time and the speed of travel of the first and wireless return signals. Multiple calculated positions over time permit rod velocity to be determined. The controller further monitors the load on the polish rod. A data radio connected to the controller wirelessly transmits information regarding polish rod load and position from the controller to a remote computer.

Description

4 This invention relates to method and apparatus for monitoring the operation of sucker rod pumping units and more particularly for determining 6 conditions of the polish rod, which are indicative of the status of a downhole 7 pump.

Apparatus for monitoring sucker rod well pumping units are 11 commonly referred to as "sucker rod pump dynamometers". A typical 12 conventional sucker rod pump dynamometer has a load cell mounted on the 13 polish rod, between the bottom polish rod clamp and the carrier bar and a 14 position sensor situated on the ground below the load cell and attached to it by a steel cable. The load cell and a position sensor are connected by electrical cable 16 to electronic conditioning interfacing circuits placed nearby. Electrical cable may 17 be used to connect conditioning circuits to a computer in a service vehicle some 18 distance away.
19 As the pump jack reciprocates during its normal pumping action it operates the position sensor by pulling the steel cable which rotates a spring-21 loaded drum. The drum is connected to a potentiometer, which converts position 22 to an electrical value for output to the electronic conditioning interface circuits.
23 The computer calculates, stores and displays a plot of load on the sucker rod 24 versus the position of the rod in its cycle.

1 One problem with the conventional equipment is that the electrical 2 cables are subject to damage including that resulting from the rough 3 environment generally or from becoming entangled in pumping equipment. If 4 entangled, the cables are either pulled apart by the pump jack movement or the cable pulls the load cell right off of the polish rod. Further, repeated connecting 6 and disconnecting of cable connectors causes wear which is an additional and 7 frequent cause of failure. The relatively low signal levels are conducted along 8 relatively long cables resulting in an analog signal which is susceptible to radio 9 frequency noise and can cause incorrect readings. Further, the low-level signal severely restricts the distance that any of the signals may be carried.
11 Yet another, and potentially more significant problem associated 12 with the conventional apparatus is the use of the steel cable with the position 13 sensor. The steel cable can become tangled or kinked thereby causing failure or 14 generate misinformation. Also, if the steel cable is ever allowed to return onto the drum in an uncontrolled manner (e.g. becomes disconnected), the 16 potentiometer will be destroyed. Further, the location of the mechanical position 17 sensor makes it susceptible to becoming inoperative due to being buried in 18 snow.

2 In a preferred form of the invention, a sucker rod pump 3 dynamometer has a movable signal device secured to the polish rod. A polish 4 rod mounted controller directs the movable signal device to send a first signal to a fixed signal receiver either on the ground or the wellhead. This signal can be 6 an ultrasonic signal or a faster triggering signal. The fixed signal receiver returns 7 an upward signal to the movable signal device. At least one of the first or return 8 signals is wireless for providing a distance or rangefinding function. The 9 controller monitors the time which elapses between sending the first signal and receiving the return signal as to enable determination of the distance between 11 the movable and fixed signal devices, indicative of the polish rod position and 12 can be extended to calculate rod velocity. In this way, the cable and drum type 13 potentiometer is replaced. If one of either the first signal or the return signal is a 14 near speed-of-light signal and the other is ultrasonic, then the travel time for the faster signal is negligible compared to that of the slower signal, the elapsed time 16 being substantially the same as the travel time of the slower signal.
Preferably, 17 polish rod position information is combined with polish rod load for transmission 18 to a computer. Wireless data modems enable the computer to be located 19 remote from the pump jack for total elimination of electrical cables.
In a broad aspect of the invention then, apparatus is provided for 21 monitoring a pump jack comprising: a first device movable with the jack's 22 reciprocating polish rod for transmitting a first signal, a second fixed device for 23 receiving the first signal and returning a second wireless signal to the first 24 device, possible merely a reflection of the first signal but more preferably an 1 independent signal, and a controller for establishing the elapsed time between 2 the triggering signal and receipt of return signal and emitting signals indicative of 3 the relative position of the polish rod with respect to the second device.
The 4 controller transmits data indicative of the polish rod position to a remote computer. Coupled with the input from other devices, the controller can transmit 6 rod position, load and environmental conditions to the computer.
7 Preferably the first signal is an ultrasonic signal. In response, the 8 fixed device reflects the first signal or sends a return wireless signal to the 9 movable device, thereby determining its instantaneous position. More preferably, a fast signal such as a radio transmission or light is utilized as one or 11 the other of the first or return signals.
12 More preferably, by producing and analyzing multiple return signals 13 of predetermined timed intervals, the polish rod velocity is also determinable.
14 The above apparatus lends itself to a novel process for monitoring a sucker rod downhole pump, comprising the steps of:
16 (a) moving a first signal device up and down with the polish rod 17 (b) initiating a first signal from the first signal device, preferably 18 being ultrasonic or a near-speed-of-light signal such as radio 19 waves or light, and directing it to a fixed signal source for reflecting or triggering the return of a wireless return signal 21 having a known speed of travel;
22 (c) initiating a timer with initiation of the first signal;

1 (d) receiving the wireless return signal at the first signal device 2 and terminating the timer thereupon for determining an 3 elapsed time indicative of the travel time between initiating 4 of the first signal and the receipt of the wireless return signal at the first signal device; and finally 6 (e) calculating the relative position of the first signal device 7 based upon the elapsed time and the travel speeds of the 8 first and wireless return signals, the position being related to 9 the polish rod position.
As stated, while the fixed signal source or device could merely 11 reflect the first signal as the wireless return signal, it is more preferable that the 12 fixed signal source be a second device which, upon receipt of the first triggering 13 signal, sends a wireless second signal back to the first device.
Advantageously, 14 if both the first and return signals are ultrasonic, then the second device can introduce a predetermined time delay prior to sending the wireless return signal 16 and thereby provide a stronger return signal and allow reflected ultrasonic 17 returns to die out before transmitting the new signal. More advantageously, if 18 the return signal is light-speed, i.e. infrared, then as soon as an ultrasonic first 19 signal is detected, an infrared signals is instantaneously returned, defining the end of the elapsed time and enabling calculation of polish rod position.
21 More preferably, the second device can send multiple return 22 signals at pre-determined intervals for enabling determination of the polish rod 23 speed. Polish rod load can be measured and transmitted with polish rod position 24 information to a remote computer.

2 Figure 1 is a schematic illustration of a pump jack incorporating an 3 apparatus according to the present invention.
4 Figures 2a-2e are schematic representations illustrative of the first and second signals in five situations, related at left to a partial view of a pump 6 jack and wellhead, more particularly:

7 Figure 2a illustrates a downward ultrasonic signal and a reflected 8 ultrasonic upward signal, spurious reflections also being shown;

9 Figure 2b illustrates a downward ultrasonic signal which is received by a second device for implementing a time delay and which then returns an 11 ultrasonic signal;
12 Figure 2c illustrates an ultrasonic downward signal which is 13 received by a second device for instantaneously returning a near speed-of-light 14 signal;
Figure 2d illustrates a near speed-of-light downward signal which is 16 received by a second device for instantaneously returning an ultrasonic signal;
17 and 18 Figure 2e illustrates a near speed-of-light downward signal which is 19 received by a second device for initiating a near speed-of-light return signal.

2 Having reference to Fig. 1, a conventional pump jack 10 is shown 3 comprising a horsehead 12, carrier bar 14 and a cable 16 connecting the carrier 4 bar 14 to the horsehead 12. A polish rod 18 is suspended from the carrier bar 14 and extends down through a wellhead 20 to the sucker rod string (not shown) 6 and hence to the downhole pump (also not shown).
7 Drive 22 causes a rocking motion in the pump jack 10 which results 8 in the pump head 12 following an arcuate path 24. The cable 16 converts the 9 arcuate movement of the horsehead 12 into reciprocating vertical movement 26 of the polish rod 18. The polish rod reciprocates between a bottom position Pbtm 11 and a top position Plop relative to a position origin Po.
12 A sucker rod pump dynamometer 28 according to the present 13 invention is provided which eliminates the need for the prior art cable and drum 14 type position sensor. The novel dynamometer 28 comprises a load cell 30 connected to and moveable with the polish rod 18 for measuring load on the 16 sucker rod string and polish rod 18. The load cell 30 is typically situate between 17 the carrier bar 14 and a bottom polish rod clamp (not shown).
18 A movable first signal device 32 is also secured to the polish rod 18 19 adjacent the carrier bar 14. The movable signal device 32 moves vertically with the polish rod 18. The movable signal device 32 is capable of sending a first 21 signal 34 and receiving a return signal 36.
22 A controller 38 is connected to the movable signal device 32. The 23 controller 38 is also secured to the carrier bar 14. Such a controller 38 is an Intel 24 87C196 microcomputer having onboard timer and TTL ports. The controller 38 1 uses a TTL port to direct the movable signal device 32 to emit the first signal 34 2 and also initiates its internal timer, starting at time to.
3 The controller 38 is conveniently included in the electronics 4 associated with the load cell 38 and in this way is movable with the polish rod 18.
The operator can remove the load cell from the other components. The 6 calibration information for the load cell 30 is contained in an EERPOM (not 7 shown) contained within the load cell. Periodic removal of the load cell and 8 plugging it into an into an external power source (such as 12V DC or AC
9 adapter) allows an internal battery to be charged for powering the load cell and controller 38.
11 In response to the first signal 34 a second and wireless 12 rangefinding return signal 36, such as an ultrasonic or infrared pulse, is 13 generated from a fixed base position or source 40, returned and subsequently 14 received by the controller 38 at time t~. In order for the distance or polish rod position to determined, at least one of the first or return signals must be wireless 16 and thus the travel time is related to distance.
17 The controller timer records the elapsed time Ot between signals 18 34 and 36 (t~-to). For the purposes of this description, two additional time periods 19 are defined: the elapsed time for the first signal 34 to travel down to the fixed source 40 is ~tdoWn; and the elapsed time for the return signal 36 arrive at the 21 controller 38 is ~tup.
22 The instantaneous distance d between the movable signal device 23 32 and the origin Po or fixed source 40 is determinable knowing the speed of 24 transmission of the rangefinding signals 34 or 36 and the elapsed time Ot.
More 1 accurate load cell, signal velocity and polish rod position calibration is possible 2 by adding a pressure sensor and a temperature sensor (not shown).
3 It is understood that all that is needed to complete the numerical 4 calculation of instantaneous position is to ascertain the time for a rangefinding signal pass one-way between the device 32 and the fixed source 40 or vice 6 versa. If the first signal 34 is very much faster than the return signal 36 then its 7 time is substantially negligible and all that is required is to determine time Otup for 8 the rangefinding return signal 36 to reach device 32 and the controller 38.
The 9 controller 38 must be able to relate the time t~, the return signal 36 is received, to the time to it was initiated or triggered.
11 Time ~tdoWn is substantially zero in the case of certain signals 12 including: a hard-wired transistor-transistor logic (TTL) signal, radio or a light 13 signal. Time OtdoWn could be much longer (e.g. 17 ms over 6 m) if the first signal 14 34 is a downwardly directed ultrasonic signal.
Controller 38 also monitors load cell 32 and receives input related 16 to the strain on the polish rod 18.
17 Having collected elapsed time 0t and knowing the timing and 18 speed of the first and second signals and load information, the controller 38 then 19 has data necessary to determine polish rod load and the position of the controller 38 relative to the fixed source 40. Having calibrated the position of the controller 21 to the base position Po,42, the polish rod position Pmeas (between Pbtm ...
Ptop) 22 can be calculated.
23 The controller 38 is connected to a data radio 42 which wirelessly 24 transmits a packet of data of polish rod position and load to a receiving data 1 radio 44. The data packet can include temperature and pressure data, load cell 2 calibration data or computed information. The data is converted to digital 3 information and then transmitted to a remote computer 46. Depending on the 4 complexity of the controller 38, it can either pre-process inputs or merely transmit raw data to the remote computer 46. Computation is preferably distributed 6 between the remote computer and the controller, with the remote computer 46 7 calculating polish rod position.
8 The remote computer 46 may be a located in a service vehicle (not 9 shown). One suitable data radio is the Phantom Wireless Datalink radio modem, model WLB-232 by Murandi Communications Ltd., of Calgary, Alberta, 11 Canada.
12 As shown in Fig. 2a, in a first embodiment, the first signal 34 is a 13 downwardly directed ultrasonic signal and the return signal 36 is a reflection of 14 the downwardly directed signal off the fixed source 40 such as the ground or a specific reflector. Such an ultrasonic sensor is model HU-US33 sensor by 16 Ahernian Proffer of Tulsa, Oklahoma, used both in the movable signal device 17 and the fixed source 40.
18 Controller 38 determines the time interval ~t between the time to 19 the downwardly directed signal 34 is sent and receipt at time t~ of a return signal 36.
21 Unfortunately, unlike a narrow laser beam, an ultrasonic signal has 22 an ever widening cone shape which may impinge on the wellhead 20 and 23 surrounding area. Due to the variable height of the first device 32 from the 24 ground, the contact of the cone varies in width, presenting significant reflective 1 clutter and it is often difficult to separate spurious reflections 36',36",36"' from 2 the actual return reflection signal 36. Accordingly, there could be a need to 3 introduce a predetermined delay, ~tdelay, built into the elapsed time Ot for 4 providing sufficient time for any spurious reflections 36',36",36"' to dissipate, such as are likely to occur when the fixed source 40 is mounted to the ground or 6 the wellhead. Accordingly, between time t~ and to there is: the time for the first 7 signal 34 to reach the base position OtdoW~; the delay time Otdelay~ and the time 8 Ot~P.
9 In the embodiment shown in Fig. 2b, where the first signal 34 is an ultrasonic signal, the implementation of a time delay Otdeiay m the return signal 36 11 is accomplished by providing a second fixed signal device 48 as the source 40.
12 This second fixed device sends an independent return signal 36 in response to 13 the received first signal 34. The advantage of providing a second fixed signal 14 device 48 is that the return signal 36 received by the movable signal device is very strong and easy to detect accurately. The second device 48 is mounted so 16 as to remain independent and stationary relative to the polish rod 18.
Mounting 17 the second device 48 to the ground would suffice.
18 The second or fixed signal device 48 adds greater flexibility to the 19 form of the first signal 34 which further can include other signals such as radio or light which travel at or near the speed of light. The advantage of using such a 21 fast signal is that it removes the necessity to correct polish rod position 22 calculations to account for the time it takes the signal 34 to reach the fixed signal 23 device 48. Further, it obviates the need for a built in time delay and it allows the 1 sampling rate to be increased as less time is wasted for triggering of the second 2 device 48.
3 In the case of a hard-wired first signal 34, a normally slack 4 electrical cable can connect the controller 38 to device 48 for transmitting a 0-5 V
signal and triggering the return signal 36. In the case of a radio or light first 6 signal 34, the second device 48 receives the first signal 34 and triggers and 7 transmits the return signal 36.
8 Having reference to Fig. 2c, an ultrasonic signal is transmitted to 9 second device 48. Upon receipt of the first signal 34, the second device 48 immediately sends a near speed-of-light signal 36 (i.e. infrared) upwards to the 11 first device 32. Time ~tdown is relatively long; in the order of 17 ms for distances 12 of about 6 m. The time Otup for the infrared signal 36 to return to the first device 13 32 is negligible (perhaps a travel time of about 50 ns). No delay Otdelay IS
14 required as the first device receives the infrared signal and is unaware any reflected ultrasound. Time ~tdown is substantially larger than OtuP and elapsed 16 time 0t is substantially equal to OtdoW~.
17 In another embodiment, as shown in Fig. 2d, a radio or infrared 18 light signal is transmitted to the second device 48. Time Otdown is negligible. No 19 delay Otdelay is required. Where the second device is an ultrasonic transducer 48 then time otUp is substantially larger than 4tdown~ and elapsed time is substantially 21 equal to ~tUp.
22 In Fig. 2e, fast signals are used both up and down. The elapsed 23 time Ot is very small and ~tdoW~ is substantially equal to Ot~P.

1 Providing repeated return signals 36, or analyzing multiple signals 2 36, can reveal additional data of interest such as polish rod velocity or pumping 3 state.
4 Velocity of the polish rod is determined from the analysis of closely spaced return signals. By analyzing two return signals 36,36 at pre-determined 6 intervals, the data collected by the controller 38 is sufficient to calculate position 7 and speed based on the time interval between receipt of the two return signals.
8 Specifically, the controller 38 can repeatedly pulse or cycle the triggering and 9 receiving of return signals 36. The change of position of the polish rod 18 during the time between pulses enables determination of polish rod velocity.
11 Further, the state of the stroke of the polish rod can be determined 12 from the relative velocity of the rod. As calculation of rod velocity is a vector, 13 including direction, the sign of the velocity states whether the rod is moving up or 14 down.
According to the method of the present invention, the movable 16 signal device 32 is caused by the controller 38 to send a signal 34 either to the 17 ground 42 or a fixed signal device 48. A return signal 36, that is either an echo of 18 the signal 34 or an independent signal 36, is emitted by the fixed signal device 19 48 and is sent back to the controller 38. The data collected by the controller 38 is used to calculate a polish rod position based on the time interval between the 21 signals 38 and 40.
22 The controller 38 also monitors the load cell 32 to determine strain 23 on the polish rod 18 at the calculated polish rod position Pmeas. The controller 38 1 wirelessly transmits both strain and position data to a computer 46 via a data 2 radios 42,44.
3 The controller 38 may additionally calculate load or some other 4 function of force on the polish rod 18 based on input from the load cell 32.
This will of course depend on the nature of position versus load curve which is to be 6 plotted.
7 The velocity of sound is an additional parameter used to improve 8 the accuracy of the calculation of the polish rod position. Accordingly, the 9 atmospheric pressure and temperature, both of which affect the velocity of sound, are measured. Another method for correcting for these parameters is to 11 predetermine the length of the pump stroke. When the length of the pump stroke 12 is known then the velocity correction can be easily calculated after the pump has 13 made one full cycle. Acoustic velocity corrections can also be made on an 14 ongoing basis using this method.
It will be appreciated that the present invention eliminates the need 16 for wire cable, drum and potentiometer arrangement for determining polish rod 17 position. Further, the present invention provides an alternative to electrical cable 18 hookup between the pump jack and a computer or between pump jack controller 19 and the ground.
The above is intended in an illustrative rather than a restrictive 21 sense. Variations to the exact description above may be apparent to persons 22 skilled in such apparatus without departing from the spirit and scope of the 23 invention as defined by the claims set out below.

Claims (24)

1. Apparatus for monitoring a pump jack which is supporting and reciprocating a polish rod comprising:
a first device movable with the reciprocating polish rod for transmitting a first signal and for receiving return signals;
a fixed signal source for receiving the first signal and returning a return signal to the first device, at least one of the first and return signals being wireless, the fixed signal source being mounted independent from the polish rod;
and a controller for establishing the elapsed time between the transmission of the first signal and receipt of the return signal at the first device and emitting signals indicative of the relative position of the polish rod with respect to the fixed signal source.

2. The pump jack monitoring apparatus as described in claim 1 wherein the controller is moveable with the reciprocating polish rod.

3. The pump jack monitoring apparatus as described in claim 1 further comprising:
a data-processing computer located apart from the pump jack; and a data transmitter, moveable with the reciprocating polish rod, for receiving data including the emitted signals indicative of the relative position of the polish rod with respect to the fixed signal source and wirelessly transmitting the data to the data-processing computer.

4. The pump jack monitoring apparatus as described in claim 3 further comprising a load cell for establishing measures of the load on the polish rod and emitting signals indicative thereof and wherein the data wirelessly transmitted by the data transmitter includes measures of the load on the polish rod .

5. The pump jack monitoring apparatus as described in claim 3 wherein the fixed signal source is a second signal device which receives the first signal and sends a return signal in response.

6. The pump jack monitoring apparatus as described in claim 5 wherein the first signal is an ultrasonic signal.

7. The pump jack monitoring apparatus as described in claim 6 wherein the return signal is a substantially speed-of-light signal transmitted to the first device.

8. The pump jack monitoring apparatus as described in claim 5 wherein the first signal is a substantially speed-of-light wireless signal and the return signal is an ultrasonic signal.

9. The pump jack monitoring apparatus as described in claim 5 further comprising an electrical conductor extending between controller and the second signal device and wherein one of the first or return signal is an electrical signal and the respective other return or first signal is a wireless signal.

10. The pump jack monitoring apparatus as described in claim 2 wherein the first device is an ultrasonic transceiver and the first signal is an ultrasonic signal.

11. The pump jack monitoring apparatus as described in claim 10 wherein the fixed signal source is an ultrasonic reflector.

12. The pump jack monitoring apparatus as described in claim 10 wherein the fixed signal source is a an ultrasonic transceiver which receives the first signal and returns the return signal after a predetermined time delay thereafter.

13. A method for monitoring a pump jack which is supporting and reciprocating a polish rod comprising the steps of:
(a) moving a first signal device with the polish rod;
(b) transmitting a first signal from the first signal device having a known speed of travel and directing it to a fixed signal source for initiating the return of a return signal having a known speed of travel;
(c) initiating a timer with the transmission of the first signal;
(d) receiving the wireless return signal at the first signal device;
(e) terminating the timer upon the first signal device's receipt of the wireless return signal for determining an elapsed time;
(f) calculating the relative position of the first signal device based upon the elapsed time and the travel speed of the first signal and the wireless return signal, the position being related to the polish rod position.

14. The method as recited in claim 13 wherein the fixed signal source is an interface reflective to the first signal.

15. The method as recited in claim 13 wherein the fixed signal source is a second signal device which sends the wireless return signal in response to receipt of the first signal.

16. The method as recited in claim 15 wherein the second signal device introduces a known time delay before sending an ultrasonic return signal.

17. The method as recited in claim 15 wherein the first signal is an ultrasonic signal and the return signal is a substantially speed-of-light signal.

18. The method as recited in claim 15 wherein the first signal is a substantially speed-of-light signal and the return signal is an ultrasonic signal.

19. The method as recited in claim 13 wherein the polish rod position is transmitted to a computer.

20. The method as recited in claim 19 wherein the transmission of the polish rod position from the first signal device to the computer is a wireless transmission.

21. The method as recited in claim 20 further comprising the step of measuring the polish rod load and also transmitting the measured load to the computer.

22. The method as recited in claim 15 wherein a plurality of return signals are received by the first signal device at predetermined timed intervals so that the position of the first signal device is determinable at a plurality of known times and the polish rod speed is determinable.

23. The method as recited in claim 15 wherein the polish rod position is transmitted to a computer via wireless transmission.

24. The method as recited in claim 23 further comprising the step of measuring the polish rod load and also transmitting the measured load to the computer.