Oil-well pump instrumentation device and method
A pumpjack monitor includes a processor and memory, a communicator for communicating with other monitors and a server, a sensor module having at least one strain gauge, and accelerometers for determining vibration and position of the monitor. Other sensors may be internal, including sensors for polished-rod rotation, and linked to the monitoring device wirelessly. Some embodiments serve as network hubs or bridges for other monitors. The server is configured to generate surface cards. A method for monitoring of pumpjacks uses the monitor to sense changes in pumpjack parameters, and communicate the changes to a server when changes exceed configurable thresholds. Some embodiments include determining location with GPS and/or relaying signals from other monitoring devices, smart power management, gas sensing, and relaying of signals from external wireless-equipped sensors such as valve position sensors, oil level sensors, and pressure sensors.
1. A polished-rod dynamometer comprising:
at least one axial load sensor that monitors axial load on a polished rod, the axial load sensor being selected from a strain gauge and a load cell;
a processor;
a memory communicatively coupled to the processor and storing firmware;
a real-time clock;
a wireless communicator that transmits at least axial load sensor readings and polished-rod position; and
an accelerometer that measures axial acceleration readings of the polished rod;
wherein the firmware comprises machine-readable instructions that, when executed by the processor, control the polished-rod dynamometer to:
identify, for each polished-rod stroke of a plurality of polished-rod strokes, a reference tick of said each polished-rod stroke to determine a duration of said each polished-rod stroke; and
estimate polished-rod position throughout each polished-rod stroke from readings from the accelerometer by:
computing a mean acceleration of the axial acceleration readings over the duration of said each polished-rod stroke;
subtracting the mean acceleration from the axial acceleration readings to obtain gravity-corrected accelerometer readings;
integrating the gravity-corrected accelerometer readings to estimate velocity throughout each polished-rod stroke;
computing and subtracting a mean velocity from the estimated velocity throughout the duration of said each polished-rod stroke to generate a corrected velocity;
integrating the corrected velocity to estimate the polished-rod position throughout said each polished-rod stroke; and
scaling the estimated polished-rod position so that a range of estimated polished-rod positions matches a known position range of the polished rod.
2. The polished-rod dynamometer of claim 1 , wherein the firmware identifying a reference tick of each polished-rod stroke uses readings of a magnetic sensor of the polished-rod dynamometer.
3. The polished-rod dynamometer of claim 1 , wherein the firmware identifying a reference tick of each polished-rod stroke is performed by processing the readings from the accelerometer by:
estimating a bias by averaging the readings from the accelerometer over a time period longer than the duration of said each polished-rod stroke;
subtracting the estimated bias from the readings from the accelerometer and integrating to determine estimated polished-rod velocity; and
searching for maxima or minima in the estimated polished-rod velocity to determine the reference tick.
4. The polished-rod dynamometer of claim 3 , wherein the firmware further includes machine-readable instructions that, when executed by the processor, control the polished-rod dynamometer to:
receive a standard reference tick wirelessly from a sensor pod comprising an inclinometer, optical sensor, or rotation sensor coupled to a crank of a pumpjack, and
calibrate the reference tick against the standard reference tick.
5. The polished-rod dynamometer of claim 4 , wherein the firmware calibrates the reference tick against the standard reference tick for each speed of pumpjack operation.
6. The polished-rod dynamometer of claim 1 , wherein the firmware includes further machine-readable instructions that, when executed by the processor, control the polished-rod dynamometer to:
compute reference polished-rod positions from pumpjack characteristics and readings received wirelessly from an angular position sensor or rotation sensor coupled to a crank of the pumpjack, and
calibrate the range of estimated polished-rod positions against the reference polished-rod positions.
7. The polished-rod dynamometer of claim 1 , the firmware further comprising machine-readable instructions that, when executed by the processor, control the polished-rod dynamometer to receive the reference tick wirelessly from a sensor pod that couples to a walking beam or crank of the pumpjack.
8. The polished-rod dynamometer of claim 7 , wherein the sensor pod is selected from the group consisting of a missing-tooth wheel sensor, a potentiometer, and an optical sensor.
9. A method of monitoring a polished rod of a pumpjack, comprising:
providing at least one axial load sensor that monitors axial load on a polished rod, the axial load sensor being selected from a strain gauge and a load cell;
reading an accelerometer that measures axial acceleration of the polished rod;
identifying, for each polished-rod stroke of a plurality of polished-rod strokes, a reference tick of each polished-rod stroke to determine a duration of said each polished-rod stroke;
estimating polished-rod position throughout each polished-rod stroke from readings from the accelerometer by:
computing a mean acceleration of the axial acceleration readings over the duration of said each polished-rod stroke;
subtracting the mean acceleration from the axial acceleration readings to obtain gravity-corrected accelerometer readings,
integrating the gravity-corrected accelerometer readings to estimate velocity throughout each polished-rod stroke;
computing and subtracting a mean velocity from the estimated velocity throughout the duration of said each polished-rod stroke to generate a corrected velocity;
integrating the corrected velocity to estimate polished-rod position throughout a polished-rod stroke, and
scaling the estimated polished-rod position so that a range of estimated polished-rod position matches a known position range of the polished rod.
10. The method of claim 9 , wherein said identifying a reference tick of each polished-rod stroke uses readings of a magnetic sensor.
11. The method of claim 9 , wherein said identifying a reference tick of each polished-rod stroke is performed by processing the readings from the accelerometer by:
estimating a bias by averaging the readings from the accelerometer over a time period longer than the duration of a polished-rod stroke;
subtracting the estimated bias from the readings from the accelerometer and integrating to determine estimated polished-rod velocity; and
searching for maxima or minima in the estimated polished-rod velocity to determine the reference tick.
12. The method of claim 11 , further comprising receiving a standard reference tick wirelessly from an optical sensor or rotation sensor coupled to a crank of the pumpjack, and calibrating the reference tick against the standard reference tick.
13. The method of claim 12 , further comprising calibrating the reference tick against the standard reference tick for each speed of pumpjack operation.
14. The method of claim 9 , further comprising computing reference polished-rod positions from pumpjack characteristics and readings received wirelessly from an angular position sensor or rotation sensor coupled to a crank of the pumpjack, and calibrating the range of estimated polished-rod positions against the reference polished-rod positions.
15. The method of claim 9 , further comprising receiving the reference tick wirelessly from a sensor pod coupled to a walking beam or crank of the pumpjack.
16. The method of claim 15 , wherein the sensor pod is selected from the group consisting of an inclinometer, a missing-tooth wheel sensor, and an optical sensor.
17. A wireless inclinometer in a first housing adapted for mounting on a walking beam of a pumpjack at a known location relative to a saddle bearing of the pumpjack, the inclinometer comprising:
sensors selected from the group consisting of: first and second physically separated accelerometers, and a collocated accelerometer and rate-gyroscopic sensor;
a processor having associated memory with firmware residing in the memory, the firmware being configured to read the sensors and compute therefrom an angle of the walking beam corrected for acceleration;
a first real-time clock; and
a wireless communicator configured to transmit the angle of the walking beam with an angle-capture time from the first real-time clock to a polished-rod dynamometer.