Conventional beam pumping unit is the most popular lifting equipment at well site, especially in mechanical oil production. To identify its operation, the indicator diagram is an effective tool. Therefore, study on indicator diagram measuring methods has been made as a key subject in major oilfields in China. Currently, force sensors and displacement sensors are commonly used to measure the polished rod load and displacement, so as to generate the indicator diagram. The force sensor is always exposed to the compression and tension of alternating loads, which will damage its elastic coefficient, finally leading to less-precision or even invalid measurements. Besides, this application may bring challenges in installation of devices, work life of the sensors, maintenance and operating cost, which will affect the analysis of well conditions. In summary, the technique cannot satisfy the current requirement of digitalized well management. In view of above issues, this paper proposes a new measurement method. The useful motor power of the beam pumping unit is acquired in real-time manner, and based upon the law of conservation of energy, the motion pattern of the unit is analyzed, to establish a mathematical model containing useful motor power, polished rod load and polished rod displacement. The model can figure out the relationship between beam pumping unit output power and load. Then, in line with field physical calibration, the indicator diagram is measured. This method doesn’t require complex installations on the site. Instead, only electric parameters for input and useful power, apparent power and power factor are acquired to determine the actual polished rod load, according to the correlation between power of the unit and load. Finally, the indicator diagram of the pumping unit is measured indirectly. This method can greatly contribute to the site installation efficiency, work lift of measuring devices and measurement accuracy. This method has been tested in 20 pumping wells. It is found that the equivalent indicator diagram illustrates accordant tendency with the measured indicator diagram; average relative error of area is less than 8%, and average relative errors of maximum and minimum loads after calibration are not greater than 10%. These suggest that the equivalent indicator diagram reconcile with the measured one, and can be used in real time monitoring of pumping well conditions by using useful motor power data. This technology has been effectively applied in an oilfield domestically.


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