Simulation Of Dynamometer Card And Working Condition Diagnosis Based On Pumping Unit’s Measured Electric Power

The pump of rod pumping units located several kilometers downhole. Under theaction of cycle alternating load in a long time, prone to a variety of fault. Seriously affectthe normal production of oil field. Realizing the remote real-time monitoring anddiagnosis of the condition of the pumping wells is important subject of the current oilindustry. The measurement of dynamometer card is the basis of condition diagnosis.Aiming at the disadvantages of the method for measuring dynamometer card directly andindirectly,this paper mainly studied the method to obtain the dynamometer card based onmeasured electric power. And on this basis, comprehensive diagnostic method of wellcondition based on pump dynamometers and measured electrical power curve is studied.This paper carried out the following research:Based on the measured motor input power, considering the instantaneous powerutilization and its affect to transmission efficiency of the motor, the simulation model ofthe motor ouput power and output shaft torque is setup. Based on the mechanicalcharacteristics of the motor, the simulation model of the motor rotor’s instantaneousmotion is setup. And based on it, this paper calculate the motion of the pumping unit’smoving parts and the polished rod.Taking the combined influence of balance system, transmission efficiency andmovement’s inertia of pumping unit, based on the simplified dynamic analysis and theprecise dynamic analysis of pumping unit, the simulation model of connection betweenthe motor power and polished rod load is bulit.This paper analyses the reason of the dynamometer card’s lower precision which isobtained by the measured electric power indirectly. According to the principle of leastsquares, the fitting method of dynamometer card is put forward. Taking the minimum sumof squared errors as the objective function of optimize design, the optimization model ofthe rod load torque is setup. And a fitting model of the polished rod load which wasexpressed by Fourier series form is built.Through the statistical analysis of the pump dynamometer characteristics of thedifferent working conditions, the calculated model of pump dynamometer characteristic parameters is setup. Through the statistical analysis of the electric power curvecharacteristics of the different working conditions, the calculated model of the electricpower curve characteristic parameters is setup. With the Elman network, thecomprehensive diagnostic model of artificial neural network is setup, which is based onthe pump dynamometer and the electric power curve characteristic parameters.Using Visual Basic6.0and Matlab to develop “the simulation software ofdynamometer and working condition diagnosis based on pumping unit’s measured electricpower”. Case study shows the fitting dynamometer card by measured electric power fitswell with the measured one. Optimize the load torque can effectively improve the fittingprecision of dynamometer card. The precision of comprehensive diagnosis is high. And itcan meet the engineering actual requirements.