Study On Numerical Simulation And Identification Of Electrical Submersible Motor Temperature

Submersible electric pump unit is widely used in mining engineering in thelarge-scale oil and gas fields in China. The complex and harsh environment thatsubmersible motor working in requires submersible motor must have adequateability of enduring high temperature to ensure the reliability of mechanical oilextraction equipment systems. At the same time, precise and advanced deep wellmotor temperature soft measurement technology and remote monitoring technologyalso supply the fundamental guarantee of improving service life and operationsecurity.There is no systematic approach to temperature rise characteristics of thesubmersible motor before, meanwhile the situation of the negative effects of hightemperature and pressure that occurs worse gradually during the late exploitationperiod in our country. This paper aims at the problems that exist in the submersiblemotor temperature rise analysis and testing methods, considering the characteristicsof the well shaft and oil field conditions, submersible motor temperature risecharacteristics of the theoretical analysis method and finite element simulationmethod are established in this paper. At the same time, according to a particularmodel of submersible motor temperature identification system platform, this paperpresents a high-precision temperature identification technology. The mechanismand influencing factors of motor torque chaos oscillation under specific temperatureidentification conditions are also studied explicitly in this paper.Firstly, according to the theory of heat exchange, the mathematical model ofheat transfer between the fluid in the oil well and motor is established, and thusjoint with fluid mechanics theory, the temperature field control equations of thewell borehole, the borehole axis, strata within the reservoir, formation surroundingrock at the oil production and their corresponding initial conditions and boundaryconditions are deduced. Besides taking into account the oil-water two-phase flowcharacteristics, this paper gives the corresponding relationship between the flowvelocity and pressure. The detail example shows that, high-precision mathematicalinversion of well temperature field can be achieved according to the proposedalgorithm.Secondly, based on finite element analysis of three-dimensional temperaturefield theory and the characteristics of the submersible motor deep well conditions,this paper studies thermodynamics modeling method of submersible pump unit andestablishes the finite difference equations and boundary conditions of the well underground, heat transfer wellbore oil well borehole axis, production layer and thesurrounding rock. Combined with a submersible motor geometric model, thethree-dimensional finite element model is established and the three-dimensionaltemperature field simulation is completed, the calculation results and the measuredresults show the correctness and validity of the method.Thirdly, based on the theory of least square method and sensitivity analysistheory, the speed calculation method according to the rotor slot harmonic frequencyis presented. A complete theoretical method to identify the rotor temperature rise isdetermined based on the submersible motor state equation. A certain typesubmersible motor temperature identification platform based on TMP-Atemperature inspecting instrument is made for the research of software filteringalgorithm integrated the fast FFT, MALLAT wavelet algorithm and the HHT signalanalysis theory. The results show that the parameters identification accuracy of therotor temperature is improved with the method.Finally, in order to extend the service life and testing period of the submersiblemotor effectively, reducing the negative effects of the traditional DC injectionmethod in the identification of submersible motor temperature, this paper presents amonitoring program that applying DC injection instantaneous sampling data toidentify the temperature in the long period of time. Stator resistance is estimatedthrough the calculation of voltage and current waveforms and DC offset, and thuswe can get the stator temperature. Experiment studies the submersible motor currentchaotic oscillations phenomenon and associated factor. Based on these studies wecan analyze the quantitative relationship between chaotic oscillation current and themotor stator and rotor ultimate temperature rise.This study can provide a theoretical basis for the high temperature environmentprotection design and reliability design of the submersible motors. It has importantpractical value for the supervision of the submersible motor in extremeenvironmental conditions and measurement techniques.