Study On The Failure Mechanism Of The Stator Bushing Of The Electric Submersible Screw Pump Under Heavy Oil Exploitation Conditions

The heavy oil of China is rich and the heavy oil reserves proven in marine oil field accounted for 69%of the total geological reserves,has good prospect for development.The conventional thermal mining methods and process technology is limited because the environment of marine oil and gas reservoirs is so complex.The progressive cavity pump(PCP)in the heavy oil production shows its unique advantages and it has attracted much attention in the oil field at home and abroad.Electric submersible progressive cavity pump(ESPCP)combines the advantages of PCP and electric submersible pump,is the ideal wellbore lifting technology in current marine heavy oil exploitation.However,due to the complex environment of marine oil and gas reservoirs,underground high temperature,high pressure,the amount of sand in the production fluid and other factors will lead to temperature of PCP stator lining rise too fast and exacerbate the wear.It's easy to cause rubber wear fracture,degumming,corrosion and overheating,resulting in the PCP premature failure.Therefore,it is necessary to carry out research on the failure mechanism of ESPCP under heavy oil recovery.In view of the above problems,this paper takes the double-headed single screw pump as the research object,synthesizes the relevant knowledge and latest research achievements in the fields of thermodynamics,material mechanics,tribology,manufacturing technology and materials science.Based on the combination of experimental research,theoretical research and numerical simulation,the failure mechanism of ESPCP under heavy oil recovery is studied.The main research contents are as follows:(1)Based on the operating characteristic of PCP,the friction and wear experiment between the stator rubber(NBR)and rotor of the PCP under the condition of heat and sand with heavy oil was designed.The kinematics analysis method and calculation formula of the oil extraction PCP were used to determine the rotational speed and the applied load range of the PCP in the experimental environment.The effects of rotational speed,sand concentration and load on the friction coefficient and wear amount of rubber were studied.The surface morphology of the rubber was observed by scanning electron microscopy(SEM),the friction and wear behavior of the rubber was analyzed,and then the friction and wear failure mechanism of rubber was obtained.(2)The tensile and compression tests of NBR on the test and simulation were carried out by uniaxial stretching instrument.The coefficients of the two-parameter M-R model and the determination of the elastic modulus of the rubber were calculated by using the experimental data.(3)Taking the double-headed single-PCP as the research object,the physical model of the PCP's stator bushing is established according to the geometrical physical characteristics of the stator and rotor of the oil extraction PCP.Based on the delayed heat generation mechanism of stator rubber,the mathematical model of PCP's stator thermal coupling is established.Using ANSYS finite element analysis software to study the influence law of working parameters,structural parameters and material parameters on the temperature rise of two types of bushing rubber caused by the delayed heat generation.And then the thermal failure mechanism of PCP's stator bushing was summed up.(4)Taking the G25-1 type oil extraction PCP as the test object,the infrared heat imager instrument was used to observe the heat generation process and the heat agglomeration effect of the stator rubber bushing of the PCP at running in the laboratory environment.The influence law of the speed on the heat generation process and the heat accumulation effect is studied,and the thermal failure mechanism of the stator bushing of the oil extraction PCP is further improved.The research results are as follows:The friction coefficient of rubber increases first and then decreases with the increase of rotational speed,decreases with the increase of load,increases and then decreases with the increase of sand content.The amounts of rubber wear increases with increasing speed,load and sand content.The failure form of rubber is abrasive wear,fatigue wear and erosion wear.The temperature rise of the stator bushing increase nonlinearly along with the increase of interference and working pressure,increase linearly along with the increase of speed,decrease nonlineasly along with the increase of friction coefficient?hardness and passion ratio.The heat resistance of the even thickness bushing is higher than that of the conventional bushing.Interference,speed and bushing types have a great influence on the temperature rise of rubber bushing,which are the main factors that causes the thermal failure of it.The thermal failure forms of rubber bushing are bum heart failure,burmer failure and degumming failure.More attention should be paid to the design and selection of the PCP.The temperature rise of the stator bushing increase linearly along with the increase of speed and the fastest temperature rise area appears in the center of the bushing's thickest position.The experimental results are consistent with the simulation analysis results.In this paper,the friction and wear mechanism and thermal failure mechanism of the ESPCP under the condition of heavy oil thermal recovery are studied in depth by means of theory analysis,experiment analysis and numerical simulation analysis.It can provide some reference and practical basis for the design of ESPCP,the selection of working parameters and model selection,which is helpful to the development of marine heavy oil in our country.