Mechanical Analysis Of Polished Rod And Optimization Of Square Clamp In The Same Well Injection Production System With Rod

At present,most of the oilfields in China have entered the stage of high water cut.The water cut of produced fluid is increasing year by year.By the end of 2016,there were about44119 oil wells with water content of more than 95%in CNPC's domestic oilfields.This phenomenon on the one hand led to the continuous reduction of the income generated by oil production.Many oil wells were forced to stop production because they no longer have economic value.On the other hand,due to the continuous increase of water content,the amount of sewage treatment is also increasing,the operation cost is high,and the environmental safety is seriously threatened.The above problems can be effectively solved by using the same well injection production technology with rod pump.However,due to the special structure of the same well injection production well,compared with the conventional well injection production well,the load outside the well increases,the alternating load increases,the sucker rod fracture of the pumping unit occurs frequently,and the operation cost increases.Therefore,it is necessary to carry out the mechanical analysis of the polished rod and the optimization of the square clamp.Firstly,based on the analysis of the structure and working principle of the injection production system of rod pump in the same well,the mechanical analysis model of the polished rod is established,which is composed of the inclination of the suspending rope device,the misalignment of the donkey head wellhead,and the double effects of two factors,so as to lay the foundation for the establishment of the three-dimensional numerical simulation model;secondly,comprehensively consider the suspension point load the influence of load,bending load and stress concentration on the fatigue failure of polished rod is simulated,the bending characteristics of the polished rod is simulated,and the factors such as bolt moment,the inclination angle of the suspending rope device and the stroke of the pumping unit are analyzed Based on the influence of the fatigue failure of the polished rod and the connection strength,the Plackett Burman test design is used to screen out the significant factors and determine the parameters that need to be optimized in response surface design.Finally,the response surface analysis method is used to select the reasonable change range of each parameter and optimize the other clamp to determine the optimal structure parameter combination.The results show that under the same well injection and production conditions,the application range of friction type square clamp bolt torque is 200N·m?350N·m,and the application range of clamp tooth type square clamp bolt torque is 60N·m?160N·m,the limit value of the polished rod fatigue fracture under the action of the friction square clamp is 2.5°and the limit value of the polished rod fatigue fracture under the action of the clamp square clamp is 1°.When the limit value of the polished rod is 2.5°,the limit value of the polished rod non moderate fatigue fracture is 50 mm.The increase of the stroke and Poisson's ratio of the material is conducive to the extension of the service life of the polished rod.The optimal combination scheme of the structural parameters of the square clip is:the thickness of the square clip is 80mm,the chamfer of the edge of the square clip is 1.2mm,and the curvature of the square clip hole is 35.318m^-1.After optimization,the maximum value of the composite stress of the polished rod is 186.61mpa,which is reduced to 59.1%of the original value,and the stress gradient distribution is more uniform,which effectively reduces the influence of the stress concentration of the square clamp,and can effectively extend the life of the polished rod.