Study On Corrosion Rules And Protective Technologies Of Production Pipes By CO₂ Flooding

Through decreasing oil viscosity,expanding the volume and reducing the interfacial tension between crude oil and water,CO₂ flooding is proved to be a grest method to exploit oil in the petroleum industry.A large amount of CO₂ dissolved in the produced liquid during the process of assisting production,which causes serious corrosion problem to the downhole equipment of the production well,and then causes serious accidents such as casing perforation and string dropping,which has already becoming one of the bottlenecks in the development of CO₂ flooding technology.Adding corrosion inhibitor to control corrosion failure of oil casing is a very effective method,howerver,the performance of corrosion inhibitor is strongly dependent on the corrosion environment,and the application of each inhibitor needs to be evaluated according to the actual corrosion environment.Therefore,this paper studies the corrosion behavior and protection technology of the well bore of the CO₂ flooding production well,which mainly includes the following points.?1?The HTHP autoclave is used to analyze the effects of temperature?60?120??,CO₂ partial pressure?0.1 MPa?0.3MPa?and Cl-concentration?1000ppm?3000ppm?on the CO₂ corrosion reactions of pipe in liquid environment?Rod,N80 and 3Cr?and gas environment?N80 and 3Cr?.Moreover,the corrosion resistance of different oil casing materials is studied.The morphology and composition of the corrosion product under different temperature are analyzed by SEM and EDS and XRD.?2?The selection and evaluation of corrosion inhibitor arecarried out by physical and chemical property test,electrochemical test and weight loss test in HTHP.Firstly,the physical and chemical properties of the inhibitor are evaluated by compatibility test.And then the corrosion inhibitor is further screened by electrochemical method.Finally,the corrosion inhibitor,which corrosion inhibition ratio of is greater than 90%,is used for the weight loss evaluation experiment in HTHP autoclave.The corrosion inhibition mechanism of the corrosion inhibitor was analyzed by SEM,FTIR and thermodynamic analysis.?3?According to the API5C3 standard,The safe service life of sucker rod under different corrosion rates,the service life of different materials under the same corrosion condition,and the variation of safety service life of tubing and casing with tensile safety factor under different corrosion influence factors are calculated,while the tensile safety factor is 1.6 and the squeezing safety factor is 1.1,and then the safe service life of production well string is obtained.Based on the safety service life of the pipe rod before and after adding the corrosion inhibitor,the cost of replacing the material of the pipe string and the and running cost of the two kinds of anticorrosion schemes are calculated,then the economical and optimal anticorrosion scheme is obtained.The research results provide theoretical references for evaluating the current corrosion risk and corrosion degree faced for the pipes in the production wells of CO₂ flooding,which play an important role on solving the problem of CO₂ corrosion.