Study On Oxygen Corrosion Behavior Of Nitrogen Injection Wellbore

With the reduction of conventional oil and gas resources and the development of many oil and gas fields in China,it is of great significance to enhance the oil and gas recovery for the sustainable and stable development of the oil industry.In recent years,the application of nitrogen flooding enhanced oil recovery technology has gradually increased,and the effect is remarkable.Due to viscous fingering and gas channeling in the pure gas flooding,the gas and water mixture is widely used,and the injection of nitrogen gas mainly includes three kinds of injection process,such as pure gas injection,pure water injection,and gas-water mixture injection.However,in the flooding process,the nitrogen oxygen and water containing oxygen resulted in the serious corrosion problems including string corrosion and scaling,perforation and fracture,directly affecting the normal production of injection well.To solve this problem,this paper mainly studies the oxygen corrosion behavior of the string material in the process of oxygen bearing gas injection:(1)The dynamic High temperature and high pressure autoclave has been used to simulate the oxygen corrosion of PI 10 and P110S steel in gas-water mixed injection,gas injection and pure water injection process.scanning electron microscope(SEM)and energy dispersive spectrometer(XRD)technologies has been applied to conduct microscopic characterization analysis of corrosion scales.The influence of different inj ection processes on the corrosion rate of the pipe was obtained,and the corrosion morphology and corrosion products were analyzed.(2)Based on different oxygen partial pressure(0.003MPa-2.5MPa)corrosion evaluation results,the effects of oxygen partial pressure on corrosion of the P110 and P110S pipe was studied in mixed injection and pure gas injection conditions.The results showed that the pipe corrosion can be reduced by lowering oxygen partial pressure and improving the injection rate of nitrogen purity.In addition,the pipe corrosion perforation time of different oxygen partial pressure was obtained.(3)Taking a domestic nitrogen flooding well as an example,the uniform corrosion rates of P110 and P110S steel were obtained under different simulation conditions.According to the API 5C3 standard,the relationship between residual tensile safety coefficient of tubing and the service life of the corrosion was calculated.Based on the tensile safety factor of 1.6,the corrosion life and safety service life of tubing string under different conditions were predicted.(4)The corrosion inhibitor with good corrosion inhibition effect was screened out by the combination of electrochemical method and corrosion simulation method.After the corrosion inhibitor was added to the surface of P110 and P110S steel,a relatively complete corrosion product film was formed,and the corrosion inhibition efficiency was 90%.The results provides the theoretical references for assessing the current corrosion risk and corrosion level of the nitrogen injection wellbore,which has important theoretical significance and practical application value in the process of oxygen corrosion.