Research On Corrosion Performance Of Pipe String In Heavy Oil Thermal Recovery Well

The viscosity of heavy oil is high but it is very sensitive to temperature,so thermal recovery is the main way of heavy oil production.Cyclic steam stimulation is one of the main methods of heavy oil recovery.The temperature and the medium in the string change with the development of the steam stimulation period so that the string is easy to be corroded.It is necessary to study the corrosion characteristics of the string in the steam stimulation production well.In this paper,the steam stimulation process is discussed in stages.The change of wellbore temperature is obtained by calculating the temperature distribution of thermal fluid and the heat transfer in the wellbore.According to the temperature distribution and the internal medium of the string in different stages,the simulated corrosion experiments were carried out in a high temperature and high pressure reactor and the corrosion characteristics of the string in different stages were obtained.The corrosion characteristics of the string under different working conditions in the whole cycle are obtained by combining the experimental results of each stage.The residual corrosion strength of the string is analyzed and the residual life of the string is predicted.In the steam injection stage,the influence of oxygen or carbon dioxide partial pressure on the corrosion of the pipe string is mainly discussed.In the oil production stage,the influence of the salt concentration of the produced water in the oxygen or carbon dioxide environment on the corrosion of the pipe string is mainly discussed.The corrosion experiments of K55 steel and L80 steel were carried out by changing the relevant factors.The experimental results show that the corrosion rate varies with the temperature in different gas environments.The compactness of the corrosion product film formed by different gases is an important factor affecting the corrosion rate.The better the compactness of the product film,the lower the corrosion rate.There is a critical value for the corrosion law of the salt content to the string,which is lower than the critical value.The corrosion rate has a negative correlation with the temperature.If it is higher than the critical value,it is a positive correlation.The critical concentration is between 0.5wt% and 1wt%.The corrosion depth after a cycle of steam stimulation can be obtained by combining the experimental results of each stage.The residual corrosion strength of the pipe string after a cycle can be calculated,and the residual life of the pipe string can be predicted by using the calculation results.The residual strength of L80 steelis higher than that of K55 under the same working condition.L80 steel has more remaining service cycles than K55 steel.It is of great significance to study the corrosion characteristics of the pipe string in thermal recovery well to prevent and eliminate the potential safety hazards in the process of thermal recovery.