Study On Corrosion Prediction Method And Anti - Corrosion Measures Of CO_2 Subcirculation In Gas Well Tubes

Corrosion is one of the most important reasons which lead to downhole tubing failure in gas well. CO2is the most general and serious material among other medium such as, H2S and SRB bacteria. Though various anti-corrosion measures can reduce the tubing corrosion speed and prolong the service life of the tubing, the tubing corrosion is inevitable in the oil and gas wells containing corrosive medium. For the corroded tubing, the tubing life forecasting must be done in case of the tubing perforation even breakage among production. The most key step among tubing life forecasting is the prediction of the corrosion rate, therefore, it’s very necessary to predict the CO2corrosion rate in downhole tubing of gas well.Based on the CO2corrosion mechanism and corrosion influence factors, this paper mainly studied methods ofprediction of corrosion rate:mathematical model and gray theory. Corrosion rate prediction mathematical model includes empirical model, semi-empirical model and mechanism model, and Norsok empirical model, De Waard semi-empirical model and NPO mechanism model are some typical prediction models. Based on the laboratory and field data, block suitable empirical and semi-empirical prediction model were obtained after regression calculation, and programming forecast was carried out. Mechanism model is not suitable for the field, due to that the required parameters are difficult to obtain. This article deduced the NPO model which based on electrochemical principle and the diffusion and mass transfer principle to understand the corrosion prediction model mechanism deeper. Grey theory is a deeper development of system thought and has applied in many areas. This article studied tubing corrosion in gas well containing CO2with the use of grey correlation and grey forecasting, and expert scoring method is improved according to the correlation of various influencing factors and corrosion rate.Finally, this article introduced injection situation of corrosion inhibitor of each well in the block on the basis of research of anti-corrosion measures at home and abroad and general situation of Shapingchang block in Datianchi gas field, and then evaluated the effect of the corrosion inhibitor.