Material Selection and Corrosion Evaluation of Down-hole Accessory for CO₂ Flooding Production Wells

The corrosion laws of six kinds of material such as 35CrMo steel, 42CrMo steel, 3Cr13 stainless steel, 45 steel, 304L stainless steel and 316L stainless steel in the CO₂ flooding outflow environment with temperature of 30~65℃, pressure of 2 MPa and liquid medium flow rate of 1.2 m/s were studied by high temperature and high pressure dynamic cycle test. The morphology and composition of corrosion products were characterized by scanning electron microscopy (SEM) and an attached energy dispersive spectrometer (EDS). The results show that in the test environment, neither 304L nor 316L stainless steel corroded; 3Cr13 stainless steel had slightly CO₂ corroded, and the corrosion rate was lower than the industry standard of 0.076 mm/a. The corrosion rates of other materials were too large, and the corrosion rate in the CO₂ flooding production well environment from large to small were as follow:45 steel > 42CrMo steel > 35CrMo steel. When the Cr content in the alloy was low (0~9%), the corrosion resistance of the Cr-containing alloy was enhanced with the increase of Cr content. When the ambient temperature was 30~65℃, the corrosion rate of the alloy increased with the increase of temperature, which was related to the growth of the corrosion product film.