减氧对空气泡沫驱井下管柱的缓蚀作用及减氧界限

Oxygen corrosion is a main factor hindering the wide application of air foam flooding. Although deoxygenation can result in the decrease of corrosion rate. In this study, the high-pressure corrosion reaction kettle is used to simulate the working conditions, and the corrosion rate of N80 casing steel is measured using weight loss method under different oxygen contents (2%-21%)at various pressures (20-50 MPa)and temperatures (70-120℃). According to the experimental results, a mathematical model of the relationship between corrosion rate and partial pressure of oxygen is established. The morphology and composition of corrosion products are characterized using the scanning electron microscope, energy disperse spectroscopy and X-ray diffraction. The results show that the corrosion rate of N80 steel presents the nonlinear decrease with the decreasing oxygen contents of air in the air foam flooding process. However, the corrosion rate is impossible to be controlled below the standard value of 0.076 mm/a. The deoxygenation limit of N80 steel is 0.021%-0.054% at 120℃ when the pressure is between 50 MPa and 20 MPa, and has reached the standard of pure nitrogen. Under the working conditions, the corrosion products of N80 steel are loose and porous with different oxygen contents as well as Fe₂O₃, FeOOH and Fe₃O₄, indicating no ability to protect base metal. In addition, the morphology and composition of corrosion products vary little with the changes in the working conditions.