Study on the Oxygen Content of Oxygen-Reducing Air Flooding Based on Anticorrosion Considerations

Oxygen-reduced air flooding (ORAF) is an important efficient development means for tight and low permeability reservoirs because of its low cost, low risk, and ability to penetrate into voids and substrates. However, the critical value of oxygen-reduced, which can take into account the cost and corrosion protection requirements, is uncertain. Therefore, the corrosion behavior of N80, J55, and 3Cr steels under simulated high pressure (30 MPa) gas injection with different oxygen content (1%–12% vol.) was studied by weight loss method and Ultra-Depth Three-Dimensional Microscope. Under this oxygen content, the corrosion behavior of N80, J55, and 3Cr steels under different total pressure (20–35 MPa), temperature (25℃–70℃), and coexistence of gas and water was further studied. The results show that under the condition of high temperature and high-pressure drying, when the oxygen content in the oxygen-reduced air is reduced to 5%, all three kinds of steels belong to slight corrosion (<0.025 mm/a), and the oxygen-reduced cost can still be kept at a low level. In addition, under the condition of 5% oxygen content, when the corrosion medium of the wellbore is only deoxidized gas, the corrosion is slight, so N80 steel at a lower cost can be used. However, when the wellbore contains liquid, the corrosion is serious, and anticorrosion measures need to be taken. This study can provide certain data support for the selection of oxygen content and the corrosion protection of gas-injection wells shaft in the process of high-pressure gas injection by ORAF.