Experimental Evaluation of Anticorrosion of a Standard 20# Gathering Pipeline by Injecting Oxygen-Reduced Air into Simulated In-Service Wells.

Oxygen-reduced air flooding (ORAF) can effectively improve oil recovery in low-permeability reservoirs, but oxygen corrosion and CO2 corrosion in downstream gathering pipelines are inevitable due to the existence of oxygen, which limits the popularization and application of ORAF. In this paper, research on the corrosion inhibitor is carried out for the gathering pipeline of an oilfield with ORAF in China. Under the conditions of a simulated onsite gathering pipeline, 6 kinds of anti-CO2 corrosion inhibitors and 6 kinds of antioxygen corrosion inhibitors were selected to evaluate and screen the effects of 20# steel by the dynamic weight loss method. Two antioxygen corrosion inhibitors KY-12 and KY-17 and one anti-CO2 corrosion inhibitor A were selected for the experiment. The corrosion inhibition rates of the three inhibitors reached 83.67, 91.49, and 78.44%, respectively, at a temperature of 40 °C and an inhibitor concentration of 1000 mg/L. Through the experimental evaluation of three primary corrosion inhibitors at different temperatures (25, 40, and 55 °C) and different concentrations (400, 500, 800, 1000, and 2000 mg/L), the KY-17 corrosion inhibitor with the best stability at different temperatures was selected, and the corrosion inhibition effect was the best at different concentrations, with the highest slow release rate reaching 92.7%. This conclusion has a good reference significance for the selection and dosage of corrosion inhibitors for downstream gathering pipelines of the ORAF oilfield.

Study on the Corrosion Mechanism of N80 Steel in Simulated Oxygen-Reduced Air Drive Production Wellbores.

In order to investigate the corrosion behavior of N80 steel in production wellbores of oxygen-reduced air drive, the main corrosion control factors are analyzed based on gray relational analysis. Taking reservoir simulation results as indoor simulation parameters, the corrosion behavior in different production periods is studied by the dynamic weight loss method combined with metallographic microscopy, XRD, 3D morphology, and other related characterizations. The results show that oxygen content is most sensitive to the corrosion of production wellbores. The corrosion rate increases significantly under oxygen-containing conditions, and the corrosion rate at an oxygen content of 3% (0.3 MPa) is about 5 times higher than that without oxygen. At the initial stage of oil displacement, the corrosion is CO2-dominated localized corrosion, and the corrosion products are mainly compact FeCO3. With the prolongation of gas injection time, the wellbore is in a CO2/O2 balanced environment, the corrosion changes into a combined action of the two, and the corrosion products are FeCO3 and loose porous Fe2O3. After continuous gas injection for 3 years, the production wellbore is in a high O2 and low CO2 environment, the dense FeCO3 is destroyed, the corrosion pit develops horizontally, and the corrosion changes to O2-dominated comprehensive corrosion.