Corrosion behavior of tubing string in CO2 flooding environment of simulated oil field

The work aims to clarify the influence rule of corrosion factors on the corrosion performance of carbon steel tubing string in CO2 flooding production environment of Changqing Oilfield and optimize and match appropriate anti-corrosion measures according to the corrosion environment. The corrosion rate of the material was obtained by weightlessness method in the simulated oilfield by high temperature autoclave, and scanning electron microscopy (SEM) or backscattering electron spectroscopy (BSES) were used to analyze the morphology of the corrosion product film and the cross section of the corrosion film. When the wellbore temperature was 80 °C and p(CO2) gradually increased in the range of 0~5 MPa, there was no obvious pitting corrosion in N80/J55 pipe, and the average corrosion rate increased linearly, with the maximum corrosion rate of 5.87 mm/a. The average corrosion rate of N80/J55 pipe decreased first and then increased gradually when the test system entered supercritical CO2 environment, i.e. p(CO2)>7 MPa. When p(CO2)=10 MPa, the maximum corrosion rate reached 6.74 mm/a. XRD phase analysis showed that the corrosion product film was mainly composed of ferrous carbonate; Adding 200 mg/L modified TG512 corrosion inhibitor to the test solution effectively alleviated the corrosion of the pipe; When the oil content of the test solution medium was more than 70%, the average corrosion rate of N80/J55 pipe was less than 0.022 mm/a, and the average corrosion rate gradually tended to be gentle. N80/J55 tubing is severely corroded in the simulated oil field when the oil content of CO2 flooding production fluid is less than 70%. Effective anti-corrosion measures must be taken before the tubing is used. Modified TG512 high-efficiency corrosion inhibitor can effectively slow down the corrosion of tubing materials and the corrosion inhibition rate is 98.2% in conformity with the needs of oil field. Controlling the water content of produced fluid below 30% will slow down the corrosion of wellbore. © 2019, Chongqing Wujiu Periodicals Press. All rights reserved.