Synergistic effects of corrosion time and stress on corrosion of casing steel in H₂S/CO₂ gas wells

Abstract

Effect of corrosion duration on C110 casing steel was investigated in the stimulated gas field solution containing both 1 MPa CO2 and 1.5 MPa H2S at 90 °C by using a high temperature autoclave. And the corrosion rate prediction model was established based on the corrosion duration effect. In addition, effect of stress on corrosion of steel was analyzed from the thermodynamics and electrochemistry theories, moreover, the casing corrosion life prediction model was established under three axis stress state with considering the influences of stress and corrosion effect. The results reveal that the corrosion rate of C110 casing steel decreases significantly as corrosion time increases, then gradually tends toward stability. In addition, the casing steel is subjected to load and corrosion solution, the thermodynamic activity and the electrochemical reaction potential are changed, ultimately aggravating the process of corrosion. Compared to corrosion time and wall thickness, the internal pressure is the main factor governing the casing corrosion. Therefore, it is suggested that the synergistic effects of corrosion time and stress should be considered in casing safety design and operation.

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