Experimental Investigation of CO2‐ and Fe3O4‐Assisted Corrosion at the Cement–Casing Interface

In this study, CO 2 ‐ and Fe 3 O 4 ‐assisted corrosion of the cement–casing interface for the magnetite (Fe 3 O 4 ) high‐density cement–casing steel system in simulated formation water is investigated under the normal and high CO 2 pressure conditions. Results show that the degradation of the cement–casing interface is affected by the competition of cement hydration and CO 2 corrosion. The migration of CO 2 and corrosive species to the cement–casing interface is facilitated under the high pressure condition, resulting in enhanced corrosion rate as compared to the normal pressure condition. The casing steel is in active corrosion state while the corrosion rate gradually increases with time. After long term of immersion, a layer of thick corrosion products with multiple cracks/microgaps forms at the cement–casing interface, which can hardly protect the casing steel from further corrosion. The corrosion products on the steel surface are mainly FeCO 3 accompanied by a small amount of CaCO 3 and Fe 3 O 4 , suggesting the prevalence of CO 2 corrosion. The mechanism of the CO 2 ‐ and Fe 3 O 4 ‐facilitated corrosion of the cement–casing interface for the magnetite high‐density cement–casing system is proposed.