The Corrosion Behavior Of Mild Steel In Simulated Casing/Cement Interfacial Environments Under A Carbon Sequestration Scenario

With the rapid development of carbon capture and storage(CCS)technology,CO2 leakage caused by corrosion becomes one of the bottlenecks of its wide application.To evaluate the corrosion risk of casing pipe in carbon dioxide geological sequestration environment,the corrosion behavior of P110 steel in simulated casing/cement interfacial environments under a carbon sequestration scenario was studied.Firstly,the synergistic effects of Cl’ ion,dissolved oxygen and CO2 partial pressure on the localized corrosion behavior of P110 steel in a simulated cement pore solution were studied by weight-loss and surface analysis methods.It was found that severe localized corrosion can be observed on the surface of P110 steel when the concentration of Cl’ and dissolved oxygen reached above a threshold(chloride concentration of 0.2 mol/L and dissolved oxygen concentration of 300 μg/L)at 80℃and 10 MPa.The general corrosion rate of P110 steel was only 0.06 mm/y after corrosion in the simulated geothermal solution with a chloride concentration of 0.6 mol/L and a dissolved oxygen concentration of 300μg/L at 80℃ and 10 MPa,but the localized corrosion rate was as high as 5.2 mm/y,and the local corrosion morphology showed a certain number of surface protrusions.The morphology of localized protrusion could be attributed to the penetration of dissolved oxygen and Cl-through the initially formed FeCO3 corrosion product film,promoting the local dissolution of steel surface under the corrosion products,producing a mixture of Fe2O3 and FeCO3.The aggregation of corrosion products and the hydrogen evolution reaction would expand the interface region and the initial corrosion product layer become curved,finally forming a macroscopic protrusion or rupture on the surface of P110 steel.To further clarify the growth kinetics of the localized protrusions,the effect of dissolved oxygen concentration in the simulated geothermal solution with a chloride ion concentration of 0.6 mol/L on the localized corrosion behavior of P110 steel was studied by electrochemical method.The results showed that the increase of trace dissolved oxygen didn’t change the cathodic reaction mechanism and the formation kinetics and composition of the initial corrosion product layer on P110 steel.However,at a certain anodic polarization potential,the localized reactivation of P110 steel occurred,and the protection potential of P110 steel to induce localized corrosion reduced.The corrosion process of P110 steel in the simulated geothermal solution at 80 ℃ and 10 MPa can be described as four stages:active dissolution(2 h),early film formation(12 h),stable protection(30 h)and localized corrosion attack(after 72 h).The localized corrosion was characterized by intermittent initiation,growth and rupture.The damage effect of localized protrusion on the cement and the casing/cement interface was verified by casing/cement interface failure simulation experiments.In this paper,the corrosion risk and key influencing factors of casing/cement interface in CCS projects were comprehensively investigated,which provided a theoretical basis for corrosion prediction and CO2 leakage monitoring based on geological environment.