Corrosion of 13Cr steel at the cement/casing interface in CO₂/H₂S environments at 4, 85 and 200 °C

A study was carried out to investigate corrosion at the cement/casing interface for 13Cr casing steel. Cement simulated pore solution (CSPS) was developed by exposing cement pieces to 5% NaCl at 100 °C and 10 MPa in equilibrium with CO₂. Pore solution was extracted from the cement pieces using a die press. Chemical analysis of the pore solution extract was performed and used for preparing CSPS for 13Cr corrosion testing. Corrosion tests were performed in CSPS at equilibrium with CO₂ or CO₂+H₂S at 10 MPa at 4, 85, and 200 °C. Corrosion rates were determined using linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), and mass loss coupons. Addition of H₂S at 4 °C increased the corrosion rate, while at 85 °C it slightly decreased the corrosion rate. Only a small effect from H₂S addition was observed at 200 °C. Cyclic voltammetry (CV) results showed passivation/depassivation of 13Cr in CSPS at 4 and 85 °C, while a transition to active corrosion was observed at 200 °C. Surface analysis using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) found that both the coverage and complexity of the corrosion products formed increased dramatically with increasing temperature.