A Critical Assessment of Test Methods for Steel–cement System Degradation in Geological CO₂ Storage Environments

Carbon Capture and Storage (CCS) is one of the key strategies identified to achieve net-zero targets. CCS well infrastructure consists of steel casing surrounded by cement sheaths in a wellbore that will be continuously exposed to chemically aggressive environments at high temperatures and high pressures (HTHP). The integrity of the well infrastructure is critical for long-term CO₂ storage. The continuous exposure of the injection well to CO₂-bearing fluids may cause degradation of the cement sheath due to carbonation and corrosion of the steel casing, thereby forming a leakage pathway for CO₂. The lack of standardized test methodologies for durability assessment of steel-cement (S-C) systems in wellbore conditions hinders the performance-based material selection for CCS injection well infrastructure. This paper presents a critical overview of durability assessment methodologies for S-C systems and the challenges in simulating wellbore conditions, such as HTHP and aggressive chemicals, including the role of impurities present alongside CO₂ on well integrity. Studies dealing with corrosion assessment and bond characteristics of S-C interfaces in CCS environments will also be discussed. Limited studies on material degradation beyond mechanical performance highlight the need for more systematic assessment approaches to decouple failure mechanisms and develop mechanistic models for accurate material selection for CCS well applications.