<p>With the growing adoption of CCUS-EOR (Carbon Capture, Utilization, and Storage-Enhanced Oil Recovery) projects, wellbore integrity under CO₂ exposure has become a critical concern. High-temperature, high-pressure (HTHP) conditions exacerbate CO₂-induced corrosion, threatening cement sheath and casing integrity, potentially leading to leakage and environmental hazards. This study investigates CO₂ corrosion effects on two cement systems (conventional and hollow-particle-modified) and three casing materials (Q125, 3Cr, 13Cr). Static corrosion experiments were conducted at 80-120°C and CO₂ partial pressures of 15-30 MPa (50-100% concentration) for 28 days. Phase composition and microstructure were analyzed via XRD and SEM, while interface integrity was evaluated pre- and post-corrosion. Cement Systems: Both systems formed similar hydration products (e.g., calcium silicate hydrates), but System #2 (with hollow particles) exhibited additional SiO₂ and C₅S₂CO₃ phases, enhancing high-temperature stability. Postcorrosion, SiO₂ dominated as the primary product, with CaCO₃ transitioning from calcite (≤90°C) to aragonite (&gt;110°C). System #2 showed denser microstructures and reduced porosity, indicating superior corrosion resistance. After corrosion, Q125 and 3Cr interfaces exhibited cement loosening and micro-pores, while 13Cr interfaces remained intact. System #2 paired with 13Cr casing demonstrated minimal degradation, highlighting optimal sealing integrity. The hollow-particle-modified cement (System #2) improves corrosion resistance, particularly when combined with 13Cr casing. These findings provide critical insights for designing durable wellbore systems in CCUS-EOR applications, mitigating leakage risks under HTHP CO₂ environments.</p>