New Insight of CO2 Corrosion Performance on Cement for Enhanced Oil Recovery and Carbon Geological Storage Based on Nuclear Magnetic Resonance Technology

Abstract

As a major means of reducing carbon emissions and achieving the carbon-zero target, CO₂ geological storage has been widely applied in depleted oil or gas reservoirs for enhanced oil recovery. However, during CO₂ injection and long-term geological storage, the carbonation-induced corrosion of the cement sheath is the main threat as CO₂ may leakage from the well to atmosphere. In this study, G-grade oil well cement was placed in different CO₂ corrosion environments to investigate the effects of the CO₂ pressure and water saturation on long-term cement corrosion. Mechanical and pore permeability properties, as well as changes in the microstructure and composition, were analyzed using uniaxial compression, X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy testing methods, respectively. Specially, nuclear magnetic resonance (NMR) technology was used to evaluate the pore changes in cement during the CO₂ corrosion. Results showed that wet-phase corrosion facilitated the occurrence of carbonation reactions and the migration of corrosive medium and products. Moreover, the microstructure and composition of the CO₂-corroded cement exhibited different characteristics at different stages of corrosion. The T₂ spectrum curve indicated that the degree of CO₂ corrosion of cement was related to the diffusion rate of the CO₂. When the pressure was low, CO₂ was difficult to penetrate deep into the cement, resulting in the smallest change in the NMR curve area under dry-phase CO₂ corrosion conditions at 5 MPa. This study employed nuclear magnetic technology to further analyze the mechanism of CO₂ corrosion on oil well cement at the microscopic level. It will contribute to a deeper understanding of the mechanism of CO₂ corrosion of cement and lay a theoretical analysis foundation for practical engineering applications of cement in CO₂ geological storage and enhanced oil recovery.