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, CO 2 geological storage has been widely applied in depleted oil or gas reservoirs for enhanced oil recovery. However, during CO 2 injection and long-term geological storage, the carbonation-induced corrosion of the cement sheath is the main threat as CO 2 may leakage from the well to atmosphere. In this study, G-grade oil well cement was placed in different CO 2 corrosion environments to investigate the effects of the CO 2 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 CO 2 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 CO 2 -corroded cement exhibited different characteristics at different stages of corrosion. The T 2 spectrum curve indicated that the degree of CO 2 corrosion of cement was related to the diffusion rate of the CO 2 . When the pressure was low, CO 2 was difficult to penetrate deep into the cement, resulting in the smallest change in the NMR curve area under dry-phase CO 2 corrosion conditions at 5 MPa. This study employed nuclear magnetic technology to further analyze the mechanism of CO 2 corrosion on oil well cement at the microscopic level. It will contribute to a deeper understanding of the mechanism of CO 2 corrosion of cement and lay a theoretical analysis foundation for practical engineering applications of cement in CO 2 geological storage and enhanced oil recovery.