Development of high-performance cementitious composites reinforced with graphene nanoplatelets for CCS wells

Carbon Capture and Storage (CCS) relies on the long-term integrity of oil-well cement to ensure the safe geological confinement of CO 2 . However, prolonged exposure to CO 2 -rich environments promotes cement carbonation and degradation, affecting well integrity. This study investigated the effect of graphene nanoplatelets (GNPs) on the hydration, mechanical properties, permeability, and carbonation resistance of API Class G cement pastes intended to CCS applications. Cement pastes containing 0–0.09% BWOC GNP were evaluated by uniaxial compressive strength, nitrogen gas permeability, accelerated carbonation under supercritical CO 2 conditions in a CO 2 -rich aqueous environment, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS). XRD and TGA results indicated enhanced hydration in formulations containing 0.03% and 0.06% BWOC GNP, evidenced by increased hydration products and reduced portlandite content. After 7 days of curing, GNP addition increased compressive strength by up to 23% and reduced nitrogen gas permeability by up to 47% with respect to the reference paste. Following 28 days of CO 2 exposure, the paste containing 0.06% BWOC GNP exhibited the lowest carbonated area (69.52%), compared with 91.12% for the reference paste, indicating improved resistance to carbonation. SEM observations revealed a denser cement matrix and confirmed GNP dispersion within the hydrated matrix. Overall, GNP addition enhanced cement hydration, mechanical performance, and durability, suggesting its potential to improve the long-term integrity of CCS wells.