Modifications of Pore Structure in Sandstone and Cement Samples Under CO ₂ –Water–Rock Interactions: An Experimental Study

ABSTRACT The long‐term security of carbon dioxide geological storage (CGS) depends on pore structure evolution driven by CO 2 –water–rock interactions. Experiments were conducted under simulated reservoir conditions (36°C, 7.2 MPa) using Ordos Basin sandstone as the reservoir rock and C30 cement as the sealing material. Pore and mineral evolution were characterized by nuclear magnetic resonance (NMR) T 2 spectra and x‐ray diffraction (XRD). Sandstone exhibited a staged evolution following a dissolution–expansion → precipitation–contraction → dynamic equilibrium pattern: an initial expansion phase, where dissolution of reactive minerals (e.g., albite and illite) increased meso‐ and macropore volume, with porosity reaching a local maximum at approximately 16 h during the early expansion stage, followed by a contraction phase marked by mineral transformation (e.g., anorthite) and particle migration, leading to a dynamic dissolution–transformation balance. In contrast, cement maintained a stable microstructure dominated by micropores. These results indicate that early dissolution may temporarily enhance permeability and leakage risk, whereas subsequent precipitation promotes pore‐throat clogging and structural self‐sealing, improving long‐term integrity. The study demonstrates that pore evolution is controlled by dissolution–precipitation cycles and that NMR T 2 spectra effectively capture these dynamics, providing an experimental basis for evaluating storage capacity and leakage risk in geological CO 2 storage.