Prediction of Corrosion Front Propagation and Safety Margins in Deep Sandstone Reservoirs: A Coupled Reactive Transport Model

To quantify the long-term integrity of deep sandstone reservoirs for CO2 sequestration, this study integrates 120-day high-pressure immersion experiments with a coupled reactive transport model. X-ray diffraction (XRD), SEM–EDS, and ion concentration analyses were employed to identify the dissolution–precipitation behaviors of minerals like calcite. Results indicate that at a reservoir pressure of 15 MPa, the corrosion depth exhibits a unique three-stage “decrease–increase–stabilization” trajectory, reaching a maximum theoretical depth of ∼36.2 m over 40 years. Thermodynamic analysis shows that increasing pressure from 15 to 45 MPa expands the corrosion zone thickness from 7.7 to 22.4 m, driven by the enhanced CO2 solubility and interfacial acidity. Spatially, the corrosion concentration exhibits exponential attenuation with depth, confirming that a reservoir thickness exceeding 80 m provides a sufficient safety margin against chemical leakage. Based on these findings, a four-stage evolution mechanism─initial structure, enhanced dissolution, secondary precipitation, and quasi-steady state─is proposed. Furthermore, a semiempirical power-law model (Lc = α·tβ·eγP) is established as a rapid engineering tool for defining the safety boundaries of large-scale sequestration projects.