Reservoir Heterogeneity Controls Long-Term CO2 Mineral Trapping and Self-Sealing in Deep Saline Aquifers: Insights from Reactive Transport Simulations

Abstract Geological carbon sequestration in deep saline aquifers is considered one of the most promising strategies for mitigating anthropogenic CO2 emissions; however, the influence of reservoir-scale heterogeneity on long-term trapping efficiency and storage permanence remains insufficiently quantified. Previous investigations have predominantly focused on short-term plume evolution, whereas the coupled impacts of permeability architecture, geochemical reactions, and petrophysical evolution over geological time scales remain poorly understood. This study systematically investigates the role of permeability heterogeneity on CO2 trapping mechanisms using fully coupled multiphase reactive transport simulations performed with CMG-GEM. Five synthetic saline aquifer models characterized by Lorenz coefficients ranging from 0.0 to 0.8 were constructed while maintaining an identical average permeability (100 mD) and porosity (0.20). A total of 30 Mt of CO2 was injected over 30 years, followed by a 970 year postinjection monitoring period. Results demonstrate a strong monotonic relationship between heterogeneity intensity and long-term mineralization efficiency. The mineral trapping fraction increased from 32.6% in the homogeneous case to 83.1% in the highly heterogeneous system, corresponding to a 2.55-fold enhancement after 1000 years. Three distinct mineralization stages were identified, including an initial lag phase (0–100 years), an accelerated precipitation regime (100–600 years), and a stabilization period beyond 600 years. Increasing heterogeneity also promoted higher pressure buildup, greater porosity reduction, and substantial permeability degradation caused by localized carbonate precipitation within preferential flow pathways. These findings reveal that reservoir heterogeneity acts as a geochemical amplifier that enhances fluid–rock interactions and promotes progressive self-sealing behavior. The Lorenz coefficient provides a practical metric for evaluating storage security, predicting long-term mineralization potential, and supporting comparative assessment of geological carbon storage sites.