Pore-scale micromodel experiments for recovery performance evaluation of carbonated water injection for carbon utilization and storage

Carbonated water injection (CWI) has emerged as a promising dual-purpose technique for enhanced oil recovery (EOR) and geological CO₂ sequestration. Despite increasing attention, the combined effects of injection rate and CO₂ phase state (gaseous, liquid, supercritical) on pore-scale displacement dynamics remain poorly understood, and no systematic investigation has been conducted to date. In this study, a custom-designed high-resolution microfluidic platform capable of operating under reservoir-relevant pressure and temperature conditions was developed to directly visualize and quantify the pore-scale displacement mechanisms during CWI. The influence of injection rate and CO₂ phase behavior on oil recovery and carbon retention was systematically evaluated across a range of controlled conditions. Quantitative image analysis reveals that capillary number (Ca) and viscosity ratio (M) jointly govern displacement patterns and residual oil saturation, highlighting the critical role of flow regime in determining recovery outcomes. A Ca–M mechanistic regime map was proposed as a predictive framework for evaluating and optimizing CWI performance under diverse operational scenarios. Furthermore, a critical transition threshold (Ca ≈ 4 × 10⁻⁴) was identified, delineating the boundary between capillary and viscous-dominated displacement regimes. Among all tested configurations, secondary carbonated water injection (SCWI) under supercritical CO₂ conditions yields the highest oil recovery (61.57 %) and CO₂ storage efficiency (51.19 %), significantly outperforming both waterflooding and tertiary injection schemes. The observed recovery enhancement was attributed to a combination of CO₂–induced oil swelling, interfacial tension reduction, and wettability alteration, which collectively promote the mobilization of trapped oil. These findings provide the first quantitative insights into coupled pore-scale flow dynamics under reservoir-relevant conditions and offer a robust scientific basis for the design and upscaling of integrated EOR–CCUS systems.