CO2 capillary trapping via Huff-n-Puff injection in a two-dimensional micromodel: Role of pressure and brine salinity in sandstone saline aquifers

Geological storage of carbon dioxide (CO 2 ) within deep sedimentary formations has emerged as a promising strategy for mitigating anthropogenic greenhouse gas emissions. Despite extensive studies on continuous injection, the pore-scale mechanisms governing residual trapping during cyclic Huff-n-Puff injection under variable salinity conditions remain poorly constrained. This study systematically investigates the effects of injection pressure, injection rate, injected pore volume, and brine salinity on CO 2 storage efficiency using the Huff-n-Puff injection technique in a two-dimensional (2D) micromodel. Experimental parameters were independently controlled to quantify pore-scale immiscible displacement, phase connectivity, snap-off, and ganglion immobilization during injection, soaking, and brine re-imbibition cycles. The results demonstrate that elevated injection pressures increase non-wetting phase connectivity and enhance capillary trapping through improved pore-scale invasion efficiency. Moderate injection rates promote more stable displacement fronts and reduce preferential channeling, while larger injected pore volumes intensify rock-fluid interactions, strengthening both solubility and capillary immobilization. Increasing brine salinity reduces trapped CO 2 saturation by altering interfacial tension (IFT) and wettability, thereby influencing ganglion stability and mobilization thresholds. By establishing mechanistic links between cyclic injection dynamics, salinity-controlled interfacial properties, and residual trapping efficiency, this work provides a physically consistent framework for improving predictive models and optimizing injection strategies for secure geological CO 2 storage. • Systematic micromodel study of CO 2 –brine displacement under Huff-n-Puff injection. • Effects of injection pressure, rate, pore volume, and brine salinity on storage efficiency. • Higher injection pressures enhanced CO 2 retention via capillary trapping. • Optimal injection rate minimized gas channelling and improved displacement. • Increased pore volume and salinity control strengthened CO 2 immobilization mechanisms.