Transport dynamics of supercritical CO2 foam in microfluidic porous media: mobility control, oil displacement, and foam-oil interactions.

Foam-assisted CO2 enhanced oil recovery (EOR) mitigates the high mobility of CO2, yet the pore-scale mechanisms governing supercritical CO2 (scCO2) foam transport and mobility control under reservoir-relevant conditions remain poorly understood due to limited direct visualization. Here, we use a high-pressure microfluidic porous medium to study scCO2 foam flow and oil displacement at 8 MPa and 40 °C. To the best of our knowledge, this work provides the first pore-scale visualization of dynamically evolving scCO2 foam and foam-oil interactions during oil displacement under high-pressure flowing conditions. By combining pore-scale visualization with pressure-drop measurements, we show that foam quality or injected gas ratio (fg) governs foam structure and flow resistance through transitions between two distinct flow regimes: bubble-dispersed wet foam at low fg (fg = 0.2, 0.4 and 0.6) and interconnected-lamella dry foam at high fg (fg = 0.8 and 0.9). Foam strength varies non-monotonically with foam quality and reaches a maximum over an intermediate foam-quality range ( = 0.6-0.8). Compared with single-phase SDS and scCO2 flooding, which recover only about 60% of the oil, scCO2 foam achieves near-complete recovery across the tested foam qualities. The intermediate foam quality range ( = 0.6-0.8) provided the most effective mobility control, characterized by the higher flow resistance and improved displacement-front stability. Pore-scale visualization further reveals that foam-oil interactions, including CO2 dissolution, oil emulsification, and lamella destabilization, dynamically restructure foam morphology and flow pathways. The pore-scale observations reported in this work highlight the dynamic nature of foam transport and foam-oil interactions under reservoir-relevant conditions and provide mechanistic insight into the observed foam structure, flow resistance, and oil-displacement behavior.