Pressure-driven variations in CO ₂ displacement patterns within heterogeneous porous structures: a high-pressure microfluidic study

The displacement patterns of CO 2 are critical for assessing the storage capacity and efficiency of geological CO 2 sequestration, yet they remain underexplored across different pressures. For this purpose, an advanced high-pressure and high-temperature microfluidic platform is developed. By integrating a high-pressure chamber equipped with an observation window and high-strength glass chips, it is capable of operating at pressures up to 50 MPa and enables real-time observation of CO 2 displacement patterns at the pore scale. Experiments conducted across a pressure range from 1 bar to 16 MPa that enables the analysis of changes in displacement patterns, CO 2 saturation, displacement front length, and fractal dimension within heterogeneous porous media. The findings reveal that at low pressures and a flow rate of 0.1 mL/min, CO 2 displacement was predominantly influenced by capillary forces, resulting in preferential invasion of larger pore throats. In contrast, at higher pressures, the displacement process was dominated by the synergistic effects of the viscous and capillary forces of supercritical CO 2 . This results in the breakthrough of the main flow channel on the outlet side and tributary structures spanning its width on the inlet side. The platform offers robust means to investigate CO 2 displacement efficiency and optimise storage strategies.