Direct Observation of Anomalous CO2 Dispersion in Multi-scale Porous Media

Abstract

The CO2 dispersion dynamics in multi-scale porous media is critical for various environmental applications. The heterogeneity of natural porous media lead to the immobile zones and preferential flow paths, resulting in a broad distribution of local velocity and giving rise to anomalous dispersion. Existing experimental methods remains challenging to establish multiscale porous media for observing anomalous dispersion of CO2 at high temporal-spatial resolution. To address this gap, we developed a novel visualization method based on micromodels and colorimetric method. The visualization of CO2 dispersion during CO2 drainage revealed that the reduced connectivity of porous media causes CO2 sub-dispersion, while high CO2 injection rates promote super-dispersion. In the fractured porous media, capillary force balance further induced anomalous multi-stage CO2 dispersion. The CO2 solute preferential flow in large fractures significantly influences CO2 dispersion in matrix. Our study reveals the synergistic effects of microscope heterogeneity of porous media and solute injection rate on dispersion dynamics, with important implications on CO2 geological sequestration and subsurface contaminant transport.