Experimental study of drying effects during supercritical CO2 displacement in a pore network

Underground storage in geological aquifers is one of the most important options for large-scale mitigation of CO₂. During the supercritical CO₂ (scCO₂) injection process, water dissolved in scCO₂ may have significant impact on the displacement process. In this study, a series of wet scCO₂ (WscCO₂, 100% water saturation) and dry scCO₂ (DscCO₂, 0% water saturation) displacement experiments were conducted in micromodels for a large range of flow rates. The displacement was visualized using fluorescence microscopy. Results showed that DscCO₂ saturations were up to 3.3 times larger than WscCO₂ saturations when the capillary fingering dominated the displacement. The specific interfacial areas and mobile fractions for the DscCO₂ displacements were also much larger than those for WscCO₂. The capillary forces combined with drying effects are identified as the leading causes for the considerably higher DscCO₂ sweep efficiency. Results from this study showed the important impact of mutual solubility of scCO₂ and water on the displacement process and saturation of scCO₂ (S_scCO2), suggesting that the conventional model describing the relationship between capillary pressure and S_scCO2 needs to be modified for the effect of the mutual dissolution of multiple phases to more adequately describe the scCO₂ displacement process in saline aquifer formation.