PNNL

Abstract

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 flowrates. 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. And 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 (SscCO2), suggesting that the conventional model describing the relationship between capillary pressure and SscCO2 need 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.