Contact angle measurement ambiguity in supercritical CO2–water–mineral systems: Mica as an example

Abstract

The current ambiguity on wettability of minerals in CO2–brine systems under the geological CO2 sequestration (GCS) reservoir conditions imparts the greatest uncertainty in predicting capillary behavior controlling safe-storage of CO2. To address this issue we conducted a series of experiments using muscovite as a representative of common aluminosilicate minerals. Based on new experimental results we identified several possible causes of the ambiguity problem in contact angle (CA) measurements. We also found that reaction with water-saturated supercritical (sc) CO2 (but not with scN2) phase severely roughened the muscovite surfaces, largely increased CA hysteresis and CO2 adhesion. Although some methodological influences on contact angle uncertainty can be reduced, the high surface-energy of clean and pristine aluminosilicate minerals have strong tendency to adsorb oppositely changed molecules and particles to reduce their surface energy, resulting in less reproducible CA values. Giving the fact that such clean and pristine mineral surfaces do not exist in real reservoirs, our future investigations shall focus on improving understanding of the effect of long-term CO2–mineral–brine reactions on reservoir wettability under realistic reservoir geochemical conditions.