Wettability is one of the most important parameters in multiphase flow through porous rocks. However, experimental measurements or theoretical predictions are difficult and open to large uncertainty. In this work we demonstrate that gas densities (which are much simpler to determine than wettability and typically well known) correlate remarkably well with wettability. This insight can significantly improve wettability predictions, thus derisking subsurface operations (e.g., CO2 geostorage or hydrocarbon recovery), and significantly enhance fundamental understanding of natural geological processes.
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Every
year, millions of tons of CO2 are stored in CO2-storage formations (deep saline aquifers) containing traces
of organic acids including hexanoic acid C6 (HA), lauric
acid C12 (LuA), stearic acid C18 (SA), and lignoceric
acid C24 (LiA). The presence of these molecules in deep
saline aquifers is well documented in the literature; however, their
impact on the structural trapping capacity and thus on containment
security is not yet understood. In this study, we therefore investigate
as to how an increase in organic acid concentration can alter mica
water wettability through an extensive set of experiments. X-ray diffraction
(Figure S2), field emission scanning electron microscopy, total organic
carbon analysis, Fourier-transform infrared spectroscopy, atomic force
microscopy, and energy-dispersive X-ray spectroscopy were utilized
to perceive the variations in organic acid surface coverage with stepwise
organic acid concentration increase and changes in surface roughness.
Furthermore, thresholds of wettability that may indicate limits for
structural trapping potential (θr < 90°)
have been discussed. The experimental results show that even a minute
concentration (∼10–5 mol/L for structural
trapping) of lignoceric acid is enough to affect the CO2 trapping capacity at 323 K and 25 MPa. As higher concentrations
exist in deep saline aquifers, it is necessary to account for these
thresholds to derisk CO2-geological storage projects.
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