PNNL

Abstract

Wettability is an important factor affecting fluid behavior in the subsurface, including oil, gas, and supercritical CO$_2$ in deep geological reservoirs. For example, CO$_2$ is generally assumed to behave as a non-wetting fluid, which favors safe storage. However, because of chemical heterogeneity of the reservoirs, mixed wettability conditions can exist. Furthermore, recent experiments suggest that with time, the wettability of super-critical CO$_2$ may change from non-wetting to partially-wetting due to changes in electrostatic interactions. These changes are caused by chemical reactions between dissolved CO$_2$ and its environment. To date, the effect of wettability alteration and mixed wettability on the long term fate of injected CO$_2$ has not well been studied. Here, we use the multiphase Pairwise Force Smoothed Particle Hydrodynamics (PF-SPH) Model to study complex pore-scale processes involved in geological CO$_2$ sequestration, including the effect of spatial and temporal wettability variations on long-term distribution of CO$_2$ in porous media. Results reveal that in the absence of dissolution of supercritical CO$_2$ and precipitation of carbonate minerals (mineral trapping), the amount of trapped supercritical CO$_2$ significantly decreases as the wettability of the porous media changes from brine-wet to partial-wet or CO$_2$-wet.