Pore-scale investigations into the stability of residual CO$_{\mathrm{2\thinspace }}$

After brine imbibition following CO$_{\mathrm{2}}$ injection, substantial volumes of supercritical CO$_{\mathrm{2}}$ (scCO$_{\mathrm{2}})$ may be disconnected from the plume and trapped in the pores. Whereas conventional multi-phase flow models assume that the residually trapped non-wetting phase is permanently immobilized, multiple physiochemical mechanisms exist which could potentially invalidate this assumption. One mechanism is CO$_{\mathrm{2}}$ transfer driven by differences in capillary pressure between disconnected neighbor ganglia, called Ostwald Ripening.work presents two experiments. In the first experiment Ostwald ripening was assessed by calculating pore-scale capillary pressure distribution in sandstones using a multi-scale synchrotron-based X-ray microtomographic (micro-CT) dataset of residually trapped air after a simple gravity-driven imbibition experiment. In the second experiment a scCO$_{\mathrm{2}}$-brine drainage-imbibition cycle was performed in a sandstone with reservoir conditions coupled with time-resolved synchrotron micro-CT imaging after imbibition stops.