The impact of co-contaminant SO2, versus salinity and thermodynamic conditions, on residual CO2 trapping during geological storage

During geological storage in deep saline aquifers, immobilization of CO2 in reservoir rock determines both storage safety and capacity. Assessment of the sensitivity of residual trapping to different parameters (interfacial tension and contact angles) and the storage conditions affecting these is therefore of great importance. One aspect of concern is the presence of co-contaminants such as SO2 in the injected gas. Using experimentally measured values of interfacial tensions and contact angles, we apply pore-network modelling (which accounts for pore-scale mechanisms such as snap-off, cooperative pore body filling and piston-type displacement) to a generic sandstone network to quantify the impact of SO2 co-injection on residual CO2 trapping, and its relative importance as compared to the influences of thermodynamic conditions and salinity. We show that the presence of small amounts of SO2 in the injected CO2 has a notable positive effect on the amount of CO2 becoming residually trapped (similar to 3% increase at 1 wt% SO2). However, this effect is small compared to that of the brine salinity (similar to 20% decrease in residually trapped CO2 over the salinity range 0.2 to 5 M NaCl). Still, co-injection of SO2 could potentially favour the residual trapping of CO2 in reservoir rocks, especially at storage sites with inclined aquifers where the CO2 is set to migrate hydro-dynamically over long distances. The salinity of the resident brine is of primary importance during storage site selection. Furthermore, sensitivity analysis shows that the advancing contact angle strongly impacts residual CO2 trapping. (c) 2018 Society of Chemical Industry and John Wiley & Sons, Ltd.