(352h) Impact of Impurities on CO2 Transport in Saline Aquifers

Large scale sequestration of CO₂ in subsurface porous media is one of the most promising methods to limit the concentration of CO₂ in the atmosphere. The transport of the injected CO₂ in subsurface formations depends on various factors including the properties of the reservoir, aquifer brine, and operational conditions. The flow behavior of CO₂ also depends on the presence of various impurities that may be present in the captured gas. This work investigates the impact of H₂S, a common impurity, on different trapping mechanisms during a long-term sequestration of CO₂ in subsurface formations.

For this purpose, we use a compositional reservoir simulator to model the injection of CO₂ with different fraction of the impurities for 10 years of active injection followed by 15 years of post-injection phase. The impact of capillary pressure, and relative permeability hysteresis effect on various CO₂ trapping mechanisms is also considered . We also investigate the impact of well trajectory on near-wellbore phenomena of halite precipitation and permeability alteration for pure CO₂ injection case and the case with impurities. Furthermore, the impact of brine with different ionic concentrations in CO₂ dissolution is assessed using different salts, commonly present in saline aquifers with varying ionic concentrations.

The results from the study showed that the presence of H₂S had a significant impact on dissolution trapping. Compared to the case with no impurity, significant enhancement of CO2 dissolution was observed throughout the reservoir. Furthermore, the results also showed that the dissolution was increased for a well with horizontal perforations compared to the vertical perforations. The halite precipitation was also significantly lower in case with horizontal perforations which resulted in only a moderate reduction in permeability compared to the vertical case. However, higher halite precipitation was observed for the case with impurities. The results were used to provide qualitative and quantitative insights which could be used to evaluate and optimize CO₂ sequestration projects efficiently.

This study represents a comprehensive reactive transport model to investigate the CO₂ sequestration in subsurface formations. The results will provide critical insights that can be used to improve upon the existing knowledge on the effect impurities on CO₂ trapping by different mechanisms.