Experimental study on the impact of H$_2$S and H$_2$SO$_4$ in CO$_2$ on five different sealant compositions under conditions relevant for geological CO$_2$-storage

The integrity of well sealants is a key challenge to secure geological storage of CO$_2$. While it has been well-established through experimental research that the exposure of such sealants to CO$_2$-bearing fluids can lead to carbonation, and potentially degradation during prolonged exposure or flow, the impact of impurities present in injected CO$_2$ has not received much consideration.
This paper reports exposure of five different sealants to simulated well conditions with supercritical CO$_2$ containing H$_2$S or H$_2$SO$_4$ as impurities. Three of these sealants are based on Portland Cement, while the other two are based on Calcium Aluminate Cement, and a rock-based geopolymer specifically developed for Geological CO$_2$ Storage (GCS). The impact of the impurities on these sealants was assessed through scanning electron microscopy with energy-dispersive X-ray spectroscopy, computed tomography scanning, and fluid chemical analysis, and compared to previous research where the same five sealants were exposed to clean CO$_2$ under otherwise identical conditions.
The results show that during exposure to CO$_2$-saturated water, the presence of H2S mostly resulted in enhanced sealant alteration depths, and reduced carbonate precipitation. ... mehrDuring exposure to wet supercritical CO$_2$, the presence of H$_2$S or H$_2$SO$_4$ resulted in reduced carbonate precipitation, and enhanced alteration depths in some (H$_2$S) or all (H$_2$SO$_4$) sealants. Additionally, relatively minor degradation was observed in the outer 100–200 μm of samples exposed in the presence of H$_2$SO$_4$. Overall, the impacts of impurities were more pronounced for sealants that were more affected by exposure to clean CO$_2$.