Experimental study on the impact of H2S and H2SO4 in CO2 on five different sealant compositions under conditions relevant for geological CO2-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 H 2 S mostly resulted in enhanced sealant alteration depths, and reduced carbonate precipitation. During 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 . • Wellbore sealants were exposed to CO 2 with impurities under in-situ conditions • During exposure to CO 2 -saturated water, H 2 S enhanced alteration depths by up to 1.5x • During exposure to wet supercritical CO 2 , H 2 S reduced carbonate precipitation • H 2 SO 4 in supercritical CO 2 enhanced alteration and surface degradation • These effects are most pronounced for sealants that are more affected by clean CO 2