Mineralogical and porous system evolution of reservoir and seal rocks: differences between wet and dry conditions

Carbon capture, utilization and storage (CCUS) is a pivotal technology for reducing atmospheric CO₂ and mitigating global warming to 1.5–2ºC. Deep geological storage plays a crucial role in this strategy, requiring a thorough understanding of the reservoir and seal rock properties before gas injection. Laboratory experiments simulating different conditions are essential to analyze how trapping mechanisms evolve over time.

This study examines the mineralogical and porous system evolution of detrital rocks from the Ebro Basin in Spain when exposed to dry CO₂ and CO₂-rich brine. Sandstones from the Lopin structure were subjected to supercritical CO₂ in an autoclave under controlled batch conditions (8 MPa, 40ºC, 30 days). The samples were analyzed using optical microscopy, digital image analysis, and scanning electron microscopy to assess structural and compositional changes.

The results demonstrate striking differences between the two experimental conditions. Exposure to CO₂-rich brine triggers significant grain detachment, mineral dissolution, and increased porosity, reflecting the high chemical reactivity of the system in the presence of fluids. Conversely, exposure to dry supercritical CO₂ results in negligible changes, as the absence of fluids inhibits chemical reactions. These findings emphasize the critical role of fluid interactions and extended timescales in enhancing the security and efficiency of long-term CO₂ storage.

Ordoñez-Casado, B.; Mediato, J.; Kovacs, T.; Martínez-Martínez, J.; Fernández-Canteli, P., González-Menéndez, L.; Roces, S.; Caicedo-Potosí, J.; Berrezueta, E., Experimental geochemical assessment of a seal-reservoir system exposed to supercritical CO₂: A case study from the Ebro Basin, Spain. International Journal of Greenhouse Gas Control 2024, 137, 104233. 10.1016/j.ijggc.2024.104233