Residual CO₂ imaged with X-ray micro-tomography

Carbon capture and storage (CCS), where CO₂ is injected into geological formations, has been identified as an important way to reduce CO₂ emissions to the atmosphere. While there are several aquifers worldwide into which CO₂ has been injected, there is still uncertainty in terms of the long-term fate of the CO₂. Simulation studies have proposed capillary trapping – where the CO₂ is stranded as pore-space droplets surrounded by water – as a rapid way to secure safe storage. However, there has been no direct evidence of pore-scale trapping. We imaged trapped super-critical CO₂ clusters in a sandstone at elevated temperatures and pressures, representative of storage conditions using computed microtomography (m-CT) and measured the distribution of trapped cluster size. The clusters occupy 25% of the pore space. This work suggests that locally capillary trapping is an effective, safe storage mechanism in quartz-rich sandstones. Citation: Iglauer, S., A. Paluszny, C. H. Pentland, and M.J. Blunt (2011), Residual CO₂ imaged with X-ray microtomography, Geophys. Res. Lett., 38, L21403, doi:10.1029/2011GL049680.