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 micro‐
tomography (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