Sinking CO₂ in Supercritical Reservoirs

Geologic carbon storage is required for achieving negative CO₂ emissions to deal with the climate crisis. The classical concept of CO₂ storage consists in injecting CO₂ in geological formations at depths greater than 800 m, where CO₂ becomes a dense fluid, minimizing storage volume. Yet CO₂ has a density lower than the resident brine and tends to float, challenging the widespread deployment of geologic carbon storage. Here, we propose for the first time to store CO₂ in supercritical reservoirs to reduce the buoyancy-driven leakage risk. Supercritical reservoirs are found at drilling-reachable depth in volcanic areas, where high pressure (p > 21.8 MPa) and temperature (T > 374°C) imply CO₂ is denser than water. We estimate that a CO₂ storage capacity in the range of 50-500 Mt yr^-1 could be achieved for every 100 injection wells. Carbon storage in supercritical reservoirs is an appealing alternative to the traditional approach.