The buoyant CO2 will collect under a curved layer of impermeable rock at the highest point, unable to move out of the formation.
The CO2 is trapped when there is a sudden change in the rock formations, so that the CO2 cannot move further upwards.
CO2 can become trapped when there is a change in the type of rock in the formation from a permeable rock to an impermeable rock.
As time goes on, increasingly secure trapping mechanisms come into play and the overall security of storage increases
CO2 will be trapped as a supercritical fluid in tiny pore spaces in the storage rock, as is shown by the blue spaces between the white grains of quartz in this photograph of a microscopic section of storage
CO2 will be injected at depths below 0.8 km (2600 feet ). CO2 increases in density with depth and becomes a supercritical fluid below 0.8 km. Supercritical fluids take up much less space, as shown in this figure, and diffuse better than either gases or ordinary liquids through the tiny pore spaces in storage rocks. The blue numbers in this figure show the volume of CO2 at each depth compared to a volume of 100 at the surface
Carbon dioxide storage needs rocks with both porosity and permeability.
Seismic imaging uses reflected sound waves to create pictures of underground rock formations. Pictures such as this show potential CO2 reservoirs and seal rocks as well as other geologic features such as faults.
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