In many parts of the world, natural carbon dioxide is found in geological formations where it has been trapped in sedimentary rock types in much the same way as oil and gas. The intention is to make the conditions for geological storage resemble the conditions in these natural CO2 storage sites.
Depleted oil and gas fields have demonstrated an ability to hold oil and gas over millions of years. They have great potential to function as long-term storage sites for CO2. Another alternative is to inject CO2 into active oil and gas fields to enhance the recovery of oil and gas.
There are also geological formations that are filled with salty water that can be suitable as storage sites. CO2 partially dissolves in the water and can in some cases slowly react with minerals and form carbonates. Regardless of what option is selected, the storage site will be covered with an impermeable layer of rock, known as cap rock, that prevents leakage. When the storage site has been filled, it will be permanently sealed and put under constant surveillance.