Proven CCS projects (Carbon Brief lists 22 at present) are few and far between at present. One of the reasons is safe, secure underground storage. Currently working CCS projects are pumping captured carbon dioxide (CO2) into depleted oil and gas reservoirs, sandstone and salt formations. The advantage of storing the CO2 in depleted oil and gas reservoirs is the proven retention that the site provides. After all, these are voids that harboured millions to billions of barrels of oil and equivalent natural gas volumes for hundreds of millions of years without significant leaks to the surface. There is no guarantee, however, that these depleted oil or gas reservoirs remain suitable after the hydrocarbons have been removed. So even these need to be assessed for suitability.
