How safe is the underground storage of CO2?
It can be said that the storage of CO2 in the deep underground has only minor, manageable risks. Storage safety basically implies two phases: the operations phase during injection, and the long term safety after the closure of the storage site. During the operations phase, the single most important safety factor is the safe technological handling as known from “best practice” procedures, developed from decades of oil & gas production and the operation of gas storage sites. Compared to natural gas (methane), CO2 is even less dangerous, because it is neither explosive nor flammable. On the other hand, long term safety is ruled by the geological conditions of the storage site and its vicinity. To ensure an impact on climate and to keep the stored CO2 safely away from the biosphere, it must remain underground for at least 10,000 years. From natural gas reservoirs, we know that certain geological strata are capable to hold gases in place for millions of years. This would also apply for CO2.
