6. Safe Operation of Geological CO₂ Storage Using the Example of the Pilot Site in Ketzin

Reservoir rocks with the potential for storing CO₂ are mainly sandstones. In them, four trapping mechanisms facilitate permanent and safe storage: (i) structural trapping below an impermeable caprock, (ii) immobilization via capillary forces in the pore space, (iii) dissolution of CO₂ in the formation water, and (iv) mineral trapping via carbonization. Because leaks can occur monitoring of CO₂ storage sites is essential. However, the technological risks appear to be manageable. This is emphasized by the experience from the first continental European field laboratory in Ketzin, Germany. The results show that: (i) the geological storage of CO₂ is safe and reliable, and poses no danger to humans or the environment, (ii) a well-thought-out combination of different geochemical and geophysical monitoring methods can detect small amounts of CO₂ and image its spatial distribution, (iii) the interactions between fluid and rock induced by CO₂ injection at the pilot site in Ketzin have no significant impacts and do not influence the integrity of the reservoir or the caprock, and (iv) numerical simulations can depict the temporal and spatial behaviour of injected CO₂. In addition, results from studies at Ketzin provide basic and transferable knowledge which is of value for a new integrated concept of CO₂ mitigation and utilization in combination with the power-to-gas concept based on a closed carbon cycle approach.