Tasks and challenges of geochemical monitoring

A variety of monitoring tools are available for the various purposes of supervision and verification of underground geological CO 2 storage. Geophysical tools can provide an indirect indication of the migration of substances in the subsurface or leakage through overburden. Geochemical techniques have to be applied though for verification of the nature of substances involved. Chemical species may be indicators for storage processes. Some can be harmful to the environment outside of the storage complex and thus appropriate monitoring of affected or endangered environments may be required. Natural CO 2 reservoirs, CO 2 ‐rich groundwater, and saline springs can be used to study fluid transport processes that could be similar to the migration and leakage associated with underground CO 2 storage. Natural sites have been used for testing monitoring tools and learning about natural background variations. Experience gained from natural analogs and from pilot CO 2 storage monitoring reveals the potential and limitations of chemical monitoring methods. Based on these experiences, the use of baseline functions and different thresholds are recommended in order to optimize detection and quantification of geochemical deviations from variable backgrounds. Chemical monitoring tools have to be incorporated into comprehensive concepts for CO 2 storage monitoring. © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd.