Before large-scale underground CO2 storage can take place, it will be necessary to demonstrate that the
processes are well understood, risks to the environment and human populations are low, and environmental
disturbances can be minimised. One way of demonstrating that CO2 can remain trapped underground for
geologically significant timescales is to provide evidence from existing naturally occurring
accumulations. These accumulations occur in a variety of geological environments and ages that
are analogous to those being considered for CO2 storage.
The study of natural analogues is crucial to understanding the long-term impact of CO2 storage.
Such long-term effects cannot be addressed by laboratory experiments. However,
long-term water-rock-gas interactions may affect the CO2 storage capacity, the porosity
and permeability of the host formation, the integrity of the caprock, ground stability, and
quality of groundwaters in overlying aquifers.
A geothermal exploration well, near St. Moritz, Switzerland. When opened,
pure CO2 and water vapour are emitted up to 5m into the air. Photo kindly supplied by Werner Leu,
Geoforms Ltd., Winterthur, Switzerland.
If geological CO2 sequestration is to become acceptable, certain key issues must be addressed.
These include the long-term safety and stability of storage underground and the potential
environmental effects of leakage from an underground reservoir. Natural CO2 fields are
direct natural analogues for geological storage. Sites where CO2 is actively migrating to
the surface, are analogues of CO2 leakage. They therefore provide natural laboratories in
which to address these issues. Specific objectives include:
- Proof of concept — does the existence of natural CO2 accumulations offer confidence that long
term geological sequestration is a viable and safe option for reducing greenhouse gas emissions?
- What environmental hazards, such as induced seismicity, ground movement, groundwater contamination,
leakage to the biosphere and atmosphere, do natural analogues indicate might be associated with the
geological storage of CO2?
- The provision of a sound basis for experiments and modelling of the long term safety and stability
of geological CO2 storage through the study of natural analogues.
- The application of field management techniques used in natural, commercially exploited CO2 fields
to potential geological sequestration of carbon dioxide.
The relationship between faults, seismicity and natural CO2 emissions in the Florina area of Greece will be studied in the NASCENT project.