Project Objectives

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.