Science and monitoring

Integral to the safe geological storage of CO2 is selection of a suitable site.Once selected the site needs to be monitored before, during and after the CO2 has been injected.

Site characterisation is the analysis and interpretation of subsurface, surface and atmospheric data in order to assess whether or not an identified site is suitable to store a specific quantity of CO2 for a defined period of time and meet all required health, safety, environmental and regulatory standards.

Comprehensive site characterisation was undertaken in selecting the site of the Otway Project.

There are a number of geological storage options for CO2. The geological conditions required are:

• a porous (containing tiny spaces which store the CO2) and permeable (containing pathways that allow the CO2 to flow from the point of injection and through into the spaces) reservoir rock;
• a trap (five basic mechanisms hold the CO2 in place: stratigraphic, structural, residual, solubility, and mineral trapping);
• and an impermeable caprock, which prevents the CO2 from migrating toward the surface.

Measurements need to be taken before, during and after the injection of the CO2 to determine the amount of CO2 in the air, soil, ground water and in the storage rock. The CO2 can be traced as it moves through the deep underground rock reservoir and any unlikely leaks can be detected. Also the environmental impact of the injection can be monitored.

Geosequestration experts from the International Energy Agency’s Greenhouse Gas Research and Development Programme reviewed the Otway monitoring program in November, 2006, and found it was one of the most comprehensive in the world.

Site characterisation and monitoring both involve a wide range of scientific techniques from areas such as geology, geochemistry, geophysics, atmospheric physics, hydrology, fluid dynamics and mathematical modelling.