After a certain quantity of CO2 has been injected, for instance into a deep lying porous sandstone formation, the propagation of the CO2 plume can be traced (monitored) by established geophysical methods. Appropriate are mainly time-lapse seismic and geoelectric monitoring.
The example below shows 3D-seismic data reflecting the development of the CO2 plume in the highly porous sandstones of the Utsira-Formation at Sleipner (Norway) between 800 and 1200 meters depth. The baseline data were acquired in 1994, followed by repeat surveys in 1999, 2001, 2002, 2004, and 2006 corresponding to 2.30, 4.20, 4.97, 6.84, and 8.4 million tonnes (Mt) of CO2 in the reservoir (Arts, R. et al. 2008).
Development of the CO2 plume over the years imaged with seismic data (Arts, R. et al. 2008).
For long term predictions of the CO2 migration, numerical modelling tools are used. These tools simplify a complex site-specific system and therefore needs to be proved by on site measurements and calibrations during the operational and post closure phase of a CO2 storage life cycle. If the results are satisfying and the measured data conform with the modelled behaviour (high level requirement), then predictions for hundreds or even thousands of years are possible with sufficient certainty.
Arts, R., Chadwick, A., Eiken, O, Thibeau, S., and Nooner, S. (2008): Ten years’ experience of monitoring CO2 injection in the Utsira Sand at Sleipner, offshore Norway, first break volume 26, January 2008, special topic – CO2 Sequestration, pp. 65-72 2008 EAGE.