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Monitoring CO2 geological storage reservoirs with seismological broadband noise - the Ketzin experiment

ESC 2010, European Seismological Commission, Montpellier, France
M. Delatre & C. Sens-Schönfelder (Univ of Leipzig)
Monitoring CO2 storage reservoirs over long periods of time is mandatory to ensure the safety of the CO2 storage process, as the European Parliament Directive states. To ensure this goal, several methods are already available; however, they either require expensive costs (time-lapse active seismic surveys) or wells that affect the reservoir integrity (downhole microseismic instrumentation). The development of long range correlation of seismic noise allows us to consider new monitoring methods : by inferring the Rayleigh wave dispersion and its variation over time from ambient seismic noise recordings, we may be able to measure S speed variations in different layers.In order to test this method, we set up a broadband array on the CO2 injection pilot at Ketzin (Germany) and recorded 5 months of data. 14 day stacks were enough to build stable correlations and allowed us to study the Rayleigh wave dispersion between 0.8 and 6 Hz. Several Rayleigh branches were observed. We were able to invert these dispersion curves and obtained the S vertical speed profile for the first hundred meters; looking at different time periods, we looked for temporal variations of S wave speed induced by the CO2 injection. We compared these observations to models of the influence of the CO2 plume presence on Rayleigh wave dispersion.