Monitoring of CO₂ Sequestration At the Sleipner Site - Time Lapse Seismic Full Waveform Inversion Versus Migrated Waveforms Available to Purchase

Time lapse seismic imaging of injection of carbon dioxide (CO2, ) into the Utsira Sand at Sleipner, Norway, has proven to be a very succesful monitoring tool. However, complex propagation modes due to strong impedance contrast could impede deduction of quantitative information from migrated images. Here we use elastic 2D full waveform inversion (FWI) in the time lapse mode to quantify changes in P-wave velocities (V, p, ) due to CO2, injection at the Sleipner site and compare these results with corresponding migrated seismic data. We find that the maximum amplitude change in migrated images does not always coincide with maximum CO2, saturation indicated by FWI. For example, there are places, where the inversion result suggests a relatively high CO2, saturation near the base of Utsira Sand and the migrated image indicates significant amplitude changes only in the upper half of the aquifer. Furthermore, CO2, saturation from FWI is laterally more heterogeneous than amplitude changes observed from migrated images suggest.