Enhanced imaging of multi-layer CO2 plumes using full-waveform inversion: Insights from the Sleipner storage site

• We apply full-waveform inversion (FWI) up to 42 Hz, using the 2010 towed-streamer data from the Sleipner storage site offshore Norway. • The inversion offers a significant imaging improvement in the lower half of the plume compared with the legacy seismic data. • Reflection-based migration methods present limitations for imaging CO₂ migration pathways. • By using the entire wavefield, the inversion captures all pathways previously interpreted with time-lapse analyses and reveals new migration pathways, providing a better understanding of vertical CO₂ migration at the site. In this study, we demonstrate the benefits of applying full-waveform inversion (FWI), for the imaging of multi-layer CO 2 plumes. We apply 3D FWI, up to 42 Hz, using the 2010 towed-streamer data from the Sleipner storage site offshore Norway. While the 3D FWI method does not aim to replace 4D FWI for CO 2 migration monitoring, the properties of the Utsira aquifer at Sleipner, with low stiffness and shallow burial depth, enable effective mapping of the CO 2 without the need of a repeated FWI application. Our FWI model and associated images offer a significant imaging improvement in the lower half of the plume compared with the legacy seismic data, revealing vertical CO 2 migration routes that have not been observed previously at the site. We show the limitations of reflection-based migration methods for imaging CO 2 migration pathways and demonstrate that FWI can improve their detection. The FWI model can support conventional time-lapse analyses by improving the interpretation of known CO 2 migration routes, by highlighting CO 2 layers with low reflectivity, and by attenuating multiples better. Our analysis suggests that CO 2 migration at Sleipner is likely controlled by several vertical communication routes, including chimneys, and linear structures, several hundreds of meters long, that connect multiple accumulations of CO 2 . Within each layer, our analysis suggests buoyancy-driven, fill-to-spill migration, constrained by the topography of the sealing units. Finally, we conclude that, while simple CO 2 accumulations can be monitored successfully using reflection-based migration methods and analyses, multi-layered CO 2 plumes will greatly benefit from complementary analyses using FWI.