Why do seismic attenuation models enhance time-lapse imaging? A 2D viscoacoustic full-waveform inversion case study from the Volve field

Seismic attenuation, which leads to amplitude decay and phase velocity dispersion, reflects the mesoscopic heterogeneities in fluid-saturated porous media. As a result, seismic attenuation offers valuable insights into the lithology of porous sediments. We apply 2D viscoacoustic full-waveform inversion (Q-FWI) to the time-lapse data sets acquired in the North Sea Volve field to characterize the shale-sandstone sequence and oil reservoir and its production-related time-lapse changes. The Hessian approximated by Newton-conjugate gradient method and frequency-independent Q viscoacoustic wave propagation modeling enable its practical application. Time-lapse Q-FWI, applied to true-amplitude seismic data, produces high-resolution baseline and monitoring velocity and attenuation models as well as their time-lapse changes related to production, all of which are correlated with well-log data and align with prior knowledge of the field’s lithology, stratigraphy, and production history. These results confirm that the porous shale-sandstone sequence, with high intrapore clay content in the overburden, is the primary source of seismic attenuation in the Volve field. Furthermore, the observed time-lapse velocity and seismic attenuation changes indicate water replacement in the reservoir and resultant geomechanical changes in the reservoir and overburden caused by oil production and water injection.