High-resolution seismic attenuation imaging from wide-aperture onshore data by visco-acoustic frequency-domain full-waveform inversion

International audience; Here we assess the potential of the visco-acoustic frequency domain full-waveform inversion (FWI) to reconstruct P-wave velocity (VP) and P-wave attenuation factor (Q) from surface onshore seismic data. First, we perform a sensitivity analysis of the FWI based upon a grid search analysis of the misfit function and several synthetic FWI examples using velocity and Q models of increasing complexity. Subsequently, we applied both the acoustic and visco-acoustic FWI to real surface wide-aperture onshore seismic data from the Polish Basin, where a strong attenuation of the seismic data is observed. The sensitivity analysis of the visco-acoustic FWI suggests that the FWI can jointly reconstruct the velocity and the attenuation factor if the signature of the attenuation is sufficiently strong in the data. A synthetic example corresponding to a homogeneous background model with an inclusion shows a reliable reconstruction of VP and Q in the inclusion, when Q is as small as 90 and 50 in the background model and in the inclusion, respectively. A first application of acoustic FWI to real data shows that a heuristic normalization of the data with offset allows us to compensate for the effect of the attenuation in the data and reconstruct a reliable velocity model. Alternatively, we show that visco-acoustic FWI allows us to reconstruct jointly both a reliable velocity model and a Q model from the true-amplitude data. We propose a pragmatical approach based upon seismic modelling and source wavelet estimation to infer the best starting homogeneous Q model for visco-acoustic FWI. We find the source wavelet estimation quite sensitive to the quality of the velocity and attenuation models used for the estimation. For example, source-to-source wavelets are significantly more consistent when computed in the final FWI model than in the initial one. A good kinematic and amplitude match between the early-arriving phases of the real and time-domain synthetic seismograms computed in the final FWI model provides an additional evidence of the reliability of the final FWI model. We find the recovered velocity and attenuation models consistent with the expected lithology and stratigraphy in the study area. We link high-attenuation zones with the increased clay content and the presence of the mineralized fluids.