Multiparameter full-waveform inversion of data from the Valhall field

It has been shown that full-waveform inversion (FWI) of data acquired in regions where the medium is known to be viscous yields distorted velocities if attenuation is not taken into account. In the case of velocity-only inversion in visco-acoustic media, the sensitivity of the inverted velocity to the values of attenuation must be investigated. When velocity and attenuation Q_p are simultaneously updated, the choice of the gradient preconditioner could influence the final result. Here, we perform visco-acoustic FWI of ocean bottom cable (OBC) dataset from the Valhall field. Monoparameter (velocity-only) inversion with different Q_p models yields velocities which are very similar to each other. Simultaneous inversion of velocity and Q_p with the same preconditioner used in the monoparameter case results in small differences in the obtained velocity. However, a modified wavefield preconditioner improves the inverted velocity and attenuation significantly.