New Model-Based PS Deghosting Boost Data Quality at Grane PRM

In permanent reservoir monitoring (PRM) PS data, acquired with buried receivers, we have observed a number of notches in the spectra. These notches were not present in the spectra of receivers on the seafloor. To restore the PRM PS data quality, a model-based PS deghosting method for buried receivers is proposed and tested on real data, assuming that the variation in spectra is created by strong contrasts in the shear wave velocity in the very near surface. Only predominantly vertically travelling SS-reflections and transmissions are considered, including important contribution from internal multiples. A shallow layered model is inverted for using picked notches on receiver spectra. Inverse filters, one per receiver, is constructed from the model response and applied to receiver gathers. The method was tested within a complete processing sequence and applied to PRM data from the Grane field in the North Sea. Results indicated very low S-velocities close to the seabed, in the order of 20–40 m/s. The deghosting clearly improved the continuity and resolution in the final image.