Joint-velocity model building and high-resolution depth imaging of full-wavefield 3D VSP data

Abstract

3D Vertical Seismic Profile (VSP) surveys play an important role in seismic exploration and reservoir development. This is mainly due to the higher data-quality and broader frequency bandwidth relative to surface seismic data, which as a result provides higher-resolution image around the borehole. Conventional VSP imaging techniques mainly utilize the separated and deconvolved Pwave reflections which provide an excellent image around the borehole but the quality and the coverage degrade both laterally away from the borehole and spatially with increasing depth. Moreover, the final migration velocity model is commonly built from checkshots as the initial flatlayered model and updated using first-break travel-time tomography and slowness inversion; however, the update only covers the cone-shaped area around the borehole which the direct-wave passed through. The full 3D borehole signal, which includes all multiple scattering from both up- and down-going wavefields data, should be used to improve the subsurface illumination and to accurately update both the image and the velocity model away from the borehole. The Joint Migration Inversion (JMI) technique offers a comprehensive solution by comparing the modeled data to the measured data iteratively. The JMI forward modeling algorithm is based on the reflectivity and the propagation velocity in which it may provide an alternative to resolve our non-linear inversion problem faced in traditional Full Waveform Inversion (FWI). Consequently, it yields a true-amplitude reflectivity image with a relatively higher resolution and larger lateral extent as well as a smooth updated background velocity model. In this paper, we apply the 3D JMI to 3D borehole field data from the Arabian Gulf of Saudi Arabia.