A Skeptic’s View of Vvaz and AVAz

We have applied a modern amplitude- and azimuth-preserving seismic data processing workflow to the SEG Advanced Modeling Corporation (SEAM) Phase II Barrett classic data set — an orthorhombic synthetic seismic model that has extremely dense sampling of all azimuths and offsets. We analyze the resulting prestack depth-migrated offset vector tiles with a variety of methods and software. Note that we only analyze the P-P wave mode, which is the focus of our study. We demonstrate that observed azimuthal changes cannot be correlated with the model’s reservoir properties. We have made the migrated data available through SEAM.

Compared to modeled data, real onshore seismic data have significantly lower amplitude fidelity, higher noise levels, and more uncertainty in the migration velocity field used for processing. Since we are unable to relate the anisotropy measured from the fully sampled clean SEAM Phase II Barrett synthetic seismic data to the model’s known anisotropy, we concluded that it is highly unlikely that azimuthal variations observed on real onshore seismic data will be predictive of reservoir fracture properties. Further to recent industry discussions, stimulated by our original publications, we are revisiting some aspects in our workflow to assess whether that will make a material difference.

Speaker Bio

Norbert Van De Coevering

Van de Coevering graduated from Utrecht University in the Netherlands with a Masters in Geophysics and started his career almost 25 years ago with CGG in London. Before joining Oxy in Houston in 2016 he worked at Murphy. Currently he is manager geophysics for Oxy Oman and served as AVOSI session chair for IMAGE21 and SEG 2020 Conferences. His main interests are in seismic data conditioning and all aspects of quantitative interpretation and data integration. He has co-authored various publications.