Building Anisotropic Models for Depth Imaging: Comparing Different Approaches

Seismic images are only as good as the velocity models used to produce them. As we move from “easy oil” to “difficult oil”, targets in subsalt, sub-basalt, and deep complex areas, we can no longer build the simple isotropic models of the past. To fully leverage the potential of new data types (e.g., wide azimuth and long offsets), we have to move to anisotropic imaging (VTI or TTI) in all geological provinces. Incorporating anisotropy increases our ability both to focus the seismic data and to accurately position our seismic images for drilling decisions. While these goals are achievable with anisotropic models, they are only met when geology and data from boreholes are intimately incorporated into velocity model building from the very start. We discuss several different approaches for anisotropic model parameter estimation and we illustrate some of the possible strategies for model building with case studies from the Gulf of Mexico and West Africa.