Building anisotropic models for depth imaging: from imaging parameters to Earth model

Velocity model is the bridge that links our data with our images of the subsurface. Therefore our images can only be as good as our velocity models. Moving to “difficult oil” in sub-salt, sub-basalt and generally deeper targets, we can no longer afford the compromises of simplistic models we did in the past. Doing that leads to poor or no image areas. To fully leverage potential of new data types (wide azimuth, long offsets), we have to put a realistic complexity into our models. To address these challenges industry moved into using anisotropic earth models as a new standard (vertical and tilted transverse isotropy or VTI and TTI). Incorporating anisotropy increases our ability to fit the data and image every single piece of it. However growing expectations requires not only focusing the image but also accurately positioning seismic images for drilling. While this is achievable with anisotropic models, it only occurs when geology and data from boreholes are intimately incorporated into velocity model building from the very start.