VIVA: Visually Interactive Velocity Analysis (NEW October 2009)

Dense, high-resolution anisotropic velocity analysis using 1D inversion

Time-domain velocity analysis remains an important component in the geophysical toolbox. With the continued growth of anisotropic imaging, it is particularly important to be able to derive accurate, reliable, and dense anisotropic parameters at various stages in an imaging workflow.

VIVA stands for Visually Interactive Velocity Analysis, and is a new approach to both interactive and automated VTI anisotropic time-domain velocity analysis. Examples of its use include generating Anisotropic Kirchhoff Prestack Time Migration (PSTM) velocity models, post-migration dense anisotropic velocity updates, creating accurate velocities for Pore Pressure Prediction (PPP) studies, and estimating initial anisotropic parameters as a starting point for depth imaging workflows.

The power of VIVA lies in its ability to directly generate interval velocity and anisotropy (interval eta) parameters.  Conventional approaches that rely on deriving effective parameters can result in incorrect estimates, which in turn reduce the accuracy of images and subsequent interpretation and inversion. The interval parameter outputs from VIVA complement our Anisotropic Ray-Traced Kirchhoff PSTM, and also provide a better starting point for an initial Depth Model Building Workflow.

The VIVA workflow is similar to a traditional Common Image Point (CIP) Tomography approach, and is built around a new 1D layered travel-time Inversion method.  The technique performs a direct non-linear inversion of P-wave reflection travel times in layered VTI media to produce interval Vpn and Vpx velocity fields (Vpn is short-spread moveout velocity, and Vpx is horizontal velocity).  Accurate ray tracing using real earth model properties rather than effective parameters are a key requirement for achieving accuracy over the wide angles needed to estimate anisotropy.

VIVA and Kirchhoff PSTM may not always be appropriate. In areas of strong structural and velocity complexity, the assumptions of time imaging methods break down. In these cases the use of a Depth Imaging approach should be considered.

Related references

• Fowler, Paul J., Jackson, A., Gaffney, J. and Boreham, D., 2008, Direct nonlinear traveltime inversion in layered VTI media, 78th Ann. Internat. Mtg., Soc. of Expl. Geophys.
• Fowler, Paul J., Jackson, A., Gaffney, J. and Boreham, D., 2008, Direct nonlinear traveltime inversion in layered VTI media, Eur. Assoc. Geosci. Eng. annual meeting.