Schlumberger

VIVA Visually Interactive Time-Domain Anisotropic Seismic Velocity Analysis

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

VIVA visually interactive time-domain anisotropic seismic velocity analysis is an approach to both interactive and automated VTI anisotropic time-domain velocity analysis. Examples of its use include generating Kirchhoff Prestack Time Migration (PSTM) velocity models, postmigration dense anisotropic velocity updates, creating accurate velocities for pore pressure prediction studies, and estimating initial anisotropic parameters as a starting point for depth imaging workflows.

The power of VIVA analysis 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 analysis complement our Kirchhoff (PSTM), and also provide a better starting point for an initial Velocity Model Building workflow.

The VIVA analysis 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 nonlinear 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 analysis 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.

 

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WesternGeco

An Example of Velocity Analysis

Anisotropic velocity field derived using manual picking and automatically using VIVA from a coarse seed grid.
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