Velocity Model Building Solutions

Geologically Constrained Model Building

Interpretive Velocity Model Building for Accurate Depth Imaging

An Interpretive Approach to Velocity Model Building

We primarily use a Kirchhoff algorithm because it allows us to calculate anisotropic traveltimes from exact source and receiver elevations in rough terrain. Taking an interpretive approach to model building, the fast turnaround of our highly optimized anisotropic depth migration algorithm allows us to experiment with a variety of velocity-model interpretations in our quest for an optimum imaging solution.

PSDM stack showing structural interpretation and depth velocity model
The automated method of generating dips (top image) is based on reflector coherency, which can result in large errors in highly structured areas due to increased noise content and event complexity. We instead use an interpretive method (bottom image), in which the dips generated from the picked horizon geometry.

Integration of Geological Knowledge and Interpretation

Building these velocity models involves close collaboration with the interpretation team. We have software to efficiently build the models and migration algorithms that produce sharp images, but it is the local domain-knowledge that allows us to converge to a geologically accurate velocity model. We further evaluate the accuracy of the model using well calibration and seismic diagnostics such as image gather flatness, reflection continuity and fault sharpness.

Kirchhoff Anisotropic (TTI) Depth Migration Workflow

Final Depth Imaging and Residual Analysis

  • Final prestack anisotropic depth migration
  • Residual velocity analysis (NMO focussing) to improve the final image
  • Stack migrated and focussed gathers; apply filter, scaling, cosmetics as necessary

Iterative Velocity Model Updating

Update velocity model and re-migrate through the required number of iterations to optimize the velocity model:

  • Maximize flatness of image gathers
  • Minimize depth error between seismic reflectors and well tops

Initial Velocity Model from Interpretation

In collaboration with interpreter, define initial velocity model from interpretation of prestack-time-migrated section

Incorporation of Anisotropic Parameters

Incorporate anisotropic parameters epsilon and delta

Use dip meter information from logs and geological input from interpreter to accurately define the dip field for TTI anisotropy correction

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