3D global tomographic velocity model building

Abstract

Accurate subsurface velocity estimation is crucial in seismic exploration, especially for prestack depth migration, depth conversion, geopressure prediction and AVO attribute computation. 3D reflection tomography is the most accurate method available for velocity estimation. The challenge that we face is in designing an accurate tomographic system capable of efficiently handling large volumes of seismic data acquired over increasingly complex targets. To address this need we have developed a 3D reflection tomography system using a tetrahedra‐based model parameterization. Tetrahedra are capable of accurately representing complex velocity models with far fewer control points compared with other methods. The input for our tomography comes from automatically scanned migration residuals and structural dips generated from Kirchhoff prestack depth migration. An adaptive layer‐based method is employed with flexible geological constraints, which enables global tomographic inversion of both compaction and competent geological environments. Application of global tomography to synthetic data demonstrates its ability to resolve strong and rapid velocity variations. Examples from 3D field data are shown to illustrate the benefits of this global tomographic system in estimating velocity models for large‐scale prestack depth migration projects.