Advances in velocity model-building technology for subsalt imaging

Seismic imaging of hydrocarbon accumulations below salt is a formidable challenge because complexly shaped salt bodies severely distort wavefronts or scatter seismic energy. We have highlighted some recent advances in building a velocity model for subsalt imaging. There are three main stages: suprasalt velocity determination, salt-model definition, and subsalt velocity update. Volumetric high-resolution tomography that incorporates high-velocity contrast boundaries is used to derive a good sediment velocity model before building a salt model. To facilitate integration of interpretation and depth processing, beam-based interactive imaging is used to refine the salt geometry. For subsalt velocity update, either subsalt tomography or subsalt scan-based techniques can be used, depending on the quality of subsalt reflections. There are concepts and techniques for attaining subsalt images suitable for hydrocarbon exploration beneath complexly shaped salt bodies.