Time migration velocity analysis by velocity continuation

Conclusions

Velocity continuation is a powerful method for time migration velocity analysis. The strength of this method follows from its ability to take into account both vertical and lateral movement of the reflection events in seismic images with the changes of migration velocity.

Efficient practical algorithms for velocity continuation can be constructed using either finite-difference or spectral methods. When applied in the post-stack (zero-offset) setting, velocity continuation can be used as a computationally attractive method of time migration. Both finite-difference and spectral approaches possess remarkable invertability properties: continuation to a lower velocity reverses continuation to a higher velocity. For the finite-difference algorithm, this property is confirmed by synthetic tests. For the spectral algorithm, it follows from the fact that velocity continuation reduces to a simple phase-shift unitary operator.

Including velocity continuation in the practice of migration velocity analysis can improve the focusing power of time migration and reduce the production time by avoiding the need for iterative velocity refinement. No prior velocity model is required for this type of velocity analysis. This conclusion is confirmed by synthetic and field data examples.

Time migration velocity analysis by velocity continuation