Aspects of 3-D prestack time migration — a summary
The improvement in imaging with 3-D prestack time migration may sometimes be marginal compared to imaging with 3-D poststack time migration of 3-D DMO-stacked volume of data. Nevertheless, the benefits of 3-D prestack time migration are not limited to the improved image of the subsurface as listed below.
- 3-D prestack time migration is the appropriate strategy for imaging conflicting dips with different stacking velocities, such as reflections from steeply dipping fault planes with 3-D geometry and gently dipping strata.
- The 3-D image volume derived from 3-D prestack time migration is used as an input to 3-D zero-offset amplitude inversion to estimate an acoustic impedance model of the earth (acoustic impedance estimation).
- The CRP gathers from 3-D prestack time migration are used to perform prestack amplitude inversion to derive amplitude variation with offset (AVO) attributes (analysis of amplitude variation with offset).
- The 3-D image volume can be inverse migrated by way of 3-D zero-offset wavefield modeling to derive an unmigrated 3-D zero-offset data volume.
- The 3-D rms velocity field estimated from the 3-D prestack time-migrated data, as from step (f) of the workflow described above, can be used to derive a 3-D interval velocity field by Dix conversion.
- Finally, the 3-D interval velocity field and the 3-D zero-offset wavefield can be used to derive an earth image in depth by 3-D poststack depth migration. The earth image volume in depth can then be interpreted to delineate a set of reflector geometries associated with key geological markers. The interval velocity field combined with the reflector geometries may be used to build an initial earth model in depth (earth modeling in depth).
- 3-D prestack time migration
- 3-D DMO correction combined with 3-D common-offset migration
- Crossline migration
- 3-D migration velocity analysis