Aspects of 3-D DMO correction — a summary
Because of irregular spatial sampling associated with 3-D recording geometries, the 3-D DMO process is best applied in the time-space domain using the integral method (principles of dip-moveout correction). A velocity analysis is then performed following the DMO correction to estimate dip- and azimuth-corrected velocities.
In principles of dip-moveout correction, we discussed the principles of DMO correction and studied its practical aspects using synthetic and field data. We now extend aspects of 2-D DMO correction outlined in principles of dip-moveout correction to 3-D DMO correction.
- The process of 3-D dip-moveout corrects for the dip and source-receiver azimuth effects on stacking velocities.
- Thus, it preserves conflicting dips with different stacking velocities during CMP stacking.
- The 3-D DMO stack, therefore, is a closer representation of a 3-D zero-offset section as compared to a conventional CMP stack volume of data based on normal-moveout correction, only.
- The 3-D DMO stack can then be migrated using a 3-D zero-offset migration algorithm with greater accuracy.
- Conflicting dips with different stacking velocities give rise to multivalued velocity picks from velocity spectra. Velocity analysis of 3-D DMO-corrected data alleviates this problem and increases the accuracy of picking an unambiguous velocity function from a velocity spectrum.
- Velocities estimated from 3-D DMO-corrected data are dip and azimuth independent; therefore, they are more suitable to derive a migration velocity field as compared to velocities estimated from data without 3-D DMO correction.
- 3-D DMO correction actually is a process of partial migration before stack. Specifically, it maps normal-moveout-corrected data to normal-incidence reflection points in the subsurface. As a result, the midpoint is a variant under DMO correction.
- As a direct consequence of aspect (g), 3-D DMO correction removes the reflection point dispersal associated with nonzero-offset recording in the presence of dipping reflectors.
- By 3-D DMO correction, prestack data can be implicitly regularized into common-midpoint gathers. This then facilitates sorting of prestack data into a set of common-offset volumes, each of which can be considered a replica of a 3-D zero-offset wavefield.
- Following 3-D DMO correction, prestack data can be migrated so as to create CMP gathers in their migrated position (next section). This then enables us to conduct velocity analysis to derive a migration velocity field with greater confidence.
- Finally, the CMP gathers from prestack time migration of 3-D DMO-corrected data can be used for amplitude variation with offset analysis.
- 3-D refraction statics corrections
- Azimuth dependence of moveout velocities
- 3-D dip-moveout correction
- Inversion to zero offset
- Velocity analysis
- 3-D residual statics corrections
- 3-D migration
- Trace interpolation