Aspects of DMO correction — a summary
We discussed the principles of DMO correction and studied its practical aspects using synthetic and field data. It now is appropriate to compile aspects of DMO correction.
- The process of dip-moveout corrects for the dip effect on stacking velocities.
- Thus, it preserves conflicting dips with different stacking velocities during CMP stacking.
- The DMO stack, therefore, is a closer representation of a zero-offset section as compared to a conventional CMP stack based on normal-moveout correction, only.
- The DMO stack can then be migrated using a 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 DMO-corrected data alleviates this problem and increases the accuracy of picking an unambiguous velocity function from a velocity spectrum.
- Velocities estimated from DMO-corrected data are dip independent; therefore, they are more suitable to derive a migration velocity field as compared to velocities estimated from data without DMO correction.
- Dip-moveout 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, midpoint coordinate is variant under DMO correction.
- As a direct consequence of aspect (g), DMO correction removes the reflection point dispersal associated with nonzero-offset recording in the presence of dipping reflectors.
- Following 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 DMO-corrected data can be used for amplitude variation with offset analysis.
Figure 5.2-34 (a) Selected moveout-corrected CMP gathers associated with the earth model of point scatteres depicted in Figure 5.1-3, with amplitudes on every other trace zeroed out; (b) selected common-offset sections; (c) same common-offset sections after DMO correction; (d) selected gathers as in (a) after DMO correction.
Figure 5.2-35 (a) Zero-offset section associated with the earth model of point scatteres depicted in Figure 5.1-3; (b) the DMO stack same as in figure 5.1-7c from the gathers as in Figure 5.1-6d without missing alternate traces; (c) the DMO stack from the gathers with missing alternate traces as in Figure 5.2-34d.
In this chapter, we discussed the dip-moveout process within the context of 2-D seismic data. Three-dimensional aspects of DMO correction are discussed in processing of 3-D seismic data.