Acknowledgments

We thank Henri Calandra (ELF) and Patrice Ricarte (IFP) for the synthetic and real data set from the North Sea and interesting discussions. The first author thanks INTEVEP S.A. for financial support.

 

kzdispesion
Figure 1 Receiver component of the dispersion equation of the extended split-step prestack migration for different reference velocities for the zero-offset case. Imaginary k_z are plotted as negative values.

 

SPKEVANESZERO
Figure 2 Impulse response with 10 reference velocities without (left) and with (right) evanescent energy in the linear interpolation. The velocity field has a lateral and vertical linear gradient of 0.5 s^-1. Notice that the migration operator using evanescent energy (figure on the right) can handle steeper events.

 

ELFNOEVANESPRE2000
Figure 3 Extended split-step prestack migration without evanescent energy using 8 reference velocities.

 

ELFEVANESPRE2000
Figure 4 Extended split-step prestack migration using evanescent energy using 8 reference velocities (close up of Figure 8).

 

ELFVEL200
Figure 5 Close up of salt dome velocity model (ELF-IFP).

 

ELFEVANESPRE32
Figure 6 Extended split-step prestack migration with evanescent energy using 5 reference velocities and maximum offset 800m (Close up of Figure 8). Observe how the very steep events are imaged using fewer offsets.

 

ELFEVANESPRE
Figure 7 Extended split-step prestack migration with evanescent energy using 8 reference velocities.

 

ELFEVANESPRE32full
Figure 8 Extended split-step prestack migration with evanescent energy using 5 reference velocities and maximum offset 800m. Notice that the salt dome base is imaged reducing the number of offsets.

 

REALelf
Figure 9 Extended split-step prestack migration of the real data set using 5 referenece velocities and with all the data offsets.

 

ELFVEL
Figure 10 Salt dome velocity model (ELF-IFP).

 

VelSEG1300
Figure 11 Velocity depth slice at 1300m of the SEG-EAEG model.

 

SEGIN10v1300
Figure 12 Depth slide at 1300m of the 3-D extended split-step zero-offset migration of the SEG-EAEG stack data using evanescent energy in the wavefield interpolation, and 10 reference velocities (see Figure 11).

 

VelSEGVEL7500T
Figure 13 SEG-EAEG velocity field for the in-line section in Figure 14.

 

SEGIN10v7500T300
Figure 14 SEG-EAEG 3-D split-step migration using 10 reference velocities, in-line section at 7500m.