ADCIGAngle Domain Common Image Gathers
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Figure 2 shows four ADCIGs obtained with wave-equation migration as described by Sava and Fomel (2003).
The transformation is defined from space data (ADCIGs) to space model (Radon-transformed domain) as:
In this way, the two dimensional space data of ADCIGs, d(z,[gamma]), is transformed into a three-dimensional space model, m(z,q,h).
In an ideal case, primaries would be perfectly horizontal in the ADCIGs and would thus map in the space model to the zero-curvature (q = 0) plane (e.g., a plane of dimensions depth and apex-shift distance (h,z)).
Figure 5 shows a close-up comparison of the primaries extracted with the standard 2D transform (Sava and Guitton, 2003) and with the apex-shifted Radon transform for the two ADCIGs at the top in Figure 5.
In order to assess the effect of better attenuation of the diffracted multiples on the angle stack of the ADCIGs, a total of 310 ADCIGs corresponding to horizontal positions 3000 m to 11000 m were processed (Figure 8).
As stated earlier, working with space images (ADCIGs in this case) is convenient because the migration takes care of the complexity of the wave field propagation, but attenuating the multiples after migration does not come out without a price.
Obviously, the flatter the primaries in the ADCIGs, the better are the chances to reduce the residual multiple energy.