| COMAZ:
Common-azimuth migration
is a
novel 3-D prestack wave-equation migration algorithm originally
proposed by Biondo Biondi (Biondi and Palach
arla, 1996), principal of 3DGeo, as an alternative to Kirchhoff
migration for marine seismic data. Recursive methods such
as COMAZ have certain intrinsic advantages over Kirchhoff
methods. First, recursive methods are potentially more accurate
and robust because they are based on the full wave-equation
and not on an asymptotic solution based on ray theory. Second,
wave-equation methods handle multi-pathing naturally, while
Kirchhoff methods do not. Third, focusing and defocusing effects
of the velocity variations are correctly modeled by wave-equation
methods. The COMAZ implementation draws on the ample industry
experience in phase shift algorithms. The velocity variations
are handled using a split-step algorithm (Stoffa et al., 1990,
Popovici, 1996) with multiple base velocities. The phase interpolation
in areas of negative square roots is handled smoothly (Malcotti,
1998) minimizing the phase interpolation artifacts.
Downward continuation can be applied independently for shots
and for receivers, or at the same time.
The common azimuth migration
software is the first wave-equation 3-D prestack migration
package developed in the oil and gas industry. COMAZ is the
only alternative to Kirchhoff migration and the superior imaging
results obtained using COMAZ, guarantee that this technique
will become a standard processing module in the 3-D imaging
portfolio of any geophysical company. Moreover, COMAZ is not
only a 3-D prestack imaging tool, but can be used without
any modification to image, 2-D postack and prestack data,
as well as 3-D poststack data. In the absence of the 3-D crossline
term, but keeping the inline offset term, the COMAZ operator
becomes a 2-D prestack downward continuation operator identical
to the one used by Popovici (1996) for DSR split-step migration.
Keeping the 3-D crossline term, but without the offset term,
the COMAZ operator becomes a 3-D poststack operator. Therefore,
COMAZ can be used in a multitude of situations, as an extremely
versatile imaging tool.
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