| K3D:
3-D Kirchhoff Prestack Depth
Migration 3DGeo's 3-D Kirchhoff prestack depth migration (K3D)
package is based on a state-of-the-art implementation of the
algorithm designed to achieve maximum efficiency on parallel-vector
and cache-based supercomputers. The algorithm includes several
choices of anti-aliasing and an amplitude equalization operator
to preserve the amplitude information in the final image even
when the spatial sampling of the input data is irregular. Through
scaling of the input and output data K3D can be run on workstations
as well as supercomputers, though the best efficiency is obtained
on larger computing platforms.
 Geophysical
Aspects
Kirchhoff migration is recognized as the most flexible method
of imaging prestack 3-D seismic data. 3-D prestack migration
of surface seismic data is the ultimate tool for imaging the
Earth's subsurface in areas of complicated geological structure
and velocity. Kirchhoff migration is particularly appropriate
for 3-D prestack data, because of its flexibility in imaging
irregularly sampled data and because of its relative computational
efficiency. Kirchhoff migration images seismic data by approximately
solving the wave equation with a boundary integral method.
The acoustic reflectivity at every point of the Earth's interior
is computed by summing the recorded data on multidimensional
surfaces; the shape of the summation surfaces and the summation
weights are computed from the Green's functions of the single
scattering wave propagation experiment.
Green's function computation
One of the main elements of 3-D prestack Kirchhoff depth migration
is the traveltime tables used to parameterize the asymptotic
Green's functions. 3DGeo's GETT3D software module offers a
very fast and stable solution for generating the 5-D traveltime
tables needed for 3-D Kirchhoff migration. GETT3D is a 3-D
traveltime computation module based on an extremely fast proprietary
finite-difference algorithm (patent pending). The algorithm
is unconditionally stable in complex velocity media and correct
to the order of accuracy of the finite-difference solution.
Green's function tables can be compressed before storage.
K3D offers both the option of using uncompressed or compressed
traveltime tables.
K3D: an advanced migration
algorithm At the core of the K3D package is the data summation
engine, designed to execute efficiently on parallel-vector
and cache-based supercomputers. The K3D inner kernel uses
very long vectors to take advantage of vector architectures
while the output image is divided into processing blocks that
are distributed over parallel processors. The problem of load
balancing the computation across processors is solved by exploiting
the locality of the Kirchhoff migration operator; that is,
a seismic data record collected in a certain area of the survey
will mostly contribute to the part of the seismic image that
is directly below the recording location. Locality is exploited
by designing an optimal partitioning scheme for both the input
and the output data.
The user can choose from
several anti-aliasing methods that enhance the imaging and
resolution of steep faults and salt-sediment interfaces.
Scalable software implementation
3-D prestack data processing requires very powerful computers
for efficiently handling the large number of computations
necessary to accurately image the data. While more efficient
on large platforms, 3DGeo's K3D software can be run on
a variety of computer sizes and architectures. Through scaling
of the input and output data, the design of the K3D ensures
that the same problem can be solved on workstations or supercomputers.
Easy Integration The K3D
package is modular in design and can be customized and integrated
into a client's specific environment. K3D is available
on Unix workstations, parallel-vector and cache-based supercomputers,
and other architectures. If desired, 3DGeo can integrate the
package into a client's processing environment or add it as
a Promax, Focus or Views module.
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