Migration Velocity Analysis Using Seismic Multiples
C. D. Manuel
Curtin University of Technology, Dept. of
Exploration Geophysics, Perth, Australia
Migration velocity analysis (MVA) is an essential component of the
velocity model
building technique in complex geological areas and
depth migration is the process whereby seismic data in the timeoffset
domain is mapped to the depth domain. After migration with
a certain velocity, the curvature remaining on a primary reflection
gives an indication of the variance from the true average velocity of
the primary. If migration is performed with the correct velocity then
the reflector will appear flat. This is done for each primary reflection
to find the velocity structure as a function of depth. The process is
repeated for other surface locations until a velocity
model
is generated
for the region.
The present research includes the analysis of multiple reflections
in MVA. Any initial error in velocity between the migration and
interval velocities will be increased as the distance traveled through
the Earth increases. Hence in migration, multiples will be more sensitive
than primaries to changes in the velocity model
. On a coherency
plot, multiples will stack in a more localized region. This should
result in increased accuracy in determining interval velocity and interval
thickness. It should also reduce the number of migration iterations
needed to converge on an accurate solution. This has implications
for reducing the time and cost of the MVA process. The
ability to create a more accurate velocity
model
will mean that the
depth image obtained from seismic data will be much more accurate.
This will in turn enable more accurate positioning of wells.
AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid