ABSTRACT: Migration
of Velocity Spectra: An Example from the Timor Sea
BEASLEY, J. CRAIG, and ROLF KLOTZ, Western Geophysical Company, Singapore
Successful seismic imaging of complex geology such as that found in the Timor Sea requires accurate migration
of the seismic data to collapse diffractions, image faults, and position reflectors in the correct spatial location. Although today's
migration
algorithms in theory generally are accurate, in practice
migration
accuracy for steep dips critically depends on the
migration
velocity.
An approach used routinely to estimate the migration
velocity is to minimize the effects of dip and azimuth by applying dip movement (
DMO
) to the data. However, velocity derived from
DMO
-corrected data is located at an unmigrated position and should be repositioned prior to use as a
migration
velocity. The effect of this phenomenon will be demonstrated through an example from the Timor Sea in which, prior to
migration
, reflections and diffractions from a complex system of faulted carbonates conflict with low-relief primary reflections resulting in poorly resolved velocity analyses.
This problem can be overcome by employing conventional migration
to migrate the
DMO
velocity to the proper spatial location prior to migrating the seismic data. Velocity spectra are generated first from
DMO
-corrected data on a regular spatial grid and then common-velocity slices are extracted and migrated. Finally, the migrated velocity is reassembled at common spatial locations into velocity spectra, which provide a better estimate of the true subsurface velocity.
By applying conventional migration
principles to migrate velocity derived from
DMO
-corrected data, velocity is placed at the correct spatial location as required for
migration
. The method provides an automated, efficient, and accurate procedure for determining
migration
velocity.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)