**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

*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.*

**velocity**
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

*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.*

**velocity**AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid