--> --> Abstract: Pitfalls in Velocity Analysis Using Common-Offset Time Migration, by Y. C. Kim and J. R. Krebs; #90981 (1994).
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Abstract: Pitfalls in Previous HitVelocityNext Hit Analysis Using Common-Offset Time Migration

Y. C. Kim, J. R. Krebs

Integral based common-offset time migration is a robust and cost-effective tool for migration Previous HitvelocityNext Hit analysis. In practice this method is not applied iteratively, and travel times are often computed without properly accounting for ray bending in a layered earth. For dipping reflectors these practices can lead to erroneous Previous HitvelocityNext Hit estimates.

The Previous HitvelocityNext Hit of an event measured by common-offset time migration Previous HitvelocityNext Hit analysis is fairly insensitive to the initial migration Previous HitvelocityNext Hit even for dipping reflectors. However, the time at which that event occurs is very sensitive to the initial migration Previous HitvelocityNext Hit. This is because errors in the initial Previous HitvelocityNext Hit result in under or over migration of the event. For example, if the initial Previous HitvelocityNext Hit is too slow, the data will be under migrated, and the Previous HitvelocityNext Hit event from a dipping reflector would appear at approximately correct Previous HitvelocityNext Hit but at a time that is too early. When velocities increase with depth, this error would cause us to pick a Previous HitvelocityNext Hit function that is faster than the correct function. However, this new Previous HitvelocityNext Hit function will generally be closer to the correct Previous HitvelocityNext Hit than the initial migration Previous HitvelocityNext Hit. Convergence to the correct Previous HitvelocityNext Hit usually occurs after a few iterations.

It is important to account for ray bending when computing travel times, even for time migration. Coincident reflections having different dips focuses at different velocities if ray bending is ignored. Thus, we must choose between the Previous HitvelocityNext Hit that optimizes one dip or the other but not both. By properly accounting for ray bending, all dips are focused at the same Previous HitvelocityTop, producing significant improvements in the final image.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994