- Copyright © 2000 Society of Exploration Geophysicists
Although Kirchhoff migration is currently the tool of choice for 3-D seismic prestack depth imaging, full volume imaging using Kirchhoff methods is costly for large surveys or interactive processing. This article describes a beam methodology for Kirchhoff imaging that leads to a theoretical speedup of up to two orders of magnitude over traditional implementations of Kirchhoff migration. Beam methodology has been used routinely in Amerada Hess for generating 3-D full-volume prestack depth images for the last several years.
Since its inception in 1994, the algorithm has been continuously enhanced with new features and capabilities for more challenging data sets. Speedups of nearly one order of magnitude have been consistently achieved over conventional Kirchhoff methods.
The theory and implementation of beam methodology are presented in detail in a companion article in the November/December 2000 issue of Geophysics. This paper presents a pictorial view of beam migration concepts.
Kirchhoff imaging: A widely used and costly tool
Prestack depth migration methods come in many varieties. Reverse-time migration by finite-differencing two-way wave equations is more accurate than migration methods using high-frequency approximation, but it is much more costly for 3-D prestack depth imaging.
Significant computational reduction over reverse-time migration has been achieved by alternative approximations such as downward continuation in space-time or Fourier domains. Further computational savings are possible with additional approximations to the migration operator. These less costly alternatives retain many benefits of finite-frequency wave propagation of reverse time migration, while avoiding difficulties with caustics and multiply scattered wavefields that plague ray theory. Despite the limitations of ray theory, however, Kirchhoff migration using ray theoretical traveltimes still has many advantages and is widely used as an imaging tool. Kirchhoff migration is in fact ideally suited for parallel implementation and for target-oriented processing, and it naturally allows for the selection of ray/traveltime branches.
The disadvantage of Kirchhoff imaging is that …