Improving plane-wave decomposition and migration

Plane-wave data can be produced by slant stacking common geophone gathers over source locations. Practical difficulties arise with slant stacks over common receiver gathers that do not arise with slant stacks over common-midpoint gathers. New techniques such as hyperbolic velocity filtering allow the production of high-quality slant stacks of common-midpoint data that are relatively free of artifacts. These techniques can not be used on common geophone data because of the less predictive nature of data in this domain. However, unlike plane-wave data, slant stacks over midpoint gathers cannot be migrated accurately using depth migration. A new transformation that links common-midpoint slant stacks to common geophone slant stacks allows the use together of optimized methods of slant stacking and accurate depth migration in data processing. Accurate depth migration algorithms are needed to migrate plane-wave data because of the potentially high angles of propagation exhibited by the data and because of any lateral velocity variations in the subsurface. Splitting the one-way wave continuation operator into two components (one that is a function of a laterally independent velocity, and a residual term that handles lateral variations in subsurface velocities) results in a good approximation. The first component is applied in the wavenumber domain, the other is applied in the space domain. The approximation is accurate for any angle of propagation in the absence of lateral velocity variations, although with severe lateral velocity variations the accuracy is reduced to 50 degrees. High-quality plane-wave data migrated using accurate wave continuation operators results in a high-quality image of the subsurface. Because of the signal-to-noise content of this data the number of sections that need to be migrated can be reduced considerably. This not only saves computer time, more importantly it makes computer-intensive tasks such as migration velocity analysis based on maximizing stack power more feasible.