Accelerating isochron-ray wavefield extrapolation migration

Wavefield extrapolation isochron-ray migration (WEIM) is a wave-equation depth migration method for common-offset sections. The method uses the concepts of isochronrays and equivalent-velocity media to extend the application of the exploding-reflector model to finite-offset imaging. WEIM is implemented as a trace-by-trace algorithm in three steps: 1) equivalent-velocity computation, 2) data-conditioning for zero-offset migration, and 3) wavefield-extrapolation migration. WEIM is attractive for migration velocity analysis (MVA) because it permits the migration of common-offset sections using standard zero-offset wave-equation algorithms, which, in turn, is favorable for development of algorithms for parallel processing. The problem, however, is that WEIM is computationally expensive. The objective here is to present strategies to improve the computational performance of WEIM, perhaps making the method feasible for MVA. The reduction in computation of WEIM is achieved by redatuming and migration of beams rather than single traces, and by reducing the migration aperture. The procedures of beam formation and redatuming differ from the conventional processes described in the literature and are simultaneously applied in the data-conditioning step. The use of beams and redatuming improves the computational performance of WEIM particularly for larger offsets. In a successful application of these strategies to a fielddata example, the effective cost reduction obtained is about seven times.