Converted-wave beam migration with sparse sources or receivers

摘要

Gaussian beam depth migration overcomes the single-wavefront limitation of most implementations of Kirchhoff migration and provides a cost-effective alternative to full-wavefield imaging methods such as reverse-time migration. Common-offset beam migration was originally derived to exploit symmetries available in marine towed-streamer acquisition. However, sparse acquisition geometries, such as cross-spread and ocean bottom, do not easily accommodate requirements for common-offset, common-azimuth (or common-offset-vector) migration. Seismic data interpolation or regularization can be used to mitigate this problem by forming well-populated common-offset-vector volumes. This procedure is computationally intensive and can, in the case of converted-wave imaging with sparse receivers, compromise the final image resolution. As an alternative, we introduce a common-shot (or common-receiver) beam migration implementation, which allows migration of datasets rich in azimuth, without any regularization pre-processing required. Using analytic, synthetic, and field data examples, we demonstrate that converted-wave imaging of ocean-bottom-node data benefits from this formulation, particularly in the shallow subsurface where regularization for common-offset-vector migration is both necessary and difficult.