Converted-wave Controlled Beam Migration with Sparse Sources or Receivers

Abstract

Gaussian Beam depth (GBM) migration overcomes the single-wavefront limitation of the majority of Kirchhoff implementations, and constitutes a cost-effective alternative to full-wavefield imaging methods such as reverse time migration. Common-offset (CO) beam migration was originally derived to exploit the symmetries available in marine towed-streamer acquisition. However, sparse acquisition geometries, such as cross-spread and ocean bottom, do not easily accommodate the requirements for common-azimuth migration. Seismic data interpolation or regularization can be used to mitigate this problem and to form well-populated common offset-vector (COV) tiles. Unfortunately, this procedure is computationally intensive and can, in the case of converted-wave imaging with sparse receivers, compromise the final image resolution. For all these reasons, we introduce a common-shot (or common-receiver) controlled-beam migration (CBM) implementation which allows the migration of datasets particularly rich in azimuth, without any regularization pre-processing required. CBM is a specialized version of GBM aimed at signal-to-noise ratio enhancement. Using some examples, we demonstrate that PS-imaging of ocean bottom-node (OBN) data benefits from this formulation, particularly in the shallow subsurface where regularization is both most necessary and most challenging.