3D plane-wave imaging of wide-azimuth data

Group GSI.IR
Location International Geological Congress,oslo 2008
Author Chemingui, Nizar۱; Van Borselen, Roald۲; Orlovich, Mikhail۱; Fromyr, Eivind۱
Holding Date 07 October 2008

New and innovative survey designs for acquiring wide-azimuth towed streamer (WATS) data have demonstrated the potential for a step change improvement in seismic data quality. In addition to better illumination of target zones, the improvement seen on WATS data can be attributed, in large part, to the superior attenuation of noise, especially from complex multiples. Synthetic and field data examples that illustrate the uplift in seismic image quality obtained from wide-azimuth data are discussed.

Correspondingly, our imaging solutions for conventional streamer data need to be extended to account for wider sampling of the seismic wavefield. In particular, better efficiency of migration algorithms are needed to handle the large volumes of data acquired from field surveys. We discuss an effective implementation of 3D plane-wave migration for imaging via wave field continuation of WATS data. Also discussed is a phase-encoding strategy for 3D plane-wave synthesis of the surface seismic data, acquired with point source signatures.

Based on the imaging equivalence of shot record and plane-wave migration, we establish formulations for estimating the number of ray-parameters required for the 3D plane-wave migration. Important considerations for the algorithm’s implementation are its efficiency along with its performance on WATS geometries. Using fundamental sampling-theory principles, we demonstrate a cost equivalence relation between shot record and plane-wave migration. We therefore confirm that the phase-encoding transformation from one linear space to another does not, in principle, change the cost of the wavefield migration. However, in practice several factors including shot spacing, velocity gradient, maximum frequency, and dip for imaging can favor one implementation over the other. Moreover, the cost of plane-wave migration can be reduced through effective decimation in the angle domain for application to wave-equation based model building.

A synthetic dataset that simulates a WATS geometry was used to assess the performance and efficiency of the 3D plane-wave migration for wide-azimuth surveys. We show that the plane-wave solution can be applied with relative efficiency on wide-azimuth data and that further performance improvements can be achieved at the expense of a modest increase in the noise level.