Paper Summary
Conventional shot domain migration constructs a subsurface image using the forward extrapolated (downgoing) wavefield from a source and reverse extrapolated (up-going) wavefield originating at the surface receiver positions. Similarly, sea surface related multiples can also be used to construct an image of the subsurface where the boundary data for the down-going and up-going wavefields are generated at the receiver locations via wavefield separation. After up-down separation the down-going and up-going wavefields act as the source and receiver surface wavefields and exist only at the receiver positions. To properly image the subsurface with the multiples, the down-going and up-going wavefields must be both recorded. Therefore, the streamer coverage, receiver density, source-receiver distribution geometry and acquisition shooting direction as well as target depth and subsurface dip are controlling factors in the effectiveness of imaging with multiples. For example, wide azimuth (WAZ) acquisition generates large streamer coverage and enhances the use of both the down-going (source) and up-going (receiver) wavefields. Anti-parallel shooting is typically required to reduce the source (down-going) wavefield directional bias and image both updip and downdip targets. Split-spread shooting geometry uses rays including downgoing and up-going wavefields recorded from different sides of the shot location and further enhances the subsurface illumination. In this paper, both synthetic and field data examples are used to demonstrate the challenges from acquisition geometry. A shallow water field data example shows the successful application of the technology to mitigate the acquisition footprint. The technology has the potential of reducing drilling hazard risks.