Concepts and Applications of Imaging with Multiples and Primaries

The goal of seismic acquisition and processing is to create a well-sampled image of the subsurface. Broadband acquisition has expanded the useable low and high frequencies of the seismic signal. Multistreamer acquisition provides a much greater receiver sampling. Wide- and full-azimuth acquisition and longer offsets have improved the azimuthal and angular illumination. The increased receiver coverage allows for a more complete sampling of the total wavefield. Multicomponent sensor technology both provides broadband acquisition and allows for separation of the downgoing and upgoing wavefields at the receivers, which subsequently can be used in imaging. Alternatively, there has been an increase in the use of ocean-bottom seismic, where the receiver sampling is relatively sparse, but the source sampling is typically dense. This presentation discusses imaging methods that take advantage of these advances in acquisition.

There is an array of imaging methods to choose from, including (1) fast beam methods used in model building, (2) Kirchhoff methods to address high-resolution imaging, (3) wavefield depth extrapolation and migration (WEM) used in more complex media, and (4) reverse time migration (RTM) for complex media and arbitrary dip.

This talk gives an overview of the principles and applications of RTM and WEM, which employ wavefield propagation of incident and reflected wavefields as part of their imaging process. It focuses on the combined use of single and higher order scattered wavefields, where the downgoing and upgoing wavefields can be used to construct subsurface images using both multiples and primaries.

The presentation covers the following topics:

1. Prerequisites of processing before imaging, including designature, deghosting, wavefield separation, and possibly surface-related multiple estimation
2. WEM and RTM imaging methods, including discussions on wavefield extrapolation, imaging conditions, and subsurface angle decompositions
3. Imaging of primary and secondary (multiple) reflections using upgoing and downgoing separated wavefields. Also included is the estimation of surface-related multiple noise and subtraction in the image space.
4. Beyond first-order imaging, including a discussion of trends in using inversion to achieve full-wavefield imaging.