Wavefield Extrapolation Migration

Shot-based WEM for outstanding image quality in the most complex geological settings

Our wavefield extrapolation migration (WEM) produces premium imaging results using an optimized shot-profile downward-continuation migration algorithm. As such it provides a complete 5D solution that is not prone to artifacts related to 2.5D assumptions when full 3D velocity variations exist. Rapidly varying velocity fields are fully honored in 3D with no smoothing required.

Dip accuracy is extremely high; the screen algorithm images dips up to 90°. Typical production deliverables include zero-offset volumes with greatly enhanced image quality and full-volume angle gathers to facilitate further velocity updating or post migration image improvements. In areas where the signal-to-noise ratio is very poor and classical migration velocity analysis is extremely difficult or simply impossible, our implementation provides an alternative method for velocity evaluation and QC using migration velocity scan techniques.

Our WEM implementation supports imaging from irregular surfaces. Standard elevation statics methods may be inadequate in areas of irregular topography because of vertical raypath assumptions. An effective solution is to perform imaging from the actual recording surface, enabling WEM to be applied to either onshore environments exhibiting irregular topography, or OBC datasets recorded at the seabed.

The latest release of WEM supports anisotropic imaging using tilted transverse isotropy (TTI), as well as a new global normalization scheme. The result is more accurate imaging in areas of complex geology, and reliable wide-azimuth angle gathers for use in velocity model updating.

The WesternGeco WEM is an ideal tool for the toughest of imaging challenges, improving structural definition, and aiding interpretation.

Related references

• Stork, C.; Kitchenside, P.; Yingst, D.; Kostov, C.; Wilson, B.; Watts, D.; Kapoor, J.; Brown, G.; Albertin, U., Comparison between angle and offset gathers from wave equation migration and Kirchhoff migration, (1200-1203), 65th EAGE Annual Conference, June 2002
• Albertin U., Watts D., Chang W., Kapoor J., Stork C., Kitchenside P., Yingst D., Improving Near-Salt Flank Imagining with Shot-profile Wave-field Extrapolation Migration in the Gulf of Mexico, SEG Annual Conference, 2002

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