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The Leading Edge; December 2002; v. 21; no. 12; p. 1232-1236; DOI: 10.1190/1.1536140
© 2002 Society of Exploration Geophysicists
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Velocity model building by wavefield-continuation imaging in the deepwater Gulf of Mexico

Moritz M. Fliedner, Sean Crawley, Dimitri Bevc and Alexander M. Popovici

3DGeo Development Incorporated, Mountain View, California, U.S.

Biondo Biondi

Stanford University, California, U.S.

Corresponding author: moritz@3dgeo.com

The first 20% of the full text of this article appears below.

Wavefield-continuation-based migration algorithms that downward extrapolate the 3D prestack wavefield (commonly known as "wave-equation migration") have been recently shown to produce better imaging results than Kirchhoff migration in many synthetic and real data cases (Popovici, 2000). Wavefield-continuation methods are potentially more accurate and robust because they are based on the full wave equation and not on an asymptotic solution based on ray theory. In addition, wavefield-continuation methods handle multipathing naturally in contrast to Kirchhoff methods, focusing and defocusing effects of velocity variations are correctly modeled, antialiasing is handled implicitly, and amplitudes are consistent with the wave equation.

This study uses data over an extensive salt body in the deep Gulf of Mexico but concentrates on a subset of the entire 1215 km2 data set consisting of two swaths of 160 and 64 inlines with 40 m line spacing and 1024 CMPs with 37.5 m spacing. CMP-fold is 48 and the recorded offset range 400–7400 m. Water depth is about 1800 m. Target lines A and B discussed below are the center lines of each swath (Figure 1).


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  		Figure 1. Perspective view of the top salt surface (yellow) of the Foldbelt Gulf of Mexico data set. Swaths A (orange) and B (gray) and their respective target lines (black) are used for this study.

 
When the salt body is absent, the local velocity structure is simple. The background sedimentary P-wave velocity model does not deviate significantly from a 1D linear Gulf of Mexico gradient—1700 m/s near the seafloor and reaching 3500 m/s at 12 750 m below sea level. The salt body is modeled as a constant velocity body with a P-wave velocity of 4500 m/s. The salt body sits in a depth range of 2300–8000 m and has a complicated shape that changes rapidly in both inline and crossline directions. The . . . [Full Text of this Article]






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