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Wang, Dapeng1, Yingping Li1, John O'Brien2, Brian Mallick2
(1) VSFusion, A Baker Hughes - CGG Company, Houston, TX 
(2) Anadarko Petroleum Corporation, Woodlands, TX

ABSTRACT: Vector 3C-3D Depth Migration of Salt Images Using Limited VSP Data

A newly developed vector 3C-3D VSP Kirchhoff migration was applied to obtain an image in 3-D of a salt boundary in the Gulf of Mexico using a VSP survey consisting of two 5-level walkaways and three offset VSPs data. 
The VSP survey was originally designed to generate migrated images of a salt flank and adjacent sediments along a 2-D profile. However, it was observed that seismic energies reflected from the salt boundary were offset from the 2-D profile. Thus, the 2-D migration image was only a projection of the 3-D image onto the 2-D profile, resulting in misposition of the salt boundary and degradation of the image quality. 
To obtain the true salt boundary location in 3-D space and improve image quality we employed the following techniques. 
1. A 3-D migration method was used 2. 3-component data were migrated. 3. Most importantly, a dynamic rotation of 3-C data within 3-D migration, (Vector 3C-3D VSP Migration), was adopted to map reflected waves to their true locations. 
This vector 3C-3D VSP migration using very limited data results in an image of a steep salt surface asymmetric to the 2-D survey line. The strongest salt reflector is located southwest of the vertical wellbore, offset from the 2-D profile. The amplitude of the salt face reflection varies laterally and vertically. The 3C-3D migration image of the salt flank agrees with results from 3-D salt proximity, travel time tomography, and surface seismic data and provides an accurate estimate of the position of the salt boundary.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.