HR: 08:30h
AN: NS21A-01    [Abstracts]
TI: Imaging Shallow Salt With 3D Refraction Migration
AU: * VanSchuyver, C J
EM: connie@houscca.com
AF: University of Houston, Room 504 Science and Research 1 4800 Calhoun Rd., Houston, TX 77204-5505 United States
AU: Hilterman, F J
EM: fhilterman@uh.edu
AF: University of Houston, Room 504 Science and Research 1 4800 Calhoun Rd., Houston, TX 77204-5505 United States
AB: In offshore West Africa, numerous salt walls are within 200 m of sea level. Because of the shallowness of these salt walls, reflections from the salt top can be difficult to map, making it impossible to build an accurate velocity model for subsequent pre-stack depth migration. An accurate definition of salt boundaries is critical to any depth model where salt is present. Unfortunately, when a salt body is very shallow, the reflection from the upper interface can be obscured due to large offsets between the source and near receivers and also due to the interference from multiples and other near-surface noise events. A new method is described using 3D migration of the refraction waveforms which is simplified because of several constraints in the model definition. The azimuth and dip of the refractor is found by imaging with Kirchhoff theory. A Kirchhoff migration is performed where the traveltime values are adjusted to use the CMP refraction traveltime equation. I assume the sediment and salt velocities to be known such that once the image time is specified, then the dip and azimuth of the refraction path can be found. The resulting 3D refraction migrations are in excellent depth agreement with available well control. In addition, the refraction migration time picks of deeper salt events are in agreement with time picks of the same events on the reflection migration.
DE: 0900 EXPLORATION GEOPHYSICS
DE: 0902 Computational methods, seismic
DE: 0910 Data processing
DE: 0930 Oceanic structures
DE: 0935 Seismic methods (3025)
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly