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Mary S. Kadri1, Louis M. Liro1, Mark J. Lahr1, Robert Hobbs1, Peter Montecchi1
(1) Veritas Exploration Services, Houston, TX

Abstract: Occurrence and distribution of seismic reflectors internal to allochthonous salt, Walker Ridge lease area, deepwater Gulf of Mexico

Examination of a 3D seismic volume covering 144 OCS lease blocks along the southern portion of the Walker Ridge lease area reveals that many of the allochthonous salt bodies contain discontinuous internal seismic reflectors. These internal reflectors can be divided into two classes: (1) high-angle to vertical reflections associated with laterally amalgamating salt masses; (2) reflectors sub-parallel to the base of salt. These latter seismic reflectors tend to occur near the base of the salt mass, and in association with high-angle ramps in the base of salt surface.

Utilizing only regional 2D or post-stack migrated seismic data, these reflectors can be mis-interpreted as the base of salt surface. The use of pre-stack depth-migrated 3D seismic data clearly distinguishes these events and suggests a more complex lateral salt intrusion history. Whereas laterally continuous salt tongues can be demonstrated in proximity to the modern Sigsbee Escarpment, the presence of high-angle reflectors suggests that many more-landward laterally extensive salt masses are actually amalgamations of short-length salt tongues and salt canopies. This observation implies a higher density of salt stock sources than previously documented.

The base of salt mimicking internal seismic reflectors are interpreted to represent earlier tops-of-salt in a multiple intrusion event salt feature. The events are present only where sufficient sediment was entrained (overridden) by a later salt intrusion event. The events are regionally discontinuous due to the nature of salt carapace deposition combined with carapace removal during salt overthrusting. Where no carapace was deposited or preserved, the lack of seismic reflection coefficient at a salt-on-salt contact gives the appearance of a vertically continuous salt mass.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana