--> Abstract: Seismic Illumination Models Applied to Subsalt Exploration, by M. Albertin and D. Sedgeley; #90933 (1998).
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Abstract: Seismic Illumination Models Applied to Subsalt Exploration

Albertin, Martin, and David Sedgeley - Amoco

Much of the sedimentary section on the outer shelf of the Gulf of Mexico is covered by allochthonous salt sheets. Seismic data quality is generally poor beneath these salt bodies, and multiple events, converted mode reflections, and out-of-plane energy are Previous HitcommonNext Hit. A valuable tool for differentiating these spurious events from primary compressional reflections is forward modeling. A particular category of forward modeling which displays the variation in seismic illumination is herein shown to be significant for subsalt interpretation.

Normal incident illumination techniques using three dimensional finite difference and ray tracing codes have proven successful for modeling complex salt structures. In model experiments, subsalt illumination has been related to salt sill thickness, salt dip, salt depth, sediment dip, sediment curvature, top salt rugosity and other variables. The rugosity of the top salt surface has only minor detrimental effect upon illumination of subsalt horizons; even in areas where the upper salt surface has large and steep remobilized ridges, subsalt illumination can be adequate for interpretation. The most pervasive loss in subsalt illumination results from a large dip Previous HitangleNext Hit between the lower salt surface and the subsalt reflectors. In Gulf of Mexico Tertiary basins, the allochthonous salt sill is typically surrounded by clastic sediments having compressional wave velocity of only about one-half salt compressional wave velocity, As a result, upward propagating seismic energy is critically refracted at the base of salt whenever the Previous HitangleTop between the base of salt and the subsalt horizons exceeds approximately 30 degrees. The selective use of mode converted seismic waves, which travel through the salt sill in a slower shear wave mode, may permit improved subsalt illumination in these situations.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil