Abstract: Seismic Modeling: Geological Predictions and Pitfalls

By

Fred J. Hilterman

Seismic sections across most geological structures are distorted by sideswipe and/or lateral velocity changes in the subsurface. Invariably, the distortion on the 20 migrated section hides the features that are most desired. However, through seismic models of similar geological structures, the interpretational pitfalls caused by sideswipe and velocity are turned into practical prediction tools.

Migrated seismic lines across-domes and anticlines normally exaggerate the size of the anomalies. Migrated seismic lines across synclines and basins are characterized with false expressions which include grabens, contemporaneous deformation, cross-stratification, high-amplitudes, and crossing reflections. Geological areas that have large lateral velocity contrasts, such as reefs, diapirs, or fault blocks exhibit false seismic expressions. These include relief faults, basement controlled tectonics, facies changes, and structures which are located in geologically ambiguous positions. Even the polarity of the seismic reflection is 3D dependent.

Modeling examples show that interpretational pitfalls, such as mapping from migrated sections and interpreting from the basement upward, must be supplemented with pseudo-3D interpretational techniques. Geologic models and their seismic analyses from salt provinces, reefs, overthrusts, etc., illustrate these pseudo-3D interpretational tools.

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