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As exploration progresses in a basin, the effort to find new reserves compels the explorationist to look for traps too subtle to have been discovered in earlier efforts. Many such traps are rendered obscure by diapirism or regional deformation. The most common approach used in finding these traps entails the preparation of isopach maps and cross sections referenced to a common stratigraphic marker. Although these methods are generally effective in revealing paleostructural trends, they are tedious and require initial determination of the best horizons to use. An analogous situation often confronts the geophysicist in areas with minor structural relief and relatively major velocity anomalies.
A faster and often more revealing technique involves interactive flattening of cross sections or seismic data on a microcomputer. This allows the explorationist to view any horizon as a paleostructural reference, thereby eliminating horizons that do not effectively depict the underlying structural trends. This technique can also provide a clearer understanding of basin development in areas that were significantly deformed after producing zones were deposited.
The utility of interactive flattening in the delineation of subtle traps is shown in the restoration of the paleostructure of salt domes in Louisiana, where significant accumulations occur on the flanks of younger structures. Examples of basin development are derived from offshore California, where wrench faulting has obscured the structural setting that existed during the deposition of important Miocene reservoirs. The application of flattening seismic profiles to remove false structure induced by shallow velocity changes is illustrated for several areas in the Mid-Continent.
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