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GCDiscontinuous Stratigraphy Complicates Matching of Synthetic Seismograms to Regional Seismic
*
Bob Hardage1
Search and Discovery Article #40926 (2012)
Posted May 14, 2012
*Adapted from the Geophysical Corner column, prepared by the author, in AAPG Explorer, May, 2012, and entitled "Geological Factors Can Lead to Poor Matches". Editor of Geophysical Corner is Satinder Chopra ([email protected]). Managing Editor of AAPG Explorer is Vern Stefanic; Larry Nation is Communications Director. AAPG©2012
1 Bureau of Economic Geology, The University of Texas at Austin ([email protected])
The traditional tool that interpreters have used to establish correspondences between subsurface stratigraphy and surface-measured seismic
data has been synthetic seismograms calculated from well log data. In some instances, however, it is difficult to create an optimal-quality match between a synthetic seismogram and
seismic
data. We consider here possible geological reasons why poor matches sometimes occur — particularly in stratigraphic intervals where rock properties change laterally.
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Consider the stratigraphic condition diagrammed on Figure 1. Here a well penetrates a sand body that has a lateral dimension less than that of the dominant wavelength λ of an illuminating The principle illustrated by this example is that a synthetic seismogram will imply a reflection should be at the depth of the sand body, but migrated The reverse of this situation also can occur – that is, a synthetic seismogram can indicate no reflection is present at a depth where surface Because log data acquired in the well indicate no impedance changes over the depth interval local to the sand bodies, a synthetic seismogram calculation will produce no reflection event. However, both migrated and unmigrated Again, the log data are correct, the synthetic seismogram calculation is correct and the If one-meter geology is significantly different from 50-meter and 100-meter geology, there often will be mismatches between synthetic seismograms and |