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The seismic reflection method is a well-established tool in the exploration for structures but is little used by the average geologist for stratigraphic analysis.
High-resolution stratigraphic profiling is a greatly scaled-down version of the technique employed in most exploration operations. A field crew consists of about six men, a small drill, a portable digital recording unit, cables, and downhole detectors. Very small dynamite shots are taken every 15 to 35 ft (5 to 10 m) along the traverse line. At each new shot point a new "pseudo" acoustic log is produced which subsequently will be correlated with borehole logs and other "pseudo" logs.
The digital recordings from each shot are then computer processed to enhance the high-frequency characteristics of the logs, compensate for variations in overlying rock velocity, and correct the logs for irregularities introduced by changes in near-surface geology and elevation along the traverse. The computer output data are integrated with borehole information prior to interpretation. Use of these seismic "pseudo" logs aids the geologists by defining more precisely the subsurface stratigraphy between boreholes and beyond wells.
The structural information derivable from the log displays includes, in addition to the location of very small faults, sand channels, and shale-outs, such information as the unique identification, thickness, and lateral persistence of particular reservoir beds.
Geologic identification of potential reservoir rock types using seismic wavelet characteristics or log-shape changes is an extremely useful supplement to the structural or purely correlative aspects of seismic-log profiling. Shape variations in the log traces can provide valuable information regarding localized depositional environments, pore-fluid characteristics, and even porosity and permeability variations across a given prospect area once a local reference has been established.
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