CASE HISTORY 8: Seismic Modeling of a Pinnacle Reef: An Example from the Williston Basin
K. W. Rudolph, S. M. Greenlee, 1991. "Seismic Modeling of a Pinnacle Reef: An Example from the Williston Basin", Seismic Modeling of Geologic Structures: Applications to Exploration Problems, Stuart W. Fagin
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By using two- and three-dimensional ray-trace seismic modeling, the subtle seismic response of a small Winnepegosis (Devonian) pinnacle reef from the Williston Basin was successfully modeled. Because of the small size and steep stratigraphic dips, the crest of the reef acts as a scattering point and generates a low amplitude diffraction on the unmigrated seismic data. Other seismic manifestations include disruption of deeper reflections, paired diffractions sourced from the toe of the slope, velocity pullup of deeper reflections, and nucleation on a structural terrace. Modeled seismic criteria are only interpretable on the actual data when the data is redisplayed using a squeezed gray-scale display. Synthetic seismic sections shot at the toe of slope and off-buildup positions show that recognition of the buildup crest is difficult without a line shot perpendicular to the axis of the hyperbolaes that represent the apparent reef crest. Three-dimensional ray-trace modeling also shows that pinnacles are detected by seismic sections shot off of the buildup. In these cases, two-dimensional migration may then result in the false imaging of a buildup along a line where none occurs. These modeling criteria are particularly useful in recognizing the occurrence and in mapping the crest of small carbonate buildups.