The Norcan-Fager fields, discovered in 1980, are stratigraphic traps that produce from northwest-southeast-trending pods of sandstone of Morrowan-Atokan age. The discovery well of the Norcan field, Ladd Petroleum 1-8 Norton, was drilled on a seismic anomaly recognized on 12-fold vibroseis data. Subsequent development drilling was guided by mapping these seismic anomalies, which reflect the drainage pattern incised on the Mississippian carbonates. This topographic surface controlled subsequent deposition, and the Morrowan-Atokan sandstones were deposited in topographic lows.

These seismic anomalies are associated with the Mississippian unconformity surface rather than the productive sandstones; they appear to be unique to the study area, and they vary in character. The most common features associated with the lows on the Mississippian unconformity surface are: (1) diffractions; (2) high-amplitude "bright spots"; (3) breaks in the seismic continuity of the Mississippian reflector (if present); (4) sagging in the overlying section due to differential compaction; and (5) sagging of the Mississippian reflector. The anomalies usually occur in differing combinations across the study area, and these combinations are controlled

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by the total thicknesses of sediment deposited within the Mississippian lows, the varying types of lithologies deposited within the lows, the lithologic variations in the overlying sediments, the angle at which the seismic is shot across the Mississippian "channels," and the geometry of the Mississippian channel cut.

Accumulations of the Norcan-Fager type are subtle traps that are difficult to discover using only wireline logs. The key to successful exploration for Norcan-Fager-type reservoirs is geologic interpretation of seismic data.

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