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Acoustic impedance contrast “dim spots” (previously described as the “fuzzy effect” in Maucione, 1993) have been associated with anomalously pressured hydrocarbon accumulations in the Powder River Basin of Wyoming (Boyd et al., 1996a, b). It is important to know if the observations made in the Powder River Basin apply to anomalously pressured hydrocarbon accumulations in other Rocky Mountain Laramide basins. In order to test the applicability of these conceptsin anotherbasin, a ~58 km (36 mi) long seismic profilefrom the AlbertaDeep Basin of western Canada has been constructed and analyzed. The profile crosses various pressure boundaries, but the reservoir geometry and seismic acquisition and processing parameters remain nearly constant throughout the length of the profile. These parameters may thus be eliminated as causes of seismic anomalies that could falsely indicate anomalous pressures.

Anomalous pressures in the Alberta Deep Basin were originally identified using well log and production information. However, using seismic data acquired and processed to detect character response changes other than those associated with structural features, one can easily observe deviation from the expected increase in velocity with depth. Understanding the exact character of anomalous seismic responses requires knowledge of some geo–logic data, including rock properties (e.g., lithology and velocity) and depo–sitional environments present in a similar geologic setting (i.e., another Laramide basin). Additionally, integration of well log and production infor–mation corroborates the seismic character response changes associated with a regional–scale pressure boundary. However, it is important to note that identification of areas of anomalous pressure using seismic data is not dependent on well information.

In the present study, four seismic response characteristics of the seismic data from the Alberta Deep Basin indicated that a regional–scale pressure compartment boundary, separating areas of normal and anomalous pressure, was present in the basin. Two of these characteristics can be observed in a routine processing flow. The other two characteristics can be observed only after an extremely detailed velocity analysis.

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