Chapter 16

Seismic Response Characteristics of a Regional-Scale Pressure Compartment Boundary, Alberta Basin, Canada

Debi T. Maucione

Exxon Exploration Company Houston, Texas, U.S.A.

Ronald C. Surdam

Institute for Energy Research, University of Wyoming Laramie, Wyoming, U.S.A.

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 concepts in another basin, a ~58 km (36 mi) long seismic profile from the Alberta Deep 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 geologic data, including rock properties (e.g., lithology and velocity) and depositional environments present in a similar geologic setting (i.e., another Laramide basin). Additionally, integration of well log and production information 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.