Westhazel General Petroleums Pool: Case history of a salt‐dissolution trap in west‐central Saskatchewan, Canada

Abstract

The Westhazel General Petroleums (GP) Pool of west‐central Saskatchewan, Canada, produces from the GP member of the Lower Cretaceous Mannville Group. This reservoir is structurally closed across the updip, eastern dissolutional edge of the underlying Middle Devonian rock salt of the Leofnard Member, Prairie Formation. The leaching of these salts occurred in post‐Mannville time in the Westhazel area and caused the regional southwest dip of the General Petroleums member to be locally reversed. The Westhazel GP Pool, from a geophysical perspective, is characteristic of many of the shallow Lower Cretaceous pools situated along the dissolutional edge of the Prairie salt. The thin, 10 m reservoir facies at Westhazel does not exhibit a diagnostic signature on either seismic or gravity data. Rather, it is the updip edge of the salt across which the reservoir is closed that can be mapped using geophysical techniques. On seismic data, the dissolutional edge of the Prairie salt is characterized by: (1) a subtle decrease in the amplitude and lateral coherency of the underlying Winnipegosis event; (2) a gradual thinning of key encompassing Paleozoic intervals; (3) dip reversal along the Beaverhill Lake (Late Devonian) event; (4) dip reversal along the Mannville (Lower Cretaceous) event; and (5) time‐structural “push down” of Lower Cretaceous and underlying reflections in areas of recent salt dissolution. On the gravity profile, the edge of the salt is manifested as a 1.5 mGal anomaly. The interpretation of both geophysical data sets is consistent with available geologic control.