ABSTRACT

Within recent years, significant new oil discoveries have been made in the Nisku Formation of the Bashaw area, central Alberta. Historically, structural drape has constituted the major play type in this area. Recent drilling activity has revealed the presence of purely stratigraphic traps in Nisku age pinnacle reefs of the Wood River area (Twp. 42, Rge. 23 W4M). Trapping of hydrocarbons occurs in isolated, dolomitized, thamnoporid coral dominated reef buildups of the normal marine lower Nisku phase. These buildups are encased in tight mudstone and evaporite of the later hypersaline upper Nisku phase.

Nisku pinnacle reef development in this area is primarily controlled by Leduc paleotopography, the pattern of Ireton Shale infill, and Camrose paleotopography.

Through construction of a residual isopach map of the Leduc Formation using all available deep penetrations, it can be demonstrated that Nisku age Wood River pinnacles develop on local topographic highs in an otherwise deeper water area of the Leduc surface.

Two distinct episodes of Ireton Shale infill affect the Wood River area: pre-Camrose and post-Camrose Ireton Shale infill. The incomplete nature of pre-Camrose Ireton Shale infill in the Wood River area, combined with pre-existing Leduc topography, directly controlled the distribution of Camrose shelf and basinal areas. Within the basinal or slightly deeper water areas, low-relief, isolated, Camrose age crinoidal grainstone shoals developed.

Post-Camrose Ireton Shale deposition appears to have largely bypassed an elongate area that extends from the Wood River area southeast to the Nevis area. Within this deeper water "moat" area, the Camrose age crinoidal shoals appear to act as precursors for later Nisku pinnacle reef development.

Using detailed mapping of the Leduc paleogeography, combined with an understanding of the pattern of Ireton Shale infill, a high-graded fairway for development of Camrose age shoal deposits can be identified. Within these shoal areas, further potential exists for the development of the prolific Wood River type Nisku age pinnacle reefs.

End_of_Record - Last_Page 210-------