In early 1957 several oil and gas-distillate discoveries were completed in a large, previously untested area in central Alberta, 100-150 miles northwest of Edmonton. All of these discoveries were in a reef member of the Beaverhill Lake formation, the oldest formation of the Upper Devonian series. The area where reefing in the Beaverhill Lake is known to occur is 60 miles east and west and 50 miles north and south and includes the Swan Hills, Virginia Hills, and Kaybob oil fields.

When first encountered the reef was correlated with the Slave Point formation of Middle Devonian age, but subsequent detailed studies indicate this reef to be of slightly later age. George Fong, stratigrapher for Home Oil Company has proposed the name Swan Hills member for this reef developed in the Beaverhill Lake formation. Typically, this reef occurs in the lower part of the Beaverhill Lake formation and is a porous limestone composed of bioclastic material containing abundant stromatoporoids and amphiporoids with a notable lack of corals. The enclosing rock consists of interbedded calcareous shales and dense argillaceous limestones. As indicated by difference in water levels in the various fields, the reef member is discontinuous. The thickness of the reef ranges widely with maxim m thickness of 475 feet in the area.

The base of the Swan Hills reef coincides with the base of the Beaverhill Lake formation and where developed to its maximum, extends up to the top of that formation. The Beaverhill Lake is underlain with no obvious nonconformity by the Elk Point Middle Devonian formation composed of dark green and red shales, sandstones, and minor anhydrite and limestones. The beds overlying the Beaverhill Lake in this area are locally referred to as the Shale unit, consisting of green calcareous shales and minor dense argillaceous limestone, equivalent to the Cooking Lake, Leduc (D-3), and Ireton of the Edmonton area.

At present insufficient drilling has taken place to permit speculation concerning factors that influence the location and build-up of reefs in this new producing area.

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