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The Swan Hills reef complex is in the subsurface of west-central Alberta, 96 mi northwest of Edmonton. Early in 1957, Home Oil Company Limited discovered oil in these rocks at Virginia Hills and Swan Hills, and other discoveries in similar reservoirs within this complex soon followed. Before this, no commercial hydrocarbon production had been obtained from the rocks of this formation in Western Canada. By the end of 1966, the Swan Hills Formation ranked second in Western Canada in order of recoverable oil reserves.

Between the year of discovery and the end of 1966, a total of 219,160,459 bbl of oil and 48 Bcf of gas have been recovered from 12 oil fields and 1 gas field. Total remaining recoverable reserves are estimated at 2,105,955,111 bbl of oil and 1,380 Bcf of gas.

The oil is a paraffin-base crude with a gravity ranging from 38° to 45° API. Sulfur content of the crude may run as high as 0.42 percent but generally is less than 0.2 percent.

Drilling depths differ considerably, depending on the position of the field relative to the regional dip, ranging from 6,950 ft in the northeast to 11,350 ft in the western parts of the producing area.

The Swan Hills Formation is probably early Late Devonian in age and occupies a stratigraphic position low in the Beaverhill Lake Group. The reef complexes of this formation are situated along the edge of a broad carbonate platform south of the Peace River arch and east of the Western Alberta ridge. Continuing reef growth formed limestone mounds that consist largely of successive layers of superimposed atolls, each having an organic rim surrounding lagoon deposits. The resulting rocks form a complex pattern of porosity and permeability. The limestones of the reservoirs, with a few exceptions, have not been dolomitized. Stromatoporoids are the dominant organisms. The fields are simple stratigraphic traps, the oil and gas being held in the porous reef rocks by the surrounding impermeable rocks.

In the productive area, the Swan Hills reefs are enclosed in a shale and dense limestone facies of the Beaverhill Lake Group. North and northeast of this area, in northern Alberta, a gradual lateral facies change to predominantly shale of the basin facies occurs. South and southeast in southern Alberta and Saskatchewan, there is a lateral facies gradation to dense limestone and dolomite, accompanied by a gradual thinning of the total thickness. A band of coarsely crystalline vuggy dolomite is present along the margin of this shelf. Farther south, anhydrite is interbedded with the dolomite and salt beds are present.

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