Abstract

The Wabasca A Oil Sand Deposit is defined as the heavy oil-impregnated sands of the Grand Rapids Formation in the Wabasca Lakes area of northeastern Alberta. These sands, of Early Cretaceous age, represent the main development of sandstone deposition of the middle Albian regression which covered most of northern Alberta. The reservoir beds of the Wabasca A Oil Sand Deposit are found in thick and laterally extensive, transitional and near-shore marine facies deposited along a trend which parallels the regional shale-out of the Grand Rapids continental sands into the marine Clearwater shales. The Grand Rapids Formation can be subdivided into three main sandstone units: an upper “A” sand, a middle “B” sand, and a lower “C” sand.

The oil sand deposit is found at depths ranging from 250 to 2000 ft (76 to 610 m) and thus is clearly within the range of in-situ recovery. Reserves have been estimated to be in excess of 30 billion barrels (17.77×10⁹m³) of oil in place. Most of the oil is found in the Grand Rapids “A” sand, with a lesser amount in the Grand Rapids “B” sand. Oil gravity varies from 5 to 7° API (1036 — 1022 Kg/m³), with a sulfur content ranging from 4.5 to 5.5 per cent. The regional dip over the area is to the southwest, with local reversals leading to closure. Oil accumulation was probably the result of updip migration and entrapment in those structural features with a favorable lithology. Tilting of the reservoirs may have taken place after degradation of the oil.

Lithological differences exist between oil-impregnated and barren sands. The oil-impregnated sands have a relatively low (0.7 to 1.8 per cent) montmorillonite content compared to the barren sands (1.5 to 6.5 per cent). The oil-impregnated sands also appear to have a somewhat lower total clay content than the barren sands. The presence of montmorillonite is a factor which will have to be considered when in-situ recovery of the oil in this deposit is attempted.