Athabasca Oil Sands

The Athabasca oil sands of the McMurray formation in northeastern Alberta cover an area of about 21,000 sq miles and contain the world's largest reserve of economically recoverable oil. Fort McMurray, a small town in the heart of the oil-sands area, is about 235 air miles northeast of Edmonton. A railway serves the town but no year-round roads connect with the rest of Alberta (Fig. 1).The McMurray formation is of early Cretaceous age, deposited unconformably on a limestone surface of Devonian age. The sediments appear to have originated from the Canadian Shield to the east and were deposited in bays and deltas of large fresh-water lakes. The lakes were later replaced by marine seas in which the overlying Clearwater shale was deposited (Fig. 2).The sand body rarely exceeds 200 ft in thickness and is made up of innumerable minor and major lenses of unconsolidated oil-bearing sand interspersed with clay and shale partings of variable thickness, carbonaceous and lignite beds, some rock and boulders. Overburden thins along a topographic trough which contains the Athabasca River and increases in thickness to about 2,000 ft along the southern and western limits of the oil impregnation. Oil sand is exposed on the banks of the Athabasca River and its tributaries. The oil sand is primarily quartz with varying percentages of silt and clay. Maximum oil saturation is about 18 percent by weight in a clean sand but decreases with increasing silt and clay content. Sand with oil saturation in excess of about 10 per cent is classed as a "good" grade while sand containing less than about 5 per cent of oil is not considered to be economically recoverable by present mining and processing techniques.The oil found in the McMurray formation is heavy, viscous and sulfurous. Specific gravity is from 1.002 to 1.027; viscosity, 3,000 to 400,000 poise at 60F. The sulfur content is from 4 to 5 per cent, and the nitrogen content is about 0.4 per cent. JPT P. 479^