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What are oil sands and heavy oil?

Heavy oil and bitumen (the primary hydrocarbon component of oil sands) are types of crude oil, a naturally occurring petroleum. Petroleum is the general term for solid, liquid or gaseous hydrocarbons. Hydrocarbons are a class of organic compounds consisting only of carbon and hydrogen and which are the basis of oil, natural gas and coal.

Technically, crude oil consists of pentanes (hydrocarbon chains consisting of five carbon atoms and 12 hydrogen atoms) and heavier hydrocarbons (hydrocarbon chains longer than five carbon atoms). It may also contain other substances such as water, natural gas, sulphur and other minerals.

Conventional crude oil is oil that flows naturally or that can be pumped without being heated or diluted. Crude oil is commonly classified as light, medium, heavy or extra heavy, referring to its gravity as measured on the American Petroleum Institute (API) Scale. The API gravity is measured in degrees and is calculated using the formula API Gravity = (141.5/SpecificGravity) - 131.5.

Industry defines light crude oil as having an API gravity higher than 31.1° (lower than 870 kilograms/cubic metre), medium oil as having an API gravity between 31.1° and 22.3° (870 kilograms/cubic metre to 920 kilograms/cubic metre), heavy oil as having an API gravity between 22.3° and 10° (920 kilograms/cubic metre to 1,000 kilograms/cubic metre), and extra heavy oil (bitumen) as having an API gravity of less than 10° (higher than 1,000 kilograms/cubic metre). The Canadian government has only two classifications, light oil with a specific gravity of less than 900 kilograms/cubic metre (greater than 25.7° API) and heavy oil with a specific gravity of greater than 900 kilograms/cubic metre (less than 25.7° API).

A less rigorous definition of heavy oil is oil that is “not recoverable in its natural state through a well by ordinary production methods.” However, some heavy oil less than 22.3° API does flow very slowly but most requires heat or dilution to flow into a well or through a pipeline. Heavy oil from the Lloydminster area of Alberta and Saskatchewan has API gravities ranging from 9° to 18°. Heavy oil makes up about 15 per cent of the world’s remaining oil reserves. It usually contains impurities such as sulphur, heavy metals, waxes and carbon residue that must be removed before it is refined.

The definition is more appropriate for bitumen, oil that “does not flow, or cannot be pumped without being heated or diluted.” The bitumen mined from the oil sands deposits in the Athabasca area of Alberta, Canada has an API gravity of around 8°, but is upgraded to an API gravity of 31° to 33°. This upgraded oil is known as synthetic oil.

Oil sands are mixtures of sand, water, clay and crude bitumen. Each oil sand grain has three layers: an ‘envelope’ of water surrounding a grain of sand, and a film of bitumen surrounding the water.


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