Oil is recovered using two main methods: mining and in situ. The method employed depends on how deep the oil sands reserves are deposited.
80 per cent of the oil sands reserves are too deep to be mined, so will be recovered through in situ methods. 20 per cent of the oil sands reserves are close enough to the surface to be mined. Mining allows operators to recover more of the oil, while using less energy. Drilling is a more energy-intensive process but allows for a smaller footprint and does not require tailings ponds.
Due to the depth of the reserves, recovery rates for the methods of extracting bitumen vary. Drilling methods cannot be used in mining areas, and vice-versa.
Stages of open-pit mining
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Mining is used when deposits lie within 70 meters (200 feet) of the earth’s surface – about 20 per cent of oil sands reserves. Like most surface mining operations, the oil sands are scooped by large shovels into trucks and taken to crushers where the large clumps of clay are broken down. The oil sands are then mixed with hot water so they can travel through a pipeline to a plant where the bitumen is separated from the other components.
Tailings ponds are an operating facility common to all types of surface mining. In the oil sands, tailings consisting of water, sand, clay and residual oil are pumped to these basins – or ponds – where settling occurs and water near the top is reused for future mining recovery.
In situ drilling
Drilling methods are used for reserves that are more than 70 meters (200 feet) below the surface, and must be recovered in place, or in situ.
Advanced technology is used to inject steam, combustion or other sources of heat into the reservoir. The heat warms the bitumen so it can be pumped to the surface through recovery wells. Advances in technology, such as directional drilling, enable in situ operations to drill multiple wells (sometimes more than 20) from a single location, further reducing surface disturbance.
The majority of in situ operations use steam-assisted gravity drainage, or SAGD. This method involves pumping steam underground through a horizontal well to liquefy the bitumen, which is then pumped to the surface through a second recovery well.
A second method – cyclic steam stimulation (CSS) – pumps steam down a vertical well to soak or liquefy the bitumen, which is then pumped to the surface through the same well. This technique is repeated until the oil is removed.
For additional information on CSS, please watch this explainer video below:
Approximately 97 per cent of the total surface area of the oil sands region could be developed in situ, allowing for a lesser impact on the land. As of 2017, there were approximately 40 commercial oil sands projects in Alberta. Find out more about oil sands land impact.
Heavy oil and bitumen processing
Since most refineries in Canada were designed to process conventional light crude oils, some heavy oil and about half the bitumen produced are upgraded to create synthetic crude oil. Synthetic oil is usually low in sulphur and contains no residue or very heavy components. Upgrading can occur at or near the producing area or the refinery.
Upgrading uses temperature, pressure and catalysts to crack the big molecules into smaller ones. Adding hydrogen or removing carbon from the oil creates hydrocarbon molecules like those in light oil. Upgraded oil is used as a replacement for conventional crude oil to make gasoline, diesel, jet fuel and heating oil.
Upgrading is usually a two-stage process:
- Coking or hydrocracking - used to break up the molecules. Coking removes the carbon, while hydrocracking adds hydrogen.
- Hydrotreating - used to stabilize the oil and remove impurities such as sulphur.
Over 30 per cent of Canadian oil production is refined in Canada. About 55 per cent of Canada's oil sands are upgraded locally. Bitumen and some heavy oils are too viscus to flow through pipelines and must be diluted with condensate or another natural gas liquid before being transported. Once mixed with a diluent, the dilbit (diluted bitumen) does not separate, but is a new mixture.