Threats: Water depletion

Publication - April 1, 2008
The tar sands are made up mostly of sand. Only 10-12 per cent is bitumen – a very heavy crude oil that must be heavily processed and refined to be turned into synthetic crude oil.

Extracting oil from the tar sands involves three major processes that deplete water and emit greenhouse gases: surface mining (also known as strip mining), in-situ extraction (or “deep mining”), and the upgrading process. Immense amounts of water are used for tar sands operations – currently 349 million cubic metres per year, twice the amount of water used by the city of Calgary - and 90 per cent of this cannot be returned to the river afterwards. People who live near tar sands projects in northern Alberta have been noticing the water levels in lakes and rivers decreasing as oil production has accelerated.

Surface Mining

Tar sands located within 100 metres from the Rarth’s surface are considered “mineable,” and so the first layer of rock and soil, known as overburden, is dug up with earthmovers so the underlying tar sands can be accessed. (Before this can happen, trees will have been clearcut and wetlands drained and demolished.) Then the tar sands are removed, and processed by “washing” with very hot water to separate the oil from the sand and clay it is mixed in with. For every two tonnes of tar sands that are removed from the ground, one barrel of synthetic crude oil is produced. Transporting and processing this amount of material means that each barrel of oil derived from the tar sands uses 250 cubic feet of natural gas, and between two and five barrels of water. Hydrotransport is becoming more and more common for mined tar sands as well: once extracted from the mine, the tar sands are mixed with hot water and caustic soda to produce a liquefied product that can be pumped through a pipeline to a processing facility where the oil will be separated from the tar.

In Situ Mining

Most tar sands lie much deeper than 100 metres from the surface, and can only be extracted by more complex processes. The main process in use in Alberta’s tar sands is known as SAGD – steam-assisted gravity drainage. SAGD injects high pressure steam underground to separate the oil from the sand and make it liquid enough to flow on its own. It is then pumped to the surface to be processed further and refined. Using this method of extraction uses two and half to four barrels of water per barrel of oil, and 1000 cubic feet of natural gas.

Upgrading

The oil that is extracted from the tar sands, bitumen, is one of the lowest quality oils available in the world. In order to be turned into synthetic crude oil, it must be heavily processed and refined. This also involves a great deal of water, which produces steam for hydrocoking and hydrocracking – intense processes that break the bitumen into smaller lighter molecules, and remove impurities such as nitrogen and sulphur.

Other Water Use

The fact that tar sands operations are mega-projects means that water is used in large quantities for reasons not specific to the tar sands – cleaning, putting out fires, toilets and drinking water for thousands of workers. Industrial operations also require water for operating pumps, producing steam for turbines, and cooling in evaporative cooling systems.

Tags