Tar sands can be often strip mined. Typically two tons of tar sand will yield one barrel of oil. A typical tar sand contains sand grains with a water envelope, covered by a bitumen film that may contain 70% oil. Various fine particles can be suspended in the water and bitumen. This type of tar sand can be processed with water extraction. Hot water is added to the sand, and the resulting slurry is piped to the extraction plant where it is agitated and the oil skimmed from the top. Provided that the water chemistry is appropriate (adjusted with chemical additives), it allows bitumen to separate from sand and clay. The combination of hot water and agitation releases bitumen from the oil sand, and allows small air bubbles to attach to the bitumen droplets. The bitumen froth floats to the top of separation vessels, and is further treated to remove residual water and fine solids. It can then be transported and processed the same way as for extra heavy crude. It is estimated that around 80% of the tar sands are too far below the surface for the current open-pit mining technique. Techniques are being developed to extract the oil below the surface. These techniques requires a massive injection of steam into a deposit, thus liberating the bitumen underground, and channeling it to extraction points where it would be liquefied before reaching the surface. The tar sands of Canada (Alberta) and Venezuela are estimated at 250 billion barrels, equivalent to the total reserves of Saudi Arabia

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