 
Oil or tar sands are naturally occurring deposits of sand and clay, with bitumen (oil) filling the spaces between the particles. This oil has, over time, risen to near the surface and mixed with the sand of an ancient river delta, where bacteria has reduced it to a sticky tar-like sludge.  Most of the economically viable tar sands in the world are located right here in Alberta, Canada, near Fort McMurray; smaller deposits also exist in Venezuela and Russia, with tiny amounts also scattered around the world in other locations. The Alberta tar sands are the only ones being actively mined, and soon will be providing 50% of Canada's oil.The amount of oil that can be recovered from Alberta's tar sands was once estimated at about 270 billion barrels, out of a total of 355 billion barrels of tar sands oil worldwide. But this figure has since been revised upwards; it has been estimated recently that the oil in Alberta's oil sands may make up fully one-third of the total known oil reserves in the world. However, less than 10% of this can be recovered by surface mining. It requires almost two tonnes of oil-bearing sand to be mined in order to produce one 159-litre barrel of crude oil. Almost all of the oil can be removed ... but sand with less than 7% oil in it is not processed. Mining the tar sands for oil happens in several ways. If the sands are near the surface, they can be mined by digging a huge pit. First, vegetation on the surface is cleared. Then the top layer of soil and gravel is removed to reveal the oil-bearing sand. Enormous bucket shovels and draglines (the booms of which are over 20 stories high) collect the sand and load it into large trucks, each of which can hold 320 tonnes of material. 
The trucks dump their loads into a large machine that breaks up the lumps in the sand, and then mixes it with hot water. This mixture, called a slurry, is sent by pipeline to a processing plant. (The sand in the tar sands is very abrasive ... it eats through the steel equipment used to mine it, making equipment repair costs quite high).   
At the plants, the oil-bearing sand is piped into a large settling tank. Sodium hydroxide is added to help the materials separate. In the tank, the heavy sand settles to the bottom; water settles above that, and the oil floats to the top, where it can be removed for refining. If the sands are too deep for open-pit mining, the oil is extracted using different methods. One way involves injecting steam down into the tar sand deposit. The heat from the steam melts the tar and helps to separate it from the sand. It is then pumped to the surface, diluted with other petroleum byproducts, and sent off by pipeline to the processing plants. There are three companies involved in mining the tar sands near Ft. McMurray. They are Syncrude Canada Ltd., Suncor Energy Inc., and Albian Sands Energy Inc. All of their mining operations at present involve open pit mines, and there are plans for huge expansions in the future, including implementing other methods for extracting the oil. Mining the oil sands by open-pit digging has a huge impact on the surrounding land. Not only is there a huge hole in the ground, but the left-over material (sand and clay from the oil-sands, as well as the topsoil and gravel that was removed) has to be stored somewhere. The left-over sand and clay is dumped in huge piles (called tailings) or settling ponds; oil-sands mining produces the greatest amount of waste material of any type of mining operation. The area affected near Ft. McMurray includes over 150 square kilometres of land. One tailings pond alone covers an area of 22 square kilometers. Plans exist to replace the sand and top layer of soil, to enable replanting and reclamation of the land. So far, however, the amount of waste produced greatly outstrips the companies' ability to reclaim the land, and planned expansions of operations make it seem unlikely that the already mined regions will be returned to the way they were any time soon, despite plans to increase reclamation activities.  |