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| Fig. 1: The extent of the oil sands in Alberta, Canada. (Source: Wikimedia Commons) |
The Albertan oil sands, also known as the Athabasca oil sands, are large deposits of bitumen in the north-eastern region of Alberta, Canada. It is comprised of three major deposits: the Athabasca, Peace River and Cold Lake deposits. Geologists believe the bitumen originally existed as light crude. When the Rocky Mountains formed 80 to 55 million years ago, a large volume of the light crude was pushed north-eastward. It was also pushed upwards, eventually reaching depths that were shallow and cool enough for bacteria to thrive, where they degraded the light crude into bitumen. For millions of years, the Athabasca river that runs through the region eroded away much of the sediment that covered the bitumen. The erosion made it possible to reach some of the bitumen deposits by electric shovels. [1]
With current extraction technologies, the estimated proven oil reserves from the three major deposits range are 143.1 billion barrels of oil. Combined with conventional oil, the proven Canadian reserves at the end of 2010 is 175.2 billion barrels. This is the third largest proven reserve in the world, after Saudi Arabia and Venezuela. [2]
The freshly-mined sands contain 75-80% mineral matter (sand, silt and clay), and 20-25% bitumen. [3] Bitumen deposits at depths down to 75 meters below surface can be surface-mined. [8] Hot water at 80 °C, and sometimes caustic soda, is used to strip wash the bitumen from the sands. Bitumen contains more carbon and less hydrogen compared to conventional oil, so an "upgrading" process is required to remove some carbon and add some hydrogen, thus reversing the degradation done by bacteria. At these upgrading facilities, bitumen is heated to 480°C and compressed to more than 100 atmospheres of pressure. Synthetic crude oil emerges, and it is pumped to refineries in Canada and the U.S for further processing. [1]
In-situ extraction (steam-assisted gravity drainage) is used for bitumen deposits deeper than 76 meters. Large amounts of steam are pumped into the ground, thereby melting and separating the bitumen from the sands. The bitumen is then pumped to the surface and transported to the upgrading facilities. In-situ extraction requires up to twice as much energy than surface-mining. [1] It is estimated that only 10 to 20% of the recoverable oil can be surface-mined, while the remainder requires in-situ extraction. [1,4]
In 2006, 1.6 million barrels of oil per day was produced from the Albertan oil sands. Output is expected to increase to 5 million barrels per day by 2030. [5]
To extract one barrel of synthetic crude oil from the oil sands using surface-mining, operators do the following: 1) cut down the boreal forest on the land over the deposits, 2) remove, on average, 2 tons of peat and dirt on top of the deposits, 3) remove 2 tons of the sand laced with bitumen, 4) heat between 2 to 3 barrels of water to 80°C for the strip washing process, then discharge the contaminated water into tailings ponds after the bitumen is separated, and 5) upgrade it into synthetic crude. [1]
Burning natural gas is the energy input required for the extraction and upgrade processes. In 2004, the oil sands industry used 4% (8.72 million cubic meters per day) of the Canadian natural gas consumption. [3] The associated greenhouse gas emissions are 62-164 kg CO2 equivalent per barrel of oil for surface mining and upgrading, and 99-176 kg CO2 equivalent per barrel of oil for in-situ extraction and upgrading. [5] The upgrading process emits the most greenhouse gases of all the oil sands mining operations, at 70-80% of the total emissions. [6] On a "wells-to-wheels" basis, the extraction and refinement of oil sands produce 15 to 40% more greenhouse gas emissions than conventional oil. [1,5]
There are efforts to capture and store these carbon emissions. The "Quest Carbon Capture and Storage" project is a joint venture between Shell Canada Energy, Chevron Canada Limited and Marathon Oil Canada Corporation to capture and sequester the carbon emissions from the upgrading process. It is estimated that this effort will sequester 1.2 million tonnes of carbon dioxide per year. In the summer of 2011 the government of Canada and Alberta signed an agreement to underwrite two-thirds of the $1.35 billion project cost. If it passes regulatory hurdles and moves forward, this project would rank among the six largest carbon capture and storage projects in the world. [7]
The contaminated tailings ponds is also a potential environmental issue, and the center of much controversy surrounding the development of oil sands projects. There are more than 130 square kilometres of these water structures in northern Alberta. The tailings ponds are separated from natural water structures such as the Athabasca River by earthen dikes. Interceptor ditches and wells are also built to prevent leakages. [1] Despite these efforts, there is an estimated 11 million litres per day of leakage from these ponds to the environment. [8] There are concerns that the leakage can contaminate drinking water supplies, and negatively impact regional wildlife that relies on the waters for habitat and drinking. [1]
© Ya-Chun Jan. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.[1] R. Kunzig, "The Canadian Oil Boom," National Geographic, March 2009.
[2] "BP Statistical Review of World Energy June 2011," British Petroleum, 2011.
[3] B. Soderbergh, F. Robelius and K. Aleklett, "A Crash Programme Scenario For the Canadian Oil Sands Industry," Energy Policy 35, 1931 (2007).
[4] G. D. Mossop, "Geology of the Athabasca Oil Sands," Science 207, 145 (1980).
[5] A. D. Charpentier, J. A. Bergerson and H. L. MacLean, "Understanding the Canadian Oil Sands Industry's Greenhouse Gas Emissions," Environ. Res. Lett. 4, 014005 (2009).
[6] G. Ordorica-Garcia et al., "Modeling the Energy Demands and Greenhouse Gas Emissions of the Canadian Oil Sands Industry," Energy and Fuels 21, 2098 (2007).
[7] B. Handwerk, "A Quest to Clean Up Canada's Oil Sands Carbon," National Geographic News, 18 Aug 11.
[8] M. Price, "11 Million Litres a Day: The Tar Sands' Leaking Legacy," Environmental Defence, December 2008.
