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| Fig. 1: Photo of tar sand mining in Alberta, Canada. (Source: Wikimedia Commons) |
In the United States the majority of a barrel of oil goes to producing fuel for transportation. We are realizing that the cheaper and more convenient substitute for conventional reservoirs is tar sands. [1] "Sand, silt, clay, water, and about 10- 12% bitumen" is found in the makeup of tar sands. [1] Crude Bitumen is the term used when talking about oil extracted from these tar sands and this substance, crude bitumen, is a "viscous, heavy oil that will not flow to a well in its natural state". [1]
There are two ways in which we can obtain the tar sands in order to create oil. One way is by mining on the surface (less than 100 meters deep). The second way is to heat the Bitumen causing the viscosity to decrease allowing it to flow into a well, which is then accessible to the oil and gas company. [1-3] In order to create one barrel of oil, four tons of soil, rock, and tar sands, combined, must be mined. In order to mine and transport this large amount of material, massive shovels are necessary. These shovels carry forty cubic meters of material at once. To get one barrel of oil it takes 2 to 5 barrels of water and 250 cubic feet of natural gas. Around 90% of the Bitumen found will be recovered from the mining process. Hot water is added to the tar sands in order to separate the bitumen from the rest of the mixture. This is the "standard process for recovering bitumen from the sand and other material in which it is bound". [4] For sustainable purposes, the hot water can be recycled and reused thereafter. [3] After this, it has to be upgraded before going to a refinery. During this process, hydrogen is added to the bitumen to create a high quality crude oil, which is sent to the refineries. [1]
Stage one deals with coking and hydrocracking. Coking consists of temperatures up to 500 degrees celsius, which remove the extra carbon by cracking the bitumen molecules with vaporization, transformation from liquid or a solid into a gas state. These extra carbon molecules form what is called coke, a solid. This is considered a waste by-product of this stage in the upgrade. Hydrocracking consists of hydrogen being added to the bitumen, which has been crack by catalysts. [1]
Stage two is hydrotreating. In this stage high temperatures and pressures remove nitrogen, sulphur, and metals from the bitumen. Ammonia (the nitrogen which is removed) is used as fuel and sulphur is altered and moved in order to be used in other industry processes. To put it in perspective, "one barrel of synthetic crude oil produces enough gasoline to fill three-quarters of a Chevy Avalanches gas tank". [1]
Natural gas plays a huge roll in extracting bitumen from the tar sands and also as a source of hydrogen in the upgrading phase before the crude oil is sent to the refineries. The reasons for using natural gas as opposed to another source of energy is because it is "relatively clean burning, readily available, and (until recently) cheap". [1] The tar sands industry uses a huge amount of natural gas per day, .6 billion cubic feet. For surface mining and upgrading, it is approximated that 750 cubic feet of natural gas is needed per barrel. For in situ production and upgrading, it is approximated that 1500 cubic feet of natural gas is needed per barrel. [1]
© Ty Montgomery. 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] D. Woynillowicz, C. Severson-Baker,and M. Raynolds, "Oil Sands Fever: The Environmental Implications of Canada's Oil Sands Rush," The Pembina Institute, November 2005.
[2] P. J. Cram, D. A. Redford, and Texaco Exploration Canada Ltd. "Thermal Recovery of Hydrocarbons from Tar Sands", US3993132, 23 Nov 76.
[3] J. H. Estes, E. P. Buinicky, and Texaco Inc., "Using Ammonium Sulfite or Bisulfite," US4250016, 10 Feb 81.
[4] R. D. Humphreys, and Geopetrol Equipment Ltd., "Tar Sands Extraction Process", US5985138, 16 Nov 99.
