Oil sands are a mixture of sand, clay, water, and bitumen that occur naturally. Bitumen is the fossil fuel component of this sand, and it is a very heavy oil that must be treated and upgraded before it can be used to produce useful fuels such as gasoline. Each grain of sand is coated first in a thin layer of water, and is then surrounded by bitumen.
Oil sand deposits are found around the globe in Venezuela, the United States, and Russia. However, the largest, most developed deposit in the world is the Athabasca deposit in Northern Alberta, Canada.
Like crude oil, the bitumen that exists in the oil sands began as a living material. It is speculated that the oil sands that exist today formed as a result of ancient oceans that existed millions of years ago covering the areas where the oil sands exist today. As the microscopic marine life within the oceans died, they decomposed with the help of bacteria removing the oxygen and nitrogen, leaving mainly hydrogen and carbon. Heat and pressure then resulted in the layering of rock, silt, and sand over time and "cooked" the dead organic material for millions of years at temperatures between 50 and 150°C. This formation of oil is similar to that of conventional oil deposits, however in this case the oil absorbed into the existing sand. Although scientists are fairly convinced that this is how the oil sands began, exactly the same as how conventional oil forms, with the one minor difference that sand is involved. The reason that oil sands contain bitumen and not conventional crude oil is a topic that is more controversial, but there are two main theories. The first of these theories is that the oil sands began as a vast reserve of crude oil, and over long periods of time the lighter crude oil escaped or was destroyed microbiologically, leaving behind bitumen. The second theory is that bitumen was formed immediately in a process similar to the formation of oil shale. In this theory, bitumen was released from shales with a large amount of organic matter (kerogen rich shales) instead of crude oil being released.
In both theoretical bitumen formation methods the bitumen collects around the particles of sand. Instead of migrating through permeable rock as traditional oil would, this bitumen-soaked sand is then forced to the surface from the pressure of mountain formation - in the Alberta oil sands it was the formation of the Rocky Mountains. Within the oil sands are fine clay particles, along with other minerals such as assorted metals and sulfur.
Although frequently referred to incorrectly as tar sands (often by people who wish to make a statement about the environmental impacts of oil sands), the term oil sands may be widely used but it is still not technically the most correct term. The term bituminous sands would be the most accurate term, as it is not tar but a thick form of oil known as bitumen that makes up the fossil fuel component of the sand. The bitumen content in these deposits varies from 1-18%. However, over time the term commonly used for these deposits has been oil sands, with widespread government and industry official acceptance of this term in the mid-1990s. Historically, oil sands were referred to as tar sands largely due to their (ineffective) use as a roofing and paving tar. Over time this term was phased out as tar is vastly different from oil. Tar is a synthetically produced product created from coal, wood, petroleum, or peat through a distillation process whereas oil is a naturally occurring petrochemical that can be upgraded into petroleum products. Because of this definition, the term "oil sand" fits more directly with the actual content and use of products extracted from this sand.
On average, it takes 2 tonnes of mined oil sand to produce a single barrel of synthetic crude oil. Depending on whether or not the deposit is located close to the surface, it can be retrieved either by surface mining or using in situ mining techniques. After extraction, the sand must be processed and the bitumen upgraded. Since bitumen is thick and has a deficiency of hydrogen upon extraction, it must be upgraded to remove carbon or add hydrogen to obtain a balanced hydrocarbon that is more valuable.
Some reserves are shallow enough to be surface mined, which simply means that earth-moving equipment can be utilized to dig out oil sand for processing. Resources recoverable by this type of extraction are estimated to be 65 billion barrels. These deposits must be within 75 meters of the surface to be mined in this fashion. Currently, around 500 square kilometers of the oil sands deposit in Northern Alberta is undergoing surface mining, which is only 3% of total oil sands.
To excavate the oil sand, large trucks use scoops (some with scoops as large as a two-car garage!) to collect the oil sand and move it to a cleaning facility. At this facility, the oil sand is immersed in a hot mix of water and some sort of diluting chemical. This separates the thick bitumen from the sand. The non-bitumen component that remains is composed of sand, water, fine clays, and minerals. This leftover component is known as tailings and is then sent to tailings ponds to allow the sand to settle out. The separated, diluted bitumen can then be sent to upgrading to obtain more useful products. In total, two tonnes of oil sand must be obtained and processed with 2-4 barrels of water to produce a single barrel of crude oil in its synthetic form.
In-situ simply means below ground deposits, which make up 80% of Canada's oil sands. These deposits are buried more deeply then 75 meters, which makes traditional mining from the surface impossible. Most of these deposits are buried more than 350-600 meters below ground. There are a variety of specific methods used to extract resources from in-situ deposits.
The two most common methods used in in-situ recovery are steam assisted gravity drainage and cyclic steam stimulation. In both of these methods steam, solvents, or heat cause the bitumen to become fluid enough that it can be pumped out of the well. One benefit of this model of extraction is that tailings ponds are not a necessity as sand remains in the ground, along with the fact that less water is used to create the oil. One barrel of crude oil in its synthetic form only requires half a barrel of water. New techniques such as pulse technology and vapour recover extraction are currently being tested.
One of the biggest issues with the development of oil sands is the environmental impacts associated with the extraction, processing, and upgrading of the bitumen. Some of the concerns include: