article

Tar sands, also referred to as oil sands or bituminous sands, are a combination of clay, sand, water, and bitumen. Technically speaking, the bitumen is neither oil nor tar, but a semisolid, degraded form of oil which will not flow toward producing wells under normal conditions, making it difficult and expensive to produce. Tar sands are mined to extract the oil-like bitumen which is upgraded into synthetic crude oil or refined directly into petroleum products by specialized refineries. Conventional oil is extracted by drilling traditional wells into the ground whereas tar sand deposits are mined using strip mining techniques, or persuaded to flow into producing wells by in situ techniques which reduce the bitumen's viscosity with steam and/or solvents. On average bitumen contains 83.2% carbon, 10.4% hydrogen, 0.94% oxygen, 0.36% nitrogen and 4.8% sulphur.

Location

Tar sands deposits are found in over 70 countries throughout the world, but three quarters of the world's reserves are in two regions, Venezuela and Alberta, Canada. While tar sands were used by the ancient Mesopotamians and Canadian Indians, they have only recently become considered to be a major part of the world's oil reserves, that is, they have become economically extractible at current prices with current technology. To distinguish the bitumen and synthetic oil extracted from tar sands from the free-flowing hydrocarbon mixtures known as crude oil that oil companies have traditionally produced from oil wells, tar sands are often referred to as non-conventional oil. See Bituminous rocks

Tar sands represent as much as 66% of the world's total reserves of oil, with at least 1.7 trillion barrels (1.7×1012 bbl or 270×109 m3) in the Canadian Athabasca Tar Sands and 1.8 trillion barrels (1.8×1012 bbl or 280×109 m3) in the Venezuelan Orinoco tar sands, compared to 1.75 trillion barrels (1.75×1012 bbl or 278×109 m3) of conventional oil worldwide, most of it in Saudi Arabia and other Middle-Eastern countries.

Between them, the Canadian and Venezuelan deposits contain about 3.6 trillion barrels of oil in place. Amazingly, this is only the remnant of vast petroleum deposits which once totaled as much as 18 trillion barrels, most of which has escaped or been destroyed by bacteria over the eons.

Canada

Most of the oil sands of Canada are located in three major deposits in northern Alberta. The three deposits are the Athabasca-Wabiskaw oil sands of north northeastern Alberta, the Cold Lake deposits of east northeastern Alberta, and the Peace River deposits of northwestern Alberta. Between them they cover over 140,000 square kilometers (54,000 square miles) an area larger than Florida and hold at least 175 billion barrels (175×109 bbl) or 28 billion cubic metres (28×109 m3) of recoverable crude bitumen, which amounts to three-quarters of North American petroleum reserves. In addition to the Alberta deposits, there are major oil sands deposits on Melville Island in the Canadian Arctic islands but they are unlikely to see commercial production in the foreseable future.

The Alberta oil sands deposits contain at least 85% of the world's total bitumen reserves but are so concentrated as to be the only such deposits that are economically recoverable for conversion to oil. The largest bitumen deposit, containing about 80% of the total, and the only one suitable for surface mining is the Athabasca Oil Sands along the Athabasca River. The mineable area as defined by the Alberta government covers 37 contiguous townships (about 3400 square kilometres or 1300 square miles) north of the city of Fort McMurray. The smaller Cold Lake deposits important because some of the oil is fluid enough to be produced by conventional production methods. All three Alberta areas are suitable for production using in-situ methods such as cyclic steam stimulation (CSS) and steam assisted gravity drainage (SAGD).

The Canadian oil sands have been in commercial production since the original Great Canadian Oil Sands (now Suncor) mine began operation in 1967. A second mine, operated by the Syncrude consortium, began operation in 1978 and is the biggest mine of any type in the world. The third mine in the Athabasca Oil Sands, the Albian Sands consortium of Shell Canada, Chevron Corporation and Western Oil Sands Inc. began operation in 2003. However, with the development of new in-situ production techniques such as steam assisted gravity drainage and the Oil price increases of 2004-2006, there are now several dozen companies planning nearly 100 oil sands mines and in-situ projects in Canada, totaling nearly $100 billion in capital investment.

Venezuela

Located in eastern Venezuela, north of the Orinoco River, the Orinoco oil belt vies with the Canadian oil sand for largest known accumulation of bitumen in the world. Venezuela prefers to call its tar sands "extra-heavy oil", and although distinction is somewhat academic, the extra-heavy crude oil deposit of the Orinoco Belt represent nearly 90% of the known global reserves of extra-heavy oil.

Bitumen and extra-heavy oil are closely related types of petroleum, differing from each other, only in the degree by which they have been degraded from the original crude oil by bacteria and erosion. The Venezuelan deposits are less degraded than the Canadian deposits and are at a higher temperature (over 50 degrees Celsius versus freezing for northern Canada) which means they are easier to produce by conventional techniques.

Although it is easier to produce, it is still too heavy to transport by pipeline or process in normal refineries. Lacking access to first-world capital and technological prowess, Venezuela has not been able to design and build the kind of bitumen upgraders and heavy oil refineries that Canada has. However, in the early 1980’s the state oil company, PDVSA, developed a method of using the extra-heavy oil resources by emulsifying it with water (70% extra-heavy oil, 30% water) to allow it to flow in pipelines. The resulting product, called Orimulsion, can be burned in boilers as a replacement for coal and heavy fuel oil with only minor modifications. Unfortunately, the fuel’s high sulphur content and emission of particulates make it difficult to meet increasingly strict international environmental regulations.

Further development of the Venezuelan resources has been curtailed by political unrest. Venezuela is much less politically stable than Canada, and a strike by employees of the state oil company, followed by the firing of most of its staff (including 70% of its technical staff and all of the PhD's at its research center), have severely limited its technological ability to develop its oil sands. As a result, Venezuelan oil production is on a downward spiral while Canada's is just starting to take off.

Extraction process

Surface Mining

For the last 38 years or so, bitumen has been extracted from the Athabasca Oil Sands by surface mining. In these oil sands there are large deposits of bitumen with little overburden, making mining the most efficient method of extracting it. The overburden consists of water-laden muskeg (peat bog) over top of clay and barren sand. The oil sands themselves are typically 40 to 60 metres deep, sitting on top of flat limestone rock. Originally, the sands were mined with draglines and bucket-wheel excavators and moved to the processing plants by conveyor belts. However, in recent years companies such as Syncrude and Suncor have switched to much cheaper shovel-and-truck operations using the biggest power shovels (100 tons) and dump trucks (400 tons) in the world. This has reduced production costs to around $15 per barrel of synthetic crude oil.

After excavation, hot water and caustic soda (NaOH) 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 to allow bitumen to separate from sand and clay, the combination of hot water and agitation releases bitumen from the tar 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. Bitumen is much thicker than traditional crude oil, so it must be either mixed with lighter petroleum (either liquid or gas) or chemically split before it can be transported by pipeline for upgrading into synthetic crude oil.

Recent enhancements to this method include Tailings Oil Recovery (TOR) units which recover oil from the tailings, Diluent Recovery Units to recover naptha from the froth, Inclined Plate Settlers (IPS) and disc centrifuges. These allow the extraction plants to recover over 90% of the bitumen in the sand.

Three oil sands mines are currently in operation. The original Suncor mine opened in 1967, while the Syncrude mine (the biggest mine in the world) started in 1978 and Shell Canada opened its Muskeg River mine in 2003. New mines under construction or undergoing approval include Shell Canada's Jackpine mine, Imperial Oil's Kearl Lake mine, Synenco Energy's Northern Lights mine, and Petro-Canada's Fort Hills mine.

It is estimated that around 80% of the Alberta tar sands and nearly all of Venezuelan sands are too far below the surface to use the open-pit mining technique used by the large producers. A number of in-situ techniques have been developed to extract this deeper oil. http://www.oilsandsdiscovery.com/oil_sands_story/insitu.html]

Cold Flow

In this technique, the oil is simply pumped out of the sands, often using specialized pumps called progressive cavity pumps. This only works well in areas where the oil is fluid enough to pump. It is commonly used in Venezuela (where the extra-heavy oil is at 50 degrees Celsius), and also in the Wabasca, Alberta Oil Sands and the southern part of the Cold Lake, Alberta Oil Sands. It has the advantage of being cheap and the disadvantage that it recovers only 5-6% of the oil in place.

Some years ago Canadian oil companies discovered that if they removed the sand filters from the wells and produced as much sand as possible with the oil, production rates improved remarkably. This technique became known as Cold Heavy Oil Production with Sand (CHOPS). Further research disclosed that pumping out sand opened "wormholes" in the sand formation which allowed more oil to reach the wellbore. The advantage of this method is better production rates and recovery (around 10%) and the disadvantage that disposing of the produced sand is a problem. A novel way to do this was spreading it on rural roads, which rural governments liked because the oily sand reduced dust and the oil companies did their road maintenance for them. However, governments have become concerned about how thick the roads were becoming, so in recent years disposing of sand in underground salt caverns has become common.

Cyclic Steam Stimulation (CSS)

The use of steam injection to recover heavy oil has been in use in the oil fields of California since the 1950's. The Cyclic Steam Stimulation or "huff-and-puff" method has been in use by Imperial Oil at Cold Lake since 1985 and is also used by Canadian Natural Resources at Primrose and Wolf Lake. In this method, the well is put through cycles of steam injection, soak, and oil production. First steam is injected into a well at a temperature of 300 degrees Celsius for a period of weeks to months, then the well is allowed to sit for days to weeks to allow heat to soak into the formation, and then the hot oil is pumped out of the well for a period of weeks or months. Once the production rate falls off, the well is put through another cycle of injection, soak and production. This process is repeated until the cost of injecting steam becomes higher than the money made from producing oil. The CSS method has the advantage that recovery factors are around 20 to 25% and the disadvantage that the cost to inject steam is high.

Steam Assisted Gravity Drainage (SAGD)

Steam assisted gravity drainage was developed in the 1980s by an Alberta government research center and fortuitously coincided with improvements in directional drilling technology that made it quick and inexpensive to do by the mid 1990's. In SAGD, two horizontal wells are drilled in the oil sands, one at the bottom of the formation and another about 5 metres above it. These wells are typically drilled in groups off central pads and can extend for miles in all directions. In each well pair, steam is injected into the upper well, the heat melts the bitumen, which allows it to flow into the lower well, where it is pumped to the surface. SAGD has proved to be a major breakthrough in production technology since it is cheaper than CSS, allows very high oil production rates, and recovers up to 60% of the oil in place. Because of its very favorable economics and applicability to a vast area of oil sands, this method alone quadrupled North American oil reserves and allowed Canada to move to second place in world oil reserves after Saudi Arabia. Most major Canadian oil companies now have SAGD projects in production or under construction in Alberta's oil sands areas and in Wyoming. Examples include Suncor’s Firebag project, Nexen's Long Lake project, Petro-Canada's MacKay River project, Husky Energy's Tucker Lake and Sunrise projects, Shell Canada's Peace River project, Encana's Foster Creek development, ConocoPhillips Surmont project, and Devon Canada's Jackfish project and Derek Oil & Gas`s LAK Ranch projekt.

Vapor Extraction Process (VAPEX)

VAPEX is similar to SAGD but instead of steam, hydrocarbon solvents are injected into the upper well to dilute the bitumen and allow it to flow into the lower well. It has the advantage of much better energy efficiency than steam injection and it does some partial upgrading of bitumen to oil right in the formation. It is very new but has attracted much attention from oil companies, who are beginning to experiment with it.

The above three methods are not mutually exclusive. It is becoming common for wells to be put through one CSS injection-soak-production cycle to condition the formation prior to going to SAGD production, and companies are experimenting with combining VAPEX with SAGD to improve recovery rates and lower energy costs.

Toe to Heel Air Injection (THAI)

This is a very new and experimental method that combines a vertical air injection well with a horizontal production well. The process ignites oil in the reservoir and creates a vertical wall of fire moving from the "toe" of the horizontal well toward the "heel", which burns the heavier oil components and drives the lighter components into the production well, where it is pumped out. In addition, the heat from the fire upgrades some of the heavy bitumen into lighter oil right in the formation. Historically fireflood projects have not worked out well because of difficulty in controlling the flame front and a propensity to set the producing wells on fire. However, some oil companies feel the THAI method will be more controllable and practical, and have the advantage of not requiring energy to create steam.

Environmental Impacts

Tar sands development has a direct impact on local and planetary ecosystems. In Alberta, the strip mining form of oil extraction completely destroys the boreal forest, the bogs, the rivers as well as the natural landscape. The mining industry believes that the boreal forest will eventually colonize the reclaimed lands, yet 30 years after the opening of the first open pit mine near Fort McMurray, Alberta, no land is considered by the Alberta Government as having been "restored."

Furthermore, for every barrel of synthetic oil produced in Alberta, more than 80 kg of greenhouse gases are released into the atmosphere and between 2 and 4 barrels of waste water are dumped into tailing ponds that have flooded about 50 km² of forest and bogs. The forecast growth in synthetic oil production in Alberta also threatens Canada's international commitments. In ratifying the Kyoto Protocol, Canada agreed to reduce, by 2012, its greenhouse gas emissions by 6% with respect to the reference year (1990). In 2002, Canada's total greenhouse gas emissions had increased by 24% since 1990.

In 2005, University of Toronto researcher Charles Jia developed a means to convert the fluid coke byproduct of oil sand extraction to activated carbon, potentially reducing waste in the extraction process.*

External links

Peak oil

Dehtové písky | Tjæresand | Ölsand | Sable bitumineux | Teerzand | Öljyhiekka | Нефтеносный пласт

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Tar sands".

Home Page • arts • business • computers • games • health • hospitals • home • kids & teens • news • physicians • recreation• reference • regional • science • shopping • society • sports • world