Tar sands, also referred to as oil sands, shale oil, and bituminous sands.
The organic portion contains on an average 83% carbon, 10.4% hydrogen, 4.8% sulphur, 0.95% oxygen and 0.36% nitrogen. The bitumen* is neither oil nor tar, but a semisolid, degraded from of oil that does not flow at normal temperatures and pressures, thus making it difficult to extract. Degradation occurs when conventional oil migrates toward the surface and encounters, at temperatures below 93° C (200° F), descending
rainwater containing oxygen and bacteria. This leads to the formation of a tar-like substance. The lighter crude-oil fractions
are removed by solution, while the paraffin is removed by the bacteria in the water.
What remains is called tar sands.
They are mined
to extract the oil-like bitumen, which is then converted into synthetic crude oil or refined directly into petroleum products
by specialized refineries. Most refineries can handle only 10-15% of input coming
from heavy oil sources. Oil sands represent as much as 2/3 of the world’s
total petroleum resource. The principle reserves are in Canada
and Venezuela, which have about 75% of the world’s total
of about 4.5 trillion barrels. Venezuela
calls their tar sands extra-heavy oil. Bitumen
and extra-heavy oil are closely related types of petroleum, differing only in the degree by which they have been degraded
from the original crude oil by bacterial and erosion. The Venezuelan deposits
re less degraded than the Canadian deposits. They are at a higher temperature
than in fridge Canada, which makes extraction easier.
Tar sands are
composed of asphaltenes, resins, sulfur, and metals (most commonly vanadium and nickel).
The nature of these deposits varies widely. Bitumen distribution in a
deposit also varies depending on the permeability and porosity of the reservoir rock.
Bitumen is a mixture of organic liquids that are highly viscous, black, sticky.
The portion soluble in carbon disulfide is composed primarily of highly condensed polycyclic aromatic hydrocarbons
(PAH).
Polycyclic aromatics
are joined benzene rings with various groups attached to it—averaging about a dozen such rings. They are formed by the incomplete combustion of carbon-containing fuels.
Oil tar contains PAHs. (Since they are found in interstellar medium (comets
and meteorites) they strongly support the thesis that there is life elsewhere in the universe.)
In British English the
word asphalt refers to a mixture of mineral aggregate and bitumen. The word tar refers to the black viscous material obtained from
the destructive distillation of coal, is chemically distinct from Bitumen. However,
in American English, bitumen is referred to as asphalt. Bitumen is believed to be formed from remains of ancient algae and other aquatic life. They were deposited in mud on the bottom of oceans and lakes where they lived. Under heat and pressure of burial deep in the earth, the remains were transformed
into bitumen, kerogen, and petroleum. This mixture consisting mostly of oil on rising near the surface was acted again upon
by water and bacteria to from the tar sands,
Extraction from oil shale most commonly occurs by heating the rock to about 500—an expensive process. The liquid oil is then refined. Most
of the solid by-products of oil shale are unusable wastes, but a few of them have commercial value. These include sulfur, ammonia, alumina, soda ash, and nahcolite (a material that can be used in an industrial
air-pollution control procedure known as stack-gas scrubbing).
Herodotus said
that hot bitumen was used as mortar in the walls of Babylon. It had many ancient uses, such as caulking for boats, and for bonding tools, weapons, mosaics, and jewelry. It was used in paints and for waterproofing baskets and mats. Artistic and religious objects were carved from bitumen impregnated sands.
The first patent for the extraction of shale oil was issued in England
in 1694. A commercial shale oil industry was founded in 1838 in Autun France
to produce lamp fuel. By that time the demand for oil was much greater than could
be supplied by the whaling industry. As prices rose, numerous oil shale retorts
were constructed along the Ohio River in the U.S. This all disappeared with the discovery of crude oil in Pennsylvania
in 1859. Other regions without available crude continued to extract oil from
shale into the 20th century--extracted by JK from Wikipedia and Britannica 2002.
