Environmental Engineering Reference
In-Depth Information
Tar sands (also known as oil sands, extra-heavy oil, and bituminous sands) are a type of unconventional petro-
leum deposit. Note that the word
petroleum
means "rock oil" or "oil from the Earth." Tar sands contain natur-
ally occurring mixtures of sand, clay, water, and an extremely dense and viscous form of petroleum. Technic-
ally, tar sands are referred to as bitumen and are found in large quantities in many countries, including Canada
and Venezuela. Bitumen is an extremely viscous form of petroleum that can be extracted by heating tar sands.
The resulting hydrocarbon requires more processing for use than crude oil, increasing both cost and environ-
mental impact. Additional environmental impacts include damage to the surrounding environment due to sur-
face mining and the disposal of waste material.
Like oil shale, tar sands yield moderate energy. Liquefying the crude oil from the sands requires injecting
steam into the sand, which takes energy. The oil is then refined much like crude oil is refined. The process of
generating useable oil from tar sand creates two to four times the amount of greenhouse gases as the produc-
tion of conventional oil. The sulfur content is also higher, so larger amounts of sulfur dioxide are produced
when the oil from tar sands is burned, resulting in an increase in acid rain.
Only since 2003 has oil shale been considered part of the world's oil reserves. The higher price of crude oil and
the new technologies developed to obtain the oil from the oil sands has made it profitable to extract this uncon-
ventional oil. There are major deposits of oil shale in many places around the world, including deposits in the
United States (Colorado, Utah, and Wyoming). The world's largest reserves are in Canada and Venezuela, each
of which has oil sand reserves approximately equal to the world's total reserves of conventional crude oil sup-
plies. Oil sands may represent as much as two-thirds of the world's total petroleum reserves.
Extraction and Purification of Crude Oil
Crude oil is a naturally occurring, complex mixture of hydrocarbons (with a variety of molecular weights) and
other organic compounds found in geological formations at varying depths beneath the Earth's surface. Crude
oil is obtained by drilling through the Earth's surface into deposits. Often, natural gas is found with these de-
posits but is usually not recovered.
Crude oil is refined into a large number of products, including gasoline and motor-vehicle fuels, kerosene, as-
phalt, and a variety of chemical reagents that can be used to make plastics, pharmaceuticals, and other chemic-
al by-products. This is accomplished mostly by heating the crude oil and separating the different components
by their boiling points.
Natural Gas
Formation of Natural Gas
Natural gas formation is similar to that of crude oil, from the remains of tiny aquatic plants and animals. When
huge amounts of these organisms die over many years, they sink to the ocean floor and then are covered with
silt and mud, decaying anaerobically (without oxygen). Over time, mud accumulates, and the pressure and heat
on the organic materials increases. Eventually, the pressure squeezes out most of the liquid, leaving behind the
dry carbons to form the long carbon chains in crude oil. The shorter chains, such as those in methane, ethane,
propane, and butane, also form and become natural gas. Usually, natural gas and crude oil are found together.
In some areas, natural gas is more abundant, and in other areas crude oil is found in larger amounts. Thus, in
any given field, a company usually drills for either natural gas or crude oil, but not both.
Methane Hydrates
Methane hydrates are a recently discovered source of natural gas locked in ice formed at low temperatures and
high pressures (often called "burning ice") and found in unique settings on Earth. On land, methane hydrates
