Crude Oil

Crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds. Oil is found in geologic formations beneath the Earth's surface and is recovered mostly through oil drilling. It is refined and separated, also known as cracking?, by relying on the differing boiling points of the various hydrocarbons within crude oil. A barrel of oil? produces a large number of consumer products, from gasoline and kerosene to asphalt? and chemical compounds to make plastics and pharmaceuticals.

Petroleum is often used interchangeably with crude oil. Commonly, petroleum includes all liquid, gaseous, and solid hydrocarbons. Under surface pressure and temperature conditions, lighter hydrocarbons such as methane, ethane?, propane? and butane occur as gases, while pentane? and heavier hydrocarbons are liquids or solids. But in an underground oil reservoir, the proportions of gas, liquid, and solids depend on the subsurface conditions and on the nature of the petroleum mixture.

Geology

Oil is found in porous rock formations in the upper strata of some areas of the Earth's crust. There is also petroleum in oil sands? or tar sands?. An oil well produces predominantly crude oil, with some natural gas dissolved in it. Because the pressure is lower at the surface than underground, some of the gas will come out of solution and be recovered or burned as it vents. A gas well produces predominantly natural gas. However, because the underground temperature and pressure are higher than at the surface, the gas may contain heavier hydrocarbons such as pentane, hexane, and heptane? in the gaseous state. At surface conditions these will condense out of the gas to form a natural gas condensate, which is often just called condensate?. Condensate resembles gasoline in appearance and is similar to volatile light crude oil?.

Types of oil

The proportion of light hydrocarbons in the petroleum mixture varies greatly among different oil fields, ranging from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumens. The proportions of these oils has led to labelling, such as 'light sweet crude?'.

The hydrocarbons in crude oil are mostly alkanes?, cycloalkanes? and various aromatic hydrocarbons?. Other organic compounds contain nitrogen?, oxygen? and sulfur? and trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular composition varies widely by formation and region.

Crude oil can vary greatly in appearance. It is usually black or dark brown, although it may be yellowish, reddish, or even greenish. Underground, the lighter natural gas forms a gas cap over the petroleum while saline water usually sinks beneath it.

Crude oil may also be found in semi-solid form, mixed with sand and water, as in the Athabasca Oil Sands? or Tar Oil Sands? in Canada. This form of crude oil is also called crude bitumen. Bitumen? is a sticky, black, tar-like form of crude oil that is so thick and heavy that it must be heated or diluted before it will flow. Venezuela? also has large amounts of oil in the Orinoco Oil Sands?, although the hydrocarbons trapped in them are more fluid than in Canada and are usually called extra heavy oil.

These oil sands resources are called unconventional oil? to distinguish them from regular crude oil, which can be extracted using traditional oil well methods. Between them, Canada and Venezuela contain an estimated 3.6 trillion barrels of unconventional oil. This may be as much as twice the volume of the world's reserves of conventional oil.

Fuels from oil

Crude oil by volume is primarily used for producing fuels and gasoline. As much as 84% by volume of the hydrocarbons present in petroleum is converted into fuels, including gasoline, diesel?, jet fuel?, heating oil?, and other fuel oils. Liquified petroleum gas? is also a coproduct. The lighter grades of crude oil produce the best yields of these fuels, but as the world's reserves of light and medium oil are depleted, oil refineries are increasingly having to process heavy oil and bitumen, and use more complex and expensive methods to produce the products required. Because heavier crude oils have too much carbon? and not enough hydrogen?, these processes generally involve removing carbon from or adding hydrogen to the molecules. The process of doing so uses fluid catalytic cracking? to convert the longer, more complex molecules in the oil to the shorter, simpler ones in fuels.

Products from oil

Gasoline makes up less than half of a barrel of crude in the United States. Roughly another third goes to making the diesel and jet fuels. Oil is an important source of raw materials for making plastics and other chemical products. Two of the products that result from additional chemical processing are ethylene? and propylene?; these are the building blocks of modern plastics?.

Lightweight and versatile, plastics in the home are found in appliances, toys, and flooring, in the workplace in computers, desks, and carpeting and on the road, making up about 50% of the volume of cars, although they account for only about 10% of the weight, according to the American Chemistry Council?.
Crude oil is also the source for aromatic fluids, which are raw materials used in a wide variety of products – including dyes and synthetic detergents to the polyurethanes? used in athletic shoes and furniture to the polyesters? used in fabrics and beverage containers. In the healthcare industry, products made from oil include disposable syringes, catheters and blood bags, as well as artificial joints used in hip and knee replacements. Even common hand sanitizers can contain as much as 65% petrochemicals. While most of a barrel of oil goes to fuel production, about 16% is used as the raw material for many chemical products, including pharmaceuticals, solvents, for fertilizer?, pesticides, and plastics?.

Energy and Reserves

Due to its high energy density, easy transportability and relative abundance, oil has become the world's most important source of energy. Reported oil reserves are typically estimated at around 1.2 trillion short scale barrels?. Including oil trapped in oil sands, that number may be as high as 3.74 trillion barrels. Oil consumption? is currently around 84 million barrels a year, and increasing steadily as the economies of India? and China? become more energy intensive. If demand were to remain static, oil supplies could theoretically last another 120 years. However, reserves are subject to reporting manipulation to influence stock prices and market share. It is difficult to predict the oil peak in any given region, due to the lack of knowledge and/or transparency in accounting of global oil reserves. Official figures are widely believed to be inflated because OPEC members over-reported reserves in the 1980s when competing for global market share.

The International Energy Agency (IEA) says peak oil for conventional crude oil was in 2006. Since virtually all economic sectors rely heavily on petroleum, peak oil has significant consequences for the global economy.