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Pumpjack pumping an oil well near Lubbock, Texas

Petroleum (L. petroleum, from Greek πετρέλαιον, lit. "rock oil") or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights, and other organic compounds, that are found in geologic formations beneath the earth's surface.

The term "petroleum" was first used in the treatise De Natura Fossilium, published in 1546 by the German mineralogist Georg Bauer, also known as Georgius Agricola.[1]

Contents

Composition

In its strictest sense, petroleum includes only crude oil, but in common usage it includes both crude oil and natural gas. Both crude oil and natural gas are predominantly a mixture of hydrocarbons. Under surface pressure and temperature conditions, the lighter hydrocarbons methane, ethane, propane and butane occur as gases, while the heavier ones from pentane and up are in the form of liquids or solids. However, in the underground oil reservoir the proportion which is gas or liquid varies depending on the subsurface conditions, and on the phase diagram of the petroleum mixture.[2]

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 associated gas or solution gas. A gas well produces predominately 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. Under surface conditions these will condense out of the gas and form natural gas condensate, often shortened to condensate. Condensate resembles gasoline in appearance and is similar in composition to some volatile light crude oils.

The proportion of hydrocarbons in the petroleum mixture is highly variable between different oil fields and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumens.

The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the 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 from formation to formation but the proportion of chemical elements vary over fairly narrow limits as follows:[3]

Composition by weight
Element Percent range
Carbon 83 to 87%
Hydrogen 10 to 14%
Nitrogen 0.1 to 2%
Oxygen 0.1 to 1.5%
Sulfur 0.5 to 6%
Metals less than 1000 ppm

Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of each varies from oil to oil, determining the properties of each oil.[2]

Composition by weight
Hydrocarbon Average Range
Paraffins 30% 15 to 60%
Naphthenes 49% 30 to 60%
Aromatics 15% 3 to 30%
Asphaltics 6% remainder
Most of the world's oils are non-conventional.[4]

Crude oil varies greatly in appearance depending on its composition. It is usually black or dark brown (although it may be yellowish or even greenish). In the reservoir it is usually found in association with natural gas, which being lighter forms a gas cap over the petroleum, and saline water which, being heavier than most forms of crude oil, generally sinks beneath it. Crude oil may also be found in semi-solid form mixed with sand and water, as in the Athabasca oil sands in Canada, where it is usually referred to as crude bitumen. In Canada, bitumen is considered a sticky, tar-like form of crude oil which is so thick and heavy that it must be heated or diluted before it will flow.[5] 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 oil which can be extracted using traditional oil well methods. Between them, Canada and Venezuela contain an estimated 3.6 trillion barrels (570×10^9 m3) of bitumen and extra-heavy oil, about twice the volume of the world's reserves of conventional oil.[6]

Petroleum is used mostly, by volume, for producing fuel oil and gasoline (petrol), both important "primary energy" sources.[7] 84% by volume of the hydrocarbons present in petroleum is converted into energy-rich fuels (petroleum-based fuels), including gasoline, diesel, jet, heating, and other fuel oils, and liquefied petroleum gas.[8] The lighter grades of crude oil produce the best yields of these products, 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, and using fluid catalytic cracking to convert the longer, more complex molecules in the oil to the shorter, simpler ones in the fuels.

Due to its high energy density, easy transportability and relative abundance, oil has become the world's most important source of energy since the mid-1950s. Petroleum is also the raw material for many chemical products, including pharmaceuticals, solvents, fertilizers, pesticides, and plastics; the 16% not used for energy production is converted into these other materials. Petroleum 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 (tar sands). Known reserves of petroleum are typically estimated at around 190 km3 (1.2 trillion (short scale) barrels) without oil sands,[9] or 595 km3 (3.74 trillion barrels) with oil sands.[10] Consumption is currently around 84 million barrels (13.4×10^6 m3) per day, or 4.9 km3 per year.

Chemistry

Octane, a hydrocarbon found in petroleum, lines are single bonds, black spheres are carbon, white spheres are hydrogen

Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly found molecules are alkanes (linear or branched), cycloalkanes, aromatic hydrocarbons, or more complicated chemicals like asphaltenes. Each petroleum variety has a unique mix of molecules, which define its physical and chemical properties, like color and viscosity.

The alkanes, also known as paraffins, are saturated hydrocarbons with straight or branched chains which contain only carbon and hydrogen and have the general formula CnH2n+2 They generally have from 5 to 40 carbon atoms per molecule, although trace amounts of shorter or longer molecules may be present in the mixture.

The alkanes from pentane (C5H12) to octane (C8H18) are refined into gasoline (petrol), the ones from nonane (C9H20) to hexadecane (C16H34) into diesel fuel and kerosene (primary component of many types of jet fuel), and the ones from hexadecane upwards into fuel oil and lubricating oil. At the heavier end of the range, paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and up, although these are usually cracked by modern refineries into more valuable products. The shortest molecules, those with four or fewer carbon atoms, are in a gaseous state at room temperature. They are the petroleum gases. Depending on demand and the cost of recovery, these gases are either flared off, sold as liquified petroleum gas under pressure, or used to power the refinery's own burners. During the winter, Butane (C4H10), is blended into the gasoline pool at high rates, because butane's high vapor pressure assists with cold starts. Liquified under pressure slightly above atmospheric, it is best known for powering cigarette lighters, but it is also a main fuel source for many developing countries. Propane can be liquified under modest pressure, and is consumed for just about every application relying on petroleum for energy, from cooking to heating to transportation.

The cycloalkanes, also known as naphthenes, are saturated hydrocarbons which have one or more carbon rings to which hydrogen atoms are attached according to the formula CnH2n. Cycloalkanes have similar properties to alkanes but have higher boiling points.

The aromatic hydrocarbons are unsaturated hydrocarbons which have one or more planar six-carbon rings called benzene rings, to which hydrogen atoms are attached with the formula CnHn. They tend to burn with a sooty flame, and many have a sweet aroma. Some are carcinogenic.

These different molecules are separated by fractional distillation at an oil refinery to produce gasoline, jet fuel, kerosene, and other hydrocarbons. For example 2,2,4-trimethylpentane (isooctane), widely used in gasoline, has a chemical formula of C8H18 and it reacts with oxygen exothermically:[11]

2\mathrm{C}_8 \mathrm{H}_{18(l)} + 25\mathrm{O}_{2(g)} \rightarrow \; 16\mathrm{CO}_{2(g)} + 18\mathrm{H}_2 \mathrm{O}_{(l)} + 10.86 \ \mathrm{MJ}

The amount of various molecules in an oil sample can be determined in laboratory. The molecules are typically extracted in a solvent, then separated in a gas chromatograph, and finally determined with a suitable detector, such as a flame ionization detector or a mass spectrometer.[12]

Incomplete combustion of petroleum or gasoline results in production of toxic byproducts. Too little oxygen results in carbon monoxide. Due to the high temperatures and high pressures involved, exhaust gases from gasoline combustion in car engines usually include nitrogen oxides which are responsible for creation of photochemical smog.

Empirical equations for the thermal properties of petroleum products

Heat of combustion:

At a constant volume the heat of combustion of a petroleum product can be approximated as follows:

Qv = 12,400 − 2,100d2

where Qv is measured in cal/gram and d is the specific gravity at 60°F.

Thermal conductivity

The thermal conductivity of petroleum based liquids can be modeled as follows:

K = \frac{0.813}{d}[1-0.0003(t-32)],

where K is measured in BTU · hr-1ft-2 , t is measured in °F and d is the specific gravity at 60°F.

Specific heat

The specific heat of a petroleum oils can be modeled as follows:

c = \frac{1}{\sqrt{d}} [0.388+0.00045t],

where c is measured in BTU/lbm-°F, t is the temperature in Fahrencecius and d is the specific gravity at 60°F.

In units of kcal/kg°C, the formula is:

\frac{1}{\sqrt{d}} [0.402+0.00081t],

where the temperature t is in Celsius and d is the specific gravity at 15°C.

Latent heat of vaporization

The latent heat of vaporization can be modeled under atmospheric conditions as follows:

L = \frac{1}{d}[110.9 - 0.09t],

where L is measured in BTU/lbm, t is measured in °F and d is the specific gravity at 60°F.

In units of kcal/kg, the formula is:

L = \frac{1}{d}[194.4 - 0.162t],

where the temperature t is in Celsius and d is the specific gravity at 15°C.[13]

Formation

According to generally accepted theory, petroleum is derived from ancient biomass.[14] It is a fossil fuel derived from ancient fossilized organic materials. The theory was initially based on the isolation of molecules from petroleum that closely resemble known biomolecules (Figure).

Structure of vanadium porphyrin compound extracted from petroleum by Alfred Treibs, father of organic geochemistry. Treibs noted the close structural similarity of this molecule and chlorophyll a.

More specifically, crude oil and natural gas are products of heating of ancient organic materials (i.e. kerogen) over geological time. Formation of petroleum occurs from hydrocarbon pyrolysis, in a variety of mostly endothermic reactions at high temperature and/or pressure.[15] Today's oil formed from the preserved remains of prehistoric zooplankton and algae, which had settled to a sea or lake bottom in large quantities under anoxic conditions (the remains of prehistoric terrestrial plants, on the other hand, tended to form coal). Over geological time the organic matter mixed with mud, and was buried under heavy layers of sediment resulting in high levels of heat and pressure (diagenesis). This process caused the organic matter to change, first into a waxy material known as kerogen, which is found in various oil shales around the world, and then with more heat into liquid and gaseous hydrocarbons via a process known as catagenesis.

Geologists often refer to the temperature range in which oil forms as an "oil window"[16]—below the minimum temperature oil remains trapped in the form of kerogen, and above the maximum temperature the oil is converted to natural gas through the process of thermal cracking. Sometimes, oil which is formed at extreme depths may migrate and become trapped at much shallower depths than where it was formed. The Athabasca Oil Sands is one example of this.

Abiogenic origin

A small number of geologists adhere to the abiogenic petroleum origin hypothesis and maintain that hydrocarbons of purely inorganic origin exist within Earth's interior. Chemists Marcellin Berthelot and Dmitri Mendeleev, as well as astronomer Thomas Gold championed the theory in the Western world by supporting the work done by Nikolai Kudryavtsev in the 1950s. It is currently supported primarily by Kenney and Krayushkin.[17]

The abiogenic origin hypothesis has not yet been ruled out. Its advocates consider that it is "still an open question"[18] Extensive research into the chemical structure of kerogen has identified algae as the primary source of oil. The abiogenic origin hypothesis fails to explain the presence of these markers in kerogen and oil, as well as failing to explain how inorganic origin could be achieved at temperatures and pressures sufficient to convert kerogen to graphite. It has not been successfully used in uncovering oil deposits by geologists, as the hypothesis lacks any mechanism for determining where the process may occur.[19] More recently scientists at the Carnegie Institution for Science have found that ethane and heavier hydrocarbons can be synthesized under conditions of the upper mantle.[20][citation needed]

Crude oil

Crude oil reservoirs

Hydrocarbon trap.

Three conditions must be present for oil reservoirs to form: a source rock rich in hydrocarbon material buried deep enough for subterranean heat to cook it into oil; a porous and permeable reservoir rock for it to accumulate in; and a cap rock (seal) or other mechanism that prevents it from escaping to the surface. Within these reservoirs, fluids will typically organize themselves like a three-layer cake with a layer of water below the oil layer and a layer of gas above it, although the different layers vary in size between reservoirs. Because most hydrocarbons are lighter than rock or water, they often migrate upward through adjacent rock layers until either reaching the surface or becoming trapped within porous rocks (known as reservoirs) by impermeable rocks above. However, the process is influenced by underground water flows, causing oil to migrate hundreds of kilometres horizontally or even short distances downward before becoming trapped in a reservoir. When hydrocarbons are concentrated in a trap, an oil field forms, from which the liquid can be extracted by drilling and pumping.

The reactions that produce oil and natural gas are often modeled as first order breakdown reactions, where hydrocarbons are broken down to oil and natural gas by a set of parallel reactions, and oil eventually breaks down to natural gas by another set of reactions. The latter set is regularly used in petrochemical plants and oil refineries.

Wells are drilled into oil reservoirs to extract the crude oil. "Natural lift" production methods that rely on the natural reservoir pressure to force the oil to the surface are usually sufficient for a while after reservoirs are first tapped. In some reservoirs, such as in the Middle East , the natural pressure is sufficient over a long time. The natural pressure in many reservoirs, however, eventually dissipates. Then the oil must be pumped out using “artificial lift” created by mechanical pumps powered by gas or electricity. Over time, these "primary" methods become less effective and "secondary" production methods may be used. A common secondary method is “waterflood” or injection of water into the reservoir to increase pressure and force the oil to the drilled shaft or "wellbore." Eventually "tertiary" or "enhanced" oil recovery methods may be used to increase the oil's flow characteristics by injecting steam, carbon dioxide and other gases or chemicals into the reservoir. In the United States, primary production methods account for less than 40% of the oil produced on a daily basis, secondary methods account for about half, and tertiary recovery the remaining 10%. Extracting oil (or “bitumen”) from oil/tar sand and oil shale deposits requires mining the sand or shale and heating it in a vessel or retort, or using “in-situ” methods of injecting heated liquids into the deposit and then pumping out the oil-saturated liquid.

Unconventional oil reservoirs

Oil-eating bacteria biodegrades oil that has escaped to the surface. Oil sands are reservoirs of partially biodegraded oil still in the process of escaping and being biodegraded, but they contain so much migrating oil that, although most of it has escaped, vast amounts are still present—more than can be found in conventional oil reservoirs. The lighter fractions of the crude oil are destroyed first, resulting in reservoirs containing an extremely heavy form of crude oil, called crude bitumen in Canada, or extra-heavy crude oil in Venezuela. These two countries have the world's largest deposits of oil sands.

On the other hand, oil shales are source rocks that have not been exposed to heat or pressure long enough to convert their trapped hydrocarbons into crude oil. Technically speaking, oil shales are not really shales and do not really contain oil, but are usually relatively hard rocks called marls containing a waxy substance called kerogen. The kerogen trapped in the rock can be converted into crude oil using heat and pressure to simulate natural processes. The method has been known for centuries and was patented in 1694 under British Crown Patent No. 330 covering, "A way to extract and make great quantityes of pitch, tarr, and oyle out of a sort of stone." Although oil shales are found in many countries, the United States has the world's largest deposits.[21]

Classification

A sample of medium heavy crude oil

The petroleum industry generally classifies crude oil by the geographic location it is produced in (e.g. West Texas Intermediate, Brent, or Oman), its API gravity (an oil industry measure of density), and by its sulfur content. Crude oil may be considered light if it has low density or heavy if it has high density; and it may be referred to as sweet if it contains relatively little sulfur or sour if it contains substantial amounts of sulfur.

The geographic location is important because it affects transportation costs to the refinery. Light crude oil is more desirable than heavy oil since it produces a higher yield of gasoline, while sweet oil commands a higher price than sour oil because it has fewer environmental problems and requires less refining to meet sulfur standards imposed on fuels in consuming countries. Each crude oil has unique molecular characteristics which are understood by the use of crude oil assay analysis in petroleum laboratories.

Barrels from an area in which the crude oil's molecular characteristics have been determined and the oil has been classified are used as pricing references throughout the world. Some of the common reference crudes are:

There are declining amounts of these benchmark oils being produced each year, so other oils are more commonly what is actually delivered. While the reference price may be for West Texas Intermediate delivered at Cushing, the actual oil being traded may be a discounted Canadian heavy oil delivered at Hardisty, Alberta, and for a Brent Blend delivered at the Shetlands, it may be a Russian Export Blend delivered at the port of Primorsk.[22]

Petroleum industry

New York Mercantile Exchange prices for West Texas Intermediate 1996–2009

The petroleum industry is involved in the global processes of exploration, extraction, refining, transporting (often with oil tankers and pipelines), and marketing petroleum products. The largest volume products of the industry are fuel oil and gasoline (petrol). Petroleum is also the raw material for many chemical products, including pharmaceuticals, solvents, fertilizers, pesticides, and plastics. The industry is usually divided into three major components: upstream, midstream and downstream. Midstream operations are usually included in the downstream category.

Petroleum is vital to many industries, and is of importance to the maintenance of industrialized civilization itself, and thus is critical concern to many nations. Oil accounts for a large percentage of the world's energy consumption, ranging from a low of 32% for Europe and Asia, up to a high of 53% for the Middle East. Other geographic regions' consumption patterns are as follows: South and Central America (44%), Africa (41%), and North America (40%). The world at large consumes 30 billion barrels (4.8 km³) of oil per year, and the top oil consumers largely consist of developed nations. In fact, 24% of the oil consumed in 2004 went to the United States alone [23], though by 2007 this had dropped to 21% of world oil consumed.[24]

In the US, in the states of Arizona, California, Hawaii, Nevada, Oregon and Washington, the Western States Petroleum Association (WSPA) is responsible for producing, distributing, refining, transporting and marketing petroleum. This non-profit trade association was founded in 1907, and is the oldest petroleum trade association in the United States.[25]

History

Oil derrick in Okemah, Oklahoma, 1922.

Petroleum, in one form or another, has been used since ancient times, and is now important across society, including in economy, politics and technology. The rise in importance was mostly due to the invention of the internal combustion engine and the rise in commercial aviation

More than 4000 years ago, according to Herodotus and Diodorus Siculus, asphalt was used in the construction of the walls and towers of Babylon; there were oil pits near Ardericca (near Babylon), and a pitch spring on Zacynthus.[26] Great quantities of it were found on the banks of the river Issus, one of the tributaries of the Euphrates. Ancient Persian tablets indicate the medicinal and lighting uses of petroleum in the upper levels of their society.

Today, about 90% of vehicular fuel needs are met by oil. Petroleum also makes up 40% of total energy consumption in the United States, but is responsible for only 2% of electricity generation. Petroleum's worth as a portable, dense energy source powering the vast majority of vehicles and as the base of many industrial chemicals makes it one of the world's most important commodities.

The top three oil producing countries are Saudi Arabia, Russia, and the United States.[27] About 80% of the world's readily accessible reserves are located in the Middle East, with 62.5% coming from the Arab 5: Saudi Arabia, UAE, Iraq, Qatar and Kuwait. A large portion of the world's total oil exists as unconventional sources, such as bitumen in Canada and Venezuela and oil shale. While significant volumes of oil are extracted from oil sands, particularly in Canada, logistical and technical hurdles remain, and Canada's oil sands are not expected to provide more than a few million barrels per day in the foreseeable future.

Price

After the collapse of the OPEC-administered pricing system in 1985, and a short lived experiment with netback pricing, oil-exporting countries adopted a market-linked pricing mechanism.[28] First adopted by PEMEX in 1986, market-linked pricing was widely accepted, and by 1988 became and still is the main method for pricing crude oil in international trade.[28] The current reference, or pricing markers, are Brent, WTI, and Dubai/Oman.[28]

Uses

The chemical structure of petroleum is heterogeneous, composed of hydrocarbon chains of different lengths. Because of this, petroleum may be taken to oil refineries and the hydrocarbon chemicals separated by distillation and treated by other chemical processes, to be used for a variety of purposes. See Petroleum products.

Fuels

The most common distillations of petroleum are fuels. Fuels include:

Other derivatives

Certain types of resultant hydrocarbons may be mixed with other non-hydrocarbons, to create other end products:

Petroleum by country

Consumption statistics

Consumption

Oil consumption per capita (darker colors represent more consumption).

This table orders the amount of petroleum consumed in 2006 in thousand barrels (bbl) per day and in thousand cubic metres (m3) per day:[29][30][31]

Consuming Nation 2006 (1000 bbl/day) (1000 m3/day) population in millions bbl/year per capita
United States 1 20,687.42 3,289.0 304 24.8
China 7,201.28 1,144.9 1369 1.9
Japan 2 5,197.70 826.4 128 14.8
Russia 1 2,810.76 446.9 142 7.2
Germany 2 2,691.81 428.0 82 12
India 2 2,571.90 408.9 1201 0.8
Canada 2,296.66 365.1 32[32] 25.7
Brazil 2,216.84 352.4 187 4.3
South Korea 2 2,179.90 346.6 49[33] 16.3
Saudi Arabia (OPEC) 2,139.42 340.1 27[34] 28.9
Mexico 1 2,077.51 330.3 107 7.1
France 2 1,981.18 315.0 61[35] 11.9
United Kingdom 1 1,812.01 288.1 61[36] 10.9
Italy 2 1,742.58 277.0 58[37] 10.9
Iran (OPEC) 1,679.20 267.0 68[38] 8.9

Source: US Energy Information Administration

1 peak production of oil already passed in this state

2 This country is not a major oil producer

Production

Oil producing countries
Graph of Top Oil Producing Countries 1960-2006, including Soviet Union[39]

In petroleum industry parlance, production refers to the quantity of crude extracted from reserves, not the literal creation of the product.

# Producing Nation 103bbl/d (2006) 103bbl/d (2007)
1 Saudi Arabia (OPEC) 10,665 10,234
2 Russia 1 9,677 9,876
3 United States 1 8,331 8,481
4 Iran (OPEC) 4,148 4,043
5 China 3,845 3,901
6 Mexico 1 3,707 3,501
7 Canada 2 3,288 3,358
8 United Arab Emirates (OPEC) 2,945 2,948
9 Venezuela (OPEC) 1 2,803 2,667
10 Kuwait (OPEC) 2,675 2,613
11 Norway 1 2,786 2,565
12 Nigeria (OPEC) 2,443 2,352
13 Brazil 2,166 2,279
14 Algeria (OPEC) 2,122 2,173
15 Iraq (OPEC) 3 2,008 2,094
16 Libya (OPEC) 1,809 1,845
17 Angola (OPEC) 1,435 1,769
18 United Kingdom 1,689 1,690
19 Kazakhstan 1,388 1,445
20 Qatar (OPEC) 1,141 1,136
21 Indonesia 1,102 1,044
22 India 854 881
23 Azerbaijan 648 850
24 Argentina 802 791
25 Oman 743 714
26 Malaysia 729 703
27 Egypt 667 664
28 Australia 552 595
29 Colombia 544 543
30 Ecuador (OPEC) 536 512
31 Sudan 380 466
32 Syria 449 446
33 Equatorial Guinea 386 400
34 Yemen 377 361
35 Vietnam 362 352
36 Thailand 334 349
37 Denmark 344 314
38 Congo 247 250
39 Gabon 237 244
40 South Africa 204 199

Source: U.S. Energy Information Administration

1 Peak production of conventional oil already passed in this state

2 Although Canadian conventional oil production is declining, total oil production is increasing as oil sands production grows. If oil sands are included, it has the world's second largest oil reserves after Saudi Arabia.

3 Though still a member, Iraq has not been included in production figures since 1998

Export

See also: Fossil fuel exporters

Oil exports by country

In order of net exports in 2006 in thousand bbl/d and thousand /d:

# Exporting Nation (2006) (103bbl/d) (103m3/d)
1 Saudi Arabia (OPEC) 8,651 1,376
2 Russia 1 6,565 1,044
3 Norway 1 2,542 404
4 Iran (OPEC) 2,519 401
5 United Arab Emirates (OPEC) 2,515 400
6 Venezuela (OPEC) 1 2,203 350
7 Kuwait (OPEC) 2,150 342
8 Nigeria (OPEC) 2,146 341
9 Algeria (OPEC) 1 1,847 297
10 Mexico 1 1,676 266
11 Libya (OPEC) 1 1,525 242
12 Iraq (OPEC) 1,438 229
13 Angola (OPEC) 1,363 217
14 Kazakhstan 1,114 177
15 Canada 2 1,071 170

Source: US Energy Information Administration

1 peak production already passed in this state

2 Canadian statistics are complicated by the fact it is both an importer and exporter of crude oil, and refines large amounts of oil for the U.S. market. It is the leading source of U.S. imports of oil and products, averaging 2.5 MMbbl/d in August 2007. [1].

Total world production/consumption (as of 2005) is approximately 84 million barrels per day (13,400,000 m3/d).

See also: Organization of Petroleum Exporting Countries.

Import

Oil imports by country

In order of net imports in 2006 in thousand bbl/d and thousand /d:

# Importing Nation (2006) (103bbl/day) (103m3/day)
1 United States 1 12,220 1,943
2 Japan 5,097 810
3 China 2 3,438 547
4 Germany 2,483 395
5 South Korea 2,150 342
6 France 1,893 301
7 India 1,687 268
8 Italy 1,558 248
9 Spain 1,555 247
10 Republic of China (Taiwan) 942 150
11 Netherlands 936 149
12 Singapore 787 125
13 Thailand 606 96
14 Turkey 576 92
15 Belgium 546 87

Source: US Energy Information Administration

1 peak production of oil already passed in this state

2 Major oil producer whose production is still increasing

Non-producing consumers

Countries whose oil production is 10% or less of their consumption.

# Consuming Nation (bbl/day) (m³/day)
1 Japan 5,578,000 886,831
2 Germany 2,677,000 425,609
3 South Korea 2,061,000 327,673
4 France 2,060,000 327,514
5 Italy 1,874,000 297,942
6 Spain 1,537,000 244,363
7 Netherlands 946,700 150,513

Source : CIA World Factbook

Environmental effects

Diesel fuel spill on a road

The presence of oil has significant social and environmental impacts, from accidents and routine activities such as seismic exploration, drilling, and generation of polluting wastes, greenhouse gases and climate change not produced by renewable energy.

Extraction

Oil extraction is costly and sometimes environmentally damaging, although Dr. John Hunt of the Woods Hole Oceanographic Institution pointed out in a 1981 paper that over 70% of the reserves in the world are associated with visible macroseepages, and many oil fields are found due to natural seeps. Offshore exploration and extraction of oil disturbs the surrounding marine environment.[40]

Oil spills

Volunteers cleaning up the aftermath of the Prestige oil spill

Crude oil and refined fuel spills from tanker ship accidents have damaged natural ecosystems in Alaska, the Galapagos Islands, France and many other places.

The quantity of oil spilled during accidents has ranged from a few hundred tons to several hundred thousand tons (e.g., Atlantic Empress, Amoco Cadiz). Smaller spills have already proven to have a great impact on ecosystems, such as the Exxon Valdez oil spill

Oil spills at sea are generally much more damaging than those on land, since they can spread for hundreds of nautical miles in a thin oil slick which can cover beaches with a thin coating of oil. This can kill sea birds, mammals, shellfish and other organisms it coats. Oil spills on land are more readily containable if a makeshift earth dam can be rapidly bulldozed around the spill site before most of the oil escapes, and land animals can avoid the oil more easily.

Control of oil spills is difficult, requires ad hoc methods, and often a large amount of manpower (picture). The dropping of bombs and incendiary devices from aircraft on the Torrey Canyon wreck produced poor results;[41] modern techniques would include pumping the oil from the wreck, like in the Prestige oil spill or the Erika oil spill.[42]

Whales

James S. Robbins has argued that the advent of petroleum-refined kerosene saved some species of great whales from extinction by providing an inexpensive substitute for whale oil, thus eliminating the economic imperative for open-boat whaling.[43]

Alternatives to petroleum

In the United States in 2007 about 70% of petroleum was used for transportation (e.g. gasoline, diesel, jet fuel), 24% by industry (e.g. production of plastics), 5% for residential and commercial uses, and 2% for electricity production.[44] Outside of the US, a higher proportion of petroleum tends to be used for electricity.[45]

Alternatives to petroleum-based vehicle fuels

Alternative propulsion refers to both:

Currently, cars can be classified into the following groups:

Alternatives to using oil in industry

Biological feedstocks do exist for industrial uses such as plastic production.[47]

Alternatives to burning petroleum for electricity

In oil producing countries with little refinery capacity, oil is sometimes burned to produce electricity. Renewable energy technologies such as solar power, wind power, micro hydro, biomass and biofuels might someday be used to replace some of these generators, but today the primary alternatives remain large scale hydroelectricity, nuclear and coal-fired generation.

Future of petroleum production

USA Today news reported in 2004 that there were 40 years of petroleum left in the ground. As similar statements have been made in the 40 previous years, it hardly carries the complex situation.[citation needed]

Consumption in the twentieth century has been abundantly pushed by automobile growth ; the 1985-2003 oil glut even fuelled the sales of low economy vehicles (SUVs) in OECD countries. In 2008, the economic crisis seems to have some impact on the sales of such vehicles ; still, the 2008 oil consumption shows a small increase. The BRIC countries might also kick in, as China briefly was the first automobile market in December 2009[48] . The immediate outlook still hints upwards. In the long term, uncertainties linger ; the OPEC believes that the OECD countries will push low consumption policies at some point in the future ; when that happens, it will definitely curb the oil sales, and both OPEC and EIA kept lowering their 2020 consumption estimates during the past 5 years [49]. Oil products are more and more in competition with alternative sources, mainly coal and natural gas, both cheaper sources.

Production will also face an increasingly complex situation ; while OPEC countries still have large reserves at low production prices, newly found reservoirs often lead to higher prices ; offshore giants such as Tupi, Guara and Tiber demand high investments and ever-increasing technological abilities. Subsalt reservoirs such as Tupi were unknown in the twentieth century, mainly because the industry was unable to probe them. Enhanced Oil Recovery (EOR) techniques (example : DaQing, China [50] ) will continue to play a major role in increasing the world's recoverable oil.

Hubbert peak theory

The Hubbert peak theory (also known as peak oil) posits that future petroleum production (whether for individual oil wells, entire oil fields, whole countries, or worldwide production) will eventually peak and then decline at a similar rate to the rate of increase before the peak as these reserves are exhausted. The peak of oil discoveries was in 1965, and oil production per year has surpassed oil discoveries every year since 1980.[51]

Controversy surrounds predictions of the timing of the global peak, as these predictions are dependent on the past production and discovery data used in the calculation as well as how unconventional reserves are considered[citation needed]. Also, these predictions do not take into account outside elements such as the current economic crisis (2008)[citation needed]. Also, many Peak Oil promoters proposed many different dates, some of them passed already[citation needed]. Despite these uncertainties, Hubbert applied his theory to predict the peak of U.S. oil production at a date between 1966 and 1970. This prediction was based on data available at the time of his publication in 1956 ; in the same paper, Hubbert predicts, quite mistakenly, the world Peak Oil for the year 2000.[52]

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.[53] Based on available production data, proponents have previously predicted the peak for the world to be in years 1989, 1995, or 1995-2000. Some of these predictions date from before the recession of the early 1980s, and the consequent reduction in global consumption, the effect of which was to delay the date of any peak by several years. Just as the 1971 U.S. peak in oil production was only clearly recognized after the fact, a peak in world production will be difficult to discern until production clearly drops off.

See also

References

  1. ^ Bauer Georg, Bandy Mark Chance (tr.), Bandy Jean A.(tr.). De Natura Fossilium.  translated 1955
  2. ^ a b Hyne, Norman J. (2001). Nontechnical Guide to Petroleum Geology, Exploration, Drilling, and Production. PennWell Corporation. pp. 1–4. ISBN 087814823X. 
  3. ^ Speight, James G. (1999). The Chemistry and Technology of Petroleum. Marcel Dekker. pp. 215–216. ISBN 0824702174. 
  4. ^ Alboudwarej et al. (Summer 2006) (PDF). Highlighting Heavy Oil. Oilfield Review. http://www.slb.com/media/services/resources/oilfieldreview/ors06/sum06/heavy_oil.pdf. Retrieved 2008-05-24. 
  5. ^ "Oil Sands - Glossary". Mines and Minerals Act. Government of Alberta. 2007. http://www.energy.gov.ab.ca/OilSands/1106.asp. Retrieved 2008-10-02. 
  6. ^ "Oil Sands in Canada and Venezuela". Infomine Inc.. 2008. http://oilsands.infomine.com/countries/. Retrieved 2008-10-02. 
  7. ^ IEA Key World Energy Statistics
  8. ^ "Crude oil is made into different fuels"
  9. ^ EIA reserves estimates
  10. ^ CERA report on total world oil
  11. ^ Heat of Combustion of Fuels
  12. ^ Use of ozone depleting substances in laboratories. TemaNord 2003:516. http://www.norden.org/pub/ebook/2003-516.pdf
  13. ^ United States Bureau of Standards, "Thermal Properties of Petroleum Products". Miscellaneous Publication No. 97, November 9th, 1929.
  14. ^ Keith A. Kvenvolden “Organic geochemistry – A retrospective of its first 70 years” Organic Geochemistry 37 (2006) 1–11. doi:10.1016/j.orggeochem.2005.09.001
  15. ^ Petroleum Study
  16. ^ http://oilismastery.blogspot.com/2008/05/oil-window.html
  17. ^ Kenney et al., Dismissal of the Claims of a Biological Connection for Natural Petroleum, Energia 2001
  18. ^ Anton Kolesnikov, Vladimir G. Kutcherov, Alexander F. Goncharov (26 July 2009). "Methane-derived hydrocarbons produced under upper-mantle conditions". Nature Geoscience 2 (8 pages=566–570). doi:10.1038/ngeo591. 
  19. ^ Glasby, Geoffrey P. (2006). "Abiogenic origin of hydrocarbons: an historical overview" (PDF). Resource Geology 56 (1): 83–96. doi:10.1111/j.1751-3928.2006.tb00271.x. http://static.scribd.com/docs/j79lhbgbjbqrb.pdf. Retrieved 2008-02-17. 
  20. ^ Hydrocarbons in the deep Earth? July 2009 (Press release)
  21. ^ Lambertson, Giles (2008-02-16). "Oil Shale: Ready to Unlock the Rock". Construction Equipment Guide. http://www.cegltd.com/story.asp?story=10092. Retrieved 2008-05-21. 
  22. ^ "Light Sweet Crude Oil". About the Exchange. New York Mercantile Exchange (NYMEX). 2006. http://www.nymex.com/lsco_fut_descri.aspx. Retrieved 2008-04-21. 
  23. ^ "International Energy Annual 2004" (XLS). Energy Information Administration. 2006-07-14. http://www.eia.doe.gov/pub/international/iealf/tablee2.xls. 
  24. ^ "Yearbook 2008 - crude oil". Energy data. http://www.enerdata.fr/enerdatauk/publications/yearbook/crude_oil.php. 
  25. ^ "Western States Petroleum Association - About Us". http://www.wspa.org/about/index.htm. Retrieved 2008-11-03. 
  26. ^ This article incorporates text from the article "Petroleum" in the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.
  27. ^ InfoPlease
  28. ^ a b c Mabro, Robert; Organization of Petroleum Exporting Countries (2006). Oil in the 21st century: issues, challenges and opportunities. Oxford Press. pp. 351. ISBN 0199207380, 9780199207381. 
  29. ^ U.S. Energy Information Administration. Excel file RecentPetroleumConsumptionBarrelsperDay.xls from web page http://tonto.eia.doe.gov/dnav/pet/pet_pri_wco_k_w.htm (direct link: http://www.eia.doe.gov/emeu/international/RecentPetroleumConsumptionBarrelsperDay.xls) "Table Posted: November 7, 2008"
  30. ^ From DSW-Datareport 2006 ("Deutsche Stiftung Weltbevölkerung")
  31. ^ One cubic metre of oil is equivalent to 6.28981077 barrels of oil
  32. ^ Beauchesne, Eric (2007-03-13). "We are 31,612,897". National Post. http://www.canada.com/nationalpost/financialpost/story.html?id=73b94aac-08f0-477f-a72a-b8b640f6658f&k=90795. Retrieved 2008-11-11. 
  33. ^ IndexMundi. South Korea Population - Demographics. "48,846,823" ... "July 2006 est." Retrieved 2008-11-11
  34. ^ Sources vary: 24,600,000 from "UNHCR / Refworld / The Worst of the Worst 2006 - Saudi Arabia". United Nations High Commissioner for Refugees. http://www.unhcr.org/refworld/docid/4917f8351e.html. Retrieved 2008-11-11. ; while IndexMundi listed a July 2006 estimate of 27,019,73: "Saudi Arabia Population - Demographics". IndexMundi. http://indexmundi.com/saudi_arabia/population.html. Retrieved 2008-11-11. 
  35. ^ IndexMundi. France Population - Demographics. "60,876,136" ... "July 2006 est." Retrieved 2008-11-11
  36. ^ IndexMundi. United Kingdom Population - Demographics. "60,609,153" ... "July 2006 est." Retrieved 2008-11-11
  37. ^ IndexMundi. Italy Population - Demographics. "58,133,509" ... "July 2006 est." Retrieved 2008-11-11
  38. ^ IndexMundi. Iran Population - Demographics. "68,688,433" ... "July 2006 est." Retrieved 2008-11-11
  39. ^ http://www.eia.doe.gov/emeu/aer/pdf/pages/sec11_10.pdf
  40. ^ Waste discharges during the offshore oil and gas activity by Stanislave Patin, tr. Elena Cascio
  41. ^ Torrey Canyon bombing by the Navy and RAF
  42. ^ Pumping of the Erika cargo
  43. ^ How Capitalism Saved the Whales by James S. Robbins, The Freeman, August, 1992.
  44. ^ "U.S. Primary Energy Consumption by Source and Sector, 2007". Energy Information Administration
  45. ^ needtitle UN Energy Program
  46. ^ Amory B. Lovins, E. Kyle Datta, Odd-Even Bustnes, Jonathan G. Koomey, Nathan J. Glasgow. "Winning the oil endgame" Rocky Mountain Institute
  47. ^ Bioprocessing Seattle Times (2003)
  48. ^ Chris Hogg (2009-02-10). "China's car industry overtakes US". http://news.bbc.co.uk/2/hi/business/7879372.stm. 
  49. ^ OPEC Secretariat (2008). "World Oil Outlook 2008". http://www.opec.org/library/World%20Oil%20Outlook/pdf/WOO2008.pdf. 
  50. ^ Ni Weiling (2006-10-16). "Daqing Oilfield rejuvenated by virtue of technology". http://en.ce.cn/Insight/200610/16/t20061016_8980162.shtml. 
  51. ^ Campbell CJ (2000-12). "Peak Oil Presentation at the Technical University of Clausthal". http://energycrisis.org/de/lecture.html. 
  52. ^ Hubbert, Marion King; Shell Development Company (1956). "Nuclear energy and the fossil fuels". Drilling and Production Practice (Washington, DC: American Petroleum Institute) 95. http://www.hubbertpeak.com/Hubbert/1956/1956.pdf. 
  53. ^ New study raises doubts about Saudi oil reserves

External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

PETROLEUM (Lat. Petra, rock, and oleum, oil), a term which, in its widest sense, embraces the whole of the hydrocarbons, gaseous, liquid and solid, occurring in nature (see Bitumen). Here the application of the term is limited to the liquid which is so important an article of commerce, though references will also be made to natural gas which accompanies petroleum. Descriptions of the solid forms will be found in the articles on asphalt or asphaltum, albertite, elaterite, gilsonite, hatchettite and ozokerite. Particulars of the shales which yield oil on destructive distillation are given in the article on paraffin.

Table of contents

Ancient History

Petroleum was collected for use in the most remote ages of which we have any records. Herodotus describes the oil pits near Ardericca (near Babylon), and the pitch spring of Zacynthus (Zante), whilst Strabo, Dioscorides and Pliny mention the use of the oil of Agrigentum, in Sicily, for illumination, and Plutarch refers to the petroleum found near Ecbatana (Kerkuk). The ancient records of China and Japan are said to contain many allusions to the use of natural gas for lighting and heating. Petroleum (" burning water ") was known in Japan in the 7th century, whilst in Europe the gas springs of the north of Italy led to the adoption in 1226 by the municipality of Salsomaggiore of a salamander surrounded by flames as its emblem. Marco Polo refers to the oil springs of Baku towards the end!of the 13th century; the medicinal properties of the oil of Tegernsee in Bavaria gave it the name of " St Quirinus's Oil " in 1436; the oil of Pechelbronn, Elsass, was discovered in 1498, and the " earthbalsam " of Galicia was known in 1506. The earliest mention 'of American petroleum occurs in Sir Walter Raleigh's account of the Trinidad pitch-lake in 1595; whilst thirty-seven years later, the account of a visit of a Franciscan, Joseph de la Roche d'Allion, to the oil springs of New York was published in Sagard's Histoire du Canada. In the 17th century, Thomas Shirley brought the natural gas of Wigan, in Shropshire, to the notice of the Royal Society. In '724 Hermann Boernaave referred to the oleum terrae of Burma, and "Barbados tar" was then well known as a medicinal agent. A Russian traveller, Peter Kalm, in his work on America, published in 1748, showed on a map the oil springs of Pennsylvania, and about the same time Raicevich referred to the " liquid bitumen " of Rumania.

Modern Development and Industrial Progress

The first commercial exploitation of importance appears to have been the distillation of the oil at Alfreton in Derbyshire by James Young,. who patented his process for the manufacture of paraffin in 1850. In 1853 and 1854 patents for the preparation of this substance from petroleum were obtained by Warren de la Rue, and the process was applied to the " Rangoon oil " brought to Great Britain from Yenangyaung in Upper Burma. The active growth of the petroleum industry of the United States began in 1859, though in the early part of the century the petroleum of Lake Seneca, N.Y., was used as an embrocation under the name of " Seneca oil," and the "American Medicinal Oil" of Kentucky was largely sold after its discovery in 1829. The Pennsylvania Rock Oil Company was formed in 1854, but its operations were unsuccessful, and in 1858 certain of the members founded the Seneca Oil Company, under whose direction E. L. Drake started a well on Oil Creek, Pennsylvania. After drilling had been carried to a depth of 69 feet, on the 28th of August 1859, the tools suddenly dropped into a crevice, and on the following day the well was found to have " struck oil." This well yielded 25 barrels a day for some time, but at the end of the year the output was at the rate of 15 barrels. The production of crude petroleum in the United States was officially reported to have been 2000 barrels in 1859, 4,215,000 barrels in 1869, 19,914,146 barrels in 1879, 35,163,513 barrels in 1889, 57,084,428 barrels in 1899, and 126,493,936 barrels in 1906. From Oil Creek, development spread first over the eastern United States and then became general, subsequently embracing Canada (1862), recently discovered fields being those of Illinois, Alberta and California (44,854,737 barrels in 1908).

For about 10 years Pennsylvania was the one great oil producer of the world, but since 1870 the industry has spread all over the globe. From the time of the completion on the Baku field of the first flowing well (which was unmanageable and resulted in the loss of the greater part of the oil), Russia has ranked second in the list of producing countries, whilst Galicia and Rumania became prominent in 1878 and 1880 respectively. Sumatra, Java and Borneo, where active development began in 1883, 1886 and 1896, bid fair to rank before long among the chief sources of the oil supplies of the world. Similarly, Burma, where the Burmah Oil Company have, since 1890, rapidly extended their operations, is rising to a position of importance. Oil fields are being continually opened up in other parts of the world, and whilst America still maintains her position as the largest petroleum producer, the world's supplies are now being derived from a steadily increasing number of centres.

Physical and Chemical Properties

Although our information respecting the chemical composition of petroleum has been almost entirely gained since the middle of the 18th century, a considerable amount of empirical knowledge of the substance was possessed by chemists at an earlier date, and there was much speculation as to its origin. In his Sylva sylvarum (1627), Francis Bacon states that " the original concretion of bitumen is a mixture of a fiery and watery substance," and observes that flame " attracts " the naphtha of Babylon " afar off." P. J. Macquer (1764), T. O. Bergman (1784) Charles Hatchett (1798) and others also expressed views with regard to the constitution and origin of bitumens. Of these early writers, Hatchett is the most explicit, the various bituminous substances being by him classified and defined. Jacob Joseph Winterl, in 1788, appears to have been the first to examine petroleum chemically, but the earliest systematic investigation was that carried out by Professor B. Silliman, Jun., in 1855, who then reported upon the results which he had obtained with the " rock oil or petroleum " of Venango county, Pennsylvania. This report has become a classic in the literature of petroleum.

The physical properties of petroleum vary greatly. The colour ranges from pale yellow through red and brown to black or greenish, while by reflected light it is, in the majority of cases, of a green hue. The specific gravity of crude petroleum appears to range from 771 to 1.06, and the flash point from below o° to 370°F. Viscosity increases with density, but oils of the same density often vary greatly; the coefficient of expansion, on the other hand, varies inversely with the density, but bears no simple relation to the change of fluidity of the oil under the influence of heat, this being most marked in oils of paraffin base. The calorific power of Baku oil appears to be highest, while this oil is poorest in solid hydrocarbons, of which the American petroleums contain moderate quantities, and the Upper Burma oils the largest amount. The boiling point, being determined by the character of the constituents of the oil, necessarily varies greatly in different oils, as do the amounts of distillate obtained from them at specified temperatures.

Even prior to the discovery of petroleum in commercial quantities, a number of chemists had made determinations of the chemical composition of several different varieties, and these investigations, supplemented by those of a later date, show that petroleum consists of about 84% by weight of carbon with 12% of hydrogen, and varying proportions of sulphur, nitrogen and oxygen. The principal elements are found in various combinations, the hydrocarbons of the Pennsylvania oils being mainly paraffins (q.v.), while those of Caucasian petroleum belong for the most part to the naphthenes, isomeric with the olefines (q.v.).

Paraffins are found in all crude oils, and olefines in varying proportions in the majority, while acetylene has been found in Baku oil; members of the benzene group and its derivatives, notably benzene and toluene, occur in all petroleums. Naphthenes are the chief components of some oils, as already indicated, and occur in varying quantities in many others. Certain crude oils have also been found to contain camphenes, naphthalene and other aromatic hydrocarbons. It is found that transparent oils under the influence of light absorb oxygen, becoming deeper in colour and opalescent, while strong acidity and a penetrating odour are developed, these changes being due to the formation of various acid and phenylated compounds, which are also occasionally found in fresh oils. The residues from petroleum distillation have been shown to contain very dense solids and liquids of high specific gravity, having a large proportion of carbon and possessed of remarkable fluorescent properties.

Natural gas is found to consist mainly of the lower paraffins, with varying quantities of carbon dioxide, carbon monoxide, hydrogen, nitrogen and oxygen, in some cases also sulphuretted hydrogen and possibly ammonia. This mixture dissolves in petroleum, escaping when the oil is stored, and conversely it invariably carries a certain amount of water and oil, which is deposited on compression.

Occurrence

Bitumen is, in its various forms, one of the most widel y -distributed of substances, occurring in strata of every geological age, from the lowest Archean rocks to those now in process of deposition, and in greater or less quantity throughout both hemispheres, from Spitzbergen to New Zealand, and from California to Japan. The occurrence of commercially valuable petroleum is, however, comparatively limited, hitherto exploited deposits being confined to rocks younger than the Cambrian and older than the Quaternary, while the majority of developed oilfields have been discovered north of the equator.

The main requisites for a productive oil or gas field are a porous reservoir and an impervious cover. Thus, while the mineral may be formed in a stratum other than that in which it is found, though in many cases it is indigenous to it, for the formation of a natural reservoir of the fluid (whether liquid or gas) it is necessary that there should be a suitable porous rock to contain it. Such a rock is typically exemplified by a coarse-grained sandstone or conglomerate, while a limestone may be naturally porous, or, like the Trenton limestone of Ohio and Indiana, rendered so by its conversion into dolomite and the consequent production of cavities due to shrinkage - a change occurring only in the purer limestones. Similarly it is necessary, in view of the hydrostatical relations of water and mineral oils, and the volatile character of the latter, that the porous stratum should be protected from water and air by an overlying shale or other impervious deposit. Water, often saline or sulphurous, is also found in these porous rocks and replaces the oil as the latter is withdrawn.

In addition to these two necessary factors, structural conditions play an important part in determining the accumulation of oil and gas. The main supplies have been obtained from strata unbroken and comparatively undisturbed, but the occurrence of anticlinal or terrace structure, however slightly marked or limited in extent, exerts a powerful influence on the creation of reservoirs of petroleum. These tectonic arches often extend for long distances with great regularity, but are frequently crossed by subsidiary anticlines, which themselves play a not unimportant part in the aggregation of the oil. Owing to difference of density the oil and water in the anticlines separate into two layers, the upper consisting of oil which fills the anticlines, while the water remains in the synclines. Any gas which may be present rises to the summits of the anticlines. When the slow folding of the strata is accompanied by a gradual local descent, a modified or " arrested " anticlinal structure, known as a " terrace " is produced, the upheaving action at that part being sufficient only to arrest the descent which would otherwise occur. The terraces may thus be regarded as flat and extended anticlines. They need not be horizontal, and sometimes have a dip of a few feet per mile, as in the case of the Ohio and Indiana oil fields, where the amount varies from one to ten feet. These slight differences in level, however, are found to have a most powerful effect in the direction already mentioned.

It is evident that accurate knowledge of the character and structure of the rock-formations in petroliferous territories is of the greatest importance in enabling the expert to select favourable sites for drilling operations; hence on well-conducted petroleumproperties it is now customary to note the character and thickness of the strata perforated by the drill, so that a complete section may be prepared from the recorded data. In some cases the depths are stated with reference to sea-level, instead of being taken from the surface, thus greatly facilitating the utilization of the records.

Oil and gas are often met with in drilled wells under great pressure, which is highest as a rule in the deepest wells. The closed pressure in the Trenton limestone in Ohio and Indiana is about 200-300 lb. per sq. in., although a much higher pressure has been registered in many wells. The gas wells of Pennsylvania indicate about double the pressure of those drilled in the Trenton limestone, 600-800 lb. not being unusual, and even 1000 lb having been recorded. The extremely high pressure under which oil is met with in wells drilled in some parts of the Russian oil fields is a matter of common knowledge, and a fountain or spouting well resulting therefrom is one of the " sights" of the country. A famous fountain in the Groznyi oil field in the northern Caucasus, which began to flow in August 1895, was estimated to have thrown up during the first three days 1,200,000 poods (over 4,500,000 gallons, or about 18,500 tons) of oil a day. It flowed continuously, though in gradually diminishing quantity, for fifteen months; afterwards the flow became intermittent. In April 1897 there was still an occasional outburst of oil and gas.

Three theories have been propounded to account for this pressure: 1. That it results from the weight of the overlying strata.

2. That it is due to water-pressure, as in artesian wells (" hydrostatic " or " artesian " theory).

3. That it is caused by the compressed condition of the gradually accumulating gas.

Of these the first has been proved untenable, and while in some instances (e.g. certain wells in Ohio), the second has held good, the third appears to be the most widely applicable.

The conditions of formation and accumulation of petroleum point to the fact that the principal oil fields of the world are merely reservoirs, which will become exhausted in the course of years, as in the case of the decreasing yield of certain of the American fields. But new deposits are continually being exploited, and there may be others as yet unknown, which would entirely alter any view that might be expressed at the present time in regard to the probable duration of the world's supply of oil and gas.

As already stated, every one of the great geological systems appears to have produced some form of bitumen, and in the following table an attempt has been made to classify on this basis the various localities in which petroleum or natural gas has been found in large or small quantities: Recent. - Lancashire (Down Holland Moss), Holland, Sweden, Sardinia, Kaluga (Russia), Red Sea, Mediterranean. Pleistocene. - Schleswig-Holstein, Minnesota, Illinois, Louisiana. Pliocene. - Spain, Italy, Albania ., Croatia, Hungary, Hesse, Hanover, Transcaspia, Algeria, Florida, Alabama, California, Mexico, Peru, Victoria, New Zealand.

Miocene

France, Switzerland, Spain, Italy, Sicily, Greece, Rumania, Turkey-in-Europe, Styria, Slavonia, Hungary, Transylvania, Galicia, Lower Austria, Wurttemberg, Brandenberg, West Prussia, Crimea, Kuban, Terek, Kutais, Tiflis, Elizabetpol, Siberia, Transcaspia, Mesopotamia, Persia, Assam, Burma, Anam, Japan, Philippine Islands, Borneo, Sumatra, Java, Algeria, Egypt, British Columbia, Alaska, Washington, California, Colorado, Texas, Louisiana, Barbados, Trinidad, Venezuela, Peru, South Australia, Victoria, New Zealand.

Oligocene

France, Spain, Greece, Rumania, Hungary, Transylvania, Galicia, Bavaria, Elsass, Rhenish Bavaria, Hesse, Saxony, Crimea, Daghestan, Tiflis, Baku, Alaska, California, Florida.

Eocene

Devonshire (retinasphalt), France, Spain, Italy, Asia Minor, Montenegro, Bosnia and Herzegovina, Rumania, Dalmatia, Istria, Hungary, Transylvania, Galicia, Moravia, Bavaria, Elsass, Kutais, Armenia, Persia, Baluchistan, Afghanistan, Punjab, Assam, Sumatra, Algeria, Egypt, Maryland, Colorado, Utah, Nevada, California, Louisiana, Texas, Cuba, Colombia, Brazil.

Cretaceous

Holland, France, Switzerland, Spain, Italy, Sicily, Greece, Hungary, Silesia, Moravia, Westphalia, Brunswick, Hanover, Schleswig-Holstein, (German) Silesia, Poland, Kutais, Uralsk, Turkestan, Armenia, Syria, Arabia, Persia, Tunis, Egypt, West Africa, British Columbia, Alberta, Assiniboia, Athabasca, Manitoba, New Jersey, South Dakota, Washington, Montana, Oklahoma, Utah, Wyoming, Colorado, California, New Mexico, Arkansas, Texas, Louisiana, Mexico, Hayti, Trinidad, Colombia, Argentina [?], New Zealand.

Neocomian

Sussex, France, Switzerland, Spain, Hungary, Transylvania, Bukowina, Galicia, Hesse, Baden, Hanover, Brunswick, California, Texas, Mexico, Bolivia, Argentina.

Jurassic

Yorkshire, Somerset, Buckingham, France, Switzer land, Spain, Italy, Lower Austria, Baden, Elsass, Hesse, Hanover, Brunswick, Sizran, Tiflis, Siberia, Persia, Madagascar, Alaska, Wyoming, Colorado, Mexico, Argentina.

Triassic

Yorkshire, Staffordshire, France, Portugal, Spain, Italy, Montenegro, Upper Austria, Tyrol, Bavaria, Wurttemberg, Baden, Elsass, Lothringen, Rhenish Bavaria, Rhenish Prussia, Hanover, Brunswick, Sweden, Spitzbergen, Punjab, China, Transvaal, Cape Colony, Connecticut, New Jersey, Virginia, North Carolina, Wyoming, Argentina, New South Wales, Queensland.

Permian

Yorkshire, Denbigh, Moravia, Bohemia, Baden, Saxony, Vologda, Afa, Kazan, Simbirsk, Samara, Kansas, Wyoming, Oklahoma, Texas (Permo-Carboniferous).

Carboniferous

Scotland, North of England, and Midlands, Wales, France, Belgium, Carniola, Moravia, Elsass, Saxony, Perm, Sizran, China, Cape Colony, Nova Scotia, Newfoundland, Pennsylvania, West Virginia, Ohio, Michigan, Indiana, Illinois, Iowa, Missouri, Tennessee, Kentucky, Alabama, Kansas, Arkansas, Colorado, Oklahoma, Tasmania, Victoria (Permo-Carboniferous), West Australia (Permo-Carboniferous).

Devonian

Scotland, Devonshire, Spain, Hanover, Archangel, Vitebsk, Athabasca, Mackenzie, Ontario, Quebec, New Brunswick, Newfoundland, New York, Pennsylvania, West Virginia, Ohio, Michigan, Wisconsin, Kentucky.

Silurian

Shropshire, Wales, Bohemia, Sweden, Esthonia, Manitoba, Ontario, Quebec, Newfoundland, New York, Pennsylvania [?], Ohio, Michigan, Indiana, Illinois, Minnesota, Tennessee, Kentucky, Georgia, Alabama, Oklahoma, New Mexico, New Caledonia.

Cambrian

Shropshire, New York.

A rchean. - France, Norway, Sweden, Ontario.

In this list, while certain occurrences in rocks of undetermined age in little-known regions have been omitted, many of those included are of merely academic interest, and a still larger number indicate fields supplying at present only local needs. All have been arranged in geographical order without reference to productive capacity or importance. It should be pointed out that the deposits which have been hitherto of chief commercial importance occur in the old rocks (Carboniferous to Silurian) on the one hand, and in the comparatively new Tertiary formations on the other, the intermediate periods yielding but little or at any rate far less abundantly.

Origin

The question of the origin of petroleum (and natural gas), though for the first half of the 19th century of little more than academic interest, has engaged the attention of naturalists and others for over a hundred years. As early as 1804, Humboldt expressed the opinion that petroleum was produced by distillation from deep-seated strata, and Karl Reichenbach in 1834, suggested that it was derived from the action of heat on the turpentine of pine-trees, whilst Brunet, in 1838, adumbrated a similar theory of origin on the ground of certain laboratory experiments. The theories propounded may be divided into two groups, namely, those ascribing to petroleum an inorganic origin, and those which regard it as the result of the decomposition of organic matter.

M. P. E. Berthelot was the first to suggest, in 1866, after conducting a series of experiments, that mineral oil was produced by purely chemical action, similar to that employed in the manufacture of acetylene. Other theories of a like nature were brought forward by various chemists, Mendeleeff, for example, ascribing the formation of petroleum to the action of water at high temperatures on iron carbide in the interior of the earth.

On the other hand, an overwhelming and increasing majority of those who have studied the natural conditions under which petroleum occurs are of opinion that it is of organic origin. The earlier supporters of the organic theory held that it was a product of the natural distillation of coal or carbonaceous matter; but though in a few instances volcanic intrusions appear to have converted coal or allied substances into oil, it seems that terrestrial vegetation does not generally give rise to petroleum. Among those who have considered that it is derived from the decomposition of both animal and vegetable marine organisms may be mentioned J. P. Lesley, E. Orton and S. F. Peckham, but others have held that it is of exclusively animal origin, a view supported by such occurrences as those in the orthoceratities of the Trenton limestone, and by the experiments of C. Engler, who obtained a liquid like crude petroleum by the distillation of menhaden (fish) oil. Similarly there is a difference of opinion as to the conditions under which the organisms have been mineralized, some holding that the process has taken place at a high temperature and under great pressure; but the lack of practical evidence in nature in support of these views has led many to conclude that petroleum, like coal, has been formed at moderate temperatures, and under pressures varying with the depth of the containing rocks. This view is supported by the fact that petroleum is found on the Sardinian and Swedish coasts as a product of the decomposition of seaweed, heated only by the sun, and under atmospheric pressure.

Consideration of the evidence leads us to the conclusion that, at least in commercially valuable deposits, mineral oil has generally been formed by the decomposition of marine organisms, in some cases animal, in others vegetable, in others both, under practically normal conditions of temperature and pressure.

Extraction (Technically termed Production.

The earliest system adopted for the collection of petroleum appears to have consisted in Early skimming the oil from the surface of the water upon Methods which it had accumulated, and Professor Lesley states, that at Paint Creek, in Johnson county, Kentucky, a Mr George and others were in the habit of collecting oil from the sands, " by making shallow canals loo or 200 ft. long, with an upright board and a reservoir at one end, from which they obtained as much as 200 barrels per year by stirring the sands with a pole." It is said that at Echigo in Japan, old wells, supposed to have been dug several hundred years ago, are existent, and that a Japanese history - called Kokushiriyaku, states that " burning water " was obtained in Echigo about A.D. 615.

The petroleum industry in the United States may be considered to date from the year 1859, when the first well avowedly drilled The for the production of oil was completed by E. L. Drake. United The present method of drilling has been evolved from States. the artesian well system previously adopted for obtaining brine and water. The drilling of petroleum wells is carried on by individuals or companies, either on lands owned by them, or on properties whose owners grant leases, usually on condition that a certain number of wells shall be sunk within a stated period, and that a portion of the oil obtained (usually from one-tenth to one-fourth) shall be appropriated as royalty to the lessor. Such leases are often transferred at a larger royalty, especially after the territory has been proved productive. The " wild-cat " wells, sunk by speculators on untested territory or on lands which had not previously proved productive, played an important part in the earlier mapping out of the petroleum fields. To discourage the sinking of wells on land immediately adjoining productive territory, it has been usual to drill along the borders of the land as far as practicable, in order to first obtain the oil which might otherwise be raised by others; and on account of the small area often controlled by the operator, the number of wells drilled has frequently been far in excess of the number which might reasonably be sunk. Experience has proved that in some of the oil fields of the United States one well to five acres is as close as they should be drilled.

After the selection of the site, the first operation consists in the erection of the rig. The chief portion of this rig is the derrick, Oil which consists of four strong uprights or legs held in Derrick position by ties and braces, and resting on strong wooden sills, which are preferred, as a foundation, to masonry. For drilling the deeper wells, the derrick, on account of the length of the " string " of drilling tools, is usually at least 7 o ft. high, about 20 ft. wide at the base, and 4 ft. wide at the summit. The whole derrick is set up by keys, no mortices or tenons being used, and thus the complete rig may be readily taken down and set up on a new site. The samson-post, which supports the walking beam, and the jack-posts, are dove-tailed and keyed into the sills. The samson-post is placed flush with one side of the main sill, the band-wheel jack-post being flush with the other side, so that the walking-beam, which imparts motion to the string of tools, works parallel with the main sill.

The boiler generally used is of the locomotive type and is usually stationary, though sometimes a portable form is preferred. It is either set in the first instance at some distance from the engine and well, or is subsequently removed sufficiently far away before the drill enters the oil-bearing formation, and until the oil and gas are under control, in order to minimize the risk of fire. A large boiler frequently supplies the engines of several wells. The engine, which is provided with reversing gear, is of 12 or 15 horse-power and motion is communicated through a belt to the band-wheel, which operates the walking-beam by means of a crank. The throttle-valve is opened or closed by turning a grooved vertical pulley by means of an endless cord, called the telegraph, passing round another pulley fixed upon the " headache-post," and is thus under the control of the driller working in the derrick. The headache-post is a vertical wooden beam placed on the main sill directly below the walking-beam, to receive the weight of the latter in case of breakage of connexions. The position of the reversing link is altered by means of a cord, passing over two pulleys, fixed respectively in the engine-house and on the derrick. At one end of the band-wheel shaft is the bull-rope pulley, and upon the other end is a crank having six holes to receive a movable wrist-pin, the length of stroke of the walking-beam being thus adjusted. The revolution of the bull-wheels is checked by the use of a powerful hand-brake.

The band-wheel communicates motion to the walking-beam, while drilling is in progress, through the crank and a connectingrod known as the pitman; to the bull-wheels, while the tools are being raised, by the bull-rope; and to the sand-pump reel, by a friction pulley, while the sand-pump is being used. It is therefore necessary that the machinery should be so arranged that the connexions may be rapidly made and broken. The sand-pump reel is set in motion by pressing a lever, the reel being then brought into contact with the face of the band-wheel. The sand-pump descends by gravitation, and its fall is checked by pressing hack the lever, so as to throw the reel against a post which serves as a brake.

The drilling tools are suspended by an untarred manila rope, 2 in. in diameter, passing from the bull-wheel shaft over a grooved wheel known as the crown-pulley, at the summit of the derrick. The string of drilling tools consists of two Drilling parts separated by an appliance known as the jars. Tools. This piece of apparatus was introduced by William Morris in 1831, and consists of a long double link with closely-fitting jaws which, however, slide freely up and down. It may be compared to a couple of elongated and flattened links of chain. The links are about 30 in. long and are interposed between the heavy iron augerstem carrying the bit and the upper rod, known as the sinker-bar. Their principal use is to give a sharp jar to the drill on the upstroke so that the bit is dislodged if it has become jammed in the rock. In addition to the appliances mentioned the tools comprise reamers to enlarge the bore of the well, the winged-substitute which is fitted above the bit to prevent it from glancing off, and above the round reamer to keep it in place, a temper-screw with clamps and wrenches. Sand-pumps and bailers are also required to remove detritus, water and oil from the bore-hole.

The action of the jars and temper-screw has been described by John F. Carll as follows: " Suppose the tools to have been just run to the bottom of the well, the jars closed and the cable slack. The men now take hold of the bull-wheels and draw up the slack until the sinker-bar rises, the ' play ' of the jars allowing it to come up 13 in. without disturbing the auger-stem. When the jars come together they slack back about 4 in., and the cable is in position to be clamped in the temper-screw. If now the vertical movement of the walking-beam be 24 in., when 'it starts on the up-stroke the sinker-bar rises 4 in., and the cross-heads come together with a smart blow, then the auger-stem is picked up and lifted 20 in. On the down-stroke, the auger-stem falls 20 in., while the sinkerbar goes down 24 in. to telescope the jars for the next blow coming up. A skilful driller never allows his jars to strike on the downstroke, they are only used to jar down when the tools stick on some obstruction in the well before reaching the bottom, and in fishing operations. An unskilful workman sometimes ' loses the jar ' and works for hours without accomplishing anything. The tools may be standing at the bottom - while he is playing with the slack of the cable or they may be swinging all the time several feet from the bottom. As the jar works off, or grows more feeble, by reason of the downward advance of the drill, it is ' tempered ' to the proper strength by letting down the temper-screw to give the jars more play. The temper-screw forms the connecting link between the walking-beam and cable, and it is ' let out ' gradually to regulate the play of the jars as fast as the drill penetrates. When its whole length is run down, the rope clamps play very near the well-mouth. The tools are then withdrawn, the well is sand-pumped, and preparations are made for the next ' run.' " The ordinary sand-pump or bailer, consists of a plain cylinder of light galvanized iron with a bail at the top and a stem-valve at the bottom. It is usually about 6 ft. in length but is sometimes as much as 15 or 20 ft., and as its valve-stem projects downwards beyond the bottom, it empties itself when rested upon the bottom of the waste-trough.

The operation of drilling is frequently interrupted by the occurrence of an accident, which necessitates the use of fishing tools. If the fishing operation is unsuccessful the well has to be abandoned, often after months of labour, unless it is found possible to drill past the tools which have been lost. In readiness for a fracture of the drilling tools or of the cable, special appliances known as fishing tools are provided. These are so numerous and varied in form that a description would be impossible within the scope of this article. The fishing tools are generally attached to the cable, and are used with portions of the ordinary string of tools, but some are fitted to pump-rods or tubing, and others to special rods.

The drilling of a well is commonly carried out under contract, the producer erecting the derrick and providing the engine and boiler while the drilling contractor finds the tools, and is Drill ing the responsible for accidents or failure to complete the well. The drilling " crew " consists of two drillers Wel l .

and two tool-dressers, working in pairs in two " tours " (noon to midnight and midnight to noon).

The earlier wells in Pennsylvania consisted of three sections, the first formed of surface clays and gravels, the second of stratified rocks containing water, and the third of stratified rocks, including the oil-sands, usually free from water. The conductor, which was a wooden casing of somewhat greater internal diameter than the maximum bore of the well, passed through the first of these divisions, and casing was used in the second to prevent percolation of water into the oil-bearing portion. In later wells the conductor has been replaced with an 8-in. wrought-iron drive-pipe, terminating in a steel shoe, which is driven to the bed-rock, and a 71-in. hole is drilled below it to the base of the lowest water-bearing stratum.. The bore is then reduced to 5Z-in., and a bevelled shoulder being made in the rock, a 5$-in. casing, having a collar to fit water-tight on the bevel shoulder, is inserted. The well is then completed with a 52 in. bit. As the water is shut off before the portion of the well below the water-bearing strata is bored the remainder of the drilling is conducted with only sufficient water in the well to admit of sand-pumping. The drill is thus allowed to fall freely, instead of being partly upheld by the buoyancy of the water, as in earlier wells.

Wells in Pennsylvania now range in depth from 300 ft. to 3700 ft. Four strings of iron casing are usually employed, having the following diameters: to in., 84 in., 64 in. and 5 in., the lengths of tube forming the casing being screwed together. Contractors will often undertake to drill wells of moderate depth at 90 cents to $1 per foot, but the cost of a deep well may amount to as much as $7000.

The rotary system of drilling which is in general use in the oilfields of the coastal plain of Texas is a modification of that invented Rotary by Fauvelle in 1845, and used in the early years of the R . industry in some of the oil-producing countries of System Europe. It is one of the most rapid and economical which can be employed in soft formations, but where hard rock is encountered it is almost useless. The principle of this system consists essentially in the use of rotating hollow drilling rods or casing, to which is attached the drilling-bit and through which a continuous stream of water, under a pressure of 40 to loo lb. per sq. in., is forced.

The yield of petroleum wells varies within very wide limits, and the relative importance of the different producing districts is also Yield of constantly changing. I. C. White, state geologist of Wells. West Virginia, estimates that in fairly good producing sand a cubic foot of rock contains from 6 to 12 pints of oil. He assumes that in what is considered a good producing district the amount of petroleum which can be obtained from a cubic foot of rock would not be more than a gallon, and that the average thickness of the oil-bearing rock would not exceed 5 ft. Taking these figures as a basis, the total yield of oil from an acre of petroliferous territory would be a little over 5000 barrels of 42 U.S. gallons.

A flow of oil may often be induced in a well which would otherwise require to be pumped, by preventing the escape of gas which issues with the oil, and causing its pressure to raise the oil. The device employed for this purpose is known as the water-packer, and consists in its simplest form of an india-rubber ring, which is applied between the tubing and the well-casing, so that upon compression it makes a tight joint. The gas thus confined in the oil-chamber forces the oil up the tubing.

For pumping a well a valved working-barrel with valved sucker is attached to the lower end of the tubing, a perforated " anchor " being placed below. The sucker carries a series of three or four leather cups, which are pressed against the inner surface of the working barrel by the weight of the column of oil. The sucker is connected by a string of sucker-rods with the walkingbeam. There is usually fixed above the sucker a short iron valverod, with a device known as a rivet-catcher to prevent damage to the pump by the dropping of rivets from the pump-rods.

On the completion of drilling, or when the production is found to decrease, it is usual to torpedo the well to increase the flow. Torpedoing The explosive employed is generally nitroglycerin, Wells. and the amount used has been increased from the original 4 to 6 quarts to 60, 80, loo and even 200 quarts. It is placed in tin canisters of about 31 to 5 in. in diameter and about to ft. in length. The canisters have conical bottoms and fit one in the other. They are consecutively filled with nitroglycerin, and are lowered to the bottom of the well, one after the other, by a cord wound upon a reel, until the required number have been inserted. Formerly the upper end of the highest canister was fitted with a " firing-head," consisting of a circular plate of iron, slightly smaller than the bore of the well, and having attached to its underside a vertical rod or pin carrying a percussion cap. The cap rested on the bottom of a small iron cylinder containing nitroglycerin. To explode the charge an iron weight, known as a go-devil, was dropped into the well, and striking the disk exploded the cap and fired the torpedo. Now, however, a miniature torpedo known as a go-devil squib, holding about a quart of nitroglycerin, and having a firing-head similar to that already described, is almost invariably employed. The disk is dispensed with, and the percussion cap is exploded by the impact of a leaden weight running on a cord. The squib is lowered after the torpedo, and, when exploded by the descent of the weight, fires the charge. It must be borne in mind that although the explosion may increase the production for a time, it is by no means certain that the actual output of a well is increased in all such cases, though from some wells there would be no production without the use of the torpedo.

The petroleum industry in Canada is mainly concentrated in the district of Petrolea, Ontario. On account of the small Drilling in depth of the wells, and the tenacious nature of the Canada. principal strata bored through, the Canadian method of drilling differs from the Pennsylvanian or American system in the following particulars: 1. The use of slender wooden boring-rods instead of a cable.

2. The employment of a simple auger instead of a spudding-bit.

3. The adoption of a different arrangement for transmitting motion.

4. The use of a lighter set of drilling tools.

Although petroleum wells in Russia have not the depth of many of those in the United States, the disturbed character of the strata, with consequent liability to caving, and the occurrence of hard concretions, render drilling a lengthy and expensive Drilling in operation. It is usual to begin by making an excava- Russia. tion 8 ft. in diameter and 24 ft. in depth, and lining the sides of this with wood or brick. The initial diameter of the well drilled from the bottom of this pit is in some instances as much as 36 in., bore-holes of the larger size being preferred, as they are less liable to become choked, and admit of the use of larger bailers for raising the oil.

The drilling of wells of large size requires the use of heavy tools and of very strong appliances generally. The system usually adopted is a modification of the Canadian system already described, the boring rods being, however, of iron instead of wood, but the cable system has also to some extent been used. For the ordinary 2-in. plain-laid manila cable a wire rope has in some cases been successfully substituted.

Rivetted iron casing, made of s -in. plate, is employed, and is constantly lowered so as to follow the drill closely, in order to prevent caving. Within recent years, owing to the initiative of Colonel English, a method of raising oil by the agency of compressed air has been introduced into the Baku oil-fields.

In Galicia the Canadian system is nearly exclusively adopted. In some instances under-reaming is found necessary. This consists in the use of an expanding reamer by means of which Drilling in the well may be drilled to a diameter admitting of the Galicia.

casing descending freely, which obviously could not be accomplished with an ordinary bit introduced through the casing. Of late years the under-reamer has been largely superseded by the eccentric bit.

The Davis calyx drill has also been employed for petroleum drilling. This apparatus may be described as a steel-pointed coredrill. The bit or cutter consists of a cylindrical The Calyx metallic shell, the lower end of which is made, by a Drill. process of gulleting, into a series of sharp teeth, which are set in and out alternately. The outward set of teeth drill the hole large enough to permit the drilling apparatus to descend freely, and the teeth set inwardly pare down the core to such a diameter as will admit of the body of the cutter passing over it without seizing. The calyx is a long tube, or a series of connected tubes, situated above the core barrel, to which it is equal in diameter.

In conclusion it may be stated that the two systems of drilling for petroleum with which by far the largest amount of work has been, and is being done, are the American or rope Comparison system, and the Canadian or rod system. The former of Systems. is not only employed in the United States, but is in use in Upper Burma, Java, Rumania and elsewhere. The latter was introduced by Canadians into Galicia and, with certain modifications, has hitherto been found to be the best for that country. A form of the rod system is used in the Russian oil-fields, but owing to the large diameter of the wells the appliances differ from those employed elsewhere.

The wells from which the supplies of natural gas are obtained in the United States are drilled and cased in the same manner as the oil wells.

Transport and Storage

In the early days of the petroleum industry the oil was transported in the most primitive manner. Thus, in Upper Burma, it was conveyed in earthenware vessels from the wells to the river bank, where it was poured into the holds of boats. It is interesting to find that a rude pipe-line formerly existed in this field for conveying the crude oil from the wells to the river; this was made of bamboos, but it is said that the loss by leakage was so great as to lead to its immediate abandonment on completion. In Russia, until 1875, the crude oil was carried in barrels on Persian carts known as " arbas." These have two wheels of 81 to 9 ft. in diameter, the body carrying one barrel, while another is slung beneath the axle. In America, crude petroleum was at first transported in iron-hooped barrels, holding from 40 to 42 American gallons, which were carried by teamsters to Oil Creek and the Allegheny River, where they were loaded on boats, these being floated down stream whenever sufficient water was present - a method leading to much loss by collision and grounding. Bulk barges were soon introduced on the larger rivers, but the use of these was partially rendered unnecessary by the introduction of railways, when the oil was at first transported in barrels on freight cars, but later in tank-cars. These at first consisted of an ordinary truck on which were placed two wooden tub-like tanks, each holding about 2000 gallons; they were replaced in 1871 by the modern type of tank-car, constructed with a horizontal cylindrical tank of boiler plate.

The means of transporting petroleum in bulk commonly used at the present day is the pipe-line system, the history of which dates from 1860. In that year 5. D. Karns suggested laying a 6-in. pipe from Burning Springs to Parkersburg, West Virginia, a distance of 36 m.; but his proposal was never carried into effect. Two years later, however, L. Hutchinson of New York, laid a short line from the Tarr Farm wells to the refinery, which passed over a hill, the oil being moved on the syphon principle, and a year later constructed another three miles long to the railway. These attempts were, however, unsuccessful, on account of the excessive leakage at the joints of the pipes. With the adoption of carefully fitted screw-joints in 1865 the pipe line gradually came into general use, until in 1891 the lines owned by the various transit companies of Pennsylvania amounted in length to 25,000 m.

The pumps employed to force the oil through the pipes were at first of the single-cylinder or " donkey " type, but these were found to cause excessive wear - a defect remedied by the use of the Worthington pump now generally adopted. The engines used on the main 6-in. lines are of 600 to Boo h.p., while those on the small-diameter local lines range from 25 to 30 h.p.

Tanks of various types are employed in storing the oil, those at the wells being circular and usually made of wood, with a content of 250 barrels and upwards. Large tanks of boiler-plate are used to receive the oil as it comes through the pipe-lines. Those adopted by the National Transit Company are 90 ft. in diameter and 30 ft. high, with slightly conical wooden roofs covered with sheet iron; their capacity is 35,000 barrels, and they are placed upon the carefully levelled ground without any foundation.

Kerosene is transported in bulk by various means; specially constructed steel tank barges are used on the waterways of the United States, tank-cars on the railroads, and tank-wagons on the roads. The barrels employed in the transport of petroleum products are made of well-seasoned white-oak staves bound by six or eight iron hoops. They are coated internally with glue, and painted in the well-known colours, blue staves and white heads. The tins largely used for kerosene are made by machinery and contain 5 American gallons. They are hermetically sealed for transport.

In Canada, means of transport similar to those already described are employed, but the reservoirs for storage often consist of excavations in the soft Erie clay of the oil district, the sides of which are supported by planks.

The primitive methods originally in use in the Russian oil-fields have already been described; but these were long ago superseded by pipe-lines, while a great deal of oil is carried by tank steamers on the Caspian to the mouth of the Volga where it is transferred to barges and thence at Tzaritzin to railway tank-cars. The American type of storage-tank is generally employed, in conjunction with clay-lined reservoirs.

Natural gas is largely used in the United States, and for some time, owing to defective methods of storage, delivery and consumption, great waste occurred. The improvements introduced in 1890 and 1891, whereby this state of affairs was put an end to, consisted in the introduction of the principle of supply by meter, and the adoption of a comprehensive system of reducing the initial pressure of the gas, so as to diminish loss by leakage. For the latter purpose, Westinghouse gas-regulators are employed, the positions of the regulators being so chosen as to equalize the pressure throughout the service. The gas is distributed to the consumer from the wells in wrought-iron pipes, ranging in diameter from 20 in. down to 2 in. Riveted wrought-iron pipes 3 ft. in diameter are also used. The initial pressure is sometimes as high as 400 lb to the sq. in., but usually ranges from 200 to 300 lb. The most common method of distribution in cities and towns is by a series of pipes from 12 in. down to 2 in. in diameter, usually carrying a pressure of about 4 oz. to the sq. in. To these pipes the service-pipes leading into the houses of the consumers are connected.

Refining of Petroleum

The distillation of petroleum, especially of such as was intended for medicinal use, was regularly carried on in the 18th century, and earlier. V. I. Ragozin states in his work on the petroleum industry that Johann Lerche, who visited the Caspian district in 1735, found that the crude Caucasian oil required to be distilled to render it satisfactorily combustible, and that, when distilled, it yielded a bright yellow oil resembling a spirit, which readily ignited. As early as 1823 the brothers Dubinin erected a refinery in the village of Mosdok, and in 1846 applied to Prince Woronzoff for a subsidy for extending the use of petroleum-distillates in the Caucasus. In their application, which was unsuccessful, they stated that they had taught the Don Cossacks to " change black naphtha into white," and showed by a drawing, preserved in the archives of the Caucasian government, how this was achieved. They used an iron still, set in brickwork, and from a working charge of forty " buckets " of crude petroleum obtained a yield of sixteen buckets of " white naphtha." The top of the still had a removable head, connected with a condenser consisting of a copper worm in a barrel of water. The " white naphtha " was sold at Nijni Novgorod without further treatment.

Some of the more viscous crude oils obtained in the United States are employed as lubricants under the name of " natural oils," either without any treatment or after clarification by subsidence and filtration through animal charcoal. Others are deprived of a part of their more volatile constituents by spontaneous evaporation, or by distillation, in vacuo or otherwise, at the lowest possible temperature. Such are known as " reduced oils." In most petroleum-producing countries, however, and particularly where the product is abundant, the crude oil is fractionally distilled, so as to separate it into petroleum spirit of various grades, burning oils, gas oils, lubricating oils, and (if the crude oil yields that product) paraffin. The distillates obtained are usually purified by treatment, successively, with sulphuric acid and solution of caustic soda, followed by washing with water.

Crude petroleum was experimentally distilled in the United States in 1833 by Prof. Silliman (d. 1864), and the refining of petroleum in that country may be said to date from about the year 1855, when Samuel M. Kier fitted up a small refinery with a five-barrel still, for the treatment of the oil obtained from his father's saltwells. At this period the supply of the raw material was insufficient to admit of any important development in the industry, and before the drilling of artesian wells for petroleum was initiated by Drake the " coal-oil " or shale-oil industry had assumed considerable proportions in the United States. Two large refineries, one on Newtown Creek, Long Island, and another in South Brooklyn, also on Long Island, were in successful operation when the abundant pr oduction of petroleum, which immediately followed the completion of the Drake well, placed at the disposal of the refiner a material which could be worked more profitably than bituminous shale. The existing refineries were accordingly altered so as to adapt them for the refining of petroleum; but in the manufacture of burning oil from petroleum the small stills which had been in use in the distillation of shale-oil were at first employed.

In the earlier refineries the stills, the capacity of which varied from 25 to 80 barrels, usually consisted of a vertical cylinder, constructed of castor wrought-iron, with a boiler-plate bottom and a cast-iron dome, on which the " goose-neck " was bolted. The charge was distilled almost to dryness, though the operation was not carried far enough to cause the residue to " coke." The operation was, however, completely revolutionized in the United States by the introduction of the " cracking process," and by the division of the distillation into two parts, one consisting in the removal of the more volatile constituents of the oil, and the other in the distillation (which is usually conducted in separate stills) of the residues from the first distillation, for the production of lubricating oils and paraffin.

Various arrangements have been proposed and patented for the continuous distillation of petroleum, in which crude oil is supplied to a range of stills as fast as the distillates pass off. The system is largely employed in Russia, and its use has been frequently attempted in the United States, but the results have not been satisfactory, on account, it is said, of the much greater quantity of dissolved gas contained in the American oil, the larger proportion of kerosene which such oil yields, and the less fluid character of the residue.

In the United States a horizontal cylindrical still is usually employed in the distillation of the spirit and kerosene, but what is known as the " cheese-box " still has also been largely used. American stills of the former type are constructed of wrought-iron or steel, and are about 30 ft. in length by 12 ft. 6 in. in diameter, with a dome about 3 ft. in diameter, furnished with a vapour-pipe 15 in. in diameter. The charge for such a still is about 600 barrels. The stills were formerly completely bricked in, so that the vapours should be kept fully heated until they escaped to the condenser, but since the introduction of the " cracking process," the upper part has usually been left exposed to the air. The cheese-box still has a vertical cylindrical body, which may be as much as 30 ft. in diameter and 9 ft. in depth, connected by means of three vertical pipes with a vapour-chest furnished with a large number, frequently as many as forty, of 3-in. discharge-pipes arranged in parallel lines. The stills employed in Russia and Galicia are usually smaller than those already described.

The " cracking " process, whereby a considerable quantity of the oil which is intermediate between kerosene and lubricating oil is converted into hydrocarbons of lower specific gravity and boiling-point suitable for illuminating purposes, is one of great scientific and technical interest. It is generally understood that the products of fractional distillation, even in the laboratory, are not identical with the hydrocarbons present in the crude oil, but are in part produced by the action of heat upon them. This was plainly stated by Professor Silliman in the earliest stages of development of the American petroleum industry. An important paper bearing on the subject was published in 1871, by T. E. Thorpe and J. Young, as a preliminary note on their experiments on the action of heat under pressure on solid paraffin. They found that the paraffin was thus converted, with the evolution of but little gas, into hydrocarbons which were liquid at ordinary temperatures. In an experiment on 3500 grams of paraffin produced from shale (melting point 44'5° C.) they obtained nearly 4 litres of liquid hydrocarbons, which they subjected to fractional distillation, and on examining the fraction distilling below loo° C., they found it to consist mainly of olefines. The hydrocarbon C20H42, for example, might be resolved into C5H12+C15H30, or CEH14+C14H28, or C7H16 +C13H26, &c., the general equation of the decomposition being C„1-1 27 ,± 2 (paraffin) =G_rH2(, - P)+2 (paraffin)+C P H 2 n (olefine).

The product actually obtained is a mixture of several paraffins and several olefines.

The cracking process practically consists in distilling the oils at a temperature higher than the normal boiling point of the constituents which it is desired to decompose. This may be brought about by a distillation under pressure, or by allowing the condensed distillate to fall into the highly heated residue in the still. The result of this treatment is that the comparatively heavy oils undergo dissociation, as shown by the experiments of Thorpe and Young, into specifically lighter hydrocarbons of lower boiling points, and the yield of kerosene from ordinary crude petroleum may thus be greatly increased. A large number of arrangements for carrying out the cracking process have been proposed and patented, probably the earliest directly bearing on the subject being that of James Young, who in 1865 patented his " Improvements in treating hydrocarbon oils." In this patent, the distillation is described as being conducted in a vessel having a loaded valve or a partially closed stop-cock, through which the confined vapour escapes under any desired pressure. Under such conditions, distillation takes place at higher temperatures than the normal boiling-points of the constituent hydrocarbons of the oil, and a partial cracking results. The process patented by Dewar and Redwood in 1889 consists in the use of a suitable still and condenser in free communication with each other - i.e. without any valve between them - the space in the still and condenser not occupied by liquid being charged with air, carbon dioxide or other gas, under the required pressure, and the condenser being provided with a regulated outlet for condensed liquid. An objectionable feature of the system of allowing the vapour to escape from the still to the condenser through a loaded valve, viz: the irregularity of the distillation, is thus removed, and the benefits of regular vaporization and condensation under high pressure are obtained. In the American petroleum refineries it is found that sufficient cracking can be produced by slow distillation in stills of which the upper part is sufficiently cool to allow of the condensation of the vapours of the less volatile hydrocarbons, the condensed liquid thus falling back into the heated body of oil.

In the earlier stages of the development of the manufacture of mineral lubricating oils, the residues were distilled in cast-iron stills, and the lubricating properties of the products thus obtained were injured by overheating. The modern practice is to employ horizontal cylindrical wrought-iron or steel stills, and to introduce steam into the oil. The steam is superheated and may thus be heated to any desired temperature without increase of pressure, which would be liable to damage the still. The steam operates by carrying the vapours away to the condenser as fast as they are generated, the injury to the products resulting from their remaining in contact with the highly-heated surface of the still being thus prevented.

In order to separate the distillate into various fractions, and to remove as much of it as possible free from condensed steam, it is now usual to employ condensing appliances of special form with outlets for running off the different fractions.

The process of distillation of lubricating oils under reduced atmospheric pressure is now in very general use, especially for obtaining the heavier products. The vapours from the still pass through a condenser into a receiver, which is in communication with the exhauster.

The products obtained by the distillation of petroleum are not in a marketable condition, but require chemical treatment to remove acid and other bodies which impart a dark colour as well as an unpleasant odour to the liquid, and in the case of lamp-oils, reduce the power of rising in the wick by capillary attraction.

At the inception of the industry kerosene came into the market as a dark yellow or reddish-coloured liquid, and in the first instance, the removal of colour was attempted by treatment with soda lye and lime solution. It was, however, found that after the oil so purified had been burned in a lamp, for a short time, the wick became encrusted, and the oil failed to rise properly. Eichler, of Baku, is stated to have been the first to introduce, in Russia, the use of sulphuric acid, followed by that of soda lye, and his process is in universal use at the present time. The rationale of this treatment is not fully understood, but the action appears to consist in the separation or decomposition of the aromatic hydrocarbons, fatty and other acids, phenols, tarry bodies, &c., which lower the quality of the oil, the sulphuric acid removing some, while the caustic soda takes out the remainder, and neutralizes the acid which has been left in the oil. This treatment with acid and alkali is usually effected by agitation with compressed air. Oils which contain sulphur-compounds are subjected to a special process of refining in which cupric oxide or litharge is employed as a desulphurizing agent.

Testing

A large number of physical and chemical tests are applied both to crude petroleum and to the products manufactured therefrom. The industry is conducted upon a basis of recognized standards of quality, and testing is necessary in the interests of both refiner and consumer, as well as compulsory in connexion with the various statutory and municipal regulations.

In the routine examination of crude petroleum it is customary to determine the specific gravity, and the amount of water and earthy matter in suspension; the oil is also frequently subjected to a process of fractional distillation in order to ascertain whether there has been any addition of distilled products or residue. Petroleum spirit is tested for specific gravity, range of boilingpoints, and results of fractional distillation. To illuminating oil or kerosene a series of tests is applied in order that the colour, odour, specific gravity and flash-point or fire-test may be recorded. In the testing of mineral lubricating oils the viscosity, flash-point, cold-test," and specific gravity are the characters of chief importance. Fuel oil is submitted to certain of the foregoing tests and in addition the calorimetric value is determined. Paraffin wax is tested for melting-point (or setting-point), and the semi-refined product is further examined to ascertain the percentage of oil, water and dirt present.

In civilized countries provision is made by law for the testing of the flash-point or fire-test of lamp-oil (illuminating oil or kerosene), the method of testing and the minimum limit of flash-point or fire-test being prescribed (see below, Legislation). The earliest form of testing instrument employed for this purpose was that of Giuseppe Tagliabue of New York, which consists of a glass cup placed in a copper water bath heated by a spirit lamp. The cup is filled with the oil to be tested, a thermometer placed in it and heat applied, the temperatures being noted at which, on passing a lighted splinter of wood over the surface of the oil, a flash occurs, and after further heating, the oil ignites. The first temperature is known as the flash-point, the second as the " fire-test." Such an apparatus, in which the oil-cup is uncovered, is known as an open-test instrument. In Saybolt's Electric Tester (1879) ignition is effected by a spark from an induction-coil passing between platinum points placed at a fixed distance above the oil.

Before long, however, it was found that the open-cup tests (though they are employed in the United States and elsewhere at the present time) were often very untrustworthy. Accordingly Keates proposed the substitution of a closed cup in 1871, but his suggestions were not adopted. In 1875 Sir Frederick Abel, at the request of the British Government, began to investigate the matter, and in August 1879 the " Abel test " was legalized. This apparatus has an oil-cup consisting of a cylindrical brass or gunmetal vessel, the cover of which is provided with three rectangular holes which may be closed and opened by means of a perforated slide moving in grooves; the movement of the slide causes a small oscillating colzaor rape-oil lamp to be tilted so that the flame (of specified size) is brought just below the surface of the lid. The oil-cup is supported in a bath or heating-vessel, consisting of two flat-bottomed copper cylinders, to contain water, heated by a spirit lamp, and provided with an air-space between the water-vessel and the oil-cup. Thermometers are placed in both oil-cup and waterbath, the temperature of the latter being raised to 130° at the commencement of the test, while the oil is put in at about 60° F. Testing is begun when the temperature reaches 66° by slowly drawing the slide open and reclosing it, the speed being regulated by the swing of a pendulum supplied with the instrument. It has been found that variations in barometric pressure affect the flash-point and accordingly corrections have to be made in obtaining strictly comparative results at different pressures. The Abel-Pensky instrument, used in India and in Germany, differs only in being provided with a clockwork arrangement for moving the slide. Numerous other forms of open-test and close-test instruments have from time to time been devised, some of which are in use in the United States and in other countries.

It is still customary to determine the open flash-point and firetest of lubricating oils, but the close flash-point is also usually ascertained, a modification of the Abel or Abel-Pensky apparatus, known as the Pensky-Martens, having been devised for the purpose. This instrument is so constructed that the higher temperature needed can be readily applied, and it is fitted with a stirrer to equalize the heating of the contents of the oil-cup.

For the testing of the viscosity of lubricating oils the Boverton Redwood standardized viscometer is generally employed in Great Britain. By means of this instrument the time occupied in the flow of a measured quantity of the oil through a small orifice at a given temperature is measured.

Uses

Petroleum has very long been known as a source of light and heat, while the use of crude oil for the treatment of wounds and cutaneous affections, and as a lubricant, was even more general and led to the raw material being an article of commerce at a still earlier date. For pharmaceutical purposes crude petroleum is no longer generally used by civilized races, though the product vaseline is largely employed in this way, and emulsions of petroleum have been administered internally in various pectoral complaints; while the volatile product termed rhigolene has been largely used as a local anaesthetic.

For illuminating purposes, the most extensively-used product is kerosene, but both the more and the less volatile portions Of petroleum are employed in suitable lamps. Petroleum products are also largely utilized in gas manufacture for, (1) the production of " air-gas," (2) the manufacture of oil-gas, and (3) the enrichment of coal-gas. For heating purposes, the stoves employed are practically kerosene lamps of suitable construction, though gasoline is used as a domestic fuel in the United States. The use of petroleum as liquid fuel is dealt with under Fuel, as is the employment of its products in motors, which has greatly increased the demand for petroleum spirit. Petroleum has largely superseded other oils, and is still gaining ground, as a lubricant for machinery and railway rolling-stock, either alone or in admixture with fixed oils. The more viscous descriptions of mineral oils have also been found suitable for use in the Elmore process of ore-concentration by oil.

Legislation

Since the inception of the petroleum industry, most civilized countries have prescribed by law a test of flash-point or inflammability, designed in most cases primarily to afford a definition of oils for lighting purposes which may be safely stored without the adoption of special precautions. In the United Kingdom the limit has, for the purpose in question, been fixed by the legislature at 73° F., by the " Abel-test," which is the equivalent of the former standard of 100° F. by the " open-test." While the subject of the testing of petroleum for legislative purposes has been investigated in Great Britain by committees of both branches of the legislature, with a view to change in the law, the standard has never been raised, since such a course would tend to reduce the available supply and thus lead to increase in price or deterioration in quality. Moreover the chief object of the Petroleum Acts passed in the United Kingdom has hitherto been to regulate storage, and it has always been possible to obtain oils either of higher or lower flash-point, when such are preferred, irrespective of the legal standard, in addition to which it may be asserted that in a properly constructed lamp used with reasonable care the ordinary oil of commerce is a safe illuminant. The more recent legislation with regard to " petroleum spirit " relates mainly to the quantity which may be stored for use on " light locomotives." The more important local authorities throughout the country have made regulations under the powers conferred upon them by the Petroleum Acts, with the object of regulating the " keeping, sale, conveyance and hawking " of petroleum products having a flash-point below 73° F., and the Port of London authority, together with other water-way and harbour authorities in the United Kingdom, have their own by-laws relating to the navigation of vessels carrying such petroleum.

In other countries the flash-point standards differ considerably, as do the storage regulations. In France, the standard is 35° C. (Granier tester, equivalent to 98° F.), and according to their flashpoint, liquid hydrocarbons are divided into two classes (below and above 35° C.), considered differently in regard to quantities storable and other regulations. In Germany, the law prescribes a close-test of 21° C., equal to about 70° F., whilst in Russia the standard is 28° C., equal to 84.4° F., by the close-test; in both these countries the weights of petroleum which may be stored in specified buildings are determined by law. In the United States, various methods of testing and various minimum standards have been adopted. In Pennsylvania, the prescribed limit is a " fire-test " of 110° F., equivalent to about 70° F., close-test, while in the State of New York it is 1 00° F., close-test.

See Sir Boverton Redwood's Petroleum and its Products (2nd ed., London, 1906); A. Beeby Thompson, Petroleum Mining (1910); L. C. Tassart, Exploitation du Petrole (1908); C. Engler and H. Hofer, Das Erda, 5 vols. (1909 seq.); A. B. Thompson, The Oil Fields of Russia (1908); and J. D. Henry, Oil Fields of the Empire (1910). (B. R.)


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English

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Etymology

From Middle English petroleum from petra (rock) + oleum (oil).

Pronunciation

Noun

Singular
petroleum

Plural
petroleums or, rarely, petrolea

petroleum (plural petroleums or, rarely, petrolea)

  1. A flammable liquid ranging in color from clear to very dark brown and black, consisting mainly of hydrocarbons, occurring naturally in deposits under earth surface.

Synonyms

Derived terms

Translations


Simple English

Petroleum, also called crude oil, is a thick and black liquid. It consists mainly of hydrocarbons. It is mainly found in the Middle East, North America, and Russia. It is the most important world energy source. It supplies 38% of the world's energy at present.

Petroleum can be separated into less complex but more useful mixtures by fractional distillation. The process is called oil refining.

Petroleum can be easily transported by pipeline. Treated petroleum can be used as fuels; mainly gasoline (petrol) for cars, Diesel fuel for Diesel engines used in trucks, trains and ships, kerosene fuel for jets and as lubricants.

Other uses of petroleum:

Contents

Problems

Petroleum resource is limited and non-renewable. Most of it would run out within 70 years. Burning petroleum adds the carbon in the oil to the oxygen in the air to create carbon dioxide. The carbon can be removed from the carbon dioxide by plants.

Crude is chemically speaking a mixture of lots of different chemicals most of which burn well. It is separated by distillation in oil refineries to give separate chemicals such as gasoline (or petrol) for cars, kerosene for airplanes and bitumen for roads. The bitumen gives crude oil its dark black colour; most of the other chemicals in crude are slightly yellow or colourless.

There is a lot of crude oil left underground. Oil companies quote "reserves" which some people confuse with the actual amount of oil underground, but are more to do with extraction costs. Most of the crude left underground is in the Middle East which is not a politically stable part of the world. Some governments with lots of oil reserves work together through OPEC to keep production low and prices high. Policitians complain about high oil prices because voters complain. However many environmentalists worry about the damage being done by using oil as a fuel source (especially global warming) and are therefore happy that prices are kept high so that people use less oil.

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