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PowerPedia:Petroleum

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Table of contents

1 History

2 Formation

2.1 Conventional theories
2.2 Biogenic theory
2.3 Abiogenic theory

3 Means of producing oil

4 Extraction

5 Petroleum industry

5.1 Classifications
5.2 Black Gold
5.3 Top petroleum-producing countries
5.4 Pricing

6 Petroleum product

7 Environmental effects

8 Oil's Future

9 References and external articles

10 See also

Petroleum (from Greek petra – rock and elaion – oil or Latin oleum – oil ) or crude oil is a black, dark brown or greenish liquid found in porous rock formations in the earth. The American Petroleum Institute, in its Manual of Petroleum Measurement Standards (MPMS), defines it as "a substance, generally liquid, occurring naturally in the earth and composed mainly of mixtures of chemical compounds of carbon and hydrogen with or without other nonmetallic elements such as sulfur, oxygen, and nitrogen."

Petroleum is found in porous rock formations in the upper strata of some areas of the Earth's crust. It consists of a complex mixture of various hydrocarbons, largely of the alkane series, but may vary much in appearance and composition. Petroleum is used mostly, by volume, for producing fuel oil and petrol (gasoline), both important "primary energy" sources (IEA Key World Energy Statistics). Petroleum is also the raw material for many chemical products, including solvents, fertilizers, pesticides, and plastics. 88% of all petroleum extracted is processed as fuel; the other 12% is converted into other materials such as plastic. Since petroleum is a non-renewable resource, many people are worried about peak oil and eventual depletion in the near future. Due to its continual demand and consequent value, oil has been dubbed black gold. The combining form of the word petroleum is petro-, as in petrodiesel (petroleum diesel).

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History

Petroleum, in some form or other, is not a substance new in the world's history. More than four thousand years ago, according to Herodotus and confirmed by Diodorus Siculus, asphalt was employed in the construction of the walls and towers of Babylon. 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. The first oil wells were drilled in China in the 4th century or earlier. They had depths of up to 243 meters and were drilled using bits attached to bamboo poles. The oil was burned to evaporate brine and produce salt. By the 10th century, extensive bamboo pipelines connected oil wells with salt springs. In the 8th century, the streets of the newly constructed Baghdad were paved with tar, derived from easily accessible petroleum from natural fields in the region. In the 9th century, oil fields were exploited in Baku, Azerbaijan, to produce naphtha. These fields were described by the geographer Masudi in the 10th century, and by Marco Polo in the 13th century, who described the output of those wells as hundreds of shiploads. (See also: Timeline of Islamic science and technology.)

The modern history of petroleum began in 1846, with the discovery of the process of refining kerosene from coal by Atlantic Canada's Abraham Pineo Gesner. Poland's Ignacy �?ukasiewicz discovered a means of refining kerosene from the more readily available "rock oil" ("petr-oleum") in 1852 and the first rock oil mine was built in Bóbrka, near Krosno in southern Poland in the following year. These discoveries rapidly spread around the world, and Meerzoeff built the first Russian refinery in the mature oil fields at Baku in 1861. At that time Baku produced about 90% of the world's oil. The battle of Stalingrad was fought over Baku (now the capital of the Azerbaijan Republic).

The first commercial oil well drilled in North America was in Oil Springs, Ontario, Canada in 1858, dug by James Miller Williams. The American petroleum industry began with Edwin Drake's discovery of oil in 1859, near Titusville, Pennsylvania; like the Chinese, Drake had been boring for salt. The industry grew slowly in the 1800s, driven by the demand for kerosene and oil lamps. It became a major national concern in the early part of the 20th century; the introduction of the internal combustion engine provided a demand that has largely sustained the industry to this day. Early "local" finds like those in Pennsylvania and Ontario were quickly exhausted, leading to "oil booms" in Texas, Oklahoma, and California. By 1910, significant oil fields had been discovered in Canada (specifically, in the province of Alberta), the Dutch East Indies (1885, in Sumatra), Persia (1908, in Masjed Soleiman), Peru, Venezuela, and Mexico, and were being developed at an industrial level.

Even until the mid-1950s, coal was still the world's foremost fuel, but oil quickly took over. Following the 1973 energy crisis and the 1979 energy crisis, there was significant media coverage of oil supply levels. This brought to light the concern that oil is a limited resource that will eventually run out, at least as an economically viable energy source. At the time, the most common and popular predictions were always quite dire, and when they did not come true, many dismissed all such discussion. The future of petroleum as a fuel remains somewhat controversial. USA Today news (2004) reports that there are 40 years of petroleum left in the ground. Some would argue that because the total amount of petroleum is finite, the dire predictions of the 1970s have merely been postponed. Others argue that technology will continue to allow for the production of cheap hydrocarbons and that the earth has vast sources of unconventional petroleum reserves in the form of tar sands, bitumen fields and oil shale that will allow for petroleum use to continue in the future, with both the Canadian tar sands and United States shale oil deposits representing potential reserves matching existing liquid petroleum deposits worldwide.

In World War II the Soviet Union sought to protect their oil fields from falling into the hands of Nazi Germany at the Battle of Stalingrad. Many countries have a strategic oil reserve in the event of war or loss of oil supplies. During the Iran-Iraq War many nations sent military ships to escort tankers carrying oil. During the Gulf War, Iraq's retreating troops burned Kuwait's oil fields in order to give them air cover, to slow the advance of pursuing coalition forces, and to damage the Kuwaiti economy. During the Iraq War the United States had military units work to quickly secure oil fields and remove boobytraps. It also had units guarding the Ministry of Petroleum in Baghdad.

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. Access to it was a major factor in several military conflicts, including World War I, World War II and the Persian Gulf War. The top three oil producing countries are Saudi Arabia, Russia, and the United States. 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 (12.5%), UAE, Iraq, Qatar and Kuwait. The USA has less than 3%.

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Formation

An oil reservoir, petroleum system or petroleum reservoir is often thought of as being an underground "lake" of oil, but it is actually composed of hydrocarbons contained in porous rock formations.

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Conventional theories

The crude oil found in oil reservoirs forms in the Earth's crust from the remains of living things. Crude oil is properly know as petroleum, and is a kind of fossil fuel. Scientific evidence indicates that millions of years of heat and pressure changed the remains of microscopic plant and animal remains into crude oil and natural gas. Most petroleum geologists prefer theories of oil formation which hold that oil originated in shallow seas as vast quantities of marine plankton which died and sank into the mud at the bottom under anaerobic conditions that prevented biodegradation. Under these conditions, anaerobic bacteria converted the lipids (fats, oils and waxes) into a waxy substance called kerogen.

As the source rock was buried deeper, overburden pressure raised temperatures into the oil window, between 60 and 120 degrees C, in which thermal depolymerization broke up the kerogen molecules into the straight-chain hydrocarbons that make up most of petroleum. Once crude oil formed, it became very fluid, and migrated upward through the rock strata. Eventually it was either trapped in an oil reservoir or oil escaped to the surface and was biodegraded by soil bacteria. Any oil buried deeper entered the gas window of 120°C to 220°C and was converted into natural gas by thermal cracking. Thus, below a certain depth, the theory predicts that no oil will be found, only unassociated gas. If it went even deeper, even natural gas would be destroyed by high temperatures.

Roy Nurmi, an interpretation adviser for Schlumberger described the process as follows: "Something in the order of 500 million years ago there was only simple life in the seas, and these shallow seas would be rich with organic, living organisms. Plankton and algae, proteins and the life that's floating in the sea, as it dies, falls to the bottom, and these organisms are going to be the source of our oil and gas. When they're buried with the accumulating sediment and reach an adequate temperature, something above 50 to 70°C they start to cook. This transformation, this change, changes them into the liquid hydrocarbons that move and migrate, will become our oil and gas reservoir."^{[1] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_quote)}

In addition to the water environment mentioned, which is usually a sea but might also be a river, lake, coral reef or algal mat, the formation of an oil or gas reservoir also requires a sedimentary basin that passes through four steps: burial under miles of sand and mud, pressure cooking, hydrocarbon migration from the source to porous rock, and trapping by impermeable rock. Timing is also an important consideration; it is suggested that the Ohio River valley could have had as much oil as the Middle East at one time, but that it escaped due to a lack of traps.^{[2] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_whatis)} The North Sea, on the other hand, endured millions of years of sea level changes that successfully resulted in the formation of more than 150 oilfields.^{[3] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_northsea)} Although the process is generally the same, various environmental factors lead to the creation of a wide variety of reservoirs. Reservoirs exist anywhere from 1,000 to 30,000 ft below the surface and are a variety of shapes, sizes and ages.^{[4] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_variety)}

The traps required in the last step of the reservoir formation process have been classified petroleum geologists into two types: structural and stratigraphic. A reservoir can be formed by one kind of trap or a combination of both. Structural traps are formed by a deformation in the rock layer that contains the hydrocarbons (e.g., fault traps and anticlinal traps). Stratigraphic traps are formed when other beds seal a reservoir bed or when the permeability changes (facies change) within the reservoir bed itself. An example of this kind of trap starts when salt deposited by shallow seas. Later, a sinking seafloor deposits organic-rich shale over the salt, which is in turn covered with sandstone. As the Earth's pressure pushes the salt up, the shale is "cooked," producing oil that seeps up into the sandstone above. In some places, the salt breaks through the shale and sandstone layers into a salt dome that effectively traps the hydrocarbons beneath it.^{[5] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_salt)} To obtain the contents of the oil reservoir, it is usually necessary to drill into the Earth's crust, although surface oil seeps exist in some parts of the world.

Active areas of surface oil reservoirs

Texas

Active areas of existing sub-sea oil reservoirs

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Biogenic theory

Most geologists view crude oil, like coal and natural gas, as the product of compression and heating of ancient organic materials over geological time. According to this theory, oil is formed from the preserved remains of prehistoric zooplankton and algae which have been settled to the sea bottom in large quantities under anoxic conditions. (Terrestrial plants tend to form coal, and very few dinosaurs have been converted into oil.) Over geological time this organic matter, mixed with mud, is buried under heavy layers of sediment. The resulting high levels of heat and pressure cause the remains to metamorphose, 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 in a process known as catagenesis. Because most hydrocarbons are lighter than rock or water, these sometimes migrate upward through adjacent rock layers until they become trapped beneath impermeable rocks, within porous rocks called reservoirs. Concentration of hydrocarbons in a trap forms an oil field, from which the liquid can be extracted by drilling and pumping.

Geologists often refer to an "oil window" which is the temperature range that oil forms in—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. Though this happens at different depths in different locations around the world, a 'typical' depth for the oil window might be 4–6 km. Note that even if oil is formed at extreme depths, it may be trapped at much shallower depths, even if it is not formed there. (In the case of the Athabasca Oil Sands, it is found right at the surface.) Three conditions must be present for oil reservoirs to form: first, a source rock rich in organic material buried deep enough for subterranean heat to cook it into oil; second, a porous and permeable reservoir rock for it to accumulate in; and last a cap rock (seal) that prevents it from escaping to the surface.

If an oil well were to run dry and be capped, it would be back to original supply rates eventually. There is considerable question about how long this would take. Some formations appear to have a regeneration time of decades. Majority opinion is that oil is being formed at less than 1% of the current consumption rate. The vast majority of oil that has been produced by the earth has long ago escaped to the surface and been biodegraded by oil-eating bacteria. What oil companies are looking for is the small fraction that has been trapped by this rare combination of circumstances. Oil sands are reservoirs of partially biodegraded oil still in the process of escaping, but 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. On the other hand, oil shales are source rocks that have never been buried deep enough to convert their trapped kerogen into oil.

The reactions that produce oil and natural gas are often modeled as first order breakdown reactions, where kerogen is 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 first set was originally 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." The latter set is regularly used in petrochemical plants and oil refineries.

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Abiogenic theory

The idea of abiogenic petroleum origin was championed in the Western world by astronomer Thomas Gold based on thoughts from Russia, mainly on studies of Nikolai Kudryavtsev. The idea proposes that hydrocarbons of purely geological origin exist in the planet. Hydrocarbons are less dense than aqueous pore fluids, and are proposed to migrate upward through deep fracture networks. Thermophilic, rock-dwelling microbial life-forms are proposed to be in part responsible for the biomarkers found in petroleum. However, this theory is a minority opinion, especially amongst geologists and no oil companies are currently known to explore for oil based on this theory. The hypothesis of abiogenic petroleum origin holds that most petroleum was formed from deep carbon deposits, perhaps deposits dating to the accretion of the Earth. The ubiquity of hydrocarbons in the solar system is taken as evidence that there may be a great deal more petroleum on Earth than commonly thought, and that petroleum may originate from carbon-bearing fluids which migrate upward from the mantle.

Various abiogenic hypotheses were first proposed in the nineteenth century; most notably, by the French chemist Marcellin Berthelot and the Russian chemist Dmitri Mendeleev. Since that time, these hypotheses have lost ground to the modern scientific consensus that petroleum is a fossil fuel. More recently, these hypotheses saw a revival in the last half of the twentieth century by Russian and Ukrainian scientists, and a degree of interest has been generated in the West after the publication of The Deep Hot Biosphere, by Thomas Gold. Gold's version of the hypothesis partly is based on the existence of a biosphere composed of thermophile bacteria in the earth's crust, which may explain the existence of certain biomarkers in extracted petroleum. ^{[6] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Gold1999)}

Although this theory, according to Gold, is widely accepted in Russia, where it was intensively developed in the 1950s and 1960s, it has only recently begun to receive attention in the West, where the biogenic theory is still believed by the vast majority of petroleum geologists. Although some denied that abiogenic hydrocarbons exist at all on earth, this is now admitted by many Western geologists. The orthodox position now is that while abiogenic hydrocarbons exist, they are not produced in commercially significant quantities, so that essentially all hydrocarbons that are extracted for use as fuel or raw materials are biogenic. ^{[7] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Lollar2002)}^{[8] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Lollar2006)}

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Foundations of the hypothesis

Within the mantle carbon may exist as hydrocarbon molecules, chiefly methane, and as elemental carbon, carbon dioxide and carbonates. The abiotic hypothesis is that a full suite of hydrocarbons found in petroleum can be generated in the mantle by abiogenic processes,^{[9] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kenney2002)} and these hydrocarbons can migrate out of the mantle, into the crust until they escape to the surface or are trapped by impermeable strata, forming petroleum reservoirs. Abiogenic theories refute the supposition that certain molecules found within petroleum, known as "biomarkers," are indicative of the biological origin of petroleum. They contend that some of these molecules could have come from the microbes that the petroleum encounters in its upward migration through the crust, and that some of them are found in meteorites, which have presumably never contacted living material, and that some can be generated by plausible reactions in petroleum abiogenically.^{[10] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kenney2001)}

The hypothesis is founded primarily upon;

The ubiquity of methane within the solar system
The presence of hydrocarbons in extraterrestrial bodies including meteors, moons and comets^{[11] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Hodgson1964)},^{[12] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Hodgson1967)}
Plausible mechanisms of abiotically chemically synthesizing hydrocarbons within the mantle
Interpretations of the chemical composition of natural petroleum
The presence of oil within non-sedimentary rocks upon the Earth ^{[13] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Brown2005)}
Perceived ambiguity in some assumptions and key evidence used in the orthodox biogenic petroleum theories ^{[14] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kenney2)}
Scaled particle theory for a simplified perturbed hard-chain, statistical mechanical model predicts that methane compressed to 30 or 40 kbar at 1000°C (conditions in the mantle) yields hydrocarbons having properties similar to petroleum ^{[15] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kenney2001)}^{[16] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kenney2002)}
Experiments in diamond anvil high pressure cells have confirmed this theory^{[17] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kenney2002)}
Similar experiments on mixtures of calcium carbonate, iron oxide and water produced methane^{[18] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Scott2004)}

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Proposed mechanisms of abiogenic petroleum

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Hydrogen generation

Hydrogen gas and water have been found more than 6 kilometers deep in the upper crust, including in the Siljan Ring boreholes and the Kola Superdeep Borehole. There is data in the western United States that aquifers from near the surface may extend to depths of 10 to 20 km. Hydrogen gas can be created by water reacting with silicates, quartz and feldspar, in temperatures in the 25° to 270°C range. These materials are common in crustal rocks such as granite. Hydrogen may react with dissolved carbon compounds in water to form methane and higher carbon compounds. ^{[19] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_MacDonald1988)}

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Serpentinite mechanism

One proposed mechanism by which abiogenic petroleum is formed was first proposed by the Ukrainian scientist, Prof. Emmanuil B. Chekaliuk in 1967. He proposed that petroleum could be formed at high temperatures and pressures from inorganic carbon in the form of carbon dioxide, hydrogen and/or methane. This mechanism is supported by several lines of evidence which are accepted by modern scientific literature. This involves synthesis of oil within the crust via catalysis by chemically reductive rocks. A proposed mechanism for the formation of inorganic hydrocarbons^{[20] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Keith2005)} is via natural analogs of the Fischer-Tropsch process known as the serpentinite mechanism or the serpentinite process ^{[21] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Szatmari)}^{[22] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Charlou2005)}.

$CH_4 + \frac{1}{2} O_2 \rarr 2 H_2 + CO$

$(2n+1)H_2 + nCO \rarr C_nH_{2n+2} + nH_2O$

Serpentinites are ideal rocks to host this process as they are formed from peridotites and dunites, rocks which contain greater than 80% olivine and usually a percentage of Fe-Ti spinel minerals. Most olivines also contain high nickel concentrations (up to several percent) and may also contain chromite or chromium as a contaminant in olivine, providing the needed transition metals.

However, serpentinite synthesis and spinel cracking reactions require hydrothermal alteration of pristine peridotite-dunite, which is a finite process intrinsically related to metamorphism, and further, requires significant addition of water. Serpentinite is unstable at mantle temperatures and is readily dehydrated to granulite, amphibolite, talc-schist and even eclogite. This suggests that methanogenesis in the presence of serpentinites is restricted in space and time to mid-ocean ridges and upper levels of subduction zones. However, water has been found as deep as 12 km,^{[23] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Smithson2000)} so water-based reactions are dependent upon the local conditions. Oil being created by this process in intracratonic regions is limited by the materials and temperature.

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Serpentinite synthesis

A chemical basis for the abiotic petroleum process is the serpentinization of peridotite, beginning with methanogenesis via hydrolysis of olivine into serpentine in the presence of carbon dioxide^{[24] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Charlou2005)}. Olivine, composed of Forsterite and Fayalite metamorphoses into serpentine, magnetite and silica by the following reactions, with silica from fayalite decomposition (reaction 1a) feeding into the forsterite reaction (1b).

Reaction 1a:
Fayalite + water → Magnetite + aquaeous silica + hydrogen

$3Fe_2SiO_4 + 2H_2O \rarr 2Fe_3O_4 + 3SiO_2 + 2H_2$

Reaction 1b:
Forsterite + aqueous silica → Serpentinite

$3Mg_2SiO_4 + SiO_2 + 2H_2O \rarr 2Mg_3[Si_2O_5(OH_4)]$

When this reaction occurs in the presence of dissolved carbon dioxide (carbonic acid) at temperatures above 500°C Reaction 2a takes place.

Reaction 2a:
Olivine + Water + Carbonic acid → Serpentine + Magnetite + Methane

$3(Fe,Mg)_2SiO_4 + nH_2O + HCO_3 \rarr 2Mg_3[Si_2O_5(OH_4)] + 2Fe_3O_4 + H_2O + CH_4$

However, reaction 2(b) is just as likely, and supported by the presence of abundant talc-carbonate schists and magnesite stringer veins in many serpentinised peridotites;

Reaction 2b:
Olivine + Water + Carbonic acid → Serpentine + Magnetite + Magnesite + Silica

$4(Fe,Mg)_2SiO_4 + nH_2O + HCO_3 \rarr 2Mg_3[Si_2O_5(OH_4)] + 2Fe_3O_4 + 2MgCO_3 + SiO_2 + H_2O$

The upgrading of methane to higher n-alkane hydrocarbons is via dehydrogenation of methane in the presence of catalyst transition metals (e.g. Fe, Ni). This can be termed spinel hydrolysis.

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Spinel polymerization mechanism

Magnetite, chromite and ilmenite are Fe-spinel group minerals found in many rocks but rarely as a major component in non-ultramafic rocks. In these rocks, high concentrations of magmatic magnetite, chromite and ilmenite provide a reduced matrix which may allow abiotic cracking of methane to higher hydrocarbons during hydrothermal events. Chemically reduced rocks are required to drive this reaction and high temperatures are required to allow methane to be polymerized to ethane. Note that reaction 1a, above, also creates magnetite.

Reaction 3:
Methane + Magnetite → Ethane + Hematite

$nCH_4 + nFe_3O_4 + nH_2O \rarr C_2H_6 + Fe_2O_3 + HCO_3 + H^+$

Reaction 3 results in n-alkane hydrocarbons, including linear saturated hydrocarbons, alcohols, aldehydes, ketones, aromatics, and cyclic compounds.^{[25] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Charlou2005)}

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Evidence from petroleum geochemistry

If the above mechanism for inorganic petroleum genesis is active and prevalent within the Earth crust and the abiogenic theory holds true, the geochemistry of petroleum deposits within the Earth’s crust should reflect this mechanism of formation. The geochemistry of petroleum deposits has been widely and deeply studied by oil companies and academia for more than a century in order to elucidate the origin of petroleum and develop predictive scientific models. Certain findings of this research can be used to interpret petroleum as being either of biogenic or abiogenic origin. These include biomarker chemicals, the optical activity of oils, chirality and the trace metal abundances of oils.

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Isotopic evidence

Methane is ubiquitous in crustal fluid and gas ^{[26] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Lollar2006)}. Research continues to attempt to characterise crustal sources of methane as biogenic or abiogenic using carbon isotope fractionation of observed gases (Lollar & Sherwood 2006). There are few clear examples of abiogenic methane-ethane-butane, as the same processes favor enrichment of light isotopes in all chemical reactions, whether organic or inorganic. δ¹³C of methane overlaps that of inorganic carbonate and graphite in the crust, which are heavily depleted in ¹²C, and attain this by isotopic fractionation during metamorphic reactions. One argument for abiogenic oil cites the high carbon depletion of methane as stemming from the observed carbon isotope depletion with depth in the crust. However, diamonds, which are definitively of mantle origin, are not as depleted as methane, which implies that methane carbon isotope fractionation is not controlled by mantle values. ^{[27] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Mello2005)} Helium isotope geochemistry is a clear indicator of mantle source within gases. Within the major precambrian shield there is no evidence of mantle helium in gases or groundwaters, which disproves the theory of continued outgassing of primordial methane and helium along structures in the Precambrian basement. Furthermore, there are few examples of primordial helium or mantle helium trapped within oil and gas occurrences. Helium trapped within most petroleum occurrences, such as the occurrence in Texas, is of a distinctly crustal character with an Ra ratio of less than 0.0001 that of the atmosphere.

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Biomarker chemicals

Certain chemicals found in naturally occurring petroleum contain chemical and structural similarities to compounds found within many living organisms. These include terpenoids, terpenes, pristane, phytane, cholestane, chlorins and porphyrins, which are large, chelating molecules in the same family as heme and chlorophyll. Materials which suggest certain biological processes include tetracyclic diterpane and oleanane. The presence of these chemicals in crude oil is assumed to be as a result of the inclusion of biological material in the oil. This is predicated upon the theory that these chemicals are released by kerogen during the production of hydrocarbon oils. However, since the advent of abiogenic theory, the veracity of these assumptions has been called into question and new lines of evidence used to provide alternative explanations.

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Odd-number carbon abundance

Members of the n-alkane series found in petroleum have a slightly greater abundance of odd-numbered carbon chains (propane, pentane, etc.) Likewise, linear carbohydrate molecules in living systems exhibit the same preference for odd carbon numbers. All mixtures of linear hydrocarbon chains, be they artificial, natural or biological, exhibit this tendency. It arises from the geometry of the covalent bond in linear molecules, so the greater abundances of odd-numbered hydrocarbons need not be of biological origin.

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Trace metals

Nickel (Ni), vanadium (V), lead (Pb), arsenic (As), cadmium (Cd), mercury (Hg) and others metals frequently occur in oils. Some heavy crude oils, such as Venezuelan heavy crude have up to 45% vanadium pentoxide content in their ash, high enough that it is a commercial source for vanadium. These metals are common in Earth's mantle, thus their compounds in oils are often called as abiomarkers. Analysis of 22 trace elements in 77 oils correlate significantly better with chondrite, serpentinized fertile mantle peridotite, and the primitive mantle than with oceanic or continental crust, and shows no correlation with seawater. ^{[28] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Szatmari)}

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Reduced carbon

Petroleum is composed mainly of n-alkanes. Sir Robert Robinson studied the chemical makeup of natural petroleum oils in great detail, and concluded that they were mostly far too hydrogen-rich to be a likely product of the decay of plant debris.^{[29] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_GoldUSGS)} Olefins, the unsaturated hydrocarbons, would have been expected to predominate by far in any material that was derived in that way. He also wrote: "Petroleum ... [seems to be] a primordial hydrocarbon mixture into which bio-products have been added." The presence of low-oxygen and hydroxyl-poor hydrocarbons in natural living media is supported by the presence of natural waxes (n=30+), oils (n=20+) and lipids in both plant matter and animal matter, for instance fats in phytoplankton, zooplankton and so on. These oils and waxes, however, occur in quantities too small to significantly affect the overall hydrogen/carbon ratio of biological materials.

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Geological framework

The proposed mechanism for abiogenic petroleum production is robust in theory, leaving aside ambiguous geochemical evidence. The abiogenic theory on the origin of petroleum seeks to explain the origin of commercial accumulations of petrochemicals via chemical mechanisms such as serpentinite catalysis. The geological observations which are used to support the abiogenic origin of petrochemical deposits should be evaluated on a case-by-case basis for each hydrocarbon deposit, with the presence of no one line of evidence used in isolation to infer genetic conclusions when equivocal or contradictory evidence is available. The geological observations proposed for the abiogenic theory are presented below, followed by investigation of several key deposits on a case by case basis to evaluate their genesis.

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Direct observations

The following are the direct tests of the abiogenic hypothesis of petroleum or impartial evidence generated by observations of the Earth which can be used to argue the theory for or against, and is presented as such.

The Siljan Ring meteorite crater, Sweden, was proposed by Thomas Gold as the most likely place to test the hypothesis because it was one of the few places in the world where the granite basement was cracked sufficiently (by meteorite impact) to allow oil to seep up from the mantle; furthermore it is infilled with a relatively thin veneer of sediment, which was sufficient to trap any abiogenic oil but was modelled as untenable for a biogenic origin of any oil (it had not developed the 'oil window' and structural traps typical of biogenic plays).

Drilling of the Siljan Ring with the Gravberg-1 7,500m borehole penetrated the lowest reservoirs. Hydrocarbons were found, though in an economically unviable form of sludge. It was proposed that the eight barrels of oil produced were from the diesel fuel based drilling fluid used to do the drilling, but the diesel was demonstrated to be not of the kind of oil found in the shaft. This well also sampled over 13,000 feet of methane-bearing inclusions. [30] (http://www.geology.wisc.edu/~pbrown/fi/pac6/mikesmith.html) To be safe, a second hole was drilled a few miles away with no diesel fuel based drilling fluid and this produced 15 tons of oil. [31] (http://web.archive.org/web/20021015163818/www.people.cornell.edu/pages/tg21/usgs.html)

Methanogenesis of groundwaters associated with ultramafic dykes and serpentinites, South Island of New Zealand
Methane outflows are common from drillholes within large Archaean serpentinised olivine adcumulate bodies, such as the Honeymoon Well complex, Yakabindie ultramafic, Mt Clifford dunite, in the Yilgarn Craton, Western Australia.
Direct observation of bacterial mats and fracture-fill carbonate and humin of bacterial origin in deep boreholes in Iran, Australia^{[32] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Bons2004)}, Sweden and Canada
Presence of deep-dwelling microbes in the Lechuguilla cave complex, New Mexico

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Example abiogenic deposits

Supergiant fields such as the Athabasca Tar Sands (Canada), Orinoco Heavy Oil Belt (Venezuela) and the Ghawar Field (Saudi Arabia) are good examples that have been interpreted as having been formed by abiogenic oils. This interpretation is based mostly on perceived deficiency in source rock volumes. Panhandle-Hugoton field in Kansas, USA is the most important gas field with commercial helium content. The White Tiger oil field in Vietnam has been proposed as an example of abiogenic oil because it is 4,000 m of fractured basement granite, at a depth of 5,000 m. ^{[33] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Sircar2004)}. However, others argue that it contains biogenic oil which leaked into the basement horst from conventional source rocks within the Cuu Long basin ^{[34] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Cuulong1)} ^{[35] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Brown2005)}.

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The geological argument for abiogenic oil

Given the known occurrence of methane and the probable catalysis of methane into higher atomic weight hydrocarbon molecules, the abiogenic hypothesis considers the following to be key observations in support;

The serpentinite synthesis, graphite synthesis and spinel catalysation models prove the process is viable ^{[36] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Szatmari)}^{[37] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Charlou2005)}
The association of oil deposits with key tectonic structures and plate boundaries, generally in arcs
The likelihood that abiogenic oil seeping up from the mantle is trapped beneath sediments which effectively seal mantle-tapping faults ^{[38] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Keith2005)}
Kudryavtsev's Rule that states petroleum can be found in all layers of a sedimentary basin; subsequently proven to be of limited application; it has also been stated as applying to hydrocarbon deposits, including natural gas, petroleum, and coal
Mass-balance calculations for supergiant oilfields which argue that the calculated source rock could not have supplied the reservoir with the known accumulation of oil, implying deep recharge (Kudryaavtsev, 1951)

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Incidental evidence

The proponents of abiogenic oil use several arguments which draw on a variety of natural phenomena in order to support the hypothesis

The ubiquitous presence of carbon, methane, ammonia and a variety of amino acids within extraterrestrial bodies such as meteorites, comets and on several moons within the Solar System. The Earth acquired a lot of carbon during its creation.
The modelling of some researchers which shows the Earth was accreted at relatively low temperature, thereby perhaps preserving primordial carbon deposits within the mantle, to drive abiogenic hydrocarbon production ^{[39] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Valley2002)}
The presence of natural gas eruptions, flames and explosions during earthquakes and during some volcanic eruptions, mainly in mud volcanoes.
The presence of vast quantities of methane hydrate (methane clathrate) within deep pelagic oozes within the oceans of the Earth, cited as evidence of abiogenic methane generation from serpentinitisation of the oceanic crust.
The presence of methane within the gases and fluids of mid-ocean ridge spreading centre hydrothermal fields^{[40] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Chapelle2002)}
The presence of intraplate earthquakes and deep focus earthquakes, apparently caused by movement of vast quantities of mantle methane and hydrocarbons
The presence of tiny diamondoids in oils. Diamondoids probably form at high pressures in the earth's mantle and they migrate together with oil and gas to low pressures in the crust.
The presence of Hydrocarbon Lakes on Saturns Moon, Titan

[edit]

The geological argument against

Key arguments against chemical reactions, such as the serpentinite mechanism, as being the major source of hydrocarbon deposits within the crust are;

The lack of available pore space within rocks as depth increases; especially within the mantle
The presence of no commercial hydrocarbon deposits within the crystalline shield areas of the major cratons especially around key deep seated structures which are predicted to host oil by the abiogenic theory ^{[41] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Mello2005)}
Limited evidence that major serpentinite belts underlie continental sedimentary basins which host oil
Lack of conclusive proof that carbon isotope fractionation observed in crustal methane sources is entirely of abiogenic origin (Lollar et al. 2006)^{[42] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Lollar2006)}
Mass balance problems of supplying enough carbon dioxide to serpentinite within the metamorphic event before the peridotite is fully reacted to serpentinite
Drilling of the Siljan Ring failed to find commercial quantities of gas^{[43] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Mello2005)}, thus disproving Kudryavtsev's Rule and failing to locate the predicted abiogenic gas
- Helium in the Siljan Gravberg-1 well was depleted in ³He and not consistent with a mantle origin^{[44] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Jeffrey1988)}
The distribution of sedimentary basins is caused by plate tectonics, with sedimentary basins forming on either side of a volcanic arc, which explains the distribution of oil within these sedimentary basins

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Arguments against the incidental evidence

Gas ruptures during earthquakes are more likely to be sourced from biogenic methane generated in unconsolidated sediment from existing organic matter, released by earthquake liquefaction of the reservoir during tremors
The presence of methane hydrate is arguably produced by bacterial action upon organic detritus falling from the littoral zone and trapped in the depth due to pressure and temperature
The likelihood of vast concentrations of methane in the mantle is very slim, given mantle xenoliths have negligible methane in their fluid inclusions; conventional plate tectonics explains deep focus quakes better, and the extreme confining pressures invalidate the theory of gas pockets causing quakes
Further evidence is the presence of diamond within kimberlites and lamproites which sample the mantle depths proposed as being the source region of mantle methane (by Gold et al). It is arguable from oxygen fugacity and carbon phase stability models that reduced carbon in the mantle is either in the form of graphite or diamond, not methane, and that oxidized carbon is present as carbon dioxide.

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History of abiogenic theory

The abiogenic petroleum theory was founded upon several archaic interpretations of geology which stem from early 19th century notions of magmatism (which at the time was attributed to sulfur fires and bitumen burning underground) and of petroleum, which was seen by many to fuel volcanoes. Indeed, Wernerian appreciation of basalts at times saw them as solidified oils or bitumen. While these notions have been disabused, the basic notion that petroleum is associated with magmatism has persisted. The chief proponents of what would become the abiogenic theory were Mendeleev^{[45] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Mendeleev)} and Berthelot. Russian geologist Nikolai Alexandrovitch Kudryavtsev was the first to propose the modern abiotic theory of petroleum in 1951. He analyzed the geology of the Athabasca Tar Sands in Alberta, Canada and concluded that no "source rocks" could form the enormous volume of hydrocarbons (estimated today 1.7 trillions barrels), and that therefore the most plausible explanation is abiotic deep petroleum. However, humic coals have been proposed for the source rocks by Stanton (2005) (http://www.searchanddiscovery.com/documents/2004/stanton/index.htm).

Although this theory is supported by geologists in Russia and Ukraine, it has recently begun to receive attention in the West, where the biogenic petroleum theory is still believed by the vast majority of petroleum geologists. Kudryavtsev's work was continued by many Russian researchers — Petr N. Kropotkin, Vladimir B. Porfir'ev, Emmanuil B. Chekaliuk, Vladilen A. Krayushkin, Georgi E. Boyko, Georgi I. Voitov, Grygori N. Dolenko, Iona V. Greenberg, Nikolai S. Beskrovny, Victor F. Linetsky and many others. Astrophysicist Thomas Gold was one of the abiogenic theory's most prominent proponents in recent years in the West, until his death in 2004. Dr. Jack Kenney of Gas Resources Corporation^{[46] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kenney2)}^{[47] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kenney2001)}^{[48] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kenney2002)} is perhaps the foremost proponent in the West. The theory receives continued attention in the media as well as in scientific publications.

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Petroleum origin, peak oil, and politics

Many aspects of the abiogenic theory were developed in the former Soviet Union by Russian and Ukrainian scientists during the Cold War. Some proponents see a pro-Western bias in the promotion of the biogenic theory. Thus, in addition to the scientific merits of competing hypothoses, political and economic considerations often influence discussions of petroleum origins. The topic of the origin of petroleum is also linked to discussions of projected declines in petroleum production, variously referred to as "peak oil" or "Hubbert's peak". The abiogenic theory stands in contrast to that of Peak Oil, which presumes a fixed and dwindling supply of oil that was formed through biological processes. Some environmentalists accuse abiogenic theory supporters of a "cornucopian" worldview. They claim that such a view incorrectly sees no limits to exploitation of petroleum supplies while simultaneously ignoring potential consequences of petroleum consumption such as global warming. Conversely, some supporters of the abiogenic theory accuse their opponents of an unwarranted Malthusian viewpoint that needlessly limits the use of hydrocarbons as an energy source and artificially inflates oil prices.

Independent of whether massive hydrocarbon reserves exist deep in the crust, they are unattainable in the short term. Additionally, oil wells are being drilled down to depths of 10 km, just shy of the world record of 12 km set by the Kola Superdeep Borehole in the Siberian Craton. Thus the "deep reservoirs" of Gold et al. are being tested successfully according to biogenic models of petroleum occurrence. Considering the dominance of the biogenic origin theory in the exploration industry, new oil discoveries based on abiogenic theory may be slow in coming. The ASPO predicts that global oil production will peak in 2007, while some other organizations such as the USGS pick as late as 20 years later. If it ever does happen, there will be serious economic ramifications. For this reason, as well as concerns about global warming, development of nuclear power and renewable energy sources continues at an accelerating pace. These aspects of the controversy may be seen in many of the online articles in the External links section below.

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State of current research

Currently there is little direct research on abiogenic petroleum or experimental studies into the synthesis of abiogenic methane. However, several research areas, mostly related to astrobiology and the deep microbial biosphere and serpentinite reactions, continue to provide insight into the contribution of abiogenic hydrocarbons into petroleum accumulations.

ocean floor hydrothermal vents as in the Lost City hydrothermal field;
Mud volcanoes and the volatile contents of deep pelagic oozes and deep formation brines
mantle peridotite serpentinization reactions and other natural Fischer-Tropsch analogs
Primoridal hydrocarbons in meteorites, comets, asteroids and the solid bodies of the solar system
- Primordial or ancient sources of hydrocarbons or carbon in Earth ^{[49] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Scott2004)}^{[50] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Stachel2006)}
isotopic studies of groundwater reservoirs, sedimentary cements, formation gases and the composition of the noble gases and nitrogen in many oil fields
the geochemistry of petroleum and the presence of trace metals related to Earth's mantle (Ni, V, Cd, As, Pb, Zn, Hg and others)

Similarly, research into the deep microbial hypothesis of hydrocarbon generation is advancing as part of the attempt to investigate the concept of panspermia and astrobiology, specifically using deep microbial life as an analog for life on Mars. Research applicable to deep microbial petroleum theories includes

Research into how to sample deep reservoirs and rocks without contamination
Sampling deep rocks and measuring chemistry and biological activity ^{[51] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Kieft2005)}
Possible energy sources and metabolic pathways which may be used in a deep biosphere ^{[52] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Lin2005)}^{[53] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Lollar2006)}
Investigations into the reworking primordial hydrocarbons by bacteria and their effects on carbon isotope fractionation

The abiogenic origin of petroleum has recently been reviewed in detail by Glasby ^{[54] (http://www.peswiki.com/index.php/PowerPedia:Petroleum#endnote_Glasby2006)} and shown to be invalid on a number of counts.

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Means of producing oil

As oil prices continue to escalate, other alternatives to producing oil have been gaining importance. The best known such methods involve extracting oil from sources such as oil shale or tar sands. These resources are known to exist in large quantities; however, extracting the oil at low cost without negatively impacting the environment remains a challenge. It is also possible to transform natural gas or coal into oil (or, more precisely, the various hydrocarbons found in oil). The best-known such method is the Fischer-Tropsch process, It was a concept pioneered in Nazi Germany when imports of petroleum were restricted due to war and Germany found a method to extract oil from coal. It was known as Ersatz ("substitute" in German), and accounted for nearly half the total oil used in WWII by Germany. However, the process was used only as a last resort as naturally occurring oil was much cheaper. As crude oil prices increase, the cost of coal to oil conversion becomes comparatively cheaper. The method involves converting high ash coal into synthetic oil in a multistage process. Ideally, a ton of coal produces nearly 200 liters (1.25 bbl, 52 US gallons) of crude, with by-products ranging from tar to rare chemicals.

Currently, two companies have commercialised their Fischer-Tropsch technology. Shell in Bintulu, Malaysia, uses natural gas as a feedstock, and produces primarily low-sulfur diesel fuels. Sasol in South Africa uses coal as a feedstock, and produces a variety of synthetic petroleum products. The process is today used in South Africa to produce most of the country's diesel fuel from coal by the company Sasol. The process was used in South Africa to meet its energy needs during its isolation under Apartheid. This process has received renewed attention in the quest to produce low sulfur diesel fuel in order to minimize the environmental impact from the use of diesel engines. An alternative method is the Karrick process, which converts coal into crude oil, pioneered in the 1930s in the United States. More recently explored is thermal depolymerization (TDP). In theory, TDP can convert any organic waste into petroleum.

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Extraction

Locating an oil field is the first obstacle to be overcome. Today, geologists use seismic surveys to search for geological structures that may form oil reservoirs. Other instruments such as gravimeters and magnetometers are also sometimes used in the search for petroleum. Generally, the first stage in the extraction of crude oil is to drill a well into the underground reservoir. When an oil bearing structure has been tapped, the wellsite geologist (known on the rig as the "mudlogger") will note its presence. Historically, in the USA, some oil fields existed where the oil rose naturally to the surface, but most of these fields have long since been depleted, except for certain remote locations in Alaska. Often many wells (called multilateral wells) are drilled into the same reservoir, to ensure that the extraction rate will be economically viable. Also, some wells (secondary wells) may be used to pump water, steam, acids or various gas mixtures into the reservoir to raise or maintain the reservoir pressure, and so maintain an economic extraction rate.

If the underground pressure in the oil reservoir is sufficient, then the oil will be forced to the surface under this pressure. Gaseous fuels, natural gas or water are usually present, which also supply needed underground pressure. In this situation it is sufficient to place a complex arrangement of valves (the Christmas tree) on the well head to connect the well to a pipeline network for storage and processing. This is called primary oil recovery. Usually, only about 20% of the oil in a reservoir can be extracted this way.

The amount of oil that is recoverable is determined by a number of factors including the permeability of the rocks, the strength of natural drives (the gas present, pressure from adjacent water or gravity), and the viscosity of the oil. When the reservoir rocks are "tight" such as shale, oil generally cannot flow through but when they are permeable such as in sandstone, oil flows freely. The flow of oil is often helped by natural pressures surrounding the reservoir rocks including natural gas that may be dissolved in the oil, natural gas present above the oil, water below the oil and the strength of gravity. Oils tend to span a large range of viscosity from liquids as light as gasoline to heavy as tar. The lightest forms tend to result in higher production rates.

Over the lifetime of the well the pressure will fall, and at some point there will be insufficient underground pressure to force the oil to the surface. If economical, and it often is, the remaining oil in the well is extracted using secondary oil recovery methods (see: energy balance and net energy gain). Secondary oil recovery uses various techniques to aid in recovering oil from depleted or low-pressure reservoirs. Sometimes pumps, such as beam pumps and electrical submersible pumps (ESPs), are used to bring the oil to the surface. Other secondary recovery techniques increase the reservoir's pressure by water injection, natural gas reinjection and gas lift, which injects air, carbon dioxide or some other gas into the reservoir. Together, primary and secondary recovery allow 25% to 35% of the reservoir's oil to be recovered.

Tertiary oil recovery reduces the oil's viscosity to increase oil production. Tertiary recovery is started when secondary oil recovery techniques are no longer enough to sustain production, but only when the oil can still be extracted profitably. This depends on the cost of the extraction method and the current price of crude oil. When prices are high, previously unprofitable wells are brought back into production and when they are low, production is curtailed. Thermally enhanced oil recovery methods (TEOR) are tertiary recovery techniques that heat the oil and make it easier to extract. Steam injection is the most common form of TEOR, and is often done with a cogeneration plant. In this type of cogeneration plant, a gas turbine is used to generate electricity and the waste heat is used to produce steam, which is then injected into the reservoir. This form of recovery is used extensively to increase oil production in the San Joaquin Valley, which has very heavy oil, yet accounts for 10% of the United States' oil production. In-situ burning is another form of TEOR, but instead of steam, some of the oil is burned to heat the surrounding oil. Occasionally, detergents are also used to decrease oil viscosity. Tertiary recovery allows another 5% to 15% of the reservoir's oil to be recovered.

Drilling mud, also called drilling fluid, is a lubricant used while drilling oil and natural gas wells and in exploration drilling rigs. The three primary purposes of drilling mud or drilling fluids are to:

Remove cuttings from the formation produced by the bit at the bottom of the hole and carry them to the surface. This is achieved by adjusting the rheology of the mud system.
Lubricate and cool the drill bit during operation as friction causes high temperatures down-hole that can limit tool life and performance.
Maintain hydrostatic equilibrium so that fluids and gas from the formation do not enter the well bore causing the well to flow, kick or blow out. This is achieved by adjusting the mud weight (density). High-density additives (barite, hematite) are used for preparation of kill-weight fluids, which create hydrostatic pressure that prevents water entering the well or hold the oil/gas inside, prevent a blowout and to physically stabilize the formation.

Other characteristics are considered important in modern drilling. Some of these include:

Safe for the environment
Prevent dispersion of reactive clays (gumbo)
Ability to seal formation fractures/voids
Non abrasive to tools and rig equipment

Offshore mud systems run in pressure from 5,000 to 7,500 psi.

On a drilling rig pumping it with mud pumps through the drill string where it sprays out of nozzles on the drill bit (cleaning the bit in the process), the mud then travels back up the annular space between the drill string and the sides of the hole being drilled, up through the surface casing, and emerges at the surface. Cuttings are then filtered out at the shale shaker and the mud enters the mud pits. The mud is then pumped back down and is continuously recirculated. The mud is treated periodically in the mud pits to give it properties that optimize and improve drilling efficiency.

Water-based drilling mud may consist of bentonite clay (gel) with additives such as barium sulfate (barite), calcium carbonate (chalk) or hematite. Various thickeners are used to influence the viscosity of the fluid, eg. Xanthan Gum, guar gum, glycol, carboxymethylcellulose, polyanionic cellulose (PAC), or starch. In turn, deflocculants are used to reduce viscosity of clay-based muds; anionic polyelectrolytes (eg. acrylates, polyphosphates, lignosulfonates (Lig) or tannic acid derivates such as Quebracho) are frequently used. Red mud was the name for a Quebracho-based mixture, named after the color of the red tannic acid salts; it was commonly used in 1940s to 1950s, then was obsoleted when lignosulfates became available. Many other chemicals are also used to maintain or create some of the properties listed in the section titled "Purpose".

One classification scheme for drilling fluids is based on their composition, and divides them to water-base, non-water (oil, olefin, or other synthetic fluid) base, and gaseous, or pneumatic. Oil Based and Synthetic Based muds are frequently classified separately due to the vast differences in regulations when using them.

The slang name given to an oil field service company individual who is charged with maintaining a drilling fluid or completion fluid system on an oil and/or gas drilling rig. This individual typically works for the company selling the chemicals for the job and is specifically trained with those products, though independent mud engineers are still common. The work schedule of the mud engineer or Drilling Fluids Engineer, as he or she is more properly called these days, is usually fairly strenuous, as are most jobs in this industry. Until a few years ago, the "mud engineer" rarely worked a set schedule and, if resident on an offshore installation, may have been on call for 24 hours a day, with few (if any) days off each month. With the advent some 15 years ago in Northern Europe, of having two mud engineers offshore due to Health, Safety and Environmental regulations and working hours restrictions in more advanced countries, the offshore mud engineer rarely works more than the normal 12 hour shift. On land, however, there usually still is only one mud engineer assigned and most of the time, he is allocated to more than one drilling rig. The economics of land-drilling demands that the land-engineer spends a greater part of the day driving from rig to rig, testing the drilling or completion fluids, making recommendations for its maintenance and then repeating the process at another rig(s). A daily stop like this, usually for an hour or two, is typically called a "Drive-By". A 24 hour assignment to a single land rig is called a "sitting" job.

Offshore drilling, with new technology and high total day costs for the operation, have wells being drilled extremely fast and day rates for operations have increased. Any down time is frowned upon and having two mud engineers makes economical sense to sensible oil companies, to prevent down time due to drilling fluid difficulties. Two mud engineers also reduce insurance loading to oil companies for possible environmental damage that oil companies are responsible for during their license to drill and produce. The cost of the drilling fluid is typically about 10% (may vary greatly) of the total cost of well construction. This large cost overhead places a demand on the competency of the mud engineer. Large cost savings can result when the mud engineer adequately performs his job. The mud engineer is not to be confused with a mudlogger, a service personnel who monitors gas from the mud and collects wellbore samples.

The compliance engineer is the most common name for a relatively new position in the oil field, emerging around 2002 due to new environmental regulations on Synthetic Mud. Previously synthetic mud was regulated in the same way as water based mud and could be disposed of into offshore waters as needed due to its low toxicity to marine mammals. New regulations restrict the amount of synthetic oil that can be discharded as a percentage by weight of synthetic fluid on cuttings that have been drilled and are being discharged overboard. For olefin based fluids the limit is 6.9%, for ester based fluids it is a bit higher. These new regulations created a significant amount of additional work in the form of tests needed to determine the "ROC" or retention on cuttings, sampling to determine the percentage of crude oil in the drilling mud, and extensive documention to substantiate all of this.

A new monthly toxicity test is also now performed to determine sediment toxicity. The species used is Leptocheirus plumulosus picture (http://www.fisheries.vims.edu/ctils/prey2/lplumulosus.png). Various concentrations of the drilling mud are added to the environment of the Leptochirus plumulosus to determine its effect on the animals. This is controversial for two reasons:

These animals are not native to many of the areas regulated by them, including the Gulf of Mexico
The test has a very large standard deviation and samples that fail horribly may pass easily upon retesting.

Directional drilling (sometimes known as slant drilling outside the oil industry) is the science of drilling non-vertical wells. Directional drilling can be broken down into three main groups; Oilfield Directional Drilling, Utility Installation Directional Drilling (commonly known as H.D.D./Horizontal Directional Drilling) and in-seam directional drilling (Coal-Bed methane).

A number of prerequisites were necessary before this suite of technologies could become productive. Probably the first requirement was the realisation that oil wells (or water wells, but since their depths are normally trivial, the development was essentially done in the oil industry) are not necessarily vertical. This realisation was quite slow, and didn't really grasp the attention of the oil industry until the late 1920s when there were several cases of lawsuits alleging that a well drilled from a rig on one person's property had actually crossed the boundary and was penetrating a reservoir on an adjacent property. Initially proxy evidence such as changes in production from pre-existing wells was accepted, but such cases fuelled the development of small diameter tools capable of surveying wells as (or during) their drilling.

Measuring the inclination of a wellbore (its deviation from the vertical) is comparatively simple—one needs a pendulum of some sort. But measuring the azimuth (direction with respect to the geographic grid in which the wellbore is running from the vertical) was much more difficult. In certain circumstances magnetic fields could be used, but were open to the influence of the metalwork used to line wellbores, as well as the metalwork used in drilling equipment itself. The big step forward was in the modification of small gyroscopic compasses by the Sperry company, who were making similar compasses for aeronautical navigation. Sperry did this work under contract to Sun Oil (who were involved in a lawsuit as described above), and a spin-off company was formed under the name "Sperry Sun", which brand continues to this day, absorbed into Halliburton, the second-largest oil services company.

Prior experience with rotary drilling had established a number of principles for the configuration of drilling equipment down hole ("Bottom Hole Assembly" or "BHA") that would be prone to "drilling crooked hole" (initial accidential deviations would be increased away from the vertical). Counter-experience had also given these early directional drillers ("DD's", on many whiteboards on many rigs around the world to this day) principles of BHA design and drilling practice which would help bring a crooked hole back towards the vertical. Combined, these survey tools and BHA designs made directional drilling possible, but it was perceived to be decidedly arcane. Some DDs allegedly took a perverse delight in making it sound more arcane than it actually was - using Ouija boards to perform calculations instead of slide rules for example. Actually the Ouija board performs simple trigonometric functions quickly and in a somewhat graphic format. [citation needed]

The next major advance was in the 1970s, when downhole drilling motors became commonplace. These allowed the bit to be rotated on the bottom of the hole, while most of the drill pipe was held stationary (power to the motor is supplied by the hydraulic effect of the drilling fluid pumped down the inside of the drill pipe). Including a piece of bent pipe (a "bent sub") between the stationary drill pipe and the top of the motor allowed the direction of the wellbore to be changed without needing to pull all the drill pipe out and place another whipstock. Coupled with the development of MWD (mud pulse telemetry or EM telemetry, which allows tools down hole to send data back to the surface without disturbing routine drilling operations), directional drilling got much easier. Certain profiles could not be drilled without the drill string in rotation at all times.

The most recent major advance in art of directional drilling has been the development of a range of Rotary Steerable tools from various companies which allow 3 dimensional control of the bit without shutting down the drill string rotation. These tools (PowerDrive from Schlumberger, AutoTrak from Baker Hughes and GeoPilot from Sperry Drilling Services/Halliburton) have almost automated the process of drilling highly deviated holes in the ground. But they are not cheap, so more traditional directional drilling will continue for the foreseeable future.

Until very recently the drive towards lowering the high cost of these devices has been led from outwith the "Big Three" oilfield service companies by individual entrepreneurs and inventors working effectively alone. However, with the advent of a recent acquisition by Halliburton, this is gradually changing and the drive to introduce a viable low-cost Rotary Steerable System is on. Directional wells are drilled for a number of purposes:

Increasing the exposed section length through the reservoir by drilling through the reservoir at an angle
Drilling into the reservoir where vertical access is difficult or not possible. For instance an oilfield under a town, under a lake, or underneath a very difficult to drill formation
Allowing more wellheads to be grouped together on one surface location can allow fewer rig moves, less surface area disturbance, and make it easier and cheaper to complete and produce the wells. For instance on an oil platform or jacket offshore, where up to about 40 wells can be grouped together. The wells will fan out from the platform into the reservoir deep below. This concept is also being applied to land wells, allowing multiple subsurface locations to be reached using only one leveled-out pad, reducing the environmental impact.
Drilling "relief wells" to relieve the pressure of a well which is producing without restraint (blown out). In this scenario, another well could be drilled starting at a safe distance away from the blow out, but intersecting the troubled wellbore beneath the surface. Then, heavy fluid (kill fluid) could be pumped in the new relief wellbore to suppress the high pressures in the original wellbore causing the blowout.

Most directional drillers are given a well path to follow that is predetermined by engineers and geologists before the actual drilling commences. When the directional driller actually starts the drilling process, he relies on a mudlogger to tell him if he is in the "zone", i.e. the target area where the hydrocarbons lay. Without the mudlogger to navigate the drilling process, the well may run into dry rock which renders the entire process useless.

With modern technology great feats can be achieved. Whereas 20 years ago wells drilled at 60 degrees through the reservoir were achieved, horizontal drilling is now quite normal. However, drilling out far from the surface location is still something that requires careful planning and design; the current record holders manage wells of over 10 km (6 miles) away from the surface location at a depth of only 1600–2600 m (5,200–8,500 ft). These are all wells drilled from a land location to underneath the sea (Wytch Farm (BP), south coast of England, ARA (Total), south coast of Argentina (TFE) Dieksand (RWE), north coast of Germany, and most recently Chayvo (ExxonMobil), east coast of Sakhalin Island, Russia. In 1990 Iraq accused Kuwait of stealing Iraq's oil through slant drilling.

A mudlogger is the common oilfield slang name for a geologist primarily tasked with gathering data and collecting samples from the drilling mud during the drilling of a well, and organizing this information in the form of a graphic log that shows the data charted in relation to wellbore depth. Mudloggers observe and interpret the indicators in the mud returns during the drilling process. The mudlogger logs at regular intervals, properties such as drilling rate, mud weight, flowline temperature, natural gas content and type, oil indicators, pump pressure, pump rate, lithology (rock type) of the drill cuttings, and various other items of interest. The job of a mudlogger requires a good deal of diligence and attention. Sampling the drill cuttings must be performed at proper intervals, for example, and can be difficult during rapid drilling. Another important task of the mudlogger is to monitor gas levels and notify other personnel on the rig when gas levels may be reaching dangerous levels. High gas levels create a fire/explosion hazard and may require the suspension of nearby work, such as welding. High gas levels may also indicate circumstances downhole that need to be addressed to avoid a dangerous well blowout. Mudlogging is an important component of formation evaluation.

In this modern era, the mudlogger is commonly a degreed geologist, but small drilling companies may task other personnel with these duties. The mudlog geologist also advises the drilling manager at the well when zones of interest have been penetrated and lets the drilling personell know when the well has reached its final stages.

Roughneck (or ruffneck) is a slang term for an unskilled or slightly skilled labourer in a number of industries. In particular, is the official name of a semi-skilled role on a North American oil rig. Originally the term was used in the travelling carnivals of 19th century America, almost interchangeably with roustabout. By the 1930s the terms had transferred to the oil drilling industry. In the United Kingdom oil industry (1970s onwards) the term roughneck was specifically for the moderately skilled people who worked on the drill floor of a drilling rig, actually handling the specialised equipment for drilling, pressure control, etc. By contrast, a roustabout would perform more general labour, such as loading and unloading cargo from crane baskets, and being assistants to the welder, mechanic, electrician or other skilled workers. Usage in America appears to have been similar, and the terms had spread to the rest of the world at least by the mid-1990s.

In the North American oilfields, roughneck is one of several roles in the hierarchy on an oil rig. A roughneck's duties could include anything involved with the connecting and "tripping" of pipe down the well bore.

The roughneck crew of a land-based oil rig can be furthered divided into several positions:

Driller: The head or boss of the crew. Responsible for the actual control of the rigs machinery during drilling operation.
Derrickhand: Responsible for the "mud" and catching samples, the water+barite+bentonite+chemical mixture used in drilling oil wells. Also assumes the position in the derrick, usually 60 to 90 feet off the ground, while "tripping pipe."
Motorhand: Responsible for the maintenance of the various engines, water pumps, waterlines, steamlines, boilers, and various other machinery incorporated into the rig.
Chainhand: Works the "make-up" or "back-up" tongs on the right side of the drilling floor. "Throws chain" (illegal but very common on drilling rigs) while tripping in the hole.
Worm: Usually the lowest member of the drilling crew. Works the "break-out" or "lea