zhurova_t_v_angliiskii_yazyk_dlya_studentovgeologov (1)

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produced from the hydrocarbon accumulation (reservoir) through an oil well. If not trapped, the hydrocarbons may migrate up to the surface, where they can be seen as seeps.

Source-rock, oil and gas samples from wells and outcrops are analyzed in different ways to assess the composition, quality and thermal maturity, i.e. what type and how much hydrocarbons the source rocks may generate, and how far in this process the source rocks have come. Hydrocarbons are correlated to their respective source rocks by comparing the contents of specific organic molecules (biomarkers) in the hydrocarbons and in extracts of the source rock.

The results from such analyses are evaluated in the context of the geological and thermal history of the sedimentary basin. By doing this, a basins petroleum system may be defined in time and space. This knowledge is important when exploring for oil and gas.

Oil and gas (hydrocarbons) are valuable resources hidden in the subsurface of the Earth.

Geologists and geophysicists use a myriad of advanced techniques in order to find commercial accumulations of oil and gas.

Oils from the Norwegian North Sea

The investigation of organic rich rocks (hydrocarbon source rocks) and their geological history is important to understand the petroleum system in a sedimentary basin. The basic elements of a petroleum system consists of a source rock, a porous and permeable reservoir rock and a tight cap rock.

When organic rich rocks (usually shales containing 4-20 weight % organic matter) are buried, they are subjected to increasing temperatures and pressures (typically 30 degrees Celsius/km).

At about 60 degrees Celsius, oil begins to form in the source rock due to the thermogenic breakdown (cracking) of organic matter (kerogen).

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The oil window is a temperature dependant interval in the subsurface where oil is generated and expelled from the source rocks. The oil window is often found in the 60-120 degree Celsius interval (aprox. 2-4 km depth), while the corresponding gas window is found in the 100-200+ degree Celsius interval (3-6 km depth).

After expulsion from the source rock, the oil and gas migrates upwards through permeable rocks (sandstones) or fractures until they are stopped by a tight, nonpermeable layer of rock, like a shale. In this case, they are trapped, and may be produced from the hydrocarbon accumulation (reservoir) through an oil well. If not trapped, the hydrocarbons may migrate up to the surface, where they can be seen as seeps.

Source-rock, oil and gas samples from wells and outcrops are analyzed in different ways to assess the composition, quality and thermal maturity, i.e. what type and how much hydrocarbons the source rocks may generate, and how far in this process the source rocks have come. Hydrocarbons are correlated to their respective source rocks by comparing the contents of specific organic molecules (biomarkers) in the hydrocarbons and in extracts of the source rock.

The results from such analyses are evaluated in the context of the geological and thermal history of the sedimentary basin. By doing this, a basins petroleum system may be defined in time and space. This knowledge is important when exploring for oil and gas.

Petroleum

Petroleum (Latin Petroleum f. Latin petra f. Greek πέτρα - rock + Latin oleum f. Greek έλαιον - oil) or crude oil is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds. The proportion of hydrocarbons in the mixture is highly variable and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumen.

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 varies over fairly narrow limits as follows:

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 generally floats

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underneath it. Crude oil may also be found in semi-solid form mixed with sand, as in the Athabasca oil sands in Canada, where it may be referred to as crude bitumen.

Petroleum is used mostly, by volume, for producing fuel oil and gasoline (petrol), both important "primary energy" sources. 84% by volume of the hydrocarbons present in petroleum is converted into energy-rich fuels (petroleumbased fuels), including gasoline, diesel, jet, heating, and other fuel oils and liquefied petroleum gas.

Due to its high energy density, easy transportability and relative abundance, it 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 140 km³ (1.2 trillion barrels) without oil sands, or 440 km³ (3.74 trillion barrels) with oil sands. However, oil production from oil sands is currently severely limited. Consumption is currently around 84 million barrels per day, or 3.6 km³ per year. Because the energy return over energy invested (EROEI) ratio of oil is constantly falling as petroleum recovery gets more difficult, recoverable oil reserves are significantly less than total oil-in-place. At current consumption levels, and assuming that oil will be consumed only from reservoirs, known recoverable reserves would be gone around 2039, potentially leading to a global energy crisis. However, there are factors which may extend or reduce this estimate, including the rapidly increasing demand for petroleum in China, India, and other developing nations; new discoveries; energy conservation and use of alternative energy sources; and new econonomically viable exploitation of nonconventional oil sources.

Oil and gas (hydrocarbons) are valuable resources hidden in the subsurface of the Earth.

Geologists and geophysicists use a myriad of advanced techniques in order to find commercial accumulations of oil and gas.

The investigation of organic rich rocks (hydrocarbon source rocks) and their geological history is important to understand the petroleum system in a sedimentary basin. The basic elements of a petroleum system consists of a source rock, a porous and permeable reservoir rock and a tight cap rock.

When organic rich rocks (usually shales containing 4-20 weight % organic matter) are buried, they are subjected to increasing temperatures and pressures (typically 30 degrees Celsius/km).

Biogenic theory

Most geologists view crude oil and natural gas as the product of compression and heating of ancient organic materials over geological time. Oil is formed from the preserved remains of prehistoric zooplankton and algae which have been settled to the sea (or lake) bottom in large quantities under anoxic conditions. Terrestrial plants,

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on the other hand, tend to form coal. 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 organic matter to chemically change during diagenesis, 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.

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 (the Athabasca Oil Sands is one example).

Hydrocarbon trap.

Because most hydrocarbons are lighter than rock or water, these often migrate upward through adjacent rock layers until they either reach the surface or become trapped beneath impermeable rocks, within porous rocks called reservoirs. However, the process is not straightforward since it is influenced by underground water flows, and oil may migrate hundreds of kilometers horizontally or even short distances downward before becoming trapped in a reservoir. Concentration of hydrocarbons in a trap forms an oil field, from which the liquid can be extracted by drilling and pumping.

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) 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.

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. Oil companies are looking for 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,

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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 in the 1800s. Gold's hypothesis was that hydrocarbons of purely inorganic origin exist in the planet Earth. Since most petroleum hydrocarbons are less dense than aqueous pore fluids, Gold proposed that they migrate upward into oil reservoirs through deep fracture networks. Although biomarkers are found in petroleum that most petroleum geologists interpret as indicating biological origin, Gold proposed that Thermophilic, rock-dwelling microbial life-forms are responsible for their presence.

This hypothesis is accepted by only a small minority of geologists and petroleum engineers, and to date has not been particularly successful in predicting petroleum deposits on earth,[8] so it is considered a fringe theory. Methods of making hydrocarbons from inorganic material have been known for some time, however no substantial proof exists that this is happening on any significant scale in the earth's crust for any hydrocarbon other than methane (natural gas). Abundant liquid methane (though not any form of petroleum) has been inferred to be present on Titan, a moon of Saturn, by research data from NASA's Cassini probe. However, Titan has completely different geology from Earth, and is 1,200,000,000 kilometres (750,000,000 mi) away, an excessively long distance to ship what is theorized to be mostly liquefied natural gas.

Natural gas

Natural gas is a gaseous fossil fuel consisting primarily of methane but including significant quantities of ethane, propane, butane, and pentane - heavy hydrocarbons removed later on as condensate as well as carbon dioxide, nitrogen, helium and hydrogen sulfide. It is found in oil fields (associated) either dissolved or isolated in natural gas fields (non associated), and in coal beds (as coalbed methane). When methane-rich gases are produced by the anaerobic decay of nonfossil organic material, these are referred to as biogas. Sources of biogas include swamps, marshes, and landfills (see landfill gas), as well as sewage sludge and manure

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by way of anaerobic digesters, in addition to enteric fermentation particularly in cattle.

Since natural gas is not a pure product, when non associated gas is extracted from a field under supercritical (pressure/temperature) conditions, it may partially condense upon isothermic depressurizing--an effect called retrograde condensation. The liquids thus formed may get trapped by depositing in the pores of the gas reservoir. One method to deal with this problem is to reinject dried gas free of condensate to maintain the underground pressure and to allow reevaporation and extraction of condensates.

Natural gas is often informally referred to as simply gas, especially when compared to other energy sources such as electricity. Before natural gas can be used as a fuel, it must undergo extensive processing to remove almost all materials other than methane. The by-products of that processing include ethane, propane, butanes, pentanes and higher molecular weight hydrocarbons, elemental sulfur, and sometimes helium and nitrogen.

Bibliography

1.Людвигова Е.В. Книга для чтения по английскому языку: учеб. пособие для технических вузов / Е.В. Людвигова, Н.В. Владинец, И.А. Кальянц. – М.: Высшая школа, 1982. – 109 с.

2.Мильничук В.С. Общая геология: учебник для вузов / В.С. Мильничук, М.С. Арабаджи. – 2е изд., перераб.и доп. – М.: Недра, 1989. – 333 с.: ил.

3.Пичугина Т. Метаморфозы лавы / Т. Пичугина // Вокруг Света. – 2007. – №

2/2797. – С. 6-14.

4.Wikipedia, the free encyclopedia.

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Учебное издание

Татьяна Викторовна Журова

АНГЛИЙСКИЙ ЯЗЫК ДЛЯ СТУДЕНТОВ-ГЕОЛОГОВ

Учебное пособие

Технический редактор Коровкина Л.П.

План 2009 г., позиция 3. Подписано в печать 19.02.2009 г. Компьютерный набор. Гарнитура Times New Roman.

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Ухтинский государственный технический университет. 169300, г. Ухта, ул. Первомайская, 13.

Отдел оперативной полиграфии УГТУ. 169300, г. Ухта, ул. Октябрьская, 13.