Origin of Oil and Gas (4200)

1. Learn the words and word combinations before reading:

decay - [dI'keI]– распад, разложение

trap - [trxp] – n трапп, ловушка(нефти или газа), моноклиналь; v улавливать, поглощать, отделять, останавливать, задерживать, удерживать

yield - [jJld] – n урожай, добыча, выход; прогиб; поддувание (почвы); v давать какой то результат, производить, выпускать

algae ['xldZJ] pl от alga - водоросли

kerogen - bituminous material occurring in shale and yielding oil when heated

to be mature – подоспеть, прийти (о сроке), созреть

protein - ['prqutJn] - белок, протеин

trigger - ['trIgq] - вызывать, играть роль спускового механизма, инициировать

squeeze - [skwJz] - сжимать, сдавливать, выжимать

expel - [Ik'spel]– выталкивать, выбрасывать

fracture - ['frxktSq] - перелом, разрыв, трещина

blob - [blPb] - капля, шарик

tarry - ['txrI] - дёгтеобразный, смолистый, просмолённый

viscous - ['vIskqs] - вязкий, вязкостный

2. Read and translate the text:

Oil and gas are derived almost entirely from decayed plants and bacteria. Energy from the sun, which fuelled the plant growth, has been recycled into useful energy in the form of hydrocarbon compounds - hydrogen and carbon atoms linked together.

Of all the diverse life^* that has ever existed comparatively little has become, or will become oil and gas. Plant remains must first be trapped and preserved in sediments then be buried deeply and slowly 'cooked' to yield oil or gas. Rocks containing sufficient organic substances to generate oil and gas in this way are known as source rocks.

Whether oil or gas is formed depends partly on the starting materials. Almost all oil forms from the buried remains of minute aquatic algae and bacteria, but gas forms if these remains are deeply buried. The stems and leaves of buried land plants are altered to coals. Generally these yield no oil, but again produce gas on deep burial.

On burial the carbohydrates and proteins of the plant remains are soon destroyed. The remaining organic compounds form a material called kerogen. Aquatic plants and bacteria form kerogen of different composition from woody land plants.

The processes of oil and gas formation resemble those of a kitchen where the rocks are slowly cooked. Temperatures within the Earth's crust increase with depth so that sediments, and kerogen which they contain, warm up as they become buried under thick piles of younger sediments.

As a source rock, deposited under the sea or in a lake, becomes hotter (typically >100^oC), long chains of hydrogen and carbon atoms break from the kerogen, forming waxy and viscous heavy oil. At higher temperatures, shorter hydrocarbon chains break away to give light oil and then, above about 160^oC, gas.

Once a source rock has started to generate oil or gas it is said to be mature. The most important products generated are gas, oil, oil containing dissolved gas, and gas containing dissolved oil which is called gas condensate. Condensate is the light oil which is derived from gas condensates to be found at high underground temperatures and pressures.

Migration

Much oil and gas moves away or migrates from the source rock. Migration is triggered both by natural compaction of the source rock and by the processes of oil and gas formation. Most sediments accumulate as a mixture of mineral particles and water. As they become buried, some water is squeezed out and once oil and gas are formed, these are also expelled. If the water cannot escape fast enough, as is often the case^* from muddy source rocks, pressure builds up. Also, as the oil and gas separate from the kerogen during generation, they take up more space and create higher pressure in the source rock. The oil and gas move through minute pores and cracks which may have formed in the source rock towards more permeable rocks above or below in which the pressure is lower.

Oil, gas and water migrate through permeable rocks in which the cracks and pore spaces between the rock particles are interconnected and are large enough to permit fluid movement. Fluids cannot flow through rocks where these spaces are very small or are blocked by mineral growth; such rocks are impermeable. Oil and gas also migrate along some large fractures and faults which may extend for great distances if as a result of movement, these are permeable.

Oil and gas are less dense than the water which fills the pore spaces in rocks so they tend to migrate upwards once out of the source rock. Under the high pressures at depth gas may be dissolved in oil and vice versa so they may migrate as single fluids. These fluids may become dispersed as isolated blobs through large volumes of rock, but larger amounts can become trapped in porous rocks. Having migrated to shallower depths than the source rocks and so to lesser pressures the single fluids may separate into oil and gas with the less dense gas rising above the oil. If this separation does not occur below the surface it takes place when the fluid is brought to the surface. Water is always present below and within the oil and gas layers, but has been omitted from most of the diagrams for clarity.

Migration is a slow process, with oil and gas travelling between a few kilometres and tens of kilometres over millions of years. But in the course of many millions of years huge amounts have risen naturally to sea floors and land surfaces around the world. Visible liquid oil seepages are comparatively rare, most oil becomes viscous and tarry near the surface as a result of oxidation and bacterial action, but traces of natural oil seepage can often be detected if sought.

Notes:

* of all the diverse life – из всего многообразия жизненных форм

* as it often the case – как это часто бывает

3. Say what verb forms are underlined and name their functions.

4. Answer the following questions:

1. What is a source rock? 2. Under what conditions is the gas formed from algae and bacteria? 3. What is kerogen? 4. When is viscous heavy oil formed? 5. Where do oil and gas migrate? 6. Is oil less dense than the water which fills the pore space?

Text 2

Trapping Oil and Gas (2750)

1. Learn the words and word combinations before reading:

spill point – точка разлива

fracture -['frxktSq] - раскол, трещина, разрыв

bubble out ['bAbql 'aut] – подниматься пузырьками, бить ключом

break – разрыв, сдвиг, малый сброс

impervious - [im'pWvjqs] - непроходимый, непроницаемый, не пропускающий (влагу и т. п.)

reservoir bed - ['rqzqvwa:] - пласт-коллектор

fault traps - ловушка, образованная сбросом

domed arch - [a:tS] - куполообразная арка

fold - [fquld] - складка, флексура

folded – складчатый

petroleum-bearing formation – нефтеносная свита

combination trap – комбинированная ловушка

truncated - ['trANkeitid] - усеченный, укорачивать, сокращать

pinch - [pIntS] - геол. выклиниваться (о жиле ; тж. ~ out)

piercement dome [piqsi'ment 'dqum]- купол протыкания, протыкающий купол

spindle top – вершина с углублением

2. Read and translate the text:

Oilfields and gasfields are areas where hydrocarbons have become trapped in permeable reservoir rocks, such as porous sandstone or fractured limestone. Migration towards the surface is stopped or slowed down by impermeable rocks such as clays, cemented sandstones or salt which act as seals. Oil and gas accumulate only where seals occur above and around reservoir rocks so as to stop the upward migration of oil and gas and form traps, in which the seal is known as the cap rock. The migrating hydrocarbons fill the highest part of the reservoir, any excess oil and gas escaping at the spill point where the seal does not stop upward migration. Gas may bubble out of the oil and form a gas cap above it; at greater depths and pressures gas remains dissolved in the oil. Since few seals are perfect, oil and gas escape slowly from most traps.

A hydrocarbon reservoir has a distinctive shape, or configur­ation, that prevents the escape of hydrocarbons that migrate into it. Geologists classify reservoir shapes, or traps, into two types: structural traps and stratigraphic traps.

Structural Traps

Structural traps form because of a deformation in the rock layer that contains the hydrocarbons. Two examples of struc­tural traps are fault traps and anticlinal traps.

Fault Traps

The fault is a break in the layers of rock. A fault trap occurs when the formations on either side of the fault move. The forma­tions then come to rest^* in such a way that, when petroleum migrates into one of the formations, it becomes trapped there. Often, an impermeable formation on one side of the fault moves opposite a porous and permeable formation on the other side. The petroleum migrates into the porous and permeable formation. Once there, it cannot get out because the impervious layer at the fault line traps it.

Anticlinal Traps

An anticline is an upward fold in the layers of rock, much like a domed arch in a building. The oil and gas migrate into the folded porous and permeable layer and rise to the top. They cannot escape because of an overlying bed of impermeable rock.

Stratigraphic Traps

Stratigraphic traps form when other beds seal a reservoir bed or when the permeability changes within the reservoir bed itself. In one stratigraphic trap, a horizontal, impermeable rock layer cuts off, or truncates, an inclined layer of petroleum-bearing rock. Sometimes a petroleum-bearing formation pinches out—that is, an impervious layer cuts it off. Other stratigraphic traps are lens-shaped. Imper­vious layers surround the hydrocarbon-bearing rock. Still another occurs when the porosity and permeability change within the reservoir itself. The upper reaches of the reservoir are nonporous and impermeable; the lower part is porous and permeable and contains hydrocarbons.

Other Traps

Many other traps occur. In a combination trap, for example, more than one kind of trap forms a reservoir. A faulted anticline is an example. Several faults cut across the anticline. In some places, the faults trap oil and gas. Another trap is a piercement dome. In this case, a molten substance—salt is a common one—pierces surrounding rock beds. While molten, the moving salt deforms the horizontal beds. Later, the salt cools and solidifies and some of the deformed beds trap oil and gas. Spindle top is formed by a piercement dome.

Notes:

* come to rest – наткнуться, уткнуться

* seal – относительно непроницаемая горная порода, которая формирует барьер или подобие шапки над или вокруг нефтяного пласта, так, что флюиды не в состоянии двигаться за пределы пласта.

3. Match the word combinations in the first column with their Russian equivalents in the second one.

Porous sandstone	Слои горной породы
Cap rock	нарушенная сбросами антиклиналь
Reservoir shape	Пористый песчаник
Layers of rock	Точка разлива
Fault trap	Разломная моноклиналь
Faulted anticline	Очертания месторождения
Spill point	Покрывающая порода

4. Answer the following questions:

1. Where do hydrocarbons become trapped? 2. What stops the upward migration of oil and gas? 3. What are traps? 4. When does a fault trap occur? 5. What is an anticline trap? 6. When do stratigraphic traps form?

Text 3

How much oil and gas (3650)

1. Learn the words and word combinations before reading:

at a profit – с прибылью

porosity - [pL'rO siti] - пористость, ноздреватость; скважинность

permeabil­ity - ["pWmjq'biliti] - проницаемость, проходимость

well log – промысловая геофизика, каротаж

rock matrix - ['meitriks] -материнская порода; цементирующая среда

core - колонка породы, керн

fluid saturation ["sxCq'reISqn] - насыщенность флюидом

fraction – фракция, частица

pressure ['preSq] - давление; сжатие, стискивание

drive [draiv]- передача; вытеснение (нефти из коллектора газом, водой) пластовый режим, проходить (горизонтальную выработку), штрек по простиранию пород

sealing [sJliN] fault – непроводящий сброс ант. nonsealing – проводящий

drillsteam test- апробирование пласта испытателем на скважине

drilling rate log = drilling time log – диаграмма скорости проходки скважины; механический каротаж

mud log – газовый каротаж, геохимическое и геофизическое исследование скважин по буровому раствору

tracer – изотопный индикатор

2. Read and translate the text:

When deciding whether to develop a field, a company must estimate how much oil and gas will be recovered and how easily they will be produced. Although the volume of oil and gas in place can be estimated from the volume of the reservoir, its porosity, and the amount of oil or gas in the pore spaces, only a proportion of this amount will be recovered. This proportion is the recovery factor, and is determined by various factors such as reservoir dimensions, pressure, the nature of the hydrocarbon, and the development plan.

More specifi­cally, petroleum engineers have to know:

-- the pore spaces of a rock (porosity). Porosity is the volume frac­tion of space not occupied by the rock matrix. Not only average porosity is important but also porosity distribution, both vertically and horizontally. Reser­voir porosity is determined from measurements on cores and well logs using relationships that are some­what empirical.

-- how the pore spaces are interconnected (permeabil­ity), if permeability is good and the reservoir fluids flow easily, oil, gas and water will be driven by natural depletion into the well and up to the surface.

-- the nature of the fluids filling the pore spaces (fluid saturation). Expansion of the gas cap and water drives oil towards the well bore. Gas and water occupy the space vacated by the oil. In reservoirs with insufficient natural drive energy, water or gas is injected to maintain the reservoir pressure.

-- the energy or pressure that may cause the fluids to flow (drives). Pressure is the driving force in oil and gas production. Reservoir drive is powered by the difference in pressures within the reservoir and the well, which can be thought of as a column of low surface pressure let into the highly pressured reservoir.

-- the vertical and areal distribution of reservoirs and pore-connected spaces, and

-- barriers to fluid flow (sealing and nonsealing faults, stratigraphic barriers, etc.).

These facts have to be determined from available information, which probably consists of: surface seismic, gravity, magnetic, and other geo­physical data, borehole logs of various types, cores taken in boreholes, analyses of fluids recovered in drillstem tests, production and pressure data, specialized geophysical measurements, occasionally tracer data, and drilling rate logs, mud logs, and other well data.

Well logs, geologic background, and well-to-well log correlations supplemented by seismic character stud­ies (will be seen further) give an overall picture of the stratigraphy and stratigraphic changes across the reservoir, and pro­duction and pressure data (and occasionally tracer data) give information about the connectivity of reser­voir members between wells. Surface geophysical data, while lacking the vertical resolution of borehole logs and cores, provides the only data source that gives detailed information about areal distributions.

The proportion of oil that can be recovered from a reservoir is dependent on the ease with which oil in the pore spaces can be replaced by other fluids like water or gas. Tests on reservoir rock in the laboratory indicate the fraction of the original oil in place that can be recovered. Viscous oil is difficult to displace by less viscous fluids such as water or gas as the displacing fluids tend to channel their way towards the wells, leaving a lot of oil in the reservoir.

Each oil and gas reservoir is a unique system of rocks and fluids that must be understood before production is planned. Of course all these facts are to be determined and calculated by a very synergistically working team of development geologists, geophysicists and petro­leum engineers using all the available data to develop a mathematical model of the reservoir. Computer simulations of different production techniques are tried on this reservoir engineering model to predict reservoir behaviour during production, and select the most effective method of recovery. For example, if too few production wells are drilled water may channel towards the wells, leaving large areas of the reservoir upswept.

Factors, such as construction requirements, cost inflation and future oil prices must also be considered when deciding whether to develop an oil or gas field. When a company is satisfied with the plans for development and production, they must be approved by the Government, which monitors all aspects of oil field development.

3. Explain the words:

porosity, permeabil­ity, fluid saturation, sealing and nonsealing faults, drillstem tests, stratigraphic changes across the reservoir, areal distribution.

4. Answer the questions:

1. How can the volume of oil and gas in place be estimated? 2. What is the reser­voir porosity determined from? 4. What gives detailed information about areal distributions? 5. What do a geologist and a geophysicist have to know about oil reservoirs?

Text 4