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?
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