SANDSTONE RESERVOIR ROCKS




Sands and sandstones are formed as a result of processes of sedimentation in which mineral fragments of assorted sizes and shapes are gradually fitted together under water, later to be compacted by the weight of super imposed strata. Tabular faces of grains assume similar orientation, developing parallel bedding planes. Small grains are deposited in the interstices between large grains and thus, a condition approaching minimum porosity for unconsolidated sand is attained.

Limestone Reservoir Rocks. Pores in limestones are much less uniform in shape and size than those of sands and sandstones. The rock openings are in many cases formed by solution and weathering and are extremely irregular in shape and distribution. Formed at prehistoric times, they are now found below younger formations resting unconfortably upon them.

Porosity of Reservoir Rocks. Porosity may be defined as the per cent of voids or pore space per unit volume. For example, in one hundred cubic feet of sandstone having an average porosity of 16 per cent, there would be sixteen cubic feet of pore space. When the term porosity is used, reference is usually made to the effective and not the absolute porosity, hence we do not ordinarily consider the very fine or unconnected openings, fractures or voids.

High porosity in a granular rock results from uniformity in size and shape of grains and is influenced also by their arrangement. It can be demonstrated mathematically that true spheres of uniform size, packed as closely as possible, will have a porosity of 25 per cent, irrespective of the diameter of the spheres. In nature, however, sand grains are not spherical. They occur in a variety of shapes and in many graduated sizes. As a result, during the process of deposition and sedimentation the small grains and fragments may shift in between the larger and posssibly more angular grains, thus materially reducing the effective porosity. In coarse-grained oil sands high initial production and rapid recovery are common.

Fine-grained oil sands having a porosity of less than 7 or 8 per cent rarely, if ever, produce oil in paying quantities. This is probably due to the fact that the interstitial openings are so small that they approach subcapillary size, and the pore friction or flow resistance established will not permit the oil and gas to move rapidly enough to be produced in paying quantities. Also, in coarse-grained sands the grains may have such angularity and be deposited in such a manner as to cause the connection between large pore spaces to be so small that they become subcapillary in size, and thus greatly retard fluid movement.

 

Exercises

I. Ответьте на вопросы:

1. In what way are sands and sandstones formed?

2. What is the difference between pore openings in limestones and those of sands and sandstones?

3. How are pore spaces formed in limestones?

4. What is porosity?

5. On what does high porosity depend?

6. What kind of oil sands/ coarse grained or fine-grained/ produce oil in paying quantities?

 

II. Переведите на русский язык:

1. Sedimentary rocks containing sufficient pore space permit accumulation of petroleum and often serve as underground reservoirs for the latter.

2. Coarse-grained oil sands have sufficient pore space for oil and gas to be accumulated in paying quantities.

3. Having resulted from sedimentation and later compaction by the overlying strata, sandstones, consisting, of grains of different size and shape arranged in such a manner as to occupy as little space as possible/ according to the law of physics/, still have high effective porosity as compared with hard compact formations such as igneous rocks.

4. The accumulation of oil in paying quantities is greatly influenced by the size of interstitial openings or pores, hence in fine-grained oil sands subcapillary interstices result in the retarded flow of fluid.

 

III. Переведите на английский язык:

1. Имея небольшую пористость, мелко зернистые нефтяные пески редко содержат нефть в больших количествах.

2. Благодаря большой пористости песчаники могут давать нефть и газ в промышленном количестве.

3. Пески, песчаники и известняки являются породами, имеющими довольно высокую пористость.

4. На пористость породы влияют размер, форма и расположение зерен.

5. Не зная пористости пород, мы не можем сделать вывод относительно нефтеносности данного района.

 

IV. Назовите синонимы к следующим словам:

gradually, to assume, case, extremely, average, to result from, arrangement, during, recovery, rapidly, also, to retard.

 

V. Назовите антонимы к следующим словам:

small, minimum, below, young, to reduce, initial, rapid, rarely, close, later, less coarse.

 

VI. Образуйте глаголы от следующих существительных:

compaction, formation, assumption, consolidation, distribution, erosion, definition, connection, demonstration, reduction.

 

VII. Переведите на русский язык:

1) bedding planes 2) reservoir rocks

3) per unit volume 4) in commercial quantities

5) coarse-grained sands 6) fine-grained sands

 

LESSON FIVE

Выучите следующие слова и выражения к тексту:

absorb – поглощать

articlinal – антиклинальный

argillaceous – глинистый

component – составной

comprise – включать, заключать в себе, содержать, охватывать

displace – вытеснять, замещать

expanse – пространство, протяжение

fold – сгиб, изгиб, складка

fracture – трещина, разлом, перелом, разрыв

frequently – часто

impervious – непроницаемый, непроходимый

invariably – неизменный, неизменяемый

lateral – побочный, боковой

lenticular – мелкозернистый, чечевицеобразный

make up – составлять, пополнять, возмещать

mark – метка, отметка, знак, клеймо

marl – мергель, известковая глина

nevertheless – тем не менее

offer – предлагать

overlie – лежать на чем-либо (под чем-либо)

permeability – проницаемость

retain – сохранять, удерживать

separate – раздельный

withstand – противостоять

yield – выход, выпуск

zone – зона

oil bearing strata – опорные слои (пласты)

cap rock – покрывающая порода

compose – составлять

storage capacity – охлад. способность

latter – последний

capillary – капиллярный, волосной

bed – основание, постель (под фундаментом), слой, пласт

shale – сланец, глинистый сланец

sufficient – достаточный

impermeable strata – непроницаемый слой, пласт

fine-grained sandstone – мелкозернистый песчаник

expanse – пространство, расширение

withstand – противостоять, выдерживать

 



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