Английский язык в сфере профессиональной коммуникации. Геология. Учебное пособие
.pdfТЕКСТЫ ДЛЯ САМОСТОЯТЕЛЬНОГО ЧТЕНИЯ
Текст 1
WORK OF THE PETROLEUM GEOLOGIST
Petroleum geology deals with many problems encountered by geologists and other scientists in their study of petroleum. Among them are geographic and stratigraphic distribution, chemical and physical properties, origin, migration, accumulation, reservoir rocks, structure, methods of discovery, and valuation of oil and gas properties.
For more than two decades after petroleum geologists became actively engaged in geological work their most important work was that of general reconnaissance of the surface and detailed surface mapping. Since 1920 there has been a progressive change from the relatively simple surface mapping methods of oil-field discovery to more specialized techniques which employ the use of geology, geophysics, and chemistry.
Many geologists are now well trained specialists in the interpretation of data furnished by the different types of exploration, such as geophysics and geochemistry, and by the drilling of many wells. The petroleum geologist of today may devote all his time to the examination of well samples in order to make stratigraphic well logs. Or he may be a specialist in micropaleontology and study fossils found in well samples and cores to determine the relative ages of the formations penetrated. He may be a subsurface geologist who correlates sample and electric logs and uses paleontological data in the construction of subsurface structure maps, paleogeographic maps, and isopachous maps.
Some petroleum geologists are specialists in the interpretation of geophysical data furnished by field crews. Others are geological observers and geophysical crews in the field, and some are well trained geophysicists. Many geologists direct the drilling and coring programme of field wells.
The future of the petroleum geologist depends on his ability to discover now oil and gas fields more economically than oil and gas can be extracted from coal and oil shale. He has been successful in the past, and the demand for his services will become greater in the future. In order to keep pace with increasing difficulties involved in the discovery of new reserves, the petroleum geologist will have to have a more detailed knowledge of stratigraphy, sedimentation, geologic history, geologic and physiographic processes, and structural geology.
Текст 2 GEOGRAPHIC AND STRATIGRAPHIC
DISTRIBUTION OF PETROLEUM
The petroleum deposits of the world are located in sedimentary basins and in geosynclines. The most important petroleum resources of the world are located in the environs of land-locked seas occupying intercontinental troughs or depressions in the earth's crust. The principal regions of this character are:
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(1)The environs of the Mediterranean, Red, Black, and Caspian seas and the Persian Gulf, occupying the depressed segment between the continents of Africa, Europe, and Asia. In this region, the prolific oil fields of the U.S.S.R. and the Near and Middle East are located.
(2)The environs of the Gulf of Mexico and the Caribbean Sea, lying in the land-locked basin between the continents of North and South America. This region contains the most important petroleum resources so far developed in the Western Hemisphere: Trinidad, Venezuela, Columbia, Mexico, and the Gulf Coast area in the United States.
(3)The environs of the shallow island-studded seas which lie between the continents of Asia and Australia in the Far East. Important petroleum resources have already been developed on the islands of Borneo, Sumatra, Java, and New Guinea, and much promising territory remains to be explored in this region.
(4)The environs of the land-locked Arctic Sea, lying in the north-polar depression between the continents of North America, Europe, and Asia. This region is almost wholly unexplored, but it is characterized throughout by conspicuous surface evidences of petroleum.
Many important oil and gas fields of the world are located in smaller geosynclines and sedimentary basins. In North America there are important petroleum resources in the Appalachian geosyncline, Michigan basin, Eastern Interior coal basin, the West Texas basin, the Rocky Mountain geosyncline, and the Pacific geosyncline. In South America the petroleum resources of Argentina are situated in local sedimentary basins and in geosynclines. In the U.S.S.R. the important oil and gas deposits of the Ural-Volga and Kama fields are located in a large interior sedimentary basin.
The supply of oil and natural gas in the world is distributed in rocks ranging in age from pre-Cambrian to Quaternary.
The younger geological periods are more productive of oil than the older ones. More than one half of the world's oil production has come from rocks of the Tertiary period. The Cretaceous period is next in importance in total oil production. More than 16 per cent of the total world production has come from Cretaceous rocks. The Pennsylvanian period is third in importance in the amount of oil produced.
Текст 3
ORIGIN OF PETROLEUM
It has been demonstrated by many chemists that hydrocarbons can be prepared by laboratory methods from both inorganic and organic substances. In the inorganic field hydrocarbons have been produced in the laboratory by the reaction of alkaline metals with carbon dioxide and water and by reactions between acids and cast iron.
The Carbide Theory. Mendeleeff proposed the carbide theory in which he assumed the existence of iron carbides within the earth. Percolating waters reacting with the iron carbides would generate hydrocarbons. It is quite improbable that the water essential to the reactions of this theory could percolate downward to a depth
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sufficient to react with iron carbides within the earth, if they are present. It is believed that pore spaces and other openings in the rocks tend to disappear within a relatively short distance of the surface. The existence of iron carbides within the earth has not yet been proved.
Organic Origin. The organic theory of the origin of petroleum is now generally accepted by most scientists, but there remain many problems which are yet unsolved. It is generally believed that petroleum originated, by a series of complex processes, from plant and animal substances. The exact nature of the original organic material is not yet known, although many valuable data have been assembled on this problem. The complex biological, chemical, and geological processes necessary in converting the organic matter of plants and animals into hydrocarbons are not completely known.
It has been reasonably established that petroleum is of organic origin because:
(1)some petroleums are optically active, and, only petroleum derived from organic matter has this property. The optical activity is attributed by some scientists to derivatives of cholesterin, of animal origin, or to its vegetable equivalent, phytosterin;
(2)petroleum contains nitrogeneous compounds, and all such compounds found in nature are either of plant or animal origin; and (3) some of it contains chlorophyll porphyrins.
Source Beds. Source beds are sedimentary deposits from which petroleum has been or may be generated. It is generally believed that petroleum develops from organic substances which are deposited in shallow water marine sediments.
In his extensive work on recent sediments, Trask noted a definite relationship between the organic content of sediments and the texture. More organic matter is preserved in fine sediments because they are usually deposited in quiet water, which contains less oxygen than agitated water. Trask found twice as much organic matter, on the average, in the clayey sediments of the Channel Islands region of California compared to the silty sediments.
He noted a similar ratio throughout the Pliocene section of the Los Angeles basin and in the Lower Cretaceous sediments of northern California. He concludes that shales should be the best source beds of petroleum.
Trask found the average quantity of organic material in recent sediments to be about 2.5 per cent by weight. That figure is based on 1.600 samples from 150 environments. The percentage of organic matter in near-shore marine sediments ranges mainly from 1 per cent to 7 per cent, being largest in areas with abundant marine life.
The quantity of organic matter in a particular sediment, which is necessary for it to be a source bed, is not definitely known. Such formations as the Pliocene and Miocene sediments of the Los Angeles basin of California, the Eagle Ford shale of Texas, and the Mowry shale of Wyoming, which are closely associated with petroleum producing sands, contain from 2 to 5 per cent organic matter. The proportion of the organic matter in the source beds, which had to be converted to form the petroleum in the Santa Fe Springs field in California, is believed to be more than 2 per cent and less than 40 per cent, but it probably varies between 5 and 10 per cent. The proportion probably varies in different oil fields.
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Biochemical Changes. If petroleum is formed from plant and animal organic matter, the reduction of the nitrogen, oxygen, sulphur, and phosphorus content of the organic matter is necessary for the formation of petroleum. It has been demonstrated that bacteria reduce those substances in recent marine sediments.
It has been known for many years that anaerobic bacteria tend to convert the organic remains of plants and animals into substances which are more like petroleum. This is accomplished by splitting oxygen, nitrogen, sulphur, and phosphorus from organic compounds, leaving residual compounds consisting primarily of carbon and hydrogen. Although this is not definite proof that bacteria have converted the organic matter of sediments into petroleum, the presence of bacteria which are capable of such changes in petroliferous sediments is of considerable importance.
Geochemical Changes. The chemical reactions necessary to convert the organic matter of sediments into petroleum apparently occur after the sediments are buried to a considerable depth. Those reactions have been influenced by heat, pressure, earth movements, geologic time, and possibly other unknown factors.
Temperature. The distillation of liquid oil from oil shale or coal by destructive methods is a well-known process. Some liquid hydrocarbons have been produced from recent sediments and from ancient sediments associated with deposits of petroleum by destructive distillation. The amount of heat necessary for such distillation varies from 100°C. to 260°C.
It is apparent from the geological and chemical evidence that petroleum has had a low-temperature history. There are no carbonaceous residues or other evidence of heat decomposition in beds associated with deposits of petroleum.
Radioactivity. Concentrations of radioactive substances are widely distributed in water and rocks near the surface of the earth, but relative amounts are variable. Measurements made on deep sea deposits and on sea water suggest that thorium and ionium are precipitated in near shore areas where conditions are slightly basic. Radioactive substances are retained differentially by plankton and algae. Radon occurs in some gas associated with petroleum.
Fine-grained sediments rich in organic material are generally high in radioactivity.
It has been demonstrated by laboratory experiments that radioactive emanations may alter organic substances. Hydrocarbon gases have been converted into substances which are more oily by bombardment. Large amounts of substances not commonly found in petroleum are produced by radioactive bombardment. Such substances should be identifiable in sediments if radioactivity is an important factor in the generation of petroleum.
Текст 4
CHEMICAL AND PHYSICAL PROPERTIES OF PETROLEUM
AND RELATED SUBSTANCES
Petroleum is a complex mixture of gaseous, liquid, and solid hydrocarbons. In addition to the hundreds of different hydrocarbons composing petroleum, there are also other compounds which contain oxygen, nitrogen, and sulphur. Relatively small amounts of water and inorganic matter are frequently present.
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The physical and chemical properties of different samples of petroleum are not uniform because of the varying chemical composition and the presence of impurities. Petroleum and related substances occur in the physical state as a liquid (as in crude oil), as a gas (as in natural gas), and in the solid or semi-solid state (as in ozokerite and asphalt). Since petroleum in the natural reservoir occurs in most cases under pressure, some of the gaseous material and certain solid materials are dissolved in the liquid petroleum.
The physical and chemical properties of petroleum in the natural reservoir are somewhat different from those observed at the surface because of changes in temperature and pressure and loss of volatile constituents.
Colour. The colour of petroleum varies considerably. Some oils may be almost colourless, others are light yellow, red, green, brown, and black, or any intermediate shade. In thin layers colours are less intense, and in black oil the thin layers are brown in colour. The higher gravity crude oils are usually amber or green in colour. The lower gravity crudes are dark brown to black in colour.
When crude oils are observed by reflected light the colour appears to be different than that observed by transmitted light. Brown oil often appears to be green by reflected light. Ultra-violet light causes crude oils to fluoresce with characteristic colours even if they are of the same colour, by transmitted and reflected light. This phenomenon is now widely used to test cores, samples, and drilling mud for oil shows.
Most of the pure hydrocarbons become coloured upon oxidation, by the addition of oxygen to colourless leuco bases and the uniting of the leuco bases with other elements or groups to give coloured compounds.
Odour. The odour of a crude oil is determined by its composition. The paraffins and naphthenes are responsible for the agreeable odours, whereas the unsaturated hydrocarbons, certain nitrogen compounds, and sulphur cause the disagreeable odours. The crude oil has a disagreeable odour because of hydrogen sulphide and other sulphur compounds. Most of crude oils have an agreeable odour.
Specific Gravity. The specific gravity of a crude oil is the ratio of the weight of a given volume at a temperature of 60° F. to the weight of an equal volume of distilled water at the same temperature. It is an index to the value of oil. In general, the lighter oils have greater value because they contain larger quantities of gasoline and other valuable products.
Since oil is lighter than water, the specific gravity is normally expressed as a decimal or fraction. The decimal scale is used in most foreign countries, but in the United States the gravity is expressed in degrees by whole numbers, using the A.P.I. scale. The A.P.I. scale is a variation of the Baume scale which is an arbitrary one. It was derived by using water as 10 degrees and a modulus of 140. Specific gravity may be converted into degrees Baume and A.P.I. and vice versa.
The A.P.I. gravity of crude oil varies with changes in depth, temperature, ago of the rocks, impurities, and with the geologic history of different areas. In general, the gravity of oil increases with depth and with increasing geologic age of the rocks. There are, however, many exceptions to this general rule. The occurrence of low-
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gravity oil in Carboniferous limestones below light oil in Cretaceous sandstones may be due to difference in origin and geologic history. The Carboniferous oils may have been exposed to weathering during Triassic and Jurassic times.
In many oil-fields associated with faults, the deep producing formations contain oil which is lower in gravity than that in the shallow formations. In the same areas the gravity of the oil in the deep formations on unfaulted structures is higher than in shallow beds. The more volatile constituents have apparently migrated upward along the fault planes to raise the gravity of oil in higher sands.
Viscosity. Viscosity is a measure of the internal resistance to motion of a fluid by reason of the forces of cohesion between molecules or molecular groups. It is a property of great importance in the movement of oil through rocks. Viscosity is usually expressed in the time necessary for a volume of oil at a definite temperature to flow through a unit opening. Viscosities are determined by means of a number of standardized viscometers.
Crude oils vary considerably in viscosity. Those with a high A.P.I. gravity, in general, have a low viscosity whereas those with a low-gravity have a high viscosity. This relationship is not always uniform, however, because two oils of the same gravity do not always have the same viscosity. The viscosity is influenced by the chemical composition.
Optical Activity. Most oils have the power of rotating the plane of polarization of polarized light. This is known as optical activity. A light ray after emerging from a Nicol prism is vibrating in one plane only. Light which is vibrating in one plane only is plane polarized light. The plane of polarized light is rotated to the right in some oils, and in others it is rotated to the left; these oils are known respectively as dextrorotatory and levulorotatory. The optical activity in most oils is caused by the presence of cholesterol, which is found in both vegetable and animal matter. It has the formula C26H45OH.
Boiling-point. The boiling-points of crude oils are quite variable and depend upon their composition. The boiling-point of an oil of a low A.P.I. gravity is usually high because of a larger proportion of hydrocarbons with a high boiling-point, whereas the boiling-point of an oil of a high A.P.I. gravity is usually low because of the presence of hydrocarbons with a low boiling-point. Therefore, the more volatile the hydrocarbons in a crude oil, the lower the boiling-point.
Fluorescence. All crude oils show a fluorescence or glow of varying degree under ultraviolet light. The slightest trace of oil will fluoresce under ultraviolet light. One part oil dissolved in 100,000 parts of carbon tetrachloride will fluoresce enough to be observed. The colour observed is usually a green-yellow.
Fluorescence of crude oil is excited when subjected to ultraviolet radiation ranging between 2,000 and 3,800 angstroms. Tests showed that there is a marked difference in the fluorescence of oils from different fields and from different formations in the same field.
The fluorescent properties of crude oil may serve as a means of correlating oil sands in certain oil fields.
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In the petroleum industry, fluorescence analysis may be used to determine the grade and purity of crude oil and its refine products, and to identify specific, zones or horizons from which a well is producing. It is also widely used in field operations to test cores, cuttings, and drilling mud for shows of oil.
Текст 5
MIGRATION AND ACCUMULATION OF PETROLEUM
Petroleum is widely disseminated in the source beds after its conversion from buried organic matter, and it ultimately becomes concentrated in oil fields in large quantities. The movement or migration of petroleum from the source beds into fields can be divided into two parts: (1) transverse migration or movement from a source bed into a carrier bed; and (2) longitudinal migration or movement through the carrier bed to a suitable trap. The movement of oil and gas through rocks is apparently caused by several types of energy, including compaction, capillarity, differential specific gravity, hydrostatic pressure, gas pressure, cementation. Pressure from volume increases when some salts are precipitated from solution, and from diastrophic movements.
TRANSVERSE MIGRATION
Compaction. It is believed that compaction within the source beds is the principal force which causes the movement of oil and gas from source beds into carrier beds. Compaction is also regarded by some as an important agent in migration through carrier beds. Although direct proof that compaction has been an important factor in the migration and accumulation of petroleum is not to be expected, the direct association of most oil-producing regions with structural basins is an indication that composition may have played an important role.
Capillarity. Capillarity is action, due to surface tension, by which the surface of a liquid, where in contact with a solid, is elevated or depressed. Surface tension is the tension of a liquid because of which it acts as an elastic, enveloping membrane, always tending to contract to the minimum area. Capillary action is effective in tubular openings having diameters between 0.0002 mm. and 0.508 mm., and in sheet openings between 0.0001 mm. and 0.254 mm. Differences in capillary action decrease with increased temperatures at depths within the earth. With a temperature gradient of approximately 1°C. per 100 feet, capillary action loses about half of its force at a depth of about 15,000 feet.
Capillarity also has to be considered as a cause of migration and accumulation of oil and gas.
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LONGITUDINAL MIGRATION AND ACCUMULATION
The term "carrier bed" is used for any porous stratum through which petroleum may have moved. Carrier beds may be widespread sandstones or cavernous limestones, or possibly a weathered and dissolved surface of a widespread limestone beneath an unconformity. The movement of petroleum from a source bed to a reservoir depends upon the permeability of the carrier bed. The permeability of some carrier beds has been reduced subsequent to deposition and increased in others. It is reduced by compaction, cementation, and re-crystallization. Permeability is increased subsequent to deposition by fracturing and by solution and weathering, if the beds are exposed at the surface. In certain carrier beds the permeability was decreased after the migration of petroleum.
Differential specific gravity is a factor in the segregation of oil, gas, and water, in the presence of other agents, such as gas pressure, moving water, or capillarity. Experiments have shown that buoyant force of gravity in sandstone reservoir rocks dipping at low angles is not sufficient to overcome the forces of friction, surface tension, and adhesion.
HYDRAULIC MOVEMENT
Munn suggested the hydraulic theory as a result of his discussions on the inadequacy of the anticlinal or gravitational theory. According to him, the fundamental idea of the hydraulic theory is that moving water under either hydraulic or capillary pressure has been the important agent of migration and accumulation of oil and gas.
The type of trap necessary to cause accumulation of petroleum depends upon the rate of movement of the water through a carrier bed. It is believed a trap with a large closure is necessary in a carrier bed which has a relatively high porosity and a strong hydraulic head.
Текст 6 DISTANCE OF MIGRATION
The distance of migration of petroleum is one of the most controversial subjects in petroleum geology. Some investigators contend that the movement has been restricted to relatively short distances, such as hundreds of feet, or at most a few miles, whereas others believe it has migrated tens or even hundreds of miles. Although most of the evidence favours short distance migration, it must be admitted that no one has yet presented evidence to prove that petroleum has migrated any definite distance to its present position. There is evidence that petroleum has migrated both short and long distances. Each producing area presents an individual problem on the relative distance of migration of oil and gas. The important factors which determine the distance of migration of oil and gas are the areal distribution, permeability, and continuity of reservoir beds. Oil, water, and gas should move through a highly permeable and uniform carrier bed for long distances under ideal conditions of wide areal distribution and with differential hydrostatic pressure.
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Short-Distance Migration. There are many lenticular sandstones enclosed within shales which have a limited areal extent of a few square miles or less. The migration of oil and gas into those sandstones was apparently accomplished during the period of compaction of the sediments while the shales were pervious enough to permit transverse migration of fluids. It seems logical to assume that the oil and gas were derived from the shales adjacent to or near the sandstones.
Long-Distance Migration. Proponents of long-distance migration of oil and gas have considered the strong artesian circulation within certain reservoir beds as evidence of migration for considerable distances. Furthermore, they have in the past considered that the organic content of the sediments was so small that it was necessary to have source beds distributed over broad areas to supply the necessary oil.
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АНГЛО-РУССКИЙ ТОЛКОВЫЙ СЛОВАРЬ ГЕОЛОГИЧЕСКИХ ТЕРМИНОВ
amphibole — амфибол. 1. Группа темных породообразующих железомагнезиальных силикатных минералов, родственных по структуре и составу. 2. Минерал группы амфибола, напр. роговая обманка, тремолит, актинолит, рибекит, глаукофан или арфведсонит;
anticline — антиклиналь. Складка, ядро которой сложено стратиграфически более древними породами; она выпукла по направлению вверх;
aqueous — водный. 1. Состоящий из воды или относящийся к воде. 2. Образованный водой, созданный водой или при помощи воды, напр. водный раствор. 3. Созданный действием воды, напр. водный осадок;
batholith — батолит. Крупное, обычно дискордантное тело плутонических пород с площадью выхода на дневную поверхность более 100 км2, сложенное гл.о. средне-крупнозернистыми породами гранодиоритового и кварц-монцонитового состава;
breccia — брекчия. Грубозернистая обломочная порода (размер частиц более 2 мм), сложенная угловатыми, неправильной формы обломками пород, сцементированными тонкозернистой массой;
cleavage — кливаж. Свойство или тенденция пород расщепляться вдоль вторичных трещин или вдоль других пространственно сближенных плоскостных структур или текстур, образовавшихся в результате деформаций или метаморфизма;
cleavage — спайность. Способность кристаллов раскалываться вдоль определенных кристаллографических плоскостей, отражающая их внутреннюю структуру;
clinometer — клинометр. Прибор, используемый для измерения углов наклона, склона, поднятия или падения;
conglomerate — конгломерат. Грубозернистая обломочная осадочная порода, состоящая из округлых до приближающихся к угловатым обломков диаметром более 2 мм (зерна, галька, булыжники, валуны), сцементированных мелкозернистым песчаным, алевритовым или другим естественным цементирующим материалом (напр. карбонатом кальция, окислами железа, кремнеземом или затвердевающей глиной); сцементированный эквивалент галечника;
diabase — диабаз. Интрузивная порода, состоящая в основном из лабрадора и пироксена и имеющая офитовую структуру;
dike — дайка. Пластинчатое тело интрузивной породы, секущее напластование вмещающих пород;
dip — падение. Угол между структурной поверхностью и горизонтальной плоскостью, замеренный перпендикулярно простиранию структуры;
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