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. Chemical Composition of Petroleum
Carbon 82.2 to 87.1 per cent
Hydrogen 11.7 to 14.7 per cent
Sulphur 0.1 to 5.5 per cent
Nitrogen 0.1 to 2.4 per cent
Oxygen 0.1 to 7.4 per cent
Minerals 0.1 to 1.2 per cent
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 colorless, 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. A 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 are colourless but may become coloured upon oxidation. Colour may be caused 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 un-saturated 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.
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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 by the following formulas:
Degrees Baume = 
Specific Gravity 60°/60° F= 
Degrees A.P.I.= 
Gravity 60°/60°F.= 
The A.P.I. gravity of crude oil varies with changes in depth, temperature, age 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-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 Jurassictimes.
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 n 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; those 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.
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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.
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.
Unit 3
I Learn the words:
1.to prepare - готовить
2.both-оба, и....и
3.field- область, поле, месторождение
4.to produce - производить
5.alkaline - щелочной
6.carbon - углерод
7.acid - кислота
8.cast iron - чугун
9.to assume - предполагать
10.existence - существование
11.to percolate - просачиваться, фильтроваться
12.to generate - порождать, образовывать
13.depth - глубина
14.pore space - поровое пространство
15.to disappear - исчезать
16.distance - расстояние
17.source beds - материнские пласты
18.average - средний
19.quantity - количество
20.to convert - превращать
21.heat - тепло, нагревать, отапливать
22.ancient - древний
23.evidence - свидетельство, доказательство
24.bed - слой, пласт, залежь
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25.to distribute - распределять, распространять
26.earth - земля
27.residue - осадок, остаток
28.relative - относительный, родственный
29.to alter - изменять
30.emanation - излучение
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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 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: (I) 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 porophyrins.
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 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 i0 per cent. The proportion probably varies in different oil fields
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 front 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.
Unit 4
I Learn the words:
1. drilling - бурение
2.cable tool method - ударно-канатный метод
3.tool - инструмент
4.hammer - молот
5.to blow - дуть, выдувать, удар
6.debris - обломки выбуренной породы
7.hole - дыра, отверстие, скважина
8.cutting - режущий, резец
9.cuttings - обломки породы, шлаки
10.горе - веревка, трос
10.to raise - поднимать
11.to drop - опускать, ронять
12.mud - грязь, буровой раствор
13.bailer - желонка
14.bottom - дно, забой скважины
15.to encounter — встречать, сталкиваться с
16.disadvantage - недостаток
17.to penetrate - проникать
18.casing - обсадка, обсадная колонна
19.derrick - буровая вышка
20.pipe (tube) -труба
21.joint - соединение, звено
22.hoisting - спуск - подъем
23.wheel - колесо
24.sand reel - тартальный (чистильный) барабан
25.swab - поршень, шваб
26.walking beam - балансир
27.spudding arm - ловильный рычаг
28.pump - насос, качать
28.bit - долото
29.chain - цепь, цепной
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