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

25. to distribute - распределять, распространять

26. earth - земля

27. residue - осадок, остаток

28. relative - относительный, родственный

29. to alter - изменять

30. emanation - излучение

II Translate the text:

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