TPO43阅读文本及答案解析

 2. The Origin of Petroleum

Petroleum is defined as a gaseous, liquid, and semisolid naturallyoccurring substance that consists chiefly of hydrocarbons (chemical compoundsof carbon and hydrogen). Petroleum is therefore a term that includes both oiland natural gas. Petroleum is nearly always found in marine sedimentary rocks.In the ocean, microscopic phytoplankton (tiny floating plants) and bacteria(simple, single-celled organisms) are the principal sources of organic matterthat is trapped and buried in sediment Most of the organic matter is buried inclay that is slowly converted to a fine-grained sedimentary rock known asshale. During this conversion, organic compounds are transformed to oil andnatural gas.

■ Sampling on the continental shelves and along the base of the continentalslopes has shown that fine muds beneath the seafloor contain up to 8 percentorganic matter. ■ Two additional kinds of evidencesupport the hypothesis that petroleum is a product of the decomposition oforganic matter: oil possesses optical properties known only in hydrocarbonsderived from organic matter, and oil contains nitrogen and certain compoundsbelieved to originate only in living matter. ■ Acomplex sequence of chemical reactions is involved in converting the originalsolid organic matter to oil and gas, and additional chemical changes may occurin the oil and gas even after they have formed. ■

It is now well established that petroleum migrates through aquifersand can become trapped in reservoirs. Petroleum migration is analogous to groundwatermigration. When oil and gas are squeezed out of the shale in which theyoriginated and enter a body of sandstone or limestone somewhere above, theymigrate readily because sandstones (consisting of quartz grains) and limestones(consisting of carbonate minerals) are much more permeable than any shale. Theforce of molecular attraction between oil and quartz or carbonate minerals isweaker than that between water and quartz or carbonate minerals. Hence, becauseoil and water do not mix, water remains fastened to the quartz or carbonategrains, while oil occupies the central parts of the larger openings in theporous sandstone or limestone. Because oil is lighter than water, it tends toglide upward past the carbonate- and quartz-held water. In this way, oilbecomes segregated from the water; when it encounters a trap, it can form apool.

Most of the petroleum that forms in sediments does not find asuitable trap and eventually makes its way, along with groundwater, to thesurface of the sea. It is estimated that no more than 0.1 percent of all theorganic matter originally buried in a sediment is eventually trapped in an oilpool. It is not surprising, therefore, that the highest ratio of oil and gaspools to volume of sediment is found in rock no older than 2.5 millionyears—young enough so that little of the petroleum has leaked away—and thatnearly 60 percent of all oil and gas discovered so far has been found in stratathat formed in the last 65 million years This does not mean that older rocks producedless petroleum; it simply means that oil in older rocks has had a longer timein which to leak away.

How much oil is there in the world? This is an extremelycontroversial question. Many billions of barrels of oil have already beenpumped out of the ground. A lot of additional oil has been located by drillingbut is still waiting to be pumped out Possibly a great deal more oil remains tobe found by drilling. Unlike coal, the volume of which can be accuratelyestimated, the volume of undiscovered oil can only be guessed at. Guessesinvolve the use of accumulated experience from a century of drilling. Knowinghow much oil has been found in an intensively drilled area, such as easternTexas, experts make estimates of probable volumes in other regions where rocktypes and structures are similar to those in eastern Texas. Using this approachand considering all the sedimentary basins of the world, experts estimate thatsomewhere between 1,500 and 3,000 billion barrels of oil will eventually be discovered.

1.According to paragraph 1, petroleum is formed in which of thefollowing ways?

O Bacteria and tiny plants undergo a change while they are buried inclay.

O Carbon and hydrogen combine to form shale.

O Ocean rocks are converted into organic compounds.

O Oil and gas rise to the surface of sediment and are trapped inrocks.

2.The word "trapped" in the passage is closest in meaningto

O hidden

O destroyed

O caught

O found

3. All of the following are cited in paragraph 2 as evidence that petroleumis a product of the decomposition of organic matter EXCEPT

O the amount of organic matter found in layers of mud below theseafloor

O the chemical changes that occur in oil and natural gas after theyhave formed

O the optical properties of oil

O the fact that oil contains nitrogen and other compounds believedto be of organic origin

4. According to paragraph 2, which of the following is true of thechange of solid organic material into oil and gas?

O It is more likely to occur along the base of continental slopesthan on the continental shelves.

O It only takes place in areas where the seafloor contains at least8 percent organic matter.

O It is a process that can be reversed through chemical changes thatoccur after the oil and gas have formed.

O It involves a complicated series of chemical reactions.

5. Which of the sentences below best expresses the essentialinformation in the highlighted sentence in the passage? Incorrect choiceschange the meaning in important ways or leave out essential information.

O When oil and gas are squeezed out of the rock in which theyoriginated, it is probably because the layer of rock above them is much morepermeable than shale.

O Sandstones, which are made of quartz grains, and limestones, whichare made of carbonate minerals, can hold much more oil and gas than any shalecan.

O When they are squeezed from the shale in which they were formed,oil and gas move easily into the much more permeable layers of sandstone orlimestone above.

O Oil and gas are squeezed out of sandstones, consisting of quartzgrains, and migrate readily into limestones, which consist of carbonateminerals and are much more permeable.

6. Why does the author include the information that "The forceof molecular attraction between oil and quartz or carbonate minerals is weakerthan that between water and quartz or carbonate minerals."?

O To help explain why petroleum behaves differently from water inbodies of sandstone and limestone

O To illustrate why petroleum migrates more rapidly throughsandstone than it does through limestone

O To help explain how water and petroleum can mix in certainaquifers

O To account for the different molecular structures of oil and water

7. The word "encounters" in the passage is closest inmeaning to

O meets

O forms

O escapes

O avoids

8. The word "suitable" in the passage is closest inmeaning to

O noticeable

O permanent

O protected

O appropriate

9. According to paragraph 4, what happens to most of the petroleumthat forms in sediments?

O It remains in underground pools.

O It is buried under organic matter.

O It rises to the surface of the ocean.

O It combines with the minerals found in groundwater.

10. Paragraph 4 supports which of the following statements aboutfuture petroleum discoveries?

O Less petroleum will be found than in the past because the ratio ofpetroleum pools to volume of sediment will decrease.

O Most of the petroleum will come from rocks that are less than 65million years old.

O Petroleum that has leaked away from older rocks will be the sourceof most new discoveries.

O More petroleum will become available because the amount of trappedorganic matter will increase.

11. The phrase "is an extremely controversial question" inthe passage is closest in meaning to

O is a question of great importance

O is a question causing strong disagreement

O is a question that has existed for a long time

O is a question composed of many related parts

12. According to paragraph 5, eastern Texas is an example of ageologic region where

O oil is located but has not yet been pumped out

O experts accurately predicted the rock types and structures foundthere

O the volume of oil can only be guessed at

O intensive oil exploration has occurred over a long time

13. Look at the four squares [■] thatindicate where the following sentence could be added to the passage.

Because such muds are a major source of petroleum, scientistsbelieve that petroleum originated as living organisms.

Where would the sentence best fit? Click on a square [■] to add the sentence to the passage.

14. Directions: An introductory sentence for a brief summary of thepassage is provided below. Complete the summary by selecting the THREE answerchoices that express the most important ideas in the passage. Some sentences donot belong in the summary because they express ideas that are not presented inthe passage or are minor ideas in the passage This question is worth 2 points.

Drag your answer choices to the spaces where they belong To removean answer choice, click on it.

To review the passage, click VIEW TEXT

Petroleum, which includes both oil and natural gas, can be agaseous, liquid, or semisolid substance.

Answer Choices

Petroleum comes from organic matter that has undergone a complexseries of chemical changes under the seafloor.

Although most of the petroleum formed leaks away into the ocean,some migrates from shale to sandstone or limestone, and is caught in pools.

Porous rocks made of quartz or carbonate minerals are particularlylikely to house oil pools because of their strong molecular attraction withoil.

Petroleum forms best when organic matter is evenly distributed overa large area and does not exceed 8 percent of the material in the clay.

More than 60 percent of the petroleum discovered so far has beenfound in rocks that are less than two-and-a-half million years old.

It is difficult to estimate the total amount of petroleum in theworld, but experts believe that 1,500-3,000 billion barrels will eventually bediscovered.