RC OA

Analysis

{The difficult words in this passage are: crust (outer layer); retrieval (recovery); geysers (hot fountains);

geothermal (heat from the earth); gradient (slope)}

(The passage talks of a new source of energy, namely, Hot Dry Rocks. Hot rocks are found at various depths

under the earth's surface. In places where there are no volcanoes, or where volcanoes have ceased to exist, such

rocks would be located deep under the earth's surface, may be even hundreds of miles below. But, in places where

volcanic activity has been recent, such rocks are available at shallower depths. In places where there are such

HDRs, and also where there is a large quantity of subsoil water in the vicinity, the water gets heated by the HDRs,

and erupts from the surface of the earth in the form of hot springs or geysers. It is possible to use these hot springs

for the production of electricity, because they represent thermal energy. But there are vast areas where HDRs are

present but there is no underground water nearby. New research suggests that if we can find a method by which

artificial reservoirs of water are created deep within the earth's surface and near the HDRs, if water from these

reservoirs is then made to circulate around the HDRs, and if the water heated thereby is brought to the surface in

the form of artificial hot springs, we can thereby get another source of energy. In this passage, the author explains

in general terms this possibility, and also estimates the amount of energy available in this form in HDRs in USA

within a depth of 10 kms. He makes the point that, if an economically feasible way to tap this source of energy is

developed, the HDRs could be a good alternative source of energy for the USA.)

1. (This is a 'Primary Purpose' question, and we must answer it by identifying the overall theme that runs

through the passage.) Most of us laymen are not aware of the existence of HDRs as an alternative energy source.

The passage (as summarised above) informs us, without much of technicalities, of the existence of this new energy

source. So, (A) can be stated to be the main purpose of the passage.

(B) is wrong, because the passage does not mention any challenge that has already been surmounted in the

recovery of energy from HDRs.

(C) contradicts what the article explicitly speculates - that it will become possible to extract energy from

HDRs through new economically feasible developments.

A new technique (namely, circulating water around the HDRs from artificially created reservoirs at sufficient

depths) has been mentioned in the passage as one which has already been developed, and no other technique has

been mentioned. So, it cannot be said that the primary purpose of the passage is to encourage the use of new

techniques. So, (D) is also wrong.

Even in the last sentence, the author mentions that the development of this source of energy depends on its

relative cost vis-a-vis the conventional sources of energy. He does not 'urge' consumers that they should 'demand'

quicker development of HDR resources. So, (E) is also wrong.

2. (This is a 'Source' question.) (A) is wrong, since the temperature-depth (or gradient) records are just

mentioned in passing in the fourth para, whereas the focus of the passage is on HDRs.

(B) is wrong, since the conservation of oil and natural gas is not even mentioned in the passage.

The coal reserves in the US are just mentioned in the penultimate sentence of the last para, and (D) is

therefore wrong.

The commercial development of HDR energy has not yet taken place, and therefore there can be no pamphlet

presently describing its advantages for home heating systems. Therefore, (E) is also wrong.

This passage could very well be an extract from a much longer article regarding newly identified energy

sources. So, (C) is the answer.

3. (The phrase used in the question is 'According to the passage'. So, this is a 'Specific Fact' question, and

must be answered with reference to what is specifically stated in the passage. 'Geothermal gradient of 22 degrees

per kilometer of depth' means that, for every additional depth of one kilometer you drill into the earth, you will

reach a temperature higher by 22 degrees C.) The key phrase in this question is 'geothermal gradient of 22° per

kilometer', which occurs in the second sentence of the last paragraph. The complete sentence here is, "If an

average geothermal temperature gradient of 22°C per kilometer of depth is used, a staggering 13,000,000

quadrillion BTUs of total energy are calculated to be contained in crustal rock to a ten kilometer depth in the

United States". So, according to the passage, the geothermal gradient can be used to estimate the total HDR

resources base in the United States. So, (E) is the answer.

None of the other choices is referred to in the proximate sentences.

4. (This is an 'Inference' question, and must be answered by logically extending a fact mentioned in the

passage.) The key phrase in this question is 'temperature-depth records' which is mentioned in the second sentence

of para 4. It says that temperature-depth records are kept by the American Association of Petroleum Geologists,

and these relate to oil and gas wells. The next sentence within brackets states that there are many areas for

which such records do not exist. We can therefore infer that such records are available only in respect of areas in

which the Petroleum Geologists have attempted to tap oil or natural gas. So, (B) is the answer.

5. (From the phrase 'According to the passage', we can say that this is a 'Specific Fact' question.) The key

word in this question is 'fluid' which occurs at the end of the second paragraph, the phrase being ".... or bounded

flow paths to facilitate the removal of heat by circulation of a fluid over the surface of the rock". So, the purpose of

the fluid in HDR recovery systems is 'the removal of the heat'. Among the choices, it is (E) - transfer of heat - that

means this, and is the answer.

6. (This is a combination of a 'Specific Fact' and 'Roman Numerals' question, and must be answered with

reference to specific pieces of information available in the passage.) In the second sentence of the last para, the

author says that a staggering 13,000,000 quadrillion BTUs of total energy is contained within a 10 kilometer

depth in USA. So, the passage predicts that the temperature at the base of a 10-kilometer well is sufficient for

the production of electricity. So, I is true.

In the last sentence of the passage, the author refers to the still unsolved problem of balancing the economics

of deeper wells against the value of the final product - electricity or heat. So, he does not predict that drilling of

wells deeper than 10 kilometers is economically feasible. So, II is not true.

The absence of sufficient water near some hot rocks is mentioned in the first paragraph, while areas where

the average geothermal gradient is 22°C is mentioned in the last paragraph. There is no information in the

passage to reliably connect these two. So, III cannot be predicted from the passage.

So, only I is true, and (A) is the answer.

7. (This is another form of the 'Main Idea' question which we have already analyzed with reference to Qn. 1)

Since the passage is not about energy from water sources, but about energy from Hot Dry Rocks, (A) is wrong.

Since volcanic activity is just mentioned in passing in the second sentence, (B) is not an appropriate title to

the passage.

Since the economic recovery of geothermal energy is not yet established, it is too early to give title (C) to the

passage.

The passage does not indicate whether 22˚C is a high or low geothermal gradient. So, (E) is wrong.

In the penultimate sentence, the author says, "If we conservatively estimate that only about 0.2 percent (of

the 13,000,000 trillion British Thermal Units of total energy) is recoverable, we find a total that is comparable to

the estimated resource base of all the coal remaining in the United States". He then adds that the remaining

problem is merely one of balancing the economics. So, he foresees a day when this problem will be sorted out and

geothermal energy is, in fact, retrieved and used. So, (D) is an appropriate title to the passage, and is the answer