After being formed deep within the earth, hydrocarbons migrate upwards

Answers and Explanation OE

1)

A global question: predict with topic, scope, and purpose. The author discusses how hydrocarbon reserves are formed (especially in ¶s 1 and 3) and how they can be located (throughout the passage, but especially in the second half of the passage). (D) repeats this nearly word-for-word.
(A): Faulty Use of Detail. While the passage does this, this choice says nothing about the location of reserves, which the passage spends significant time on.
(B): Faulty Use of Detail. The flip side of the above answer choice. The passage discusses seismic exploration, but it also discusses the formation of hydrocarbons before this.
(C): Faulty Use of Detail. The author argues in ¶5 that stratigraphic traps are harder to locate than structural traps, but this isn‘t itself the main idea of the passage; the author mentions this in order to explain the method for discovering stratigraphic traps.
(D): The correct answer
(E): No such argument is made in the passage

2)

A detail question; ―According to the passage…‖ tips you off. Where are difficulties mentioned? Go back to ¶6. The last sentence of ¶6 states what the question does, that it‘s difficult to distinguish reflections between the two materials. The beginning of the sentence gives the reason: ―the density contrasts between oil-bearing sandstones and the shales that provide stratigraphic seals for the oil are often very small.‖ (B) says the same.(A): Faulty Use of Detail. While the author mentions this in the same paragraph, it‘s used in the context of how resolution can be improved, not why it‘s
difficult to distinguish between the sandstone and shale.
(B): The correct answer
(C): Faulty Use of Detail. This is part of the ―primary limitation with the seismic method‖ that the author discusses towards the beginning of the paragraph, not the direct cause of the particular problem in the question.
(D): Out of Scope. As above, thinness has to do with the primary limitation of the method, not the specific problem mentioned in the question.
(E): The passage never states this.

3)

A scattered detail question. Either eliminate wrong answer choices or look for a choice that sticks out as correct. (C) should jump out immediately; since not all traps are stratigraphic, it wouldn‘t make sense for the author to have said that oil couldn‘t be extracted without a density contrast between reservoir rocks and a stratigraphic seal.
(A): Opposite. The author states in ¶1 that ―hydrocarbons…will eventually reach the surface and be lost unless they encounter impermeable rocks.‖
(B): Opposite. The author ties oil reserves to hydrocarbons in ¶s1 and 4, so it‘s reasonable to believe that it‘s not possible to get oil if an original source of hydrocarbons aren‘t present.
(C): The correct answer
(D): Opposite. The author says in ¶1 that ―if the rock within which they are trapped is highly permeable…the hydrocarbons can be extracted by drilling.‖ In other words, drilling can‘t happen unless hydrocarbons are trapped within permeable rocks.
(E): Opposite. This is mentioned in ¶1.

4)

What is the author‘s opinion of seismology? The author discusses why seismology isn‘t a great way to find stratigraphic traps in ¶6, and raises the hope that seismology will become more effective in the future in ¶7. Paraphrase: Seismology has its problems, but will hopefully improve in the future. (A) says the same.
(A): The correct answer
(B): Distortion. Though seismology has limitations, there‘s no indication that it‘s intrinsically flawed. If it were, the author wouldn‘t argue for its improvement.
(C): Distortion. The author believes that seismology has promise, but spends a significant part of the passage explaining why seismology isn’t extremely effective. Nothing at all is said about profitability, so this choice is out of scope also.
(D): Distortion. The author doesn‘t discuss the theory of seismology, instead focusing exclusively on the practical method and its limitations. Further, theauthor only suggests that seismology is ineffective for stratigraphic exploration, not completely ineffectual.
(E): The passage does not say anything to this effect.