Question

Natural accumulation of hydrocarbons are expected to occur

• A. in an anticline
• B. in stratigraphic traps
• C. along synclinal axial troughs
• D. in ancient delta-mouth bars

Hint:

Stratigraphic traps are formed by changes in rock type or permeability that prevent hydrocarbons from escaping, making them excellent locations for natural accumulation.

Answer 1

The Correct Option is B

Step 1: Understanding hydrocarbon accumulation.
The natural accumulation of hydrocarbons occurs when organic material (mainly plankton) is deposited in sedimentary basins, buried, and subjected to heat and pressure, forming oil and gas.
For hydrocarbons to accumulate, they must be trapped in a reservoir rock, which is often an impermeable layer that prevents the hydrocarbons from escaping. Such traps can be structural or stratigraphic.

Step 2: Analyzing the types of traps.
- Option (A): In an anticline: Hydrocarbons can accumulate in structural traps, such as anticlines, where the rock layers fold and trap oil and gas beneath them. While this is a valid trapping mechanism, it is not the best description for the question.
- Option (B): In stratigraphic traps:
Stratigraphic traps occur when changes in rock type or stratigraphy create a barrier for hydrocarbons. These traps are highly effective and common in oil and gas exploration. This is the correct answer.
- Option (C): Along synclinal axial troughs: While hydrocarbons may be found along some troughs, synclinal troughs are generally less effective for trapping hydrocarbons compared to anticlines and stratigraphic traps.
- Option (D): In ancient delta-mouth bars: Delta-mouth bars can be good source rocks but are not typically primary sites for hydrocarbon accumulation. Stratigraphic traps formed by variations in rock type or permeability are better suited for trapping hydrocarbons.

Step 3: Conclusion.
The correct answer is (B) in stratigraphic traps, as they are highly effective at trapping hydrocarbons formed from organic material.
\[ \boxed{\text{in stratigraphic traps}} \]