Which rock type is impermeable to fluids such as oil and natural gas?

Which rock type is impermeable to fluids such as oil and natural gas?

• A. Permeable
• B. Impermeable
• C. Porous
• D. Sedimentary

Answer: (B)

The key idea is that impermeability describes a rock’s ability to block fluid flow. A rock that is impermeable does not let liquids like oil or natural gas pass through it, which is exactly what a cap rock or seal in a hydrocarbon system does. That makes the term describing impermeable the best fit for the question, because it directly states the property being asked for. Permeable would allow fluids to pass, so it doesn’t fit the requirement. Porous refers to having pores and the capacity to store fluids, but it doesn’t guarantee that those fluids can flow through—connectivity of the pores matters. Sedimentary describes a rock type, but impermeability is about flow, and not all sedimentary rocks are impermeable.

The key idea is that impermeability describes a rock’s ability to block fluid flow. A rock that is impermeable does not let liquids like oil or natural gas pass through it, which is exactly what a cap rock or seal in a hydrocarbon system does. That makes the term describing impermeable the best fit for the question, because it directly states the property being asked for.

Permeable would allow fluids to pass, so it doesn’t fit the requirement. Porous refers to having pores and the capacity to store fluids, but it doesn’t guarantee that those fluids can flow through—connectivity of the pores matters. Sedimentary describes a rock type, but impermeability is about flow, and not all sedimentary rocks are impermeable.