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Difficulty: MediumRock Types, Formation, and Economic Importance

A geological survey of a sedimentary basin identifies a fine-grained, impermeable rock formed from the compaction of mud and clay particles, which frequently acts as an effective cap rock for trapping petroleum. Which rock type exhibits these specific origin and structural characteristics?

  1. ShaleAnswer
  2. B
    Marble
  3. C
    Granite
  4. D
    Quartzite

Answer

Shale is the fine-grained sedimentary rock formed from compressed mud and clay that serves as an impermeable cap rock in petroleum reservoirs.
Shale is a mechanically formed, fine-grained argillaceous sedimentary rock produced through the diagenesis and compaction of mud, clay, and silt particles. Because of its microscopic pore spaces and low permeability, shale acts as an impermeable seal or cap rock that prevents crude oil and natural gas from escaping upward out of porous reservoir rocks.

Step-by-Step Solution

1
Analyze the rock characteristics given in the stem: fine-grained texture, origin from mud/clay compaction, and low permeability serving as petroleum cap rock.
Identified that the target rock belongs to the argillaceous group of mechanically formed sedimentary rocks.
Sedimentary rocks derived from clay and silt deposits compact into fissile, fine-grained argillaceous rocks.
2
Match these physical properties and economic importances to the correct rock classification.
Shale fits all criteria (argillaceous sedimentary origin, fine-grained mud/clay composition, impermeable structure trapping hydrocarbons).
Metamorphic rocks (marble, quartzite) and igneous rocks (granite) have different origins and structural properties.

Key Concept

Sedimentary rock classification by origin, texture, and economic significance in hydrocarbon trapping
Estimated Time:1m 0s
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Topics

Rock Types, Formation, and Economic Importance

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