Houston Geological Society

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HGS Petroleum Exploration Methods
What Geologists and Geophysicists do to find oil
and gas
Cerro Azul 4 blow-out, Veracruz, Mexico
February 1916
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HGS Petroleum Exploration Methods
Part II Petroleum System Migration
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Migration Oil and gas migrates from source
rock into reservoir rock
Micro-fractures

• Oil is formed under very high pressure
• The pressure caused hair-line fractures to
• develop in the overlying rocks
• Allowing the oil to migrate

Reservoir Rock
Source Rock
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Migration Oil and gas migrates through
reservoir rock to trap

• If migrating oil encountered a reservoir rock it
• preferentially flowed through this conduit
• If it led straight to the surface,
• the petroleum escaped
• If the reservoir was folded or faulted,
• the oil may have been trapped.

oil gas seeps
Reservoir Rock
trapped oil gas
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HGS Petroleum Exploration Methods
Part II Petroleum System Trap
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Traps

• Anticlinal - Rock layers folded into a dome
• Stratigraphic - Rock layers changing from a
  good reservoir to non-reservoir due to change
  in rock type (pinch-out), reservoir quality
  (diagenesis), or removal (erosional
  unconformity)
• Fault - Offset of rocks such that oil and
  gas accumulates in reservoir rock

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Anticlines are folds in the earth
Oil accumulates in anticlines
Oil is lighter than water and gas is even
lighter. This phenomenon creates the basic
petroleum trap
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Trap Oil and gas migrates from source rock,
through reservoir rock to trap
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HGS Petroleum Exploration Methods
Part II Petroleum System Seal
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Seal Seal rock prevents petroleum from
leaking out of a trap