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Geology
101
| Hydrocarbon Migration
& Traps |
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The
Canje started generating oil during the Miocene (25 ma) and continues
to expel oil today |
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Oil
and gas, being lighter than the embedded seawater, will migrate updip,
along permeable formations, or vertically through faults |
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We
postulate Eagle is a turbidite sand, sealed with impermeable shales
on its top and base |
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If
the oil encountered a water-filled trap such as Eagle, the oil would
rise to the top, pushing the water out the bottom of the structure |
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Seismic
responds to density differences in the sedimentary strata |
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Initially,
shale and water-filled rock have similar densities, so the amplitude
of the reflection at the interface is small |
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When
the sand is filled with light hydrocarbons, the density differences
cause a high amplitude reflection |
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AVO
or Amplitude vs Offset analysis requires very long microphone arrays,
technology that was not practical until recently |
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If
AVO response is positive, it is a good indirect hydrocarbon indicator
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