This document discusses key concepts in petroleum geology, including the geologic cycle of erosion, deposition, and uplift that forms sedimentary basins. Depositional environments like marine, deltaic, and fluvial systems impact reservoir properties. Geologic time periods are defined using fossils and dating methods. Potential reservoir rocks include sandstone, limestone, and dolomite formed from sediment. Traps such as anticlines, faults, and pinch outs can accumulate oil and gas within porous and permeable reservoir rocks sealed below impermeable caprock. Geologic maps and cross-sections are used to interpret subsurface structures and stratigraphy.

1. Petroleum Geology
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Section #1

2. Reservoir Formation
▸Geologic cycle
▸Geologic time
▸Depositional Environment
▸Types of reservoir rocks
▸Main elements of petroleum reservoirs
▸Geologic subsurface maps
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3. Geologic Cycle
▸The cooling and movements of earth inner molten
rocks caused warping and movements of the crust
resulting in the formation of mountains and valleys
▸Erosion/weathering (wind, water and temp.) is the
process of earth breakdown into rock grains.
▸Rock grains are transported by water and deposited
in the sedimentary basins (valleys or the sea) in
horizontal beds.
▸Sedimentary beds are uplifted by structural
movements and the cycle is repeated
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4. How sedimentary basins are formed
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5. Erosion Effects !!
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6. Depositional
Environment
▪ Continental
▸ Alluvial
▸ Braided streams
▸ Dunes
▪ Transitional
▸ Upper deltaic plains
▸ Lower deltaic plains
▸ Fringe
▪ Marine
▸ Shallow marine
▸ Deep marine
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7. Impact of Depositional Environment
▪ Pinnacle Reef (Keg
River)
▸ High relief, small
areal extent
▪ MarineTransitional
▸ Good continuity
▸ Large areal extent
Reservoir configuration
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8. Impact of Depositional Environment
▪ Permeability:
▸ Good “K” for high energy
(channel)
▪ Grain size distribution
▸ Fining upward (channel)
▸ Fining downward (deltaic)
Reservoir quality
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9. Aerial View of Deposition Environments
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10. Geologic Time
• Oldest beds are deposited in the bottom
• Due to erosion and/or non-deposition, no single
sequence is a complete record of geologic time
(Table 1)
• Paleontology (study of fossils) is used to define
geologic periods
• Natural radioactivity of minerals (Uranium &
Thorium) determines absolute rock age.
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11. Geologic Periods
History of plants &
organic life
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12. Geologic
Time Table
Table 1
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13. Types of Reservoir Rocks
• Sedimentary
Formed by the cementation of sediment grains/particles on or
near surface at ordinary temperature
¾ Sandstone
¾ Limestone (CaCO3)
¾ Dolomite (CaMg(CO3)2
• Igneous
Formed by solidification of molten minerals/materials:
¾ Beneath surface (magma): Granite
¾ At surface (lava): Basalt
• Metamorphic
Formed within earth’s crust by transformation of other rocks at
high pressure and temperature (marble, slate) P
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14. Main Elements of Reservoirs
▸Source rock (source of hydrocarbons)
▸Reservoir trap (structural & stratigraphic)
▸Reservoir seal (to contain hydrocarbons within reservoir
trap)
▸Quality of Reservoir rock (should have reasonable porosity
and permeability)
-7-
Migrate
Generate Accumulate
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15. Source Rocks
▸Rivers carried masses of sediments to the sea with plants &
animal life (organic materials)
▸Organic materials, deposited at the bottom of sea were
covered and compacted with sand & silt. Sealed from oxygen,
the organic material decomposed under pressure, temperature,
and bacteria into hydrocarbons.
▸Continuous sedimentation exerted high overburden pressure
which “squeezed” hydro-carbons out the source beds into
porous sedimentary structures.
Source rocks are classified according to the amount of &
type of organic matters, the degree of maturation and
thermal alteration
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16. Reservoir Traps
▸Structural:
– Folding (anticline)
– Fault (normal, thrust)
– Unconformity
– Salt Dome
▸Stratigraphic
– Pinch out
– Reef
▸Combination
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17. Structural Trap (Anticline)
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18. Structural Trap (Anticline)
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19. Structural Trap (normal fault)
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20. Structural Trap (thrust fault)
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21. Structural Trap (salt dome)
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22. Stratigraphic Trap (pinch out)
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23. Stratigraphic Trap (reef)
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25. Structure Integrity
▪Structure Seal
Impermeable cap
rock that prevents
hydro-carbons from
leaking
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26. Structure Integrity, cont.
▪ Structure Relief
Structural relief will
have different structural
closure, according to
the regional dip
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27. Type of trapped fluids
-10-
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28. Types of trapped fluids, cont.
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29. Quality of Reservoir Rocks
▸Porosity
Connected porosity to store economic volume
of hydrocarbons
▸Permeability:
The ease at which fluids can move through the
porous rock
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30. Geologic Subsurface Maps
▸Structure contour maps of structure or zone tops
▸Data is obtained from open hole logs or seismic interpretations
▸Net pay map using specific cut-off values to gross pay
thickness
▸Hydro-carbon pore volume map (HCPV)
▸Geologic Cross-sections:
– Structural: Open hole logs are illustrated, as such, “hanging on the
wells” is based on a selected datum depth in subsea
– Stratigraphic: Open hole logs are illustrated, as such, “hanging on the
wells” is based on a selected strata or zone
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