Section 1-GEOLOGY

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
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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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