Petroleum Geology - Origin of Petroleum

Petroleum Geology, Petroleum Engineering, Origin of Petroleum (Formation, Migration, & Accumulation of Petroleum)

1. JAMES A. CRAIG

2. Formation
Migration
Accumulation

3. ORIGIN OF PETROLEUM
To be considered are these 3 stages:
Formation of Petroleum
Migration of Petroleum
Accumulation of Petroleum

4. Formation of Petroleum
There are 2 theories concerning the
formation of petroleum:
The Inorganic theory
The Organic theory

5. Inorganic Theory
Berthelot (1860) & Dmitri Mendeleev (1902):
Iron carbide in the earth’s mantle would react with
percolating water to form methane.
FeC
2+ 2H
2O →CH
4+ FeO
2

This theory is called Deep-Seated Terrestrial
Hypothesis.

6. Sokoloff (1890):
Hydrocarbons precipitated as rain from the
original nebular matter from which solar system
was formed.
The hydrocarbons were the ejected from earth’s
interior onto surface rocks.

This theory is called Extraterrestrial Hypothesis

7. Problems with Inorganic Theories :
No field evidence that inorganic processes have
occurred in nature.
Commercial accumulations are restricted to
mainly sedimentary basins.
Accumulations are absent from igneous and
metamorphic rocks.

8. Organic Theory
Early marine life forms living on earth were
primarily plankton (rich in hydrogen & carbon)
Over 95% of living matter in the ocean is
plankton.

9. As these plankton died, their remains were
captured by the process of erosion and
sedimentation.

10. Successive layers of organic- rich mud & silt
covered preceding layers of organic- rich
sediments & overtime created layers on the
sea floor rich in the fossil remains of previous
life.

11. Thermal maturation processes (decay, heat,
pressure) slowly converted the organic
matter into oil & gas over periods of millions
of geologic years.

Conversion of the organic material is called
Catagenesis.
It usually occurs under anaerobic conditions.

12. Clay & silt are carried together with the dead
organic remains & deposited under deltaic,
lacustrine & marine conditions to form
Source rocks.
Black- coloured, organically- rich shales
deposited in a non- oxidizing, quiet marine
environment are considered the best source rocks.

13. Shales

14. Shale rock =
99% clay
mineral + 1%
organic material.
Kerogen
Insoluble
High molecular
weight
Polymeric
compound

15. Thermal alteration of kerogen forms crude oil
by increasing the carbon contents.

At shallow depths (< 3,000 ft), bacteria actions on organic materials form
Biogenic
Gas(natural gas).
At great depths (high temperature & overburden),
Thermogenic Gasis formed.
Later stages of thermogenesis will form wet gas and condensate.

16. Hydrocarbon maturation

17. Supports for organic hypothesis:
Carbon & hydrogen are the primary constituents
of organic material, both plant & animal.

Nitrogen & Porphyrinsare found in organic
matter & in many petroleum.
Porphyrins are chlorophyll derivatives in plants & blood derivatives in animals.

18. Migration of Petroleum
Produced hydrocarbons migrates upward
from the deeper, hotter parts of the basin
through permeable strata into suitable
structures.
There are 2 stages of migration:
Primary Migration –Kerogen transformation
causes micro- fracturing of the impermeable &
low porosity source rock, allowing hydrocarbons
to move into more permeable strata.

19. Secondary Migration –The generated fluids
move more freely along bedding planes and
faults into a suitable reservoir structure.
Migration can occur over several tens of
kilometers in lateral directions.

23. Accumulation of Petroleum
Accumulation & storage occur when the
migrating fluids encounter an impermeable
shale or dense layer of rock.
This is called a Trap.
After accumulation, the fluids tend to stratify according to their relative densities:
Gas
Oil
Water

24. If the migrating fluids do not encounter a
trap, they tend to flow to the surface or
deposited on the ocean floor.
Examples are:
Seepages
Escaping natural gas
Bituminous lakes

25. Reservoirs are composed of either:
Clastic formation –sandstone reservoirs made
from silicates (quartz, SiO
2).
Carbonate formation –carbonate reservoirs
made from detritus(coral or shell fragments).
Reservoirs must be:
Porous
Permeable
Trapped.

26. Types of Traps
Anticlinal Traps
Result of ductile
crustal
deformations.
HCWC

27. Fault Traps
Result of brittle
crustal
deformations.
HCWC

28. Stratigraphic
Traps
Impermeable
strata seal the
reservoir.
HCWC

29. Salt Dome Traps
Combination Traps
Fault bound anticlinal structures, i.e.
combination of anticlinal & fault traps. Many
global reservoirs have this type.