2. Course Outline
• Origin of petroleum
• Geology of petroleum system
1. Source rocks
2. Reservoir rocks
3. Seal rocks
4. Trapping mechanism
5. Migration pathways and time
• Step of exploration
• Reserve and risk analysis
4. Petroleum System
A system where hydrocarbon is allowed to be produced and
accumulated within lithosphere
1. Source rocks
2. Reservoir rocks
3. Seal rocks
4. Trapping mechanism
5. Migration pathways and time
Hydrocarbons commonly occur in sedimentary basins and are
absent from intervening areas of igneous and metamorphic rocks
(North, 1971)
5. Source rocks
The formation of hydrocarbon liquids from an organic rich source
rock with kerogen and bitumen to accumulates as oil or gas.
Generation depends on three main factors:
• the presence of organic matter rich enough to yield hydrocarbons,
• Sufficient time to bring the source rock to maturity.
• adequate temperature, pressure and the presence of bacteria and
catalysts also affect generation.
Generation is a critical phase in the development of a petroleum
system.
6. Organic matter
Formation of source rocks.
Only a small fraction of the
organic matter is preserved.
The formation or organic-rich
source rocks requires
restricted water circulation
and oxygen supply
9. Kerogen
Diagram (Van Krevelen diagram)
showing the primary composition
of the different types of kerogen
and the changes as a function of
heating (maturation) during
progressive burial
(Selley, 1998)
14. Reservoir rocks
• Any rocks in suitable stratigraphic position with possessing both
the porosity and permeability necessary to contain oil, gas or both
in commercial quantities. (North, 1985)
100
.
.
(%)
rock
of
vol
Total
voids
of
Vol
L
A
P
P
K
Q
)
2
1
(
Q: rate of flow
K: permeability
(P1-P2): pressure drop across the sample
A: cross-sectional area of sample
µ: viscosity of fluid
;ø: porosity
15. Seal rocks
• Seal rocks are any rocks may act as a seal as long as it is
impermeable. (Downey, 1994)
• Shales are the commonest seals, but evaporates the most
effective. (shales commonly porous, but due to their fine grain
size, have very high capillary forces that prevent fluid flow. (Selley,
1998)
• Several mechanisms allow the leakage of gas from a trap
• Tectonic movements may thus destroy the effectiveness of a brittle
shale seal.
• This circumstance may change thus shale may become a
reservoir rock (due to fracturing process)
16. Trapping mechanism
A configuration of rocks suitable for containing hydrocarbons and
sealed by a relatively impermeable formation through which
hydrocarbons will not migrate.
Traps are described as:
• structural traps: Hydrocarbon traps that form in geologic structures
such as folds and faults
• stratigraphic traps: Hydrocarbon traps that result from changes in
rock type or pinch-outs, unconformities, or other sedimentary
features such as reefs or buildups
A trap is an essential component of a petroleum system.
18. Migration Pathways and Time
The movement of hydrocarbons from their source into reservoir rocks.
• The movement of newly generated hydrocarbons out of their source
rock is primary migration, also called expulsion.
• The further movement of the hydrocarbons into reservoir rock in a
hydrocarbon trap or other area of accumulation is secondary
migration.
• Migration typically occurs from a structurally low area to a higher area
in the subsurface because of the relative buoyancy of hydrocarbons
in comparison to the surrounding rock.
• Migration can be local or can occur along distances of hundreds of
kilometres in large sedimentary basins, and is
critical to the formation of a viable petroleum system.
19. Basic Petroleum Exploration
• Looking for
• Define quality
• Define quantity
• Planning for exploitation
• Producing
• Controlling
• Refinering, sale, …
Geologists -
Geophysicist
Petroleum Eng.
20. Exploration step
The objective of Geology and Geophysics method is to recognize
petroleum systems in a certain area and its hydrocarbon potency.
Investigation processes:
1. Regional geology study
1. Tectonics and basin study
2. Remote sensing
3. Gravity/ magnetic
2. Semi detail study
1. Seismic 2D
2. Wells data correlation (extrapolation)
3. Detail study
1. Drilling
