2. The science of petroleum geology
• Chemistry
Geochemistry is a major component of petroleum
geology
• Detailed knowledge of the mineralogical
composition of rocks – reservoir quality.
• Pore-fluid chemistry
Pore-
• Physics
Geophysics contributes to:
• Understanding the structures involved in trapping:
folds, faults
• Understanding the wells: wireline logs, lithology,
porosity
3. • Biology
• Biochemistry: transformation of plant and animal
tissues into kerogen and through to oil and gas.
• Study of fossil life: Paleontology
4. Formation of an oil accumulation
Burial of adequate organic source material.
most petroleum is derived from the accumulation of trillions of
individual micro-organisms.
micro-
Burial to the appropriate depths.
depths of 2-6 km and temperatures of 60-160º C.
2- 60-
Presence of a reservoir-quality rock.
reservoir-
a porous storage space. Sandstone and limestones are the
most common reservoir rocks. To be a reservoir they must
have:
Porosity,
Porosity, to hold the hydrocarbons
Permeability,
Permeability, to allow fluid flow
5. Presence of an adequate seal
A seal is an impermeable bed (such as a shale or a bed of salt)
that sits on top of the trap and prevents the hydrocarbons rising
any further.
Presence of a trap
In order to prevent the hydrocarbons rising to the surface and
escaping they must be caught in a confined space, termed a
trap. i.e. the source, reservoir and seal must be arranged in such
a way that the petroleum is trapped.
6. Organic Matter
When an organism (plant or animal) dies, it is
normally oxidized
Under exceptional conditions: organic matter is buried
and preserved in sediments
The composition of the organic matter strongly
influences whether the organic matter can produce
coal, oil or gas.
7. Basic components of organic
matter in sediments
• PROTEINS
• CARBOHYDRATES
• LIPIDS (Fats)
• LIGNIN
All of these + Time + Temperature +
Pressure = KEROGEN
8. Types of Kerogen
• Type I : algal kerogen
– “best” oil source
– Lipid-rich
Lipid-
• Type II: herbaceous
II:
kerogen
– Good oil source
– Includes zooplankton
(sapropelic)
• Type III: woody
III:
kerogen (coaly)
– Good gas source
11. The Source Rock
• A type of rock
which contains
organic matter
and is capable
to generate the
hydrocarbons.
• Best example of
source rock is
shale.
12. The Reservoir Rock
• A reservoir rock
is that kind of
rock which can
hold the
hydrocarbons.
• Most common
examples of
reservoir rocks
are sandstone
and Carbonates
(limestone and
dolomite).
13. The Reservoir Rock: Dolomite
• This is an example of
an important reservoir
rock type.
• Fossils have been
hollowed out by the
chemical conversion
of limestone to
dolomite, creating
pore spaces so large
that they are
sometimes called
“cavernous porosity”
porosity”
14. The Seal
• The seal or cap rock
is an impermeable
rock which don’t
allow the
hydrocarbons to
escape from the
reservoir rock.
• Common examples
of cap rocks are,
chalks , shales, clays
etc.
15. The Trap
• A subsurface obstacle to flow of petroleum
to the earth’s surface.
• Classified (broadly) into
Structural Traps
Examples: folds and faults.
Stratigraphic Traps
Examples: pinch out and unconformity traps
18. Migration Processes
• Primary Migration:
involves the
expulsion of
petroleum from
the source rocks to
reservoir rock.
• Secondary
Migration: involves
the movement of
petroleum through
permeable layers
(carrier beds) to
the trap.
trap.
19. Reservoir Porosity and
Permeability
There are two fundamental
physical properties that a
good reservoir must
have:
(1) porosity, or sufficient
void space to contain
significant petroleum.
petroleum.
(2) permeability, the
ability of petroleum to
flow through these voids.
voids.
21. Reservoir properties are to be
confirmed through
• Direct methods (Core)
• Indirect method (logs)
22. Presence of Oil/Gas is confirmed through
(1) Logs (2) Cuttings/cores (3) Testing
Seal Integrity is the most important factor for
preservation of hydrocarbon in pools
