Petroleum Geology
College of Petroleum Engineering
LECTURE1
INTRODUCTION OF PETROLEUM
GEOLOGY(origin of petroleum)
Petroleum geology
• Is one branches of earth sciences refers to study of origin, occurrence, movement,
accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of
geological disciplines that are applied to the search for hydrocarbons oil (oil exploration).
• Petroleum geologist is a geoscientist who works in the field of petroleum geology, which
involves all aspects of oil discovery and production. Or a geologist who specializes in the
exploration, and the production of petroleum.
Relationship of petroleum geology to other geology sciences
• Petroleum geology is the application of geology to the exploration for and production of
oil and gas.
• Geology it self is firmly based on chemistry, physics and biology.
• The application of chemistry to the study of rocks (geochemistry) has many uses in
petroleum geology:-
A. Detailed knowledge of the mineralogy of reservoir is essential for the accurate
interpretation of geophysical well logs through reservoirs.
B. Knowledge the chemistry of fluids and their effect on the stability of minerals
C. Organic chemistry is involved in the analysis of oil and gas and in the study of diagenesis
of plant and animals tissues in sediments and the way in which the resultant organic
compound generates petroleum.
• The application of physics to the study of rocks (geophysics) is very important in
petroleum geology:-
A. Physical concepts are required to understand structural geology (fold,fault,diaparis--)
B. Modern petroleum exploration is unthinkable without the aid of mangnetic, gravity and
seismic surveys in finding petroleum traps.
C. Geophysical wireline logs used to measure lithology, porosity and petroleum content in
reservoir.
• (Biology) is related with geology in :-
A. Study the fossils (palenotology) and establishing biostratigraphic zones for regional
stratigraphic correlation.
B. Study the relationship between living organisms and their environment.
C. Study the transformation of plant and animals tissues into kerogen during burial and the
generation of oil and gas.
D. Oil companies exist not only to find oil and gas but to make mony thus every step of
journey from leasing to drilling to production and finally to enhanced recovery is
monitored by accountants and economists.
Some terms in petroleum geology
Oil field:- An area consisting of a single reservoir or multiple reservoirs all grouped on, or
related to, the same individedual geological structural feature and/ or stratigraphic
condition.
Or is a region with an abundance of oil wells extracting petroleum (crude oil) from below
ground.
Hydrocarbons:- are chemical compounds consisting wholly of hydrogen and carbon.
Petroleum:- is a complex mixture of gaseous, liquid , and solid hydrocarbons.In addition
there are compounds which contain oxygen ,nitrogen, and sullphur.Frequently , relatively
small amounts of water and inorganic matter are present.
Natural gas :- is the portion of petroleum that exists either in the gaseous phase or is in
solution in grude oil in natural underground reservoirs , and which is gaseous at
atmospheric conditions of pressure and temperature .Natural gas may include amounts of
non-hydrocarbons.
Crude oil:- is the portion of petroleum that exists in the liquid phase in natural
underground reservoir and remains liquid at atmospheric conditions of pressure and
temperature . Crude oil may include small amounts of non-hydrocarbons produced with
the liquids.
Dry Hole:- Any exploratory or development well that does not find commerical quantities
of hydrocarbons.
Reservoir:- Any rock having enough porosity and permeability to contain apperciable
hydrocarbons most often resrvoirs are sandstone and limestone(limestone/dolomite).
Petroleum Systems Analysis
A petroleum system encompasses a pod of active source rock and all genetically
related oil and gas accumulations. It includes all the geologic elements and processes
that are essential if an oil and gas accumulation is to exist .
Petroleum systems
Petroleum Systems Elements Petroleum Systems Processes
• Source rock • Generation
• Reservoir rock • Migration
• Seal rock • Accumulation
• Migration route • Preservation
• Timing
• trap
WHAT IS PETROLEUM?
Petroleum : a natural, yellow-to-black, flammable, liquid
hydrocarbon found beneath the earth’s surface.
Hydrocarbon : an organic compound made up of carbon and
hydrocarbon atoms.
Petroleum: A general term for all naturally occuring hydrocarbons
(hydrocarbon+carbon).
Soild Hydrocarbons: Asphalt
Liquid Hydrocarbons: Crude oil
Gas Hydrocarbons: Natural gas, methane, butane, propane, etc.
Elemental composition of typical petroleum are:
84.5% carbon .
13.0% hydrogen.
1.5% sulphur.
1% N,O,Ni,V.
The Origin of petroleum
TYPES OF PETROLEUM
The oil and gas are formed by the thermal cracking of the organic compounds
buried in fine grained rocks.
ORIGIN OF PETROLEUM
To be considered are these 3 stages:
Formation of petroleum.
Migration of Petroleum.
Accumulation of Petroleum.
Formation of Petroleum: There are 2 theories concerning the formation of petroleum :
The Inorganic theory (abionic)
The Organic theory (bionic)
INORGANIC THEORY
Inorganic theories were the first advanced to account for the formation of petroleum
This theory state that the petroleum is inorganic origin , The owners of this theory depended
on a number of phrnomena, including:-
1. Occurrence of hydrocarbon gases in surrounding parts of earth and outer planets
2. Gaseous hydrocarbon have been recorded to emanate from volcanoes in many parts of
the world
3. Occurrence of hydrocarbon deposits near thermal springs
4. Occurrence of solid petroleum deposits filling dikes as igneous rocks cutting
sedimentary rocks.
5. Particular class of meteorites (carbonaceous condrites) contain traces of various
hysrocarbons
6. Capability of perparing the oil from imorganic material that available in the earth.
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.
Inorganic theory can be divided to :-
a) Metal carbide Theory
Berthelot (1860) & Dmitri Mendeleev (1902):
Iron carbide in the earth’s mantle would react with percolathing water to
form methane.
FeC2 + 2H2O → CH4+ FeO2
This theory is called Deep-seated terrestrial hypothesis.
b) Cosmic origin theory
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.
ORGANIC THEORY
Successive layers of organic rich mud & silt covered preceding layers
of organic rich sediments & overtime created layer on the sea floor rich
in the fossil remains of previous life.
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.
The following points have been considered as supporting od the organic theory :-
1. 99% of hydrocarbon deposits occurs into sedimentary rock, in which organism are buried
in the basins during deposition.
2. Optical activity is property of most petroleum , and it s due to the presence of cholesterol
which is found in both plant or animal matter.
3. Petroleum contains nitrogenous compounds.All such compounds found in nature are
either of plant or animal origin.
4. Some petroleum contains chlorophII porphyrins, which are derivatives obtained from the
chlorophII of plants or from the blood cells of animals.
5. Some petroleum contian hydrogen sulfied gas which results from bacterial
decomposition of plants and animals.
