Petroleum geology is the study of origin, accumulation, and exploration of hydrocarbon fuels. It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons (oil exploration).

1. SANGAR AMEENsangar2201@yahoo.com
sangarameen775@gmail.com

2. •
The word comes from the Greek word Means ‘Rock oil’
‘petra’ (meaning ‘rock’)+ ‘oleum’ (meaning ‘oil’).=petroleum
Petroleum
A thick, flammable,
yellow-to-black
mixture of gaseous,
liquid, and solid
hydrocarbons that
occurs naturally
beneath the earth's
surface, can be
separated into
fractions including
natural gas, gasoline,
naphtha, kerosene,
fuel and lubricating
oils, paraffin wax, and
asphalt and is used as
raw material for a
wide variety of
derivative products.
•
• The oil we find underground is called crude oil.
• Crude oil is made of a mixture of different chemicals called
hydrocarbons. These were produced when tiny plants and animals
decayed under layers of sand and mud.
• Sometimes it is:
almost color less, or it can be thick and black. But crude oil usually
looks like thin, brown treacle.
• When it comes out of a well (especially an undersea well), the crude oil
is often mixed with gases, water and sand.
• Crude oil doesn't always look the same – it depends where it comes
from.

3. Natural Gas
• Petroleum in gaseous state; ‘it is the lightest form ofpetroleum with little complexity’
• It can also be defined as petroleum that is noncondensableat ≥ 200C and atmospheric conditions (i.e.
at ῀ surface conditions)
• Can be classified as dissolved gas (if it occurs in solutionin crude oils); associated gas or ‘gas cap’ (above oil
column in HC reservoirs); or non associated gas or ‘NAG’(no associated oil column)
• Natural gas can also be termed as Wet gas (methane +ethane, propane and butane and other higher HC’s ) if
it contains liquid oil vapour (i.e. ≥ 0.3 gal/1000ft3 ofcondensate) or Dry gas (mainly methane) if it contains
very little or no liquid oil vapour (i.e. ≤ 0.1 gal/1000ft3 ofcondensate).
• Natural gas may exist as liquids (Natural gas liquids) at the surface under certain conditions. These are termed:
– Liquefied Petroleum gas (LPG): natural gas (thatexist normally in gaseous state at STP) liquefied and condensed at
very low T and High T. chemically, LPG is mainly propane and butane
– Condensate: wet gas; liquid at STP. Chemically, condensate comprises of Pentanes and other higher HC’s
• Occurrences of non HC gases like He, H2S, Ar, H, Co2,O2, etc have been reported in association with Natural gas.

4. • Tiny (microscopic) animals and plants that live in the sea are
called plankton.
• The plankton that lived in hundreds of millions years ago
made our crude oil.
• When they died they sank to the bottom and slowly got
buried by sand and mud.
• Over millions of years, the dead animals and plants got
buried deeper and deeper.
• The heat and pressure gradually turned the mud into rock
and the dead animals and plants into oil and gas .
Animal plankton
10,000ofthesebugswouldfitonapinhead!
Plant Plankton

5. 1. Crude oil is a mixture of Hydrocarbon.
2. As the name suggests these are large molecules made up of hydrogen atoms attached to a backbone of
3. They are often chains of carbon atoms with hydrogens attached.
4. The longer chains have higher boiling points, so they can be separated by distillation.
5. The simplest groups are the alkanes and alkenes. They all end with 'ane' and 'ene' respectively.
6. The simplest groups are the alkanes and alkenes. They all end with 'ane' and 'ene' respectively.

6. • Petroleum generation takes place in source rocks, which may be defined
as organic rich, fine grained sediments deposited under low energy,
reducing conditions.
• Most commonly, petroleum source rocks containing a minimum of 0.3%
to 0.5% by weight of organic matter.
• Preservation of the organic matter is the key to the development of
potential source rocks.
• The environment of source rock deposition is therefore characterized by
a relatively deep, unagitated (low energy) body of water with an oxygen
starved bottom but abundant life at the surface.
• Basic components of organic matter in sediments
• {PROTEINS,CARBOHYDRATES, LIPIDS (Fats) ,LIGNIN}+Time +Heat+
Pressured Converting to KEROGEN

7. • The generation of hydrocarbons from the source material depends
primarily on the temperature to which the organic material is subjected.
• Hydrocarbon generation appears to be negligible at temperatures less
than 150oF (65oC) in the subsurface and reaches a maximum within the
range of 225o to 350oF (107o and 176oC), the “hydrocarbon window”.
• Increasing temperatures convert the heavy hydrocarbons into lighter
ones and ultimately to gas. However, at temperatures above 500oF
(260oC), the organic material is carbonized and destroyed as a source
material.
• Consequently, if source beds become too deeply buried no
hydrocarbons will be produced.

8. The naturally occurring, solid, insoluble organic matter that
occurs in source rocks and can yield oil upon heating.
Kerogen is the portion of naturally occurring organic matter
that is non extractable using organic solvents. Typical organic
constituents of kerogen are algae and woody plant material.
Kerogens have a high molecular weight relative to bitumen, or
soluble organic matter. Bitumen forms from kerogen during
petroleum generation. Kerogens are described as Type I,
consisting of mainly algal and amorphous (but presumably
algal) kerogen and highly likely to generate oil; Type II, mixed
terrestrial and marine source material that can generate waxy
oil; and Type III, woody terrestrial source material that
typically generates gas.

9. • Diagenesis of kerogen is characterised by an important
decrease of oxygen and a corresponding increase of
carbon content with increasing depth.
• CO2, H2O and some heavy N, S, O compounds are
released.
• Source rocks are considered as immature at this stage.
• A significant decrease in hydrogen content and in the
H/C ratio takes place due to the generation and
release of hydrocarbons.
• This is the main zone of oil generation and the
beginning of the cracking phase which produces wet
gas with a rapidly increasing proportion of methane.

10. • Begins at temperature exceeding 175oC.
• During this stage, a rearrangement of the aromatic
sheets occurs.
• The stacks of aromatic layers, previously distributed at
random in kerogen, now gather to form larger clusters.
• At this stage, only dry gas is generated.
Color Maturity level Dominate of HC
Yellow Immature Biogenic Methane
Orange Mature Oil
Brown Mature Wet Gas
Black Metamorphosed Dry Gas

11. Diagenesis

12. Molecular groups of hydrocarbons:
• Paraffins = alkanes (aliphatics)
• Napthenes (cycloparaffins) = cycloalkanes
• Aromatics = arenes
• Naphtheno-aromatics (complex polycyclic molecules)
• Olefins = alkenes
Paraffins = alkanes (aliphatics)
• Can occur as straight chain (normal alkanes) or branched chain (iso-alkanes)
• Saturated HC’s (all carbon bonds (C-C) are saturated with hydrogen) with a general formula of CnH2n + 2, where n
=1– >60.
• n = 1–4 are gases (1-3 dominate natural gas); n = 5–17 are mainly liquids (dominate gasoline fraction of petroleum) n
=> 17 are waxes, semi-solids, asphalts, etc.
• They form a homologous series (each successive member
differ by CH2)

13. • Isomers of n-paraffins
•same composition and same general formula with n-
paraffins
• differ in structure, physical and molecular properties

14. • Saturated; general formula of : CnH2n
• C-atoms are joined in a ring
• Dominant structures in petroleum
• Form a homologous series up to n=30
• Generally, rings greater than C7 are unstable and become strained in crude oil

15. • Unsaturated;General formula: CnH2n-6r (where r =number of benzene rings)
• They react to add CH3 (akyl benzene) to the ring (i.e. Hatoms can be substituted; soluble in water)
• mainly found in heavy fractions.
• Toluene is most common form.

16. • ‘’Complex, condensed polycyclic hydrocarbons produced by joining of rings, chains, etc.’’
• Common in heavy fractions of petroleum. Some are carcinogenic.
• Unsaturated with General formula of CnH2n
• Form homologous series
• Rare in natural crudes—normally reduced to
paraffins
• highly reactive

17. • Non HC’s; abundant in the heavy solid to semi solid residual fractions of petroleum; may also be present in lighter
HC’s (crude oil).
• As a rule of thumb, the lower the °API Gravity (higher the viscosity), the higher the proportion of NSO-compounds
Examples include:
Nitrogen Compounds
• Pyridines
• Quinolenes
• Indoles
Range in natural crude oils: < 0.25–0.8% N
• most abundant after HC’s
• Thiols (mercaptans)
• Thoiophenes
• Free S and H2S
Range in natural crude oils: < 0.5–5% S

18. • Common in Immature oils
• Organic acids
• Alcohols, phenols, esters
• Indoles
Range in natural crude oils: < 0.1–2.0% O
Other components include various metallic compounds, spores, altered microfossil remains(geochemical fossils or
biomarkers), etc.

19. Specific Gravity:
• A measure of the weight of a given material compared to the weight of an equal volume of water at standard temp
& pressure
• The degree API or API is the Industry standard scale of measure. It relates to SG by: “API0 = (141.5/S.G) - 131.5’’
• API is used as an index to adjust the prices of crude.
Viscosity:
• Measures the fluid’s resistance to flow. It is affected by the amount of dissolved gases in the oil at a definite T
&P.
• Viscosity is measured in centipoises (cp = 10-2 poise).
Measures the lowest temperature at which a crude oil will flow, just before it starts to turn into a solid. Generally,
the higher the paraffin content of a crude the higher will be the pour point. Lower pour point is preferred to higher
pour point.
Pour Point:

20. Crude oils vary in color from colorless (very light crudes) to greenish-yellow to reddish to black (generally the heavy
crudes).
Color:
Various crudes oils smell like gasoline (sweet crudes) or rotten eggs (sour crudes) or have a sickly fruity smell
(aromatic crudes).
Odour:
Cloud point:
Defined as “ the Temp. at which the first cloud appears during cooling of heated oil”. It is a consequence of settling
out of paraffin waxes. N/B: non waxy crudes show no cloud point.
Flash point & Burning point:
• Flash point is ‘the temperature at which vapor rising from a heated oil will be ignited with a flash of short duration
when a flame is passed over it
• Burning point is the lowest temperature at which a heated oil will ignite and burn with a steady flame
(these props. are useful when evaluating potential hazards of handling and storing crude oil)

21. • Evamy et al.(1978) found out that in some fields, heavy oil was found in shallow reservoirs while lighter oil
was found at deeper levels
• Dickey et al. (1987) studied Imo River, Odidi, Afiesere, Batan, Oroni and Agbada fields and observed the
change from heavy to light crude is often dramatic.
• Furthermore, heavy oil was found to be associated with meteoric, connate and mixed water (no link with
meteoric water and heavy oil)
• Undegraded oil was found with meteoric water.
References