The document discusses the physical and chemical properties of petroleum. It defines various types of hydrocarbons such as oil, natural gas, condensates, and their classification. It describes the composition of natural gas and crude oil. It also discusses the key terms used in petroleum geology such as source rock, reservoir rock, seal rock, and the refining process.

1. THE PHYSICAL AND CHEMICAL
PROPERTIES OF PETROLEUM
SHAN SHAHZAD – 41
Contact Email:
ahmadraza2502@gmail.com
UNIVERSITY OF THE PUNJAB
LAHORE

2. INTRODUCTION
• Oil and gas are two chemically and physically
diverse groups of compounds termed as
hydrocarbons.
• Physically, hydrocarbons grade from gases, via
liquids and plastic substances to solids.
• The hydrocarbon gases include dry gas
(methane) and the wet gases ( ethane,
propane, butane etc.)

3. • Condensates: are H.C that are gaseous in the
sub-surface, but condense to liquid when they
are cooled at the surface.
• Liquid H.C are termed as oil, crude oil, or just
crude.
• The plastic H.C include asphalt & related
substances.
• Solid H.C include coal and Kerogen.

4. Basic Terms
• Natural Gas: “ H.C & non H.C (gas or in soln.)
with crude oil in underground reservoirs”.
• It is divided into three types :
• Dissolved Gas: is in soln. with crude oil in the
reservoir.
• Associated Gas: commonly known as gas cap,
overlies & is in contact with crude oil in the
reservoir.

5. • Non-Associated Gas: is in the reservoir that don’t
contain significant quantities of crude oil.
• Gases are classified as dry or wet according to the
amount of liquid vapor that they contain.
• Dry Gas: A dry gas is a gas with < 0.1 gal/ 1000ft3
of condensate. e.g! Methane.
• Wet Gas: A wet gas is a gas with >0.3 gal/1000ft3
of condensate. e.g! ethane, propane, butane.
• Refining: The process of separating the various
constituents/ Fractions of petroleum is known as
refining. It is carried out in a petroleum refinery.

7. • Porous Rock: Rock, which contains pores in it.
• Permeable Rock: Rock, which contains interconnected
pores in it.
• Source Rock: “ Porous Rock, which generate
hydrocarbons”.
• Reservoir Rock: “Porous and permeable rock unit,
which holds hydrocarbons”.
• Seal Rock: “Porous & impermeable Rock which seal or
stop the upward movement of oil.
• Organic Matter can be usefully divided into two
components:
• Bitumen: which is composed of compounds that are
soluble in organic solvents; and
• kerogen: the insoluble components.

8. Natural Gases
• There are 2 categories :
• Hydrocarbon Gases:
1. Methane
2. Ethane
3. Propane etc.
• Non Hydrocarbon Gases:
1. Inert Gases
2. Nitrogen
3.Hydrogen
4.CO2
5.H2S

10. Hydrocarbon Gases
• The major constituents of natural gas are the
H.C of the Paraffin series.
• The heavier members of the series decline in
abundance with increasing molecular weight.

12. Methane
• Methane is also known as “Marsh Gas” if it is found at
the surface.
• It is called “fire Damp” if it is present down a coal mine.
• Occurrence: Traces of methane are commonly recoded
as shale gas or background gas during the drilling of all.
It is produced by the destructive distillation of coal .
• Properties: Colorless, flammable gas, sparingly soluble
in H2O and lighter than air.
• Use: Domestic purposes in Europe until replaced by
Natural Gas, itself largely composed of methane

13. Sources of Methane:
• Three Sources:
1. Mantle
2. Thermal Maturation of Buried O.M.
3. Bacterial degradation of O.M.
Other H.C:
• They don’t form biogenically.
• They are only produced by the thermal
maturation of O.M
• If they detected during drilling, indicates
proximity to a significant petroleum
accumulation or source rock.

14. Non-Hydrocarbon Gases
• Inert Gases: He is minor accessory in many
natural Gases & traces of Ar & Radon have also
been found in the sub-surface.
• He occur in Atm. At 5ppm & also recorded in
mines, hot springs & fumaroles.
• Sources: He is produced by the decay of various
radioactive elements, principally U, Th, radium.
• Use: It can b used in dirigibles
• Hazards: Radon may cause lung cancer.

15. Nitrogen
N2: Frequently occurs naturally & associated
with both inert gases & H.C.
Sources:
• Volcanic eruption & I.R .
• N2 also form organically as by the degradation
of nitrates via ammonia. But only in shallow
conditions
• Some Atm. N2 may occur as a connate gas.

16. Hydrogen & CO2
Hydrogen:
• Free H2 gas rarely occurs in the sub-surface,
partly because of its reactivity & partly because
of its mobility.
• H2 is commonly dissolved in sub-surface H2O
& in petroleum as traces.
• Subsurface H2 is probably produced by the
thermal maturation of O.M.
CO2:
• CO2 is found as a minor accessory in H.C natural
gases.
• It is also associated with N2 & He.

17. Sources: has both organic & inorganic sources.
• It is a major constituent of volcanic activity and EQ.
• Permeable L.st and Dolomite can also yield CO2 .
• Thermal maturation of kerogen.
• CH4 in the presence of Oxygenated H2O may yield
CO & H2O.
• Uses: Dry Ice and to enhance the oil recovery.

18. Hydrogen Sulfide
• H2S occurs in sub-surface both as free gas and
in solution because of its high solubility with
brine and oil.
Properties: Poisonous , evil-smelling gas, highly
corrosive to steel & quickly attacking production
pipes.
On the basis of presence of SO2, gases may be
Sour Gas: Gas or oil containing significant traces
of SO2.
Sweet Gas: Oil or gas without H2S.

19. Sources: It is commonly expelled from volcanic
eruption.
• Euxinic environments, such as black sea.
• Anhydrite in the presence of O.M converted
into calcite & giving off H2S.
• It is also associated with evaporites &
carbonates.
Hazards: Small traces of H2S may caused:
• Corrosion
• Washing plants.

20. Gas Hydrates
Definition: Compounds of frozen water contain gas
molecules are known as “hydrates”.
Clathrates: The ice molecules themselves are
referred to as “Clathrates”.
Properties: Look similar to white, powdery snow.
Structure: It has 2 types of unit structures:
-Small Structures : Small structure with a lattice
structure of 12A0 holds upto 8 CH4 within 46 H2O
molecules.
• This clathrates may contain not only methane but
also ethane, H2S,CO2.

21. • Larger Structure: with a lattice structure of 17.4 A0,
consists of 136 H2O molecules.
• This clathrate can hold the larger H.C molecules of
the pentane & n-butanes.

22. Occurences and sources: They occur only in specific
PT conditions.
• They are stable at high P and low T.

23. • They also has shallow biogenic origin.
• They also occur in deep ocean deposits.
Economic Significance:
• They are climate change indicator.
• Due to low permeability, they form seal that
prevent upward movement of free gas.

24. Crude Oil
• A mixture of H.C that existed in the liquid
phase at atm. pressure.
• Properties: It may be yellow, green, & brown
to dark brown or black in color.
• Oil are naturally viscous & and oily.
• Surface oil is more viscous than sub-surface
oil.

26. Chemistry
• H. Series: The components of natural
hydrocarbons belong to 4 groups or series:
Paraffins or n-alkanes : Are straight chain
series, with the general formula CnH2n+2.
• For n = 1 to 4, these are gases.
• They are the most abundant H.C present in
both gaseous and liquid petroleum. E.g!
Methane etc

27. Naphthenes: Also called Cycloparaffins or
cylcloalkanes.
• Are a closed ring series with the general formula
CnH2n, form saturated ring.
• Unlike parafins, all napthenes are liquid at normal T.
• They make up about 40% of both light & heavy crude
oil.
Aromatics: generally a minor group of hydrocarbons
that contain at least
• one benzene ring (C6H6) in which all carbons share
the fourth bond.
• They are present in all petroleum except their %age
are small. E.g Benzene, Toluene etc.

28. Resins and Asphaltenes:
• Are composed of fused benzene ring networks,
but they contain impurity atoms like N,S,O.
• They are not true H.C.
• These impurities are the high molecular weight.
• They are the heaviest components of crude oil .

30. Crude oil Classification

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