Physical and Chemical Properties of Hydricarbons

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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