UNIVERSITY OF AL MOSUL
FACULTY: PETROLEUM AND MINING ENGINEERING
SECTION: OIL RESERVOIRS
OIL AND GAS
CHEMISTRY
COURSE BINDING
MUHAMMAD ERFAN MAJEED
Introduction
The word petroleum originated from the Latin words, Petra,
meaning rock and oleum, meaning oil. Literally it means ‘Rock Oil,’
and can also be defined as a nonrenewable fossil fuel or oil that is
found underground. It’s also known as ‘crude oil’ or ‘mineral oil’.
Petroleum is a complex mixture of hydrocarbons that occur in the
sedimentary rocks in the form of gases (natural gas), liquids (crude
oil), semisolids (bitumen), or solids (wax or asphaltite).
Petroleum is used as:
1. A main source of energy for industry.
2. Heating and transportation.
3. It also provides the raw materials for the petrochemical plants to
produce polymers, plastics, and many other products.
Not only does petroleum provide fuel to run our vehicles, cook our
food, heat our homes and generate electricity, it is also used in
plastics, medicines, food items, and countless other products, from
aspirin to umbrellas.
Transportation needs use 66% of all available petroleum to fuel cars,
buses, trucks and jets. That means 34% of oil is used for all the other
items that make our daily lives easier.
Occurrence of petroleum and its formation:
The main elements of petroleum are carbon (C) and hydrogen (H)
and some small quantities of sulfur (S), nitrogen (N), and oxygen (O).
There are basically two theories explaining the origin of oil:
1. Organic Theory (Biotic Theory)
2. Inorganic Theory
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Organic Theory (Biotic Theory):
1. Oil developed millions of years from organic material remains of
dead plants and animals (algae and planktons).
2. The dead organisms sank to the bottom of water bodies (seas
and lakes), where the environment tends to be anaerobic.
3. They accumulated in the mud on the beds of the water bodies,
partially decomposed.
4. Sediment deposition on the bed of the water body, burying and
compressing the organic matter under its weight.
5. Increase in temperatures(100-160°C) and pressures resulted due
to continued sediment deposition.
6. With time, the conditions broke down the organic compounds
into shorter hydrocarbon chains, forming oil and natural gas
Inorganic Theory::
This theory assume the oil hydrocarbon compounds produced from
reaction hot water vapor with carbides which will form the
hydrocarbon substances under high pressure and temperature as
follows:
CaCO3 + alkali metal → CaC2 (calcium carbide)
∆ &P
CaC2 + H2O → HC CH (acetylene) → petroleum
≡
Chemical Composition of Petroleum
The different types of hydrocarbons that crude oil has are paraffins,
aromatics, cycloaliphatic or naphthenes and olefins.
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Paraffins:
The paraffin series of hydrocarbons is characterized by the rule that
the carbon atoms are connected by a single bond and the other
bonds are saturated with hydrogen atoms. The simplest paraffin is
methane, CH4, followed by the homologous series of ethane,
propane, normal and isobutane, etc.
Naphthenes or cycloparaffins:
Cycloparaffin hydrocarbons in which all of the available bonds of
the carbon atoms are saturated with hydrogen are called
naphthenes. Typical examples of these are cyclopentane,
cyclohexane, etc.
Aromatics:
The aromatic series of hydrocarbons is chemically and physically
very different from the paraffins and cycloparaffins (naphthenes).
Aromatic hydrocarbons contain a benzene ring which is
unsaturated but very stable and frequently behaves as a saturated
compound.
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Heteroatom compounds (non hydrocarbon compounds)
Sulfur compounds: It is the most important one that increase as
the density increased. The types of sulfur components in the
petroleum are:
Hydrogen sulfide H-S-H (or H2S)
Mercaptan: H-S-R, where R is Alkyl (H-S-CH3)
Hydrogen sulfide H-S-H (or H2S)
Disadvantages of sulfur components:
1. Environmental pollution
2. Decreases the life of machinery
3. Corrodes of pipes machines and equipment
4. Reduce O.N. (octane number) of gasoline
Nitrogen Compounds:
Organic nitrogen compounds occur in crude oils either in a simple
heterocyclic form as in pyridine (C5H5N) and pyrrole (C4H5N), or in a
complex structure as in porphyrin
Light petroleum streams may contain trace amounts of nitrogen
compounds, which should be removed because they poison many
processing catalysts
Oxygen Compounds:
Oxygen compounds in crude oils are more complex than the sulfur
types. However, their presence in petroleum streams is not
poisonous to processing catalysts
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Metallic Compounds:
Many metals occur in crude oils. Some of the more abundant are
sodium (Na), calcium (Ca), magnesium (Mg), aluminium (Al), iron
(Fe), vanadium (V), and nickel (Ni).
Disadvantages of Metallic Compounds::
1. Affected on catalyst activity
2. Reduced the yield of the gasoline
3. Form ash deposits – power generation plants
4. Causes corrosion of metal equipment and machinery in oil
refineries
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Classification of Petroleum
Classification as a hydrocarbon resource:
Petroleum is referred to generically as a fossil energy resource and
is further classified as a hydrocarbon resource, coal and oil shale
kerogen have also been included in this classification.
Classification by chemical composition:
The hydrocarbons found in petroleum are classified into the
following types:
1. Paraffine
2. cycloparaffins
3. Aromatic
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1.Paraffins, i.e., saturated hydrocarbons with straight or branched
chains, but, without any ring structure.
2.Cycloparaffins (naphthenes), i.e., saturated hydrocarbons
containing one or more rings, each of which may have one or
more paraffin side-chains (more
correctly known as (alicyclic hydrocarbons).
3.Aromatics, i.e., hydrocarbons containing one or more aromatic
nuclei such as benzene, naphthalene.
Classification by density and API gravity:
Density (specific gravity) has been, since the early years of the
industry, the principal, and often the only specification of crude oil
products and was taken as an index of the proportion of gasoline
and, particularly, kerosene present
Classification by viscosity
At the same time, and in concert with the use of API gravity, the
line of demarcation between petroleum and heavy oil vis-à-vis tar
sand bitumen has been drawn at 10,000 centipoises.
Briefly, materials having viscosity less than 10,000 centipoises (cp)
are conventional petroleum and heavy oil.
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Evaluation of Crude Oil
Evaluation of crude oil is important for refiner
because it gives the following types of information:
1. Base and general properties of the crude oil.
2. Presence of impurities such as sulfur, salt, and emulsions which
cause general difficulties in processing.
3. Operating or design data. Primarily this necessitates curves of
temperature and gravity vs. percent distilled.
4. Curves of the properties of the fractions vs. percent distilled (mid
per cent curves) or the average properties of a series of fractions
vs. percentage yield (yield curve).
5. Finished products. Having established the general properties
and yield by means of distillation and property curves and
exploring the economy of the various breakups of the crude oil
Physical Properties of Petroleum:
Petroleum exhibits a wide range of physical properties and several
relationships can be made between various physical properties.
Whereas properties such as viscosity, density, and boiling point of
petroleum may vary widely, the ultimate or elemental analysis
varies, as already noted, over a narrow range for a large number of
petroleum samples. The carbon content is relatively constant, while
the hydrogen and heteroatom contents are responsible for the
major differences between petroleum samples.
Refractive index (n):
Refractive index is a ratio technique that takes the velocity of light
in air at a specific wavelength and compares that to the velocity in
the sample tested Normally this is performed under the guidelines
of ASTM D-1218
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Surface and Interfacial Tension:
Surface tension is a measure of the force acting at a boundary
between two phases. If the boundary is between a liquid and a solid
or between a liquid and a gas (air) the attractive forces are referred
to as surface tension, but the attractive forces between two
immiscible liquids are referred to as interfacial tension.
Temperature and molecular weight have a significant effect on
surface tension. For example, in the normal hydrocarbon series, a
rise in temperature leads to a decrease in the surface tension, but
an increase in molecular weight increases the surface tension.
Octane number: (For gasoline):
Automotive engineers learned that straight-chain paraffins have a
much higher tendency to knock than do branched-chain paraffins.
The tendency of a particular gasoline to knock is expressed by its
octane number (ON).
The straight-chain paraffin heptane, C7H16, is arbitrarily assigned an
octane number of 0
To determine the octane number, the combustion performance of
a gasoline is compared in a standardized test engine with various
blends of heptane and isooctane. The octane number of the
gasoline is equal to the percentage of iso-octane in the blend that
gives the same knock performance as the gasoline being tested.
For example, a gasoline with ON=87 has the same engine
performance as a blend of 87% iso-octane and 13% heptane
The higher the octane number, the less likely it is that a gasoline
will cause engine knock
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Cetane number (diesel fuel):
The straight-chain paraffins, which are undesirable in gasoline, are
highly desirable components in diesel fuels. The standard of
performance of a diesel fuel is the cetane number. The cetane
number is determined in analogous fashion to the octane number.
In this case, the two reference compounds are hexadecane
(‘cetane’), C16H34, and methylnaphthalene, C11H10 Cetane is
assigned a cetane number of 100 and 1 methylnaphthalene, an
aromatic compound very unlikely to knock, is assigned a cetane
number of 0. Most commercially available diesel fuels have cetane
numbers in the range 30- 60. For automobiles or light trucks with
diesel engines a fuel with cetane number 52-54 is appropriate
Molecular weight:
Molecular weight (M) is perhaps the most important
characterization parameter for petroleum fractions and many
physical properties may be calculated from this parameter.
M can be predicted by using the following equation:
This equation can be applied to hydrocarbons with molecular
weight ranging from 70 to 700, which is nearly equivalent to boiling
point range of 300-850 K (90-1050F, 27-576 °C) and the API gravity
range of 14.4-93
For heavy petroleum fractions based on the molecular weight of
heavy fractions in the range of 200-800:
The three input parameters are kinematic viscosities (in cSt) at 38
and 98.9°C (100 and 210F) shown by v38(100) and v99(210),
respectively, and the specific gravity (SG) at 15.6°C.
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Metals content :
The metals concentration in crude oil can range from a few to
several thousand ppm. Low values of certain elements such as
nickel and vanadium can severely affect catalyst activity. In the past
metals were determined by Atomic Absorption, but now most
metals are determined by Inductively Coupled Plasma Emission
Spectroscopy ICPCES. X-ray fluorescence can be a viable technique
depending on the concentration
Crude Oil Pretreatment” Preparation of
Crude Oil for Distillation”: (DegassingDehydration & Desalting)
In a producing oil field, the fluid obtained at the wellhead is
submitted to degassing and dehydration operations
Degassing:
At the high pressure existing at the bottom of producing well,
crude oil contains great quantities of dissolved gases. When crude
oil is brought to the surface, it is at a much lower pressure.
Consequently, the gases that were dissolved in it at the higher
pressure tend to come out from the liquid
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Two – Phase Gas – Oil Separation (GOSP):
High pressure crude oils containing large amount of free dissolved
gas flow from the wellhead into the flow line, which routes the
mixture to the (GOSP). This is usually done by admitting the well
fluid into a gas – oil separator plant (GOSP) through which the
pressure of the gas – oil mixture is successively reduced to
atmospheric pressure in a few stages
In the separator, crude oil separates out, settles, and collects in the
lower part of the vessel
Gas goes out the top of the separators to a gas collection system, a
vapor recovery unit (VRU), or a gas flow line
Crude oil, on the other hand, goes out the bottom and is routed to
other stages of separation, if necessary, and then to the stock tank
Fig.: Separation of gas from oil.
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