34
The Chemistry and Technology of Petroleum
In summary, the classification of petroleum and natural gas as naturally occurring mixtures
of hydrocarbons occurs by virtue of the fact that can be separated into their original hydrocarbon constituents that have not been altered by any applied process. The hydrocarbon constituents separated from petroleum and natural gas are the hydrocarbon constituents that existed
in the reservoir. Naturally occurring hydrocarbons are major contributors to the composition
of petroleum and natural gas. Coal and kerogen do not enjoy this means of separation, and
methods of thermal decomposition must be applied before hydrocarbons are produced. And
these hydrocarbon products, generated by the thermal process, are not naturally occurring
hydrocarbons.
2.2.2 ClAssIFICAtIon By CHemICAl ComPosItIon
Composition refers to the specific mixture of chemical compounds that constitute petroleum.
The composition of these materials is related to the nature and mix of the organic material that
generated the hydrocarbons. Composition is also subject to the influence of natural processes
such as migration (movement of oil from source rock to reservoir rock), biodegradation (alteration
by the action of microbes), and water washing (effect of contact with water flowing in the subsurface) upon that composition. Thus, petroleum is the result of the metamorphosis of natural
products as a result of chemical and physical changes imparted by the prevailing conditions at a
particular locale.
The composition of petroleum obtained from the well is variable and depends not only on the
original composition of the oil in situ but also on the manner of production and the stage reached
in the life of the well or reservoir. In general terms, petroleum (conventional crude oil) ranges
from a brownish green to black liquid having a specific gravity (at 60°F, 15.6°C) that varies from
about 0.75 to 1.00 (57° to 10°API), with the specific gravity of most crude oils falling in the range
0.80–0.95 (45°–17°API). The boiling range of petroleum varies from about 20°C (68°F) to above
350°C (660°F), above which active decomposition ensues when distillation is attempted. Petroleum
can contain from 0% to 35% or more of gasoline, as well as varying proportions of kerosene hydrocarbons and higher boiling constituents up to the viscous and nonvolatile compounds present in
lubricant oil and in asphalt.
Thus, petroleum varies in composition from one oil field to another, from one well to another in
the same field, and even from one level to another in the same well. This variation can be in both
molecular weight and the types of molecules present in petroleum. Petroleum may well be described
as a mixture of organic molecules drawn from a wide distribution of molecular types that lie within
a wide distribution of molecular weight.
Petroleum is often described as a hydrocarbon resource. However, by definition, a hydrocarbon
contains carbon and hydrogen only (Morrison and Boyd, 1973; Fessenden and Fessenden, 1990).
On the other hand, if an organic compound contains nitrogen, and/or sulfur, and/or oxygen, and/or
metals, it is a heteroatomic compound and not a hydrocarbon. Organic compounds containing heteroelements (elements such as nitrogen, oxygen, and sulfur), in addition to carbon and hydrogen,
are defined in terms of the locations of these heteroelements within the molecule. In fact, it is, to a
large extent, the heteroatomic function that determines the chemical and physical reactivity of the
heteroatomic compounds (Morrison and Boyd, 1973; Fessenden and Fessenden, 1990). And the
chemical and physical reactivity of the heteroatomic compounds is quite different from the chemical and physical reactivity of the hydrocarbons.
Naturally occurring hydrocarbons are those molecules that contain carbon and hydrogen only
and that occur in nature. The term naturally occurring hydrocarbons does not apply to those
hydrocarbons that are produced by applied processes such as the thermal decomposition of coal to
produce liquids and gases or the retorting (thermal decomposition) of oil shale kerogen to produce
shale oil.
The Chemistry and Technology of Petroleum
In summary, the classification of petroleum and natural gas as naturally occurring mixtures
of hydrocarbons occurs by virtue of the fact that can be separated into their original hydrocarbon constituents that have not been altered by any applied process. The hydrocarbon constituents separated from petroleum and natural gas are the hydrocarbon constituents that existed
in the reservoir. Naturally occurring hydrocarbons are major contributors to the composition
of petroleum and natural gas. Coal and kerogen do not enjoy this means of separation, and
methods of thermal decomposition must be applied before hydrocarbons are produced. And
these hydrocarbon products, generated by the thermal process, are not naturally occurring
hydrocarbons.
2.2.2 ClAssIFICAtIon By CHemICAl ComPosItIon
Composition refers to the specific mixture of chemical compounds that constitute petroleum.
The composition of these materials is related to the nature and mix of the organic material that
generated the hydrocarbons. Composition is also subject to the influence of natural processes
such as migration (movement of oil from source rock to reservoir rock), biodegradation (alteration
by the action of microbes), and water washing (effect of contact with water flowing in the subsurface) upon that composition. Thus, petroleum is the result of the metamorphosis of natural
products as a result of chemical and physical changes imparted by the prevailing conditions at a
particular locale.
The composition of petroleum obtained from the well is variable and depends not only on the
original composition of the oil in situ but also on the manner of production and the stage reached
in the life of the well or reservoir. In general terms, petroleum (conventional crude oil) ranges
from a brownish green to black liquid having a specific gravity (at 60°F, 15.6°C) that varies from
about 0.75 to 1.00 (57° to 10°API), with the specific gravity of most crude oils falling in the range
0.80–0.95 (45°–17°API). The boiling range of petroleum varies from about 20°C (68°F) to above
350°C (660°F), above which active decomposition ensues when distillation is attempted. Petroleum
can contain from 0% to 35% or more of gasoline, as well as varying proportions of kerosene hydrocarbons and higher boiling constituents up to the viscous and nonvolatile compounds present in
lubricant oil and in asphalt.
Thus, petroleum varies in composition from one oil field to another, from one well to another in
the same field, and even from one level to another in the same well. This variation can be in both
molecular weight and the types of molecules present in petroleum. Petroleum may well be described
as a mixture of organic molecules drawn from a wide distribution of molecular types that lie within
a wide distribution of molecular weight.
Petroleum is often described as a hydrocarbon resource. However, by definition, a hydrocarbon
contains carbon and hydrogen only (Morrison and Boyd, 1973; Fessenden and Fessenden, 1990).
On the other hand, if an organic compound contains nitrogen, and/or sulfur, and/or oxygen, and/or
metals, it is a heteroatomic compound and not a hydrocarbon. Organic compounds containing heteroelements (elements such as nitrogen, oxygen, and sulfur), in addition to carbon and hydrogen,
are defined in terms of the locations of these heteroelements within the molecule. In fact, it is, to a
large extent, the heteroatomic function that determines the chemical and physical reactivity of the
heteroatomic compounds (Morrison and Boyd, 1973; Fessenden and Fessenden, 1990). And the
chemical and physical reactivity of the heteroatomic compounds is quite different from the chemical and physical reactivity of the hydrocarbons.
Naturally occurring hydrocarbons are those molecules that contain carbon and hydrogen only
and that occur in nature. The term naturally occurring hydrocarbons does not apply to those
hydrocarbons that are produced by applied processes such as the thermal decomposition of coal to
produce liquids and gases or the retorting (thermal decomposition) of oil shale kerogen to produce
shale oil.