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2
Classification
2.1 INTRODUCTION
By definition (Chapter 1), petroleum (also called crude oil) is a mixture of gaseous, liquid, and solid
hydrocarbon compounds. Petroleum occurs in sedimentary rock deposits throughout the world and
also contains small quantities of nitrogen-, oxygen-, and sulfur-containing compounds, as well as
trace amounts of metallic constituents (Speight, 2000; Hsu and Robinson, 2006; Ancheyta and
Speight, 2007; Gary et al., 2007). Thus, the classification of petroleum as a hydrocarbon mixture
should follow from this definition. But some clarification is required.
Petroleum itself is defined as a naturally occurring mixture of hydrocarbons, generally in a liquid state, which may also include compounds of sulfur nitrogen oxygen metals and other elements
(ASTM D4175). In more specific terms, petroleum has also been defined (ITAA, 1936) as
1. Any naturally occurring hydrocarbon, whether in a liquid, gaseous, or solid state
2. Any naturally occurring mixture of hydrocarbons, whether in a liquid, gaseous, or solid
state
3. Any naturally occurring mixture of one or more hydrocarbons, whether in a liquid,
gaseous, or solid state, and one or more of the following, that is to say, hydrogen sulfide,
helium, and carbon dioxide
The definition includes any petroleum as defined by paragraphs (1), (2), or (3) that has been returned
to a natural reservoir.
One of the disadvantages in attempting to classify petroleum, compared to the classification of
coal, is that the elemental (ultimate) composition of petroleum (Chapter 8) is not reported to the
same extent as it is for coal (Lowry, 1945, 1963; Meyers, 1981; Hessley, 1990; Speight, 2013). The
proportions of the elements in petroleum vary only slightly over fairly narrow limits in spite of the
wide variation in physical properties from the lighter, more mobile (conventional) crude oil to bitumen at the other extreme. Thus, as a result of the wide variety of organic constituents and physical
conditions that can play a role in the formation of petroleum, it is not surprising that there exists a
wide variation in composition and properties resulting in a variety of attempts to classify petroleum.
Like coal, petroleum exhibits a wide range of physical properties, but these properties are less
well defined than they are in coal classification systems. The general classification of petroleum into
conventional petroleum, heavy oil, and extra heavy oil involves not only an inspection of several
properties but also some acknowledgment of the method of recovery (Chapter 6). However, there is
a correlation that can be made between various physical properties. Whereas the properties such as
viscosity, density, boiling point, and color 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
(Chapters 8 and 10).
In terms of the elemental composition of petroleum, the carbon content is relatively constant, while
the hydrogen and heteroatom contents are responsible for the major differences between petroleum.
Nitrogen, oxygen, and sulfur can be present in only trace amounts in some petroleum, which as a
result consists primarily of hydrocarbons. On the other hand, a crude oil containing 9.5% heteroatom
constituents may contain essentially no true hydrocarbon constituents insofar as the constituents
contain at least one or more nitrogen, oxygen, and/or sulfur atoms within the molecular structures.
2
Classification
2.1 INTRODUCTION
By definition (Chapter 1), petroleum (also called crude oil) is a mixture of gaseous, liquid, and solid
hydrocarbon compounds. Petroleum occurs in sedimentary rock deposits throughout the world and
also contains small quantities of nitrogen-, oxygen-, and sulfur-containing compounds, as well as
trace amounts of metallic constituents (Speight, 2000; Hsu and Robinson, 2006; Ancheyta and
Speight, 2007; Gary et al., 2007). Thus, the classification of petroleum as a hydrocarbon mixture
should follow from this definition. But some clarification is required.
Petroleum itself is defined as a naturally occurring mixture of hydrocarbons, generally in a liquid state, which may also include compounds of sulfur nitrogen oxygen metals and other elements
(ASTM D4175). In more specific terms, petroleum has also been defined (ITAA, 1936) as
1. Any naturally occurring hydrocarbon, whether in a liquid, gaseous, or solid state
2. Any naturally occurring mixture of hydrocarbons, whether in a liquid, gaseous, or solid
state
3. Any naturally occurring mixture of one or more hydrocarbons, whether in a liquid,
gaseous, or solid state, and one or more of the following, that is to say, hydrogen sulfide,
helium, and carbon dioxide
The definition includes any petroleum as defined by paragraphs (1), (2), or (3) that has been returned
to a natural reservoir.
One of the disadvantages in attempting to classify petroleum, compared to the classification of
coal, is that the elemental (ultimate) composition of petroleum (Chapter 8) is not reported to the
same extent as it is for coal (Lowry, 1945, 1963; Meyers, 1981; Hessley, 1990; Speight, 2013). The
proportions of the elements in petroleum vary only slightly over fairly narrow limits in spite of the
wide variation in physical properties from the lighter, more mobile (conventional) crude oil to bitumen at the other extreme. Thus, as a result of the wide variety of organic constituents and physical
conditions that can play a role in the formation of petroleum, it is not surprising that there exists a
wide variation in composition and properties resulting in a variety of attempts to classify petroleum.
Like coal, petroleum exhibits a wide range of physical properties, but these properties are less
well defined than they are in coal classification systems. The general classification of petroleum into
conventional petroleum, heavy oil, and extra heavy oil involves not only an inspection of several
properties but also some acknowledgment of the method of recovery (Chapter 6). However, there is
a correlation that can be made between various physical properties. Whereas the properties such as
viscosity, density, boiling point, and color 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
(Chapters 8 and 10).
In terms of the elemental composition of petroleum, the carbon content is relatively constant, while
the hydrogen and heteroatom contents are responsible for the major differences between petroleum.
Nitrogen, oxygen, and sulfur can be present in only trace amounts in some petroleum, which as a
result consists primarily of hydrocarbons. On the other hand, a crude oil containing 9.5% heteroatom
constituents may contain essentially no true hydrocarbon constituents insofar as the constituents
contain at least one or more nitrogen, oxygen, and/or sulfur atoms within the molecular structures.