358
The Chemistry and Technology of Petroleum
Petroleum is a continuum and each component fraction depends upon the other for the stability
of the whole oil. The omission of a critical fraction in these referenced studies (Sheu et al., 1992)
may have serious consequences on the data and the magnitude of the conclusions.
For example, questions related to the role played by this fraction in the structure and stability
of the micelle are not answered. Furthermore, there is also some doubt about the viability of the
data as they relate to petroleum macrostructure that, in turn, is very real in terms of the structure and the behavior of petroleum in refining operations, especially as the CMC relates to coke
formation.
It therefore appears that another means of data analysis would be preferable in studies of CMC.
The fractions chosen for such a study must be chosen carefully, and, based on the precept that
petroleum is a continuum, conclusions derived from separate fractions must be subject to question.
It is the general consensus that it is the polar, that is, heteroatom, constituents of petroleum,
which are responsible for the formation of suspended organic solids during a variety of recovery
processes (Islam, 1994; Park et al., 1994). However, an area that remains largely undefined, insofar
as the chemistry and physics are still speculative, is the phenomenon of the incompatibility of the
crude oil constituents, as might occur during these operations. The formation of a suspended solid
phase during recovery (as well as during refining operations) is related to the chemical and physical
structure of petroleum; the latter is greatly influenced by the former.
By way of a brief series of definition, the failure of petroleum fractions to mix and the separation
of a separate phase is usually referred to as incompatibility. When incompatibility occurs, the constituents (usually the asphaltenes and the resins) that form a separate phase are variously referred
to as precipitate, sediment, and/or sludge depending upon the nature of the material and the causes
of the separation.
Asphaltenes and asphaltene-related materials are known to deposit as sediments during recovery
operations in the vicinity of production wells during miscible floods, after acid stimulation, or during pressure changes (Burke et al., 1990; Islam, 1994; Park et al., 1994). Many reservoirs produce
without any such problems until the oil stability is perturbed during later stages of oil production.
The parameters that govern sediment formation and deposition of asphaltene constituents
(as a bulk fraction) from petroleum are related to the composition of the crude oil (Chapters 10
and 12). It must also be recognized that the material that deposits from the crude oil as a separate
phase is more aromatic and richer in heteroatom compounds than the original crude oil. In fact, in
some cases, especially when oxidation has occurred, the deposited material is more aromatic and
richer in heteroatoms than the asphaltenes.
In terms of the crude oil parameters that influence sediment formation, there has been considerable focus on the asphaltene content as well as the chemistry and physics of the asphaltenes relationship to the remainder of the oil. For example, while the asphaltene content of petroleum oils varies
over a wide range (Koots and Speight, 1975), asphaltene content is not the single determining influence on sediment formation. It has been noted that asphaltene/resin ratios are usually below unity
in oils that are stable and higher than unity in oils that exhibit ready precipitation of asphaltenic
material (Sachanen, 1945).
Even though it is generally understood that asphaltene content of a crude oil increases with
decreasing American Petroleum Institute (API) gravity, asphaltene precipitation has also been
reported in light oils as well. Such an effect (gas deasphalting) arises from the increased solubility of hydrocarbon gases in the petroleum as reservoir pressure increases during maturation.
Incompatibility will also occur when asphaltenes interact with reservoir rock, especially acidic functions of rocks, through the functional groups (e.g., the basic nitrogen species) just as they interact
with adsorbents. And, there is the possibility for interaction of the asphaltene with the reservoir rock
through the agency of a single functional group in which the remainder of the asphaltene molecule
remains in the liquid phase (vertical association relative to the rock surface). On the other hand, the
asphaltene constituents can react with the rock at several points of contact (horizontal association
relative to the rock surface), thereby enhancing the bonding to the rock and, in some cases, effecting
The Chemistry and Technology of Petroleum
Petroleum is a continuum and each component fraction depends upon the other for the stability
of the whole oil. The omission of a critical fraction in these referenced studies (Sheu et al., 1992)
may have serious consequences on the data and the magnitude of the conclusions.
For example, questions related to the role played by this fraction in the structure and stability
of the micelle are not answered. Furthermore, there is also some doubt about the viability of the
data as they relate to petroleum macrostructure that, in turn, is very real in terms of the structure and the behavior of petroleum in refining operations, especially as the CMC relates to coke
formation.
It therefore appears that another means of data analysis would be preferable in studies of CMC.
The fractions chosen for such a study must be chosen carefully, and, based on the precept that
petroleum is a continuum, conclusions derived from separate fractions must be subject to question.
It is the general consensus that it is the polar, that is, heteroatom, constituents of petroleum,
which are responsible for the formation of suspended organic solids during a variety of recovery
processes (Islam, 1994; Park et al., 1994). However, an area that remains largely undefined, insofar
as the chemistry and physics are still speculative, is the phenomenon of the incompatibility of the
crude oil constituents, as might occur during these operations. The formation of a suspended solid
phase during recovery (as well as during refining operations) is related to the chemical and physical
structure of petroleum; the latter is greatly influenced by the former.
By way of a brief series of definition, the failure of petroleum fractions to mix and the separation
of a separate phase is usually referred to as incompatibility. When incompatibility occurs, the constituents (usually the asphaltenes and the resins) that form a separate phase are variously referred
to as precipitate, sediment, and/or sludge depending upon the nature of the material and the causes
of the separation.
Asphaltenes and asphaltene-related materials are known to deposit as sediments during recovery
operations in the vicinity of production wells during miscible floods, after acid stimulation, or during pressure changes (Burke et al., 1990; Islam, 1994; Park et al., 1994). Many reservoirs produce
without any such problems until the oil stability is perturbed during later stages of oil production.
The parameters that govern sediment formation and deposition of asphaltene constituents
(as a bulk fraction) from petroleum are related to the composition of the crude oil (Chapters 10
and 12). It must also be recognized that the material that deposits from the crude oil as a separate
phase is more aromatic and richer in heteroatom compounds than the original crude oil. In fact, in
some cases, especially when oxidation has occurred, the deposited material is more aromatic and
richer in heteroatoms than the asphaltenes.
In terms of the crude oil parameters that influence sediment formation, there has been considerable focus on the asphaltene content as well as the chemistry and physics of the asphaltenes relationship to the remainder of the oil. For example, while the asphaltene content of petroleum oils varies
over a wide range (Koots and Speight, 1975), asphaltene content is not the single determining influence on sediment formation. It has been noted that asphaltene/resin ratios are usually below unity
in oils that are stable and higher than unity in oils that exhibit ready precipitation of asphaltenic
material (Sachanen, 1945).
Even though it is generally understood that asphaltene content of a crude oil increases with
decreasing American Petroleum Institute (API) gravity, asphaltene precipitation has also been
reported in light oils as well. Such an effect (gas deasphalting) arises from the increased solubility of hydrocarbon gases in the petroleum as reservoir pressure increases during maturation.
Incompatibility will also occur when asphaltenes interact with reservoir rock, especially acidic functions of rocks, through the functional groups (e.g., the basic nitrogen species) just as they interact
with adsorbents. And, there is the possibility for interaction of the asphaltene with the reservoir rock
through the agency of a single functional group in which the remainder of the asphaltene molecule
remains in the liquid phase (vertical association relative to the rock surface). On the other hand, the
asphaltene constituents can react with the rock at several points of contact (horizontal association
relative to the rock surface), thereby enhancing the bonding to the rock and, in some cases, effecting