56
The Chemistry and Technology of Petroleum
Except for the production of methane, bacteria tend to leave organic compounds bearing carboxyl
(–CO 2 H), hydroxyl (–OH), amine (–NH 2 ), and sulfhydryl (–SH) groups rather than effect the complete removal of oxygen, nitrogen, or sulfur atoms to produce hydrocarbons. From the observation
that tyrosine could be fermented to yield either phenol or p-cresol, it was assumed that phenylalanine might be made to yield benzene or toluene, but using the same cultures, no trace of either
hydrocarbon could be detected.
The abundant production of methane (CH 4 ) originally suggested that the higher paraffins may
also be produced in this manner. However, analysis of the products of a wide variety of microbial
fermentation processes failed to show anything more than trace amounts of ethane (C 2 H 6 ) or higher
molecular weight paraffins (C n H 2n+2 , where n > 3).
Hydrocarbons are synthesized by bacteria as a part of their cell substance. Extracts of autotrophic bacteria cultures (which use molecular hydrogen as the sole source of energy and carbon dioxide or carbonate as the sole source of carbon) were demonstrated to contain at least 25% paraffins
and cycloparaffins (naphthenes). It appears likely that this is, at least, one of the sources of some
of the heavier hydrocarbons in recent sediments. The possibility that biocatalysts or enzymes are
involved in the formation of hydrocarbons cannot be discounted at the present time. A wide variety of such organic catalysts is produced by bacteria; it is possible that, under the prevailing lowtemperature anaerobic conditions, these substances may function for some time after the organisms
that produced them have ceased to exist.
Ring formation (cyclization) and polymerization reactions have been noted to occur in the same
temperature range for several unsaturated fatty acids of marine organisms, and it is conceivable that
such polyene-type reactions may well contribute substantially to the naphthene-aromatic fraction
of crude oil. Chemical reactions of this type are particularly attractive because the clays and other
fine-grained materials, which are always present in the sediment, may act as catalysts for hydrocarbon synthesis as well as for the degradation of the organic source material to hydrocarbons. In fact,
it has been suggested that any of several naturally occurring minerals might be active in promoting
polymerization, and the idea has been developed further to include hydro-polymerization, isomerization, and cyclization to explain the variety of hydrocarbon types present in petroleum.
The most serious objection to be raised against the catalytic investigations is that the majority of
the laboratory studies have been carried out in the absence of water, whereas water is always present in sediments. The adsorption of water on the mineral components may substantially reduce any
catalytic activity and also seriously alter their catalytic nature. However, some components of crude
oil, as well as source material types, can be adsorbed by clays from an aqueous medium. It has been
shown that a wide variety of substances will enter the clay lattice to form highly stable complexes.
For example, protein in combination with clay is substantially more resistant to bacterial destruction
than protein alone; possibly, in the adsorbed condition, time is available for slow chemical reaction
that might otherwise not occur.
It is appropriate at this point to introduce the concept of organic facies, which are stratigraphic
rock units differentiated from adjacent or associated units by appearances or by characteristics that
usually reflect the origin (Bates and Jackson, 1980; Demaison et al., 1984).
Organic facies I (strongly oil prone) are typical of the strongly anoxic environments of stratified
lacustrine and marine locales. The strata are laminated, and the absence of bioturbation (mixing)
indicates that benthic organisms were absent from the depositional environment. Organic facies II
(oil prone) are also typical of anoxic environments but may include moderately oxic environments
that had high rates of deposition. The carbon contents of the type II facies are generally lower than
those of type I facies and are often in the range of 1%–10% total organic carbon. On the other hand,
organic facies III (gas prone) are typical of the mildly oxic conditions in coal swamps or shallow
marine environments.
Any planktonic or algal material deposited in such an environment is usually degraded quickly
by benthic organisms. Preserved material of aquatic origin is usually thoroughly bioturbated.
Finally, organic facies IV (nonsource) are typical of aquatic environments in which organic matter
The Chemistry and Technology of Petroleum
Except for the production of methane, bacteria tend to leave organic compounds bearing carboxyl
(–CO 2 H), hydroxyl (–OH), amine (–NH 2 ), and sulfhydryl (–SH) groups rather than effect the complete removal of oxygen, nitrogen, or sulfur atoms to produce hydrocarbons. From the observation
that tyrosine could be fermented to yield either phenol or p-cresol, it was assumed that phenylalanine might be made to yield benzene or toluene, but using the same cultures, no trace of either
hydrocarbon could be detected.
The abundant production of methane (CH 4 ) originally suggested that the higher paraffins may
also be produced in this manner. However, analysis of the products of a wide variety of microbial
fermentation processes failed to show anything more than trace amounts of ethane (C 2 H 6 ) or higher
molecular weight paraffins (C n H 2n+2 , where n > 3).
Hydrocarbons are synthesized by bacteria as a part of their cell substance. Extracts of autotrophic bacteria cultures (which use molecular hydrogen as the sole source of energy and carbon dioxide or carbonate as the sole source of carbon) were demonstrated to contain at least 25% paraffins
and cycloparaffins (naphthenes). It appears likely that this is, at least, one of the sources of some
of the heavier hydrocarbons in recent sediments. The possibility that biocatalysts or enzymes are
involved in the formation of hydrocarbons cannot be discounted at the present time. A wide variety of such organic catalysts is produced by bacteria; it is possible that, under the prevailing lowtemperature anaerobic conditions, these substances may function for some time after the organisms
that produced them have ceased to exist.
Ring formation (cyclization) and polymerization reactions have been noted to occur in the same
temperature range for several unsaturated fatty acids of marine organisms, and it is conceivable that
such polyene-type reactions may well contribute substantially to the naphthene-aromatic fraction
of crude oil. Chemical reactions of this type are particularly attractive because the clays and other
fine-grained materials, which are always present in the sediment, may act as catalysts for hydrocarbon synthesis as well as for the degradation of the organic source material to hydrocarbons. In fact,
it has been suggested that any of several naturally occurring minerals might be active in promoting
polymerization, and the idea has been developed further to include hydro-polymerization, isomerization, and cyclization to explain the variety of hydrocarbon types present in petroleum.
The most serious objection to be raised against the catalytic investigations is that the majority of
the laboratory studies have been carried out in the absence of water, whereas water is always present in sediments. The adsorption of water on the mineral components may substantially reduce any
catalytic activity and also seriously alter their catalytic nature. However, some components of crude
oil, as well as source material types, can be adsorbed by clays from an aqueous medium. It has been
shown that a wide variety of substances will enter the clay lattice to form highly stable complexes.
For example, protein in combination with clay is substantially more resistant to bacterial destruction
than protein alone; possibly, in the adsorbed condition, time is available for slow chemical reaction
that might otherwise not occur.
It is appropriate at this point to introduce the concept of organic facies, which are stratigraphic
rock units differentiated from adjacent or associated units by appearances or by characteristics that
usually reflect the origin (Bates and Jackson, 1980; Demaison et al., 1984).
Organic facies I (strongly oil prone) are typical of the strongly anoxic environments of stratified
lacustrine and marine locales. The strata are laminated, and the absence of bioturbation (mixing)
indicates that benthic organisms were absent from the depositional environment. Organic facies II
(oil prone) are also typical of anoxic environments but may include moderately oxic environments
that had high rates of deposition. The carbon contents of the type II facies are generally lower than
those of type I facies and are often in the range of 1%–10% total organic carbon. On the other hand,
organic facies III (gas prone) are typical of the mildly oxic conditions in coal swamps or shallow
marine environments.
Any planktonic or algal material deposited in such an environment is usually degraded quickly
by benthic organisms. Preserved material of aquatic origin is usually thoroughly bioturbated.
Finally, organic facies IV (nonsource) are typical of aquatic environments in which organic matter