111
Kerogen
and high for type III kerogen. In contrast to the hydrocarbon products, the proportion of carbon
dioxide generated is higher for type III kerogen, and the transformation of type III kerogen is progressive and extends over a wide temperature range. The transformation interval is much narrower
and the temperature of maximum weight loss is higher for type I kerogen.
Thus, the main feature in laboratory-simulated kerogen evolution is the emergence of a carbon
order that progressively extends over wider areas and becomes stronger with increasing temperature. Elimination of the steric hinders the order of the results in the formation of a wide range of
compounds, including medium- to low-molecular-weight hydrocarbons, carbon dioxide, water, and
hydrogen sulfide.
Interesting as these observations may be, natural modifications observed in sedimentary organic
matter are brought about at relatively low temperatures with compensation by the long geological
periods involved. In addition, the occurrence of catalytic effects should also be invoked to explain
the low-temperature reaction processes that can occur over geological time. Thus there are important differences between pyrolysis and natural evolution.
The concept of the low-temperature maturation of kerogen has been developed further (Quigley
et al., 1987) and has resulted in the classification of kerogen into reactive and nonreactive types.
Thus kerogen is postulated as composed of labile, refractory, and inert moieties that can decompose
into gas and oil depending upon the prevailing conditions. It is assumed that the general categories
of materials or organisms that are shown to produce the oil and/or the kerogen are consistent with
those chemicals assumed to be precursors to petroleum (Chapter 3). In fact, there has been the suggestion that asphaltene constituents contain the same chemical moieties as kerogen (Béhar et al.,
1984; Orr, 1986; Pelet et al., 1986). This can also be interpreted as a divergence in the maturation
path in which kerogen takes one route and the protopetroleum another.
What also makes this hypothesis interesting, and perhaps more realistic than others, is the inclusion of a provision for the generation of petroleum without the intermediate formation of kerogen.
I believe this is more in keeping with petroleum formation than any theory that requires kerogen
as a necessary intermediate in the formation of petroleum.
REFERENCES
Barakat, A.O. and Yen, T.F. 1988. Novel identification of 17-β-(H)-hopanoids in Green River oil shale kerogen.
Energy Fuels, 2(1): 105–108.
Béhar, F., Pelet, R., and Roucache, J. 1984. Geochemistry of asphaltenes. Organic Geochemistry, 6: 595.
Béhar, F. and Vandenbroucke, M. 1986. Representation chimique de la structure des kérogènes et des
asphaltènes en fonction de leur origine et de leur degré d’évolution. Revue Institut Français du Pétrole,
41: 173–188.
Brooks, J. 1981. Organic Maturation Studies and Fossil Fuel Exploration. Academic Press, London, U.K.
Brooks, J. and Welte, D. 1984. Advances in Petroleum Geochemistry. Academic Press, London, U.K.
Burnham, A. K. 1995. Relationship between hydrous and ordinary pyrolysis. In Composition, Geochemistry
and Conversion of Oil Shales, C. Snape (Ed.). Kluwer Academic Publishers, Dordrecht, the Netherlands,
pp. 211–227.
Cane, R. F. 1976. The origin and formation of oil shale. In Oil Shale, T. F. Yen and G. V. Chilingarian (Eds.).
Elsevier, Amsterdam, the Netherlands.
Cummins, J. J. and Robinson, W. E. 1964. Normal and isoprenoid hydrocarbons. Isolated from oil-shale bitumen. Journal of Chemical Engineering Data, 9: 304–307.
Durand, B. 1980. Kerogen: Insoluble Organic Matter from Sedimentary Rocks. Editions Technip, Paris, France.
Durand, B., Espitalité, J., Nicase, G., and Combaz, A. 1972. Analyse Élémentaire, Études en Microscopie et
Diffraction Électroniques. Revue Institut Français du Pétrole, 27: 865–884.
Erdman, J. G. 1981. Geochemistry of petroleum. In Origin and Chemistry of Petroleum, G. Atkinson and J. J.
Zuckerman (Eds.). Pergamon Press, New York.
Espitalité, J., Durand, B., Roussel, J.C., and Souron, C. 1973. Etude de la Matière Organique Insoluble
(Kérogène) des Argiles du Toarcien du Bassin de Paris. II—Etudes en Spectrométrie Infrarouge, en
Analyse Thermique Différentielle et en Analyse Thermogravimétrique. Révue Institut Français du
Petrole, 28: 37–66.
Kerogen
and high for type III kerogen. In contrast to the hydrocarbon products, the proportion of carbon
dioxide generated is higher for type III kerogen, and the transformation of type III kerogen is progressive and extends over a wide temperature range. The transformation interval is much narrower
and the temperature of maximum weight loss is higher for type I kerogen.
Thus, the main feature in laboratory-simulated kerogen evolution is the emergence of a carbon
order that progressively extends over wider areas and becomes stronger with increasing temperature. Elimination of the steric hinders the order of the results in the formation of a wide range of
compounds, including medium- to low-molecular-weight hydrocarbons, carbon dioxide, water, and
hydrogen sulfide.
Interesting as these observations may be, natural modifications observed in sedimentary organic
matter are brought about at relatively low temperatures with compensation by the long geological
periods involved. In addition, the occurrence of catalytic effects should also be invoked to explain
the low-temperature reaction processes that can occur over geological time. Thus there are important differences between pyrolysis and natural evolution.
The concept of the low-temperature maturation of kerogen has been developed further (Quigley
et al., 1987) and has resulted in the classification of kerogen into reactive and nonreactive types.
Thus kerogen is postulated as composed of labile, refractory, and inert moieties that can decompose
into gas and oil depending upon the prevailing conditions. It is assumed that the general categories
of materials or organisms that are shown to produce the oil and/or the kerogen are consistent with
those chemicals assumed to be precursors to petroleum (Chapter 3). In fact, there has been the suggestion that asphaltene constituents contain the same chemical moieties as kerogen (Béhar et al.,
1984; Orr, 1986; Pelet et al., 1986). This can also be interpreted as a divergence in the maturation
path in which kerogen takes one route and the protopetroleum another.
What also makes this hypothesis interesting, and perhaps more realistic than others, is the inclusion of a provision for the generation of petroleum without the intermediate formation of kerogen.
I believe this is more in keeping with petroleum formation than any theory that requires kerogen
as a necessary intermediate in the formation of petroleum.
REFERENCES
Barakat, A.O. and Yen, T.F. 1988. Novel identification of 17-β-(H)-hopanoids in Green River oil shale kerogen.
Energy Fuels, 2(1): 105–108.
Béhar, F., Pelet, R., and Roucache, J. 1984. Geochemistry of asphaltenes. Organic Geochemistry, 6: 595.
Béhar, F. and Vandenbroucke, M. 1986. Representation chimique de la structure des kérogènes et des
asphaltènes en fonction de leur origine et de leur degré d’évolution. Revue Institut Français du Pétrole,
41: 173–188.
Brooks, J. 1981. Organic Maturation Studies and Fossil Fuel Exploration. Academic Press, London, U.K.
Brooks, J. and Welte, D. 1984. Advances in Petroleum Geochemistry. Academic Press, London, U.K.
Burnham, A. K. 1995. Relationship between hydrous and ordinary pyrolysis. In Composition, Geochemistry
and Conversion of Oil Shales, C. Snape (Ed.). Kluwer Academic Publishers, Dordrecht, the Netherlands,
pp. 211–227.
Cane, R. F. 1976. The origin and formation of oil shale. In Oil Shale, T. F. Yen and G. V. Chilingarian (Eds.).
Elsevier, Amsterdam, the Netherlands.
Cummins, J. J. and Robinson, W. E. 1964. Normal and isoprenoid hydrocarbons. Isolated from oil-shale bitumen. Journal of Chemical Engineering Data, 9: 304–307.
Durand, B. 1980. Kerogen: Insoluble Organic Matter from Sedimentary Rocks. Editions Technip, Paris, France.
Durand, B., Espitalité, J., Nicase, G., and Combaz, A. 1972. Analyse Élémentaire, Études en Microscopie et
Diffraction Électroniques. Revue Institut Français du Pétrole, 27: 865–884.
Erdman, J. G. 1981. Geochemistry of petroleum. In Origin and Chemistry of Petroleum, G. Atkinson and J. J.
Zuckerman (Eds.). Pergamon Press, New York.
Espitalité, J., Durand, B., Roussel, J.C., and Souron, C. 1973. Etude de la Matière Organique Insoluble
(Kérogène) des Argiles du Toarcien du Bassin de Paris. II—Etudes en Spectrométrie Infrarouge, en
Analyse Thermique Différentielle et en Analyse Thermogravimétrique. Révue Institut Français du
Petrole, 28: 37–66.