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Geology & Geochemistry of Combustible Minerals No. 3 (180) 2019, 25-40.

Yuri Khokha, Oleksandr Lyubchak, Myroslava Yakovenko

Institute of Geology and Geochemistry of Combustible Minerals of National Academy of Sciences of Ukraine, Lviv,


The article reviews the chemical structure of type II kerogen. The changes that occur with the structure of type II kerogen as it passes through the stages of catagenesis from immature to post-mature are evaluated. Structural models of type II kerogen at different stages of catagenesis are presented: both obtained empirically after studying the structure by physical and chemical methods and the results of modelling by molecular dynamics method.

Methods of equilibrium thermodynamics are used to calculate the composition of the kerogen–gas system for crust sections in the range of 1–20 km with a heat flux of 40 to 100 mW/m2. The composition of kerogen/fluid geochemical system is calculated using the E. T. Jaynes formalism. It boils down to determining the optimal distribution of 5 elements (C, H, O, N, S) among the 44 additive constituents of the solid phase (i. e., type II kerogen) and other individual components that are included in the system (CO2, H2O, H2S, NH3, CH4, C2H6, C3H8, i-C4H10, n-C4H10, i-C5H12, neo-C5H12, n-C5H12).

Comparison with the experiments showed that the results of the calculations do not contradict the experiments, with study the structure and changes in type II kerogen with increasing degree of catagenesis. In the analysis of changes in the concentrations of water, carbon dioxide and hydrogen sulfide, it is founded that kerogen could be not only a donor of atoms for gas components, but also their acceptor in contact with a high-energy fluid stream. It is shown that the determination of sulfur-containing atomic groups of kerogen by thermodynamic modelling yields gives more reliable results than molecular dynamics methods.

Established is that the concept of “methane-graphite death”, which takes place in the state of thermodynamic equilibrium in the transformation of organic matter, is erroneous. The calculation shows that the composition of the kerogen–gas system, in addition to methane and carbon, includes solid-phase heteroatom groups, various additive components of aromatic structures and gases, both organic and inorganic. The distribution of elements between the additive components of kerogen and gases in this system controls the pressure and temperature in a complex way. The nature of changes in hydrocarbon gas concentrations in equilibrium with type II kerogen indicates the presence of an “oil window” in low-warmed zones within 2–4 km depths.


type II kerogen, catagenesis, “oil window”, equilibrium thermodynamics, Jaynes formalism.


Behar, F., & Vandenbroucke, M. (1987). Chemical modelling of kerogens. Organic Geochemistry, 11, 15-24.
Behar, F., Kressmann, S., Rudkiewicz, J. L., & Vandenbroucke, M. (1992). Experimental simulation in a confined system and kinetic modelling of kerogen and oil cracking. Organic Geochemistry, 19 (1-3), 173-189.
Behar, F., Roy, S., & Jarvie, D. (2010). Artificial maturation of a Type I kerogen in closed system: Mass balance and kinetic modelling. Organic Geochemistry, 41, 1235-1247.
Bell, I. H., Wronski, J., Quoilin, S., & Lemort, V. (2014). Pure and Pseudo-pure Fluid Thermophysical Property Evaluation and the Open-Source Thermophysical Property Library CoolProp. Industrial & Engineering Chemistry Research, 53 (6), 2498-2508.
Durand, B. (1980). Sedimentary organic matter and kerogen. Definition and quantitative importance of kerogen. In B. Durand (Ed.), Kerogen, Insoluble Organic Matter from Sedimentary Rocks (pp. 13-34). Paris: Editions Technip.
Forsman, J. P., & Hunt, J. M. (1958). Insoluble organic matter (kerogen) in sedimentary rocks. Geochimica et Cosmochimica Acta, 15, 170-182.
Helgeson, H., Richard, L., McKenzie, W., Norton, D., & Schmitt, A. (2009). A chemical and thermodynamic model of oil generation in hydrocarbon source rocks. Geochimica et Cosmochimica Acta, 73 (3), 594-695.
Kelemen, S. R., Afeworki, M., Gorbaty, M. L., Sansone, M., Kwiatek, P. J., Walters, C. C., … Behar, F. (2007). Direct Characterization of Kerogen by X-ray and SolidState 13C Nuclear Magnetic Resonance Methods. Energy Fuels, 21 (3), 1548−1561.
Khokha, Yu. V. (2014). Termodynamika hlybynnykh vuhlevodniv u prohnozuvanni rehionalnoi naftohazonosnosti [Thermodynamics of abyssal hydrocarbons in the forecast of oil and gas deposits]. Kyiv: Naukova dumka. [in Ukrainian]
Khokha, Yu., Lyubchak, O., & Yakovenko, M. (2018). Vplyv temperaturnoho rezhymu na hazoheneratsiinyi potentsial huminovykh kyslot orhanichnoi rechovyny [Effect of temperature flow on gas-generating potential of humic acids of organic matter]. Geology and Geochemistry of Combustible Minerals, 3-4 (176-177), 49-63. [in Ukrainian]
Khokha, Yu., Lyubchak, O., & Yakovenko, M. (2019). Enerhiia Hibbsa utvorennia komponentiv pryrodnoho hazu v osadovykh tovshchakh [Gibbs Free Energy of natural gas components formation in sedimentary strata]. Geology and Geochemistry of Combustible Minerals, 2 (179), 37-47. [in Ukrainian]
Lindsey, A. S., & Jeskey, H. (1957). The Kolbe-Schmitt Reaction. Chemical Reviews, 57 (4), 583-620.
Lyubchak, O. V., Khokha, Yu. V., & Yakovenko, M. B. (2018). Spivvidnoshennia strukturnykh elementiv vuhlevodnevoi skladovoi arhilitiv skhidnykh karpat za formalizmom Dzheinsa [Correlation of the hydrocarbon components structural elements of the Eastern Carpathians argillites by the Jaynes’ formalism]. Visnyk of Karazin Kharkiv National University, series “Geology. Geography. Ecology”, 49, 83-94. [in Ukrainian]
Nikonov, V. N. (1961). Tyazhelyye uglevodorody i ikh sootnosheniye v gazakh neftyanykh i gazovykh zalezhey. Geologiya nefti i gaza, 8, 15-21. [in Russian]
Planche, H. (1996). Finite time thermodynamics and the quasi-stability of closed-systems of natural hydrocarbon mixtures. Geochimica et Cosmochimica Acta, 22 (60), 4447-4465.
Stuermer, D. H., Peters, K. E., & Kaplan, I. R. (1978). Source indicators of humic substances and proto-kerogen. Stable isotope ratios, elemental compositions and electron spin resonance spectra. Geochimica et Cosmochimica Acta, 42 (7), 989-997.
Tisso, B., & Velte, D. (1981). Obrazovaniye i rasprostraneniye nefti. Moskva: Mir. [in Russian]
Tomic, J., Behar, F., Vandenbroucke, M., & Tang, Y. (1995). Artificial maturation of Monterey kerogen (Type II-S) in a closed system and comparison with Type II kerogen: implications on the fate of sulfur. Organic Geochemistry, 23 (7), 647-660.
Ungerer, P., Collell, J., & Yiannourakou, M. (2015). Molecular Modeling of the Volumetric and Thermodynamic Properties of Kerogen: Influence of Organic Type and Maturity. Energy Fuels, 29 (1), 91-105.
Van Krevelen, D. W., & Chermin, H. A. G. (1951). Estimation of the free enthalpy (Gibbs free energy) of formation of organic compounds from group contributions. Chemical Engineering Science, 1 (2), 66-80.
Vandenbroucke, M., & Largeau, C. (2007). Kerogen origin, evolution and structure. Organic Geochemistry, 38, 719-833
Zhao, T., Li, X., Zhao, H., Li, M. (2017). Molecular simulation of adsorption and thermodynamic properties on type II kerogen: Influence of maturity and moisture content. Fuel, 190 (15), 198-207.