Posted on


Home > Archive > No. 2 (179) 2019 > 37-46

Geology & Geochemistry of Combustible Minerals No. 2 (179) 2019, 37-46.

цифровий ідентифікатор DOI цієї статті

Yuri KHOKHA, Oleksandr LYUBCHAK, Myroslava YAKOVENKO

Institute of Geology and Geochemistry of Combustible Minerals of National Academy of Sciences of Ukraine, Lviv, e-mail:


The main methods of calculating the composition of geochemical systems in the thermodynamic equilibrium state were considered in the article. It was shown that the basis for such calculations was the determination of the Gibbs Free Energy of each system components at given temperatures and pressures. The methods of Gibbs Free Energy calculation at standard pressure and under conditions that are realized within the sedimentary strata were analyzed. The equations of state for natural gas individual components were selected and their Gibbs Free Energies for heat fluxes ranging from 40 to 100 mW/m2 and depths of 0–20 km were calculated. The results showed that the pressure significantly affects the value of Gibbs Free Energies formation of natural gas components within the sedimentary strata. Changes of the Gibbs Free Energies of natural gas components formation, as a function of depth, subordinated to the same laws for each compound. This regularity was better expressed in more heated areas.
It was shown that with depth increasing the Gibbs Free Energy of natural gas components formation first rapidly decreases and reaches its minimum ranging from 2 to 6 km. Moreover, as the value of the heat flux increases, the maximum value of the Gibbs Free Energy of formation of natural gas components, expressed in kilometers, decreases. With further immersion/deepening to depths greater than 6 km, the Gibbs Free Energy of the formation of natural gas components gradually increases, and in areas with greater heat flux, a sharp increase was characteristic, and with less, it was slow and weakly expressed. There is a stability area for hydrocarbon and non-hydrocarbon components of natural gas ranging from 2 to 6 km. With the increase of Carbon number in the hydrocarbon chain, the value of Gibbs Free Energy of the natural gas hydrocarbon components formation decreases, which indicates the presence of a stability zone for heavy natural gas components (it should be expected that oil also) within the depths of 2–6 km.


Gibbs Free Energy, heat flow, natural gas, sedimentary strata.


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.

Blecic, J., Harrington, J., & Bowman, M. O. (2016). TEA: A code for calculating thermochemical equilibrium abundances. The Astrophysical Journal Supplement Series, 225 (1). doi:10.3847/0067-0049/225/1/4.

Buecker, D., & Wagner, W. (2006). Reference Equations of State for the Thermodynamic Properties of Fluid Phase n-Butane and Isobutane. J. Phys. Chem. Ref. Data, 35 (2), 929–1019.

Chekalyuk, E. B. (1967). Neft verhney mantii Zemli [Oil of the Earth’s upper mantle]. Kiev: Naukova dumka. [in Russian]

Dziewonski, A. M., & Anderson, D. L. (1981). Preliminary reference Earth model. Physics of the Earth and Planetary Interiors, 25 (4), 297–356.

Hasterok, D., & Chapman, D. S. (2011). Heat production and geotherms for the continental lithosphere. Earth and Planetary Science Letters, 307, 59–70.

Glushko, V. P. (1979). Termodinamicheskiye svoystva individualnykh veshchestv. T. 1 (1) [Thermodynamic properties of individual substances. Vol. 1 (1)]. Moskva: Nauka. [in Russian]

Koukkari, P. (2014). Introduction to constrained Gibbs energy methods in process and materials research. Espoo: VTT Technical Research Centre of Finland. VTT Technology, N 160.

Lemmon, E. W., McLinden, & M. O., Wagner, W. (2009). Thermodynamic Properties of Propane. III. A Reference Equation of State for Temperatures from the Melting Line to 650 K and Pressures up to 1000 MPa. J. Chem. Eng. Data, 54, 3141–3180.

Lemmon, E. W., & Span, R. (2006). Short Fundamental Equations of State for 20 Industrial Fluids. J. Chem. Eng. Data, 51, 785–850.

Lyubchak, O. V. (2009). Termobarychni umovy utvorennia pryrodnogo gazu v nadrakh Zemli [Thermobaric conditions of natural gas formation in the subsoils of the Earth]. Heolohiia i heokhimiia horiuchykh kopalyn, 1, 18–24. [in Ukrainian]

Sanford, G., & McBride, B. J. (1994). Computer program for Calculation of Complex Chemical Equilibrium Composition and Application. NASA Reference Publication 1311, 58.

Setzmann, U., & Wagner W. (1991). A New Equation of State and Tables of Thermodynamic Properties for Methane Covering the Range from the Melting Line to 625 K at Pressures up to 1000 MPa. J. Phys. Chem. Ref. Data, 20 (6), 1061–1151.

Sokolov, V. A. (1971). Geokhimiya prirodnykh gazov [The geochemistry of natural gases]. Moskva: Nedra. [in Russian]

Span, R., (2000). Multiparameter Equations of State – An Accurate Source of Thermodynamic Property Data. Berlin: Springer.

Span, R., & Wagner, W. (1996). A New Equation of State for Carbon Dioxide Covering the Fluid Region from the Triple Point Temperature to 1100 K at Pressures up to 800 MPa. J. Phys. Chem. Ref. Data, 25, 1509–1596.

Stull, D. R., Westrum Jr., E. F., & Sinke, G.C. (1969). The chemical thermodynamics of organic compounds. New York: John Wiley and Sons, Inc.

Tissot, B. P., & Welte, D. H. (1984). Petroleum Formation and Occurrence. Berlin; Heildelberg; New York; Tokyo: Springer-Verlag.

Wagner, W., & Buecker, D. (2006). A Reference Equation of State for the Thermodynamic Properties of Ethane for Temperatures from the Melting Line to 675 K and Pressures up to 900 MPa. J. Phys. Chem. Ref. Data, 35 (1), 205–266.

Wagner, W., & Pruß, A. (2002). The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use. J. Phys. Chem. Ref. Data, 31, 387–535.