Tag: heat flow

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INFLUENCE OF THE PORE STRUCTURE OF FOSSIL ORGANIC MATTER ON METHANOGENESIS IN FREE-CHAIN RADICAL REACTIONS

Home > Archive > No. 2 (202) 2026 > 62–75

Geology & Geochemistry of Combustible Minerals No. 2 (202) 2026, 62–75

ISSN 0869-0774 (Print), ISSN 2786-8621 (Online)

https://doi.org/10.15407/ggcm2026.202.062

Myroslava YAKOVENKOa, Yurii KHOKHAb, Oleksandr LYUBCHAKc

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

a e-mail: myroslavakoshil@ukr.net, https://orcid.org/0000-0001-8967-0489
b e-mail: khoha_yury@ukr.net, https://orcid.org/0000-0002-8997-9766
c e-mail: oleksandr.lyubchak@gmail.com, https://orcid.org/0000-0002-0700-6929

Abstract

The paper considers the role of pore structure in the formation of local thermobaric conditions that may support methane generation in fossil organic matter through chain free-radical reactions. The gas–organic matter system is treated as a heterogeneous dispersed medium in which nano-, micro- and mesopores cannot be described only by bulk pressure and temperature. A dimensionless pore-pressure coefficient π = Pp/P∞ is used, where Pp is the pore pressure and P∞ is the geostatic pressure. The value π = 1 corresponds to equality between pore and geostatic pressures, whereas π < 1 indicates a pore-pressure deficit; therefore, 1 − π can be interpreted as a relative measure of rarefaction. Model data are analysed for pore diameters of 0.5, 1, 2, 5, 10, 20, 50, 100 and 1000 nm within the depth range 0–10 km. Additional trends are discussed for peat and brown coal, medium-rank coal and anthracite under heat flows of 40 and 100 mW/m2. The results show that pore size is the main factor controlling the deviation of pore pressure from geostatic pressure. In pores of 0.5–2 nm, π remains far below unity even at a depth of 10 km, whereas pores of 100–1000 nm approach a quasi-equilibrium state. A higher heat flow slightly lowers π in small pores and can promote the formation of free radicals, but this effect is secondary to the geometric restriction imposed by pore size and shape. The evolution from peat and brown coal to anthracite is therefore interpreted not only as a change in sorption capacity and transport properties, but also as a change in the abundance of local pore domains favourable to the mechanical destruction of organic matter, radical stabilization, and methane generation. The proposed interpretation links pore-scale pressure heterogeneity with the kinetics of homolytic reactions and provides a basis for further quantitative modelling of methane formation in a three-phase coal matrix.

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Keywords

coal, peat, anthracite, porosity, methane, pore pressure, rarefaction, free radicals, geostatic pressure, heat flow

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Received: April 21, 2026
Accepted: May 08, 2026
Published: May 29, 2026

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GIBBS FREE ENERGY OF NATURAL GAS COMPONENTS FORMATION IN SEDIMENTARY STRATA

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

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

https://doi.org/10.15407/ggcm2019.02.037

Yuri KHOKHA, Oleksandr LYUBCHAK, Myroslava YAKOVENKO

Institute of Geology and Geochemistry of Combustible Minerals of National Academy of Sciences of Ukraine, Lviv, e-mail: igggk@mail.lviv.ua

Abstract

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.

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Keywords

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

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