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/
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 khoha_yury@ukr.net, https://orcid.org/0000-0002-8997-9766
c 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.
Keywords
coal, peat, anthracite, porosity, methane, pore pressure, rarefaction, free radicals, geostatic pressure, heat flow
Referenses
Boelter, D. H. (1969). Physical properties of peats as related to degree of decomposition. Soil Science Society of America Journal, 33(4), 606–609. https://doi.org/10.2136/sssaj1969.03615995003300040033x
Bulat, A. F., Zviagilskii, E. L., Lukinov, V. V., Perepelitca, V. G., Pimonenko, L. I., & Shevelev, G. A. (2008). Ugleporodnyi massiv Donbassa kak geterogennaia sreda. Kiev: Naukova dumka. [in Russian]
Clarkson, C. R., & Bustin, R. M. (1996). Variation in micropore capacity and size distribution with composition in bituminous coal of the Western Canadian Sedimentary Basin: Implications for coalbed methane potential. Fuel, 75(13), 1483–1498. https://doi.org/10.1016/0016-2361(96)00142-1
Clarkson, C. R., & Bustin, R. M. (1999a). The effect of pore structure and gas pressure upon the transport properties of coal: A laboratory and modeling study. 1. Isotherms and pore volume distributions. Fuel, 78(11), 1333–1344. https://doi.org/10.1016/S0016-2361(99)00055-1
Clarkson, C. R., & Bustin, R. M. (1999b). The effect of pore structure and gas pressure upon the transport properties of coal: A laboratory and modeling study. 2. Adsorption rate modeling. Fuel, 78(11), 1345–1362. https://doi.org/10.1016/S0016-2361(99)00056-3
Dziewonski, A. M., & Anderson, D. L. (1981). Preliminary reference Earth model. Physics of the Earth and Planetary Interiors, 25(4), 297–356. https://doi.org/10.1016/0031-9201(81)90046-7
Ettinger, I. L. (1988). Neobiatnye zapasy i nepredskazuemye katastrofy: Tverdye rastvory gazov v nedrakh Zemli. Moskva: Nauka. [in Russian]
Gan, H., Nandi, S. P., & Walker, P. L. (1972). Nature of the porosity in American coals. Fuel, 51(4), 272–277. https://doi.org/10.1016/0016-2361(72)90003-8
Hasterok, D., & Chapman, D. S. (2011). Heat production and geotherms for the continental lithosphere. Earth and Planetary Science Letters, 307(1–2), 59–70. https://doi.org/10.1016/j.epsl.2011.04.034
Khokha, Yu. V., Liubchak, O. V., & Yakovenko, M. B. (2019). Enerhiia Hibbsa utvorennia komponentiv pryrodnoho hazu v osadovykh tovshchakh. Heolohiia i heokhimiia horiuchykh kopalyn, 2(179), 37–46. https://doi.org/10.15407/ggcm2019.02.037 [in Ukrainian]
Khramov, V., & Liubchak, O. (2009). Mekhanizm heneratsii metanu v porovomu prostori vuhillia. Heolohiia i heokhimiia horiuchykh kopalyn, 3–4(148–149), 44–54. [in Ukrainian]
Kleimeier, C., Rezanezhad, F., Van Cappellen, P., & Lennartz, B. (2017). Influence of pore structure on solute transport in degraded and undegraded fen peat soils. Mires and Peat, 19, 18. https://doi.org/10.19189/MaP.2017.OMB.282
Klym, M. M., & Yakibchuk, P. M. (2003). Molekuliarna fizyka. Lviv: Lvivskyi natsionalnyi universytet imeni Ivana Franka. [in Ukrainian]
Li, Y., Liu, W., Song, D., Ren, Z., Wang, H., & Guo, X. (2023). Full-scale pore characteristics in coal and their influence on the adsorption capacity of coalbed methane. Environmental Science and Pollution Research, 30, 72187–72206. https://doi.org/10.1007/s11356-023-27298-2
Liu, D., Qiu, F., Liu, N., Cai, Y., Guo, Y., Zhao, B., & Qiu, Y. (2022). Pore structure characterization and its significance for gas adsorption in coals: A comprehensive review. Unconventional Resources, 2, 139–157. https://doi.org/10.1016/j.uncres.2022.10.002
McCarter, C. P. R., Rezanezhad, F., Quinton, W. L., Gharedaghloo, B., Lennartz, B., Price, J., Connon, R., & Van Cappellen, P. (2020). Pore-scale controls on hydrological and geochemical processes in peat: Implications on interacting processes. Earth-Science Reviews, 207, 103227. https://doi.org/10.1016/j.earscirev.2020.103227
Nie, B., Liu, X., Yang, L., Meng, J., & Li, X. (2015). Pore structure characterization of different rank coals using gas adsorption and scanning electron microscopy. Fuel, 158, 908–917. https://doi.org/10.1016/j.fuel.2015.06.050
Pan, J., Wang, K., Hou, Q., Niu, Q., Wang, H., & Ji, Z. (2016). Micro-pores and fractures of coals analysed by field emission scanning electron microscopy and fractal theory. Fuel, 164, 277–285. https://doi.org/10.1016/j.fuel.2015.10.011
Rezanezhad, F., Price, J. S., & Craig, J. R. (2012). The effects of dual porosity on transport and retardation in peat: A laboratory experiment. Canadian Journal of Soil Science, 92(5), 723–732. https://doi.org/10.4141/cjss2011-050
Rezanezhad, F., Price, J. S., Quinton, W. L., Lennartz, B., Milojevic, T., & Van Cappellen, P. (2016). Structure of peat soils and implications for water storage, flow and solute transport: A review update for geochemists. Chemical Geology, 429, 75–84. https://doi.org/10.1016/j.chemgeo.2016.03.010
Rezanezhad, F., Quinton, W. L., Price, J. S., Elrick, D., Elliot, T. R., & Heck, R. J. (2009). Examining the effect of pore size distribution and shape on flow through unsaturated peat using computed tomography. Hydrology and Earth System Sciences, 13, 1993–2002. https://doi.org/10.5194/hess-13-1993-2009
Sing, K. S. W., Everett, D. H., Haul, R. A. W., Moscou, L., Pierotti, R. A., Rouquerol, J., & Siemieniewska, T. (1985). Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity (Recommendations 1984). Pure and Applied Chemistry, 57(4), 603–619. https://doi.org/10.1351/pac198557040603
Zou, G., She, J., Peng, S., Yin, Q., Liu, H., & Che, Y. (2020). Two-dimensional SEM image-based analysis of coal porosity and its pore structure. International Journal of Coal Science & Technology, 7, 350–361. https://doi.org/10.1007/s40789-020-00301-8
Received: April 21, 2026
Accepted: May 08, 2026
Published: May, 2026