Tag: organic matter

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ESTIMATION OF THE METHANE-GENERATING CAPACITY OF FOSSIL ORGANIC MATTER

Home > Archive > No. 1 (201) 2026 > 51–62

Geology & Geochemistry of Combustible Minerals No. 1 (201) 2026, 51–62

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

https://doi.org/

Yurii KHOKHAa, Oleksandr LYUBCHAKb, Myroslava YAKOVENKOc

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

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

Abstract

The methane-generative capacity of fossil organic matter (FOM) controls both the resource potential of sedimentary successions (natural gas) and the environmental implications of CH4 generation and migration. While equilibrium thermodynamic models provide an upper bound for methane yield, methane generation in geological settings is predominantly kinetic-controlled, and comprehensive equilibrium/kinetic reconstructions often require detailed structural inputs that are unavailable in routine practice.

Aim. To develop a minimal-parameter, chemically consistent framework for quantifying methane generation from FOM in the “solid organic matrix–fluid” system using measurable quantities and a kinetics-centered descriptor applicable under limited structural information.

Approach and methods. Methane formation is treated as a radical-controlled demethanation process, formalized by the rate expression d[CH4]/dt = k[CH3][H]. Here [CH3] denotes the amount of structural methyl fragments (–CH3) bound within the macromolecular matrix (kerogen/coal/peat), whereas [H] represents the pool of chemically bound donor hydrogen, excluding –OH and –COOH hydrogen in the baseline formulation. Conditions under which protonic (heterolytic) stages may become significant (high polarity, pore water, strong acidity/alkalinity, Lewis-acid catalysis, oxidants, transition metals, mineral surfaces, irradiation) are outlined, and it is shown that explicitly accounting for such pathways would substantially complicate the kinetic equation set. An analytical solution is discussed together with a practical reduction to an exponential law, [CH4] = [CH4]0 + [CH3]0 (1 − e−t/τ), where the characteristic time τ is defined from the initial slope of the methane accumulation curve CH4(t) and can be estimated graphically via the tangent at t = 0. The paper specifies an experimental–analytical workflow to determine [CH4]0 by gas chromatography and to quantify the –CH3 reservoir using direct structural methods: FTIR spectroscopy (integration of –CH3/–CH2 bands with spectral approximation and peak separation of overlapping features) and quantitative solid-state 13C MAS NMR (integration of methyl carbon at 0–22 ppm, with explicit separation of methoxyl O–CH3 at 55–60 ppm when peat/soils are considered). Product-oriented techniques (pyrolysis GC/GC-MS and Rock-Eval) are discussed as complementary controls of CH4 release during thermal decomposition.

Key results and interpretation. The proposed framework reduces methane-generative capacity to two experimentally anchored descriptors: the structural reservoir of methyl fragments and the kinetic parameter τ, interpreted as an integral measure of reactive-site accessibility and the overall rate of radical transformations in a given matrix. Using τ enables laboratory characterization within shortened observation windows, by passing the impracticality of directly determining k on geological time scales, and provides a consistent basis for comparing samples of different origin and maturity. The applicability domain is delineated, emphasizing external factors capable of shifting mechanisms and kinetics (O2, water, mineral/metal catalysis, oxidants, irradiation), and the necessity to discriminate aliphatic –CH3 from methoxyl O–CH3 in oxygen-rich matrices is highlighted.

Conclusion and significance. The study delivers an analytically transparent and experimentally verifiable route to quantify methane-generative capacity of FOM as the coupled outcome of a measurable –CH3 structural reserve and the characteristic time τ. The approach is suitable for comparative assessments across kerogen, coal, peat and soil organic matrices and provides a methodological foundation for further predictive modelling.

Full Text

Keywords

organic matter, kerogen, methane, methane generation, kinetics, FTIR, 13C MAS NMR, programmed pyrolysis

Referenses

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Received: January 25, 2026
Accepted: February 20, 2026
Published: April 2026

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LITHOLOGICAL-GEOCHEMICAL TYPES OF DEPOSITS OF CRETACEOUS-PALEOGENE FLYSCH OF THE UKRAINIAN CARPATHIANS AND CONDITIONS OF THEIR FORMAITION

Home > Archive > No. 4 (181) 2019 > 116-133

Geology & Geochemistry of Combustible Minerals No. 4 (181) 2019, 116-133.

https://doi.org/10.15407/ggcm2019.04.116

Ihor Popp, Petro Moroz, Mykhailo Shapovalov

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

Abstract

The results of lithological, mineralogical and geochemical investigation of Cretaceous-Paleogene flysch deposits of the Ukrainian Carpathians are cited here. There are three main lithological-geochemical types of these deposits which differ in the composition of rock-forming ingredients of biogenic origin (SiO2 biog, CaCO3, Corg): grey limestone-clayey-terrigenous (type-I), non-carbonate or low-carbonate-clayey-terrigenous (type-II), and black carbonate-silica-terrigenous-clayey (type-III). The deposits of the first type are attributed to alkaline-oxic (oxic-calcitic), the second – to acid and low-alcaline oxic (oxic with redeposited glauconite), the third – to reducing (siderite, dolomite or ferrodolomite and low-reducing calcitic) and strong by reducing (primary-sulfidic or hydrogen sulfidic) mineralogical-geochemical facies. The forming of the Barremian-Albian (Shypot suite; Spas suite) and Oligocene (Menilite suite; Dusynska suite) organic-rich sediments in the Ukrainian Carpathians we associate with the phase of oceanic anoxic events OAE-1 and OAE-4 in the Carpathian segment of the Tethys, where anoxic reducing environments favoured to fossilization of huge amount of the dispersed organic matter. The structural-fabric features and composition of separate lithological types of silicites and diagenetic concretions of the Lower Cretaceous and Oligocene of the Ukrainian Carpathians show that their sedimentogenesis and diagenesis took place in conditions of strong oxygen deficit. The studied siliceous rocks can be considered as indicators of the anoxic events in the Carpathian segment of Tethys ocean. It is shown, that alcaline-reducting environments which was the most favourable for the diagenetic transformation of sedimentary organic matter in to petroleum hydrocarbons, prevailed in the organic-rich deposits of Oligocene age.

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Keywords

sedimentogenesis, diagenesis, silica, carbonate, sulfides, organic matter, mineralogical-geochemical facies, Cretaceous-Paleocene flysch, Ukrainian Carpathians.

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