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Home > Archive > No. 1 (182) 2020 > 52-61

Geology & Geochemistry of Combustible Minerals No. 1 (182) 2020, 52-61.

Yurii KHOKHA, Oleksandr LYUBCHAK, Myroslava YAKOVENKO, Dmytro BRYK

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


This paper considers the issue of determining the maximum hydrocarbons amount that can be generated by kerogen using thermodynamic methods. It is shown that the chemical composition of natural gas or gas condensate contains information about the generative capacity of kerogen from which it was formed. Based on experiments of type II and I kerogen pyrolysis and thermodynamic calculations by entropy maximization method, we propose a new method for determining the amount of kerogen from which gas was formed, which contains 1 dm3 of methane at a given ratio of butane isomers. The obtained data are interpreted as an indicator of kerogen maturity in the context of the depth of its destruction.

This method is applied to theWestern oil and gas region of Ukraine hydrocarbon deposits. The analysis of kerogen transformations in the region sedimentary strata, using criteria of the GASTAR diagram, is carried out. We assessed the trends of kerogen conversion in the region in the areas of “maturity” and “biodegradation” in the ratio of ethane/propane (C2/C3) to ethane/isobutane (C2/i-C4). It is shown that the majority of deposits in the Western oil and gas region developed in the direction of maturation and only a small group of gas deposits – biodegradation.

To establish the gases genesis in the region, we built a graph of the two geochemical indicators dependence – the methane/ethane ratio (C1/C2) and ethane/propane ratio (C2/C3). It is shown that some of the gas fields is formed due to the conversion of organic material of oil deposits. At the same time, gas condensate fields in the region, with few exceptions, are formed due to the primary destruction of kerogen.

Based on the results of the calculations, maps of the methane (generated by type II kerogen) amount distribution were constructed. It is established that kerogen, which was the source material for hydrocarbon deposits of Boryslav-Pokuts oil and gas region, has practically exhausted its gas generation potential. Instead, kerogen from gas and gas condensate fields in the Bilche-Volytska oil and gas district still retains the potential to generate hydrocarbons.


kerogen, butane isomers, thermodynamic modelling, gas-generating potential.


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Home > Archive > No. 1 (178) 2019 > 47-62

Geology & Geochemistry of Combustible Minerals No. 1 (178) 2019, 47-62.

Yuri KHOKHA, Oleksandr LYUBCHAK, Myroslava YAKOVENKO

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


The analysis of literature was carried out and the main criteria for determining the gas generating potential of rocks were determined. These criteria are divided into two groups: the first one is geochemical, which includes the content of organic carbon and the thermal maturity of the rocks. The second group combines the geological and economic criteria that determine the suitability of rocks for the removal of hydrocarbon gases from them. In our opinion, the most important group of criteria should be considered a geochemical group.
Traditionally, to determine the ability of organic matter to form hydrocarbons, the Rock-Eval analysis was used. As a result, determined are the total organic carbon (TOC) and other parameters, such as hydrogen index (HI) or production index (PI).
In this paper, we are trying to expand the range of parameters that can be used to determine the gas generation potential of the rocks. The elemental composition of the organic matter dissipated in the rocks, in general terms, should affect on the composition and amount of hydrocarbons that they synthesize. To determine the influence of elemental composition on the gas-generating potential, equilibrium thermodynamics is used in conjunction with the Jaynes’ formalism.
Samples for investigation – bituminous argillites from Menilite suite of Oligocene, were taken from two fields of the Ukrainian Carpathians. For samples, the elemental composition of the organic matter and the mineral composition of the inorganic part (by X-ray crystallography) are determined. The data on the elemental composition came into the calculation, the result of which is the distribution of the additive components in the organic matter and the composition of gases.
The results of the calculations were compared with the results obtained by the Rock-Eval method. It was found that the calculation by the thermodynamic method gives understated results. On the other hand, it allows the establishment of a change in the chemical structure of organic matter of rocks. We are outlined ways to further improvement of the method.


gas-generating potential, Jaynes’ formalism, equilibrium thermodynamic, dissipated organic matter.


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