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KEROGEN AMOUNT CALCULATION REQUIRED FOR THE FORMATION OF HYDROCARBON DEPOSITS IN THE WESTERN OIL AND GAS REGION OF UKRAINE

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


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

цифровий ідентифікатор DOI цієї статті

Yurii KHOKHA, Oleksandr LYUBCHAK, Myroslava YAKOVENKO, Dmytro BRYK

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

Abstract

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.

Keywords

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

REFERENCES

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Gai, H., Tian, H., & Xiao, X. (2018). Late gas generation potential for different types of shale source rocks: Implications from pyrolysis experiments. International Journal of Coal Geology, 193, 16–29.

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Khokha, Yu., Liubchak, O., & Yakovenko, M. (2018). Vplyv temperaturnoho rezhymu na hazoheneratsiinyi potentsial huminovykh kyslot orhanichnoi rechovyny. Heolohiia i heokhimiia horiuchykh kopalyn, 3–4 (176–177), 37–47. [in Ukrainian]

Khokha, Yu., Liubchak, O., & Yakovenko, M. (2019). Termodynamika transformatsii kerohenu II typu. Heolohiia i heokhimiia horiuchykh kopalyn, 3 (180), 25–40. [in Ukrainian]

Langford, F. F., & Blanc-Valleron, M.-M. (1990). Interpreting Rock-Eval pyrolysis data using graphs of pyrolizable hydrocarbons vs. total organic carbon. AAPG Bulletin, 74 (6), 799–804.

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EQUILIBRIUM TEMPERATURES OF HYDROCARBON GAS FORMATION IN SEDIMENTARY STRATA OF THE WESTERN OIL AND GAS REGION OF UKRAINE (according to thermodynamic modelling)

Home > Archive > No. 4 (181) 2019 > 66-77


Geology & Geochemistry of Combustible Minerals No. 4 (181) 2019, 66-77.

цифровий ідентифікатор DOI цієї статті

Dmytro Bryk, Oleg Gvozdevych, Lesya Kulchytska-Zhyhaylo, Myroslav Podolskyy

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

Abstract

The article reviews the question of interpretation of natural gases component composition from the aspect of their evolution. The parameters available for study, which show a strong correlation with the conditions of formation, migration and accumulation of natural hydrocarbon gases, are selected.

Among these parameters, the ratio of the butanes isomeric form (i-C4/n-C4) was selected for thermodynamic analysis as a dependable indicator of the kerogen degradations temperature regime. It is shown that the dependence of the i-C4/n-C4 ratio on the normalized methane content shows the trend of increasing kerogen maturity, and deviations from this trend indicate a distant migration of hydrocarbon fluid from the formation zone to the current deposit.

Analysis of the residence and thermodynamic conditions of hydrocarbons in the deposits of the Western oil and gas region showed that kerogen/gas systems are in a state close to equilibrium, in terms of thermodynamics.

The composition of the gas/kerogen equilibrium system in the conditions of sedimentary thickness for two heat fluxes – 75 and 100 mW/m2 was calculated by the method based on Jaynes’s formalism. Among hydrocarbons in gases, the content of isomeric forms of butane and pentane, as well as methane, ethane and propane was calculated. The results of the calculations revealed a monotonic dependence of the equilibrium temperature and depth of formation on the ratio of isobutane to n-butane. It was found that the results of thermodynamic calculations coincide with experiments on kerosene pyrolysis and correlate with studies of the composition and residence of natural gases.

Equilibrium formation temperatures were determined for 59 gas, oil and gas condensate fields of the Western oil and gas region, the information on which contained data on the i-C4/n-C4 ratio. Based on the results of calculations, maps of these temperatures distribution within the region were constructed.

The analysis of the maps showed the presence of two distinct temperature maxima, which are concentrated in the Boryslav-Pokuttya oil and gas region and are located at the intersection of regional faults. It has been suggested that the hydrocarbon source is significantly distant from modern deposits for the study region. The results of the calculation are compared with the data obtained using the model of fossil hydrocarbons inorganic origin.

Keywords

butane isomers, gas evolution, formation temperature, Jaynes’s formalism.

REFERENCES

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Khokha, Yu. V. (2014). Termodynamika hlybynnykh vuhlevodniv u prohnozuvanni rehionalnoi naftohazonosnosti. Kyiv: Naukova dumka. [in Ukrainian]

Khokha, Yu. V., Liubchak, O. V., & Yakovenko, M. B. (2019). Termodynamika transformatsii kerohenu II typu. Heolohiia i heokhimiia horiuchykh kopalyn, 3 (179), 25–40. [in Ukrainian]

Krupskyi, Yu. Z. (2001). Heodynamichni umovy formuvannia i naftohazonosnist Karpatskoho ta Volyno-Podilskoho rehioniv Ukrainy. Kyiv: UkrDHRI. [in Ukrainian]

Prinzhofer, A., & Battani, A. (2003). Gas Isotopes Tracing: an Important Tool for Hydrocarbons Exploration. Oil & Gas Science and Technology – Rev. IFP, 58 (2), 299–311.

Prinzhofer, A., Mello, M. R., & Takaki, T. (2000). Geochemical Characterization of Natural Gas: A Physical Multivariable Approach and its Applications in Maturity and Migration Estimates. AAPG Bulletin, 84 (8), 1152–1172.

Tisso, B., & Velte, D. (1981). Obrazovaniye i rasprostraneniye nefti. Moskva: Mir. [in Russian]

Vandenbroucke, M., & Largeau, C. (2007). Kerogen origin, evolution and structure. Organic Geochemistry, 38, 719–833.

Wood, J. M., & Sanei, H. (2016). Secondary migration and leakage of methane from a major tight-gas system. Nature Communications, 7. https://doi.org/10.1038/ncomms13614