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Origin and maturity of oils in the Ukrainian Carpathians and their Mesozoic basement

Więcław D., Kotarba M. J., Kowalski A., Koltun Y. V.

Geological Quarterly

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2012

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Vol. 56, No 1

158-168

EN

Geochemical characteristics of 25 oils collected from Skiba Unit of the Outer Carpathians, Boryslav-Pokuttya Unit of the Carpathian Foredeep and their Mesozoic basement in the western Ukraine are presented in the paper. The first recognised oil family consists of almost all oils accumulated in the flysch sequence of the Outer Carpathians and the Carpathian Foredeep which have very similar geochemical characteristics. These oils were generated from Type II or II/III kerogen deposited in clastic sediments. They are low-sulphur and migrated short distances. Slight biodegradation processes are visible only in oils accumulated in shallow deposits in the Skiba Unit. Their source rocks are the Oligocene Menilite Shales from the Boryslav-Pokuttya Unit. Oils from the Kokhanivka and Orkhovychi deposits (the Mesozoic basement of the Carpathian Foredeep) constitute the second family. These oils are extremely heavy, high-sulphur and were generated from high-sulphur Type IIS kerogen deposited in the carbonate environment. The most probable source rocks for these oils are the Upper Jurassic strata. Oil collected from the Vola Blazhivska deposit (the Boryslav-Pokuttya Unit) shows intermediate parameters between the oil families described above. It is characterized by the presence of oleanane and high sulphur content. It was generated from the Menilite Shales containing high-sulphur kerogen. All oils were generated at an early stage or the peak of oil window.

2

Assessment of hydrocarbon potential of the Lower Palaeozoic strata in the Tarnogród–Stryi area (SE Poland and western Ukraine)

Więcław D., Kosakowski P., Kotarba M.J., Koltun Y. V., Kowalski A.

Annales Societatis Geologorum Poloniae

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2012

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Vol. 82, No. 1

65–-80

EN

Quantity, genetic type and maturity of organic matter dispersed in the Lower Palaeozoic sequence from the Lower Cambrian to Silurian strata of the Polish and Ukrainian parts of the Carpathian Foredeep basement in the Tarnogród–Stryi area were evaluated based on the results of geochemical analyses of 475 rock samples collected from 45 wells. The best source rocks were found in the Silurian strata where the present total organic carbon (TOC) content is up to 2.6 wt%. They occur in the vicinity of Wola Obszańska, where the median of the present and the initial total organic carbon (TOC) contents in the individual wells amount to 0.98 and 1.6 wt%, respectively. The Cambrian and Ordovician strata have a poorer hydrocarbon potential and their present TOC content never exceeds 1 wt%. In all of the investigated Lower Palaeozoic strata, organic matter is represented by the oil-prone Type-II kerogen deposited in anoxic or sub-oxic conditions. The maturity of source rocks ranges from early mature (the initial phase of the low-temperature thermogenic processes) in selected zones of the Silurian strata in the vicinity of Wola Obszańska, through the middle and the final phase of “oil window” in the Ordovician and Cambrian strata in the Polish part of the study area, to the overmature stage in the Ordovician strata in the south-eastern part of the study area (Ukraine).

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Petroleum systems in the Palaeozoic–Mesozoic basement of the Polish and Ukrainian parts of the Carpathian Foredeep

Kotarba M. J., Więcław D., Kosakowski P., Wróbel M., Matyszkiewicz J., Buła Z., Krajewski M., Koltun Y. V., Tarkowski J.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 3

487-522

EN

Comprehensive geochemical analyses (Rock-Eval pyrolysis, stable carbon isotopes, biomarkers and aromatic hydrocarbons and elemental composition of kerogen) provide an explanation of genetic relationships between dispersed organic matter in various source rock horizons of the Palaeozoic–Mesozoic basement in the Carpathian Foredeep and also the liquid (oils and condensates) and gaseous hydrocarbons accumulated in reservoirs in the area between Kraków and Ivano-Frankivs’k. The study region was divided into seven zones around oil, condensate and gas deposits for detailed determination of genetic oil – natural gas – source rock correlation. Based on source, reservoir, seal and overburden rocks, generation, expulsion, migration and accumulation of hydrocarbons and trap formation along with 1-D and 2-D modelling, two separated petroleum systems of the Palaeozoic–Mesozoic strata were established. One petroleum system occurs in the western part of the Małopolska Block, the second one in the eastern part of the Małopolska Block and western part of the Kokhanivka Zone (south-eastern Poland – western Ukraine). In addition, nine generation and expulsion areas were identified. The comparison of the two petroleum systems reveals that the western part of the Małopolska Block has considerably greater prospects for oil and gas exploration than the eastern part of the Małopolska Block and the western part of the Kokhanivka Zone.

4

Origin of natural gases in the autochthonous Miocene strata of the Ukrainian Carpathian Foredeep and its Mesozoic basement

Kotarba M. J., Koltun Y. V.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 3

425-441

EN

Methane concentrations in natural gases accumulated in the Lower and Upper Badenian and Lower Sarmatian reservoirs of the Bilche-Volytsia Unit in the western part of the Ukrainian Carpathian Foredeep usually exceed 96 vol%. Methane was generated by microbial reduction of carbon dioxide in the marine environment. Microbial methane and ethane were produced mainly during sedimentation of Miocene clays and muds. It is possible that this microbial process continues today. Higher light hydrocarbons (ethane in part, and mainly propane, butanes and pentanes) were generated during the diagenesis and the initial stage of the low-temperature, thermogenic processes from Type III and III/II kerogen deposited in Miocene strata and/or Middle and Upper Jurassic basement rocks. Limited variations in the values of geochemical hydrocarbon indices and stable isotope ratios of methane, ethane and propane with the depth indicate similar gas generation conditions within the whole Miocene succession. The microbial gases (methane and partly ethane) generated during microbial processes within the Miocene strata later migrated to the Upper Jurassic and the Upper Cretaceous (Cenomanian) reservoirs of the Mesozoic basement, and to the bottommost Lower Badenian reservoirs of the analysed Letnia, Orkhovychi, Rudky and Vereshchytsia fields. The low hydrogen concentrations within the Miocene strata as well as within the Upper Jurassic and the Upper Cretaceous (Cenomanian) reservoirs of the Mesozoic basement, and within the bottommost Lower Badenian reservoirs are also related to microbial processes. Carbon dioxide and nitrogen, which are common minor constituents, were generated by both microbial and low-temperature thermogenic processes. Moreover, CO2 also underwent secondary processes, mainly dissolution in water, during migration. At least part of the nitrogen accumulated in the Rudky field, which is remarkably high in N2 (96.9 vol%), is probably of atmospheric origin and was introduced to the reservoir by secondary recovery methods.

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Microbial gas system and prospectives of hydrocarbon exploration in Miocene strata of the Polish and Ukrainian Carpathian Foredeep

Kotarba M. J., Peryt T. M., Koltun Y. V.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 3

523-548

EN

Molecular composition of natural gases accumulated in autochthonous Miocene strata of the Polish and Ukrainian Carpathian Foredeep is dominated by methane, which usually constitutes over 98 vol%. Methane was generated by the carbon dioxide reduction pathway of microbial processes. Ethane was generated both during microbial and thermogenic processes ("oil window") and propane at the initial stage of the low-temperature thermogenic processes, and also by the microbial processes. The rhythmic and cyclic deposition of Miocene clays and sands as well as the vigorous generation of microbial methane caused that the gas produced in claystone beds was accumulated in the overlaying sandstones, and capped, in turn, by the succeeding claystones. Such generation and accumulation system of microbial gases gave rise to the formation of multi-horizontal gas fields. Analysis of the distribution of immature humic dispersed organic matter in the Upper Badenian and Lower Sarmatian sequences indicates that it is practically homogeneous. A migration range of microbial gases was insignificant and locations of their accumulations would depend only on the existence of proper type of traps (compactional anticlines situated above basement uplifts, sealed by the Carpathian Overthrust and/or by faults; stratigraphic pinching out and stratigraphic traps related to unconformities). Another situation is encountered in the south, beneath the Carpathian Overthrust. The thickness of the autochthonous Miocene strata in this area is more than 1,500 metres. Geochemical studies reveal that from a depth of 2,500 metres starts the process of low-temperature thermogenic hydrocarbon generation (“oil window”). At greater depths, more than 7,500 metres, within the autochthonous Lower Miocene basin only the high-temperature methane ("gas window") could be produced and accumulated.

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Evaluation of hydrocarbon potential of the autochthonous Miocene strata in the NW part of the Ukrainian Carpathian Foredeep

Kotarba M. J., Więcław D., Kosakowski P., Koltun Y. V., Kowalski A.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 3

395-407

EN

The quantity, genetic type, maturity and hydrocarbon potential of dispersed organic matter were determined for the complete sequence of the autochthonous Miocene ranging from the Lower Badenian Sandy-Calcareous Series to the Lower Sarmatian Upper Dashava Formation of the Bilche-Volytsia Unit. Geochemical analyses were conducted on 78 core samples collected from 11 wells in the Ukrainian Carpathian Foredeep between the Ukrainian-Polish state border and the Stryi River. The most favourable source-rock parameters characterize the Upper Badenian Kosiv Formation where the highest TOC contents, from 0.44 to 2.01 wt% (median 0.76 wt%), were found. Only slightly lower values were obtained for the Lower and the Upper Dashava formations – from 0.01 to 1.45 wt% (median 0.72 wt%) and from 0.62 to 0.77 wt% (median 0.71 wt%), respectively. In the Lower Badenian Sandy-Calcareous Series, the Lower Badenian Baraniv beds, and the Upper Badenian Tyras Formation, the TOC content is lower and varies from 0.00 to 0.77 wt%. Immature type III (terrestrial) kerogen dominates the analysed sections of the Kosiv and Dashava formations. Marine organic matter was detected sporadically, and only in the Upper Badenian Kosiv Formation in the vicinity of Kokhanivka, and in the Upper Badenian Kosiv and Tyras formations.

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1-D modelling of the hydrocarbon generation history of the Jurassic source rocks in the Tarnogród–Stryi area (SE Poland – western Ukraine)

Kosakowski P., Wróbel M., Koltun Y. V.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 3

473-485

EN

Reconstruction of burial and thermal history was modelled for the Mesozoic strata in the basement of the Polish and Ukrainian parts of the Carpathian Foredeep and in the marginal part of the Outer Carpathians. The 1-D modelling was carried out in profiles of the wells located in the area between Tarnogród and Stryi towns. In the Polish part, the modelling were performed in the profiles of the Księżpol 15, Lubliniec 9, Markowice 2 and Opaka 1 wells, and in the Ukrainian part in the profiles of the Chornokuntsi 1, Korolyn 6, Mosty 2, Podiltsi 1 and Voloshcha 1 wells. The geochemical characteristics of the Mesozoic stratigraphical horizons revealed that the best features of source rocks were present in the Middle Jurassic strata in the Polish part of the study area and in the Middle and Upper Jurassic strata in the Ukrainian part. Within these strata, the horizons of source rocks were distinguished and their quantitative evaluations were characterized. For these horizons, reconstruction of processes for hydrocarbon generation and expulsion were performed. The source rocks in the Polish part reached maturity only in the initial phase of “oil window”. However, the maturity achieved towards the end of the Upper Jurassic was insufficient to exceed the 10% threshold of the transformation degree for hydrocarbon generation. Therefore, the amount of generated hydrocarbons was minimal. Slightly higher maturity of organic matter in the Ukrainian part resulted in exceeding the thresholds of kerogen transformation and the initiation of hydrocarbon generation and expulsion processes. The process began after the deposition of thicker Miocene formations and developed even up to the main phase of the "oil window". The amount of the generated hydrocarbons reached ca. 150 mg/g TOC with an insignificant volume of expulsion.

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Potencjał naftowy utworów jurajskich podłoża Karpat i zapadliska przedkarpackiego w rejonie Lwów-Sambor-Stryj (SW Ukraina)

Więcław D., Kotarba M. J., Kosakowski P., Koltun Y. V., Dudok I.

Prace Naukowe Instytutu Nafty i Gazu

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2010

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nr 170 wyd. konferencyjne

669--673

PL

Geochemiczna charakterystyka macierzystości utworów jurajskich w ukraińskiej części mezozoicznego podłoża zapadliska przedkarpackiego została wykonana w oparciu o wyniki badań 182 próbek pobranych z profili 12 odwiertów. Najbogatsze w materię organiczną są utwory jury środkowej, gdzie mediana TOC wynosi 0,72% wag. Utwory jury górnej są znacznie uboższe w węgiel organiczny (mediana TOC wynosi 0,11% wag). Utwory jury dolnej są całkowicie płonne (TOC poniżej 0,2% wag.). Potencjał węglowodorowy utworów środkowo- i górnojurajskich jest generalnie niski i zwykle nie przekracza 1 mg HC/g skały. W utworach jury środkowej dominuje gazotwórczy kerogen III typu. W węglanach górnojurajskich obserwuje się lokalnie zwiększony udział ropotwórczego kerogenu II typu. Dojrzałość utworów jury środkowej odpowiada początkowej i środkowej fazie generowania węglowodorów termogenicznych w„oknie ropnym", a górnej jury — przejściu z fazy generowania węglowodorów mikrobialnych do fazy „okna ropnego".

EN

Geochemical source-rock characteristics of the Jurassic strata in the basement of the Ukrainian part of the Carpathian Foreland was based on Rock-Eval results of 182 samples collected from 12 wells. The richest in organic matter are the Middle Jurassic strata, where TOC median equals 0.72 wt%. The Upper Jurassic carbonates are much poorer in organic carbon (TOC median equals 0.11 wt%). The Lower Jurassic strata are totally barren (TOC below 0.2 wt%). The hydrocarbon potential of the Middle and Upper 7urassic strata is generally low and usually do not exceed 1 mg HC/g rock. In the Middle Jurassic strata gas-prone Type III kerogen dominate. In the Upper Jurassic carbonates locally increased share of the oil-prone Type II kerogen is observed. Maturity of the Middle Jurassic strata responds to the initial and middle phase of the "oil window", and the Upper Jurassic rocks — transition between microbial hydrocarbon generation phase and "oil window".