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Habitat and hydrocarbon potential of the Mesozoic strata in the Kraków–Rzeszów area (SE Poland)

Kosakowski P., Więcław D., Kotarba M. J., Kowalski A.

Geological Quarterly

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2012

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Vol. 56, No 1

139-152

EN

The Mesozoic strata in the southeastern Poland were geochemically characterized to determine their hydrocarbon potential on the basis of 483 core samples from 36 boreholes. The Lower and Middle Triassic, Middle and Upper Jurassic, and Lower and Upper Cretaceous turned out to be highly variable. Middle Jurassic rocks represent the highest geochemical quality. Their total organic carbon (TOC) contents range between 0.0 and 17.0 wt.%, with a median of 0.89 wt.%. The highest TOC was observed in the rocks of the Tarnawa 1 borehole. In the remaining boreholes analysed the organic carbon contents were much lower and usually did not exceed 1 wt.%. Gas-prone Type-III kerogen with an admixture of Type-II kerogen is present in the study area. The lowest TOC values were observed in the Cretaceous rocks, where median values were 0.05 wt.% and 0.04 wt.% for Upper Cretaceous and Lower Cretaceous strata respectively. Low TOC contents were also observed in the Lower Triassic and Upper Jurassic strata. Accordingly, those horizons could not be regarded as effective source rocks. The petroleum potential of these stratigraphic horizons is additionally significantly reduced by low maturity, below the threshold for the generation of hydrocarbons. The Mesozoic organic matter was found to be generally immature, i.e. below 0.5% of vitrinite reflectance.

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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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Potencjał węglowodorowy i charakterystyka geochemiczna substancji organicznej w profilu otworu Tarnawa 1

Kotarba M., Wagner M., Więcław D., Kosakowski P., Kowalski A.

Prace Państwowego Instytutu Geologicznego

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2001

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T. 174

161--172

PL

Badania geochemiczne i petrograficzne wykonano w celu określenia zawartości, typu genetycznego, stopnia przeobrażenia i potencjału węglowodorowego substancji organicznej zdeponowanej w utworach kenozoicznych, mezozoicznych i paleozoicznych, profilu otworu Tarnawa 1. Utwory ilasto-mułowcowe sfałdowanego miocenu jednostki zgłobickiej oraz miocenu autochtonicznego zawierają stosunkowo niewielkie ilości lądowej substancji organicznej (gazotwórczy kerogen typu III). W utworach węglanowych górnej jury i keloweju substancja organiczna praktycznie nie występuje. W utworach mułowcowo-ilastych jury środkowej (baton–aalen) występują zmienne ilości substancji organicznej, do 15,7% wag. całkowitego węgla organicznego (TOC), o charakterze morskim (ropotwórczy kerogen typu II). Utwory te charakteryzują się dobrymi parametrami macierzystości. Niewielka ilość substancji organicznej zawarta w nierozdzielonych utworach permu i triasu (greisbach i thuryng) ma charakter lądowy (gazotwórczy kerogen III typu). Substancja organiczna w utworach wszystkich wyżej wymienionych jednostek stratygraficznych jest niedojrzała lub wykazuje niewielki stopień przeobrażenia termicznego co wskazuje na mikrobialny proces generowania węglowodorów (głównie metan bakteryjny) i początkową fazę niskotemperaturowych procesów termogenicznych. Utwory permu górnego (thuryng) zawierają znikome ilości substancji organicznej (TOC do 0,07% wag). Utwory dolnego permu i utwory namuru A (?i górnego wizenu), obok rozproszonej substancji organicznej, prawdopodobnie zawierają większe wkładki substancji węglowej (TOC do 79,8% wag.). W utworach tych dominuje typowo lądowa, gazotwórcza substancja organiczna, która weszła już w początkową fazę niskotemperaturowych procesów termogenicznych („okno ropne”). Substancja organiczna w utworach węglanowych turneju i famenu występuje w niewielkich ilościach do 0,27 % wag. TOC. Posiada ona charakter algowy (ropotwórczy kerogen typu II) i znajduje się w środkowej fazie niskotemperaturowych procesów termokatalitycznych.

EN

Geochemical and petrographic analyses were performed in order to determine the content, genetic type, maturity and hydrocarbon potential of organic matter deposited in Cenozoic, Mesozoic and Palaeozoic strata in Tarnawa 1 well profile. The claystone-mudstone strata of the folded Miocene in the Zgłobice unit and autochthonous Miocene sediments contain relatively small quantities of terrestrial organic matter (gas-prone type III kerogen). Organic matter is practically absent in the Upper Jurassic and Callovian carbonate sequence. The mudstone-claystone Bathonian-Aalo character (oil-prone type II kerogen). The Bathonian-Aalenian strata have good source parameters. The small amounts of organic matter present in undivided Greisbachian and Thuryngian strata are of terrestrial character (gas-prone type III kerogen). The organic matter of all the above mentioned stratigraphic units is either immature or of low degree of thermal maturity. This shows to the microbial process of hydrocarbon generation (mainly bacterial methane) and initial phase of low-temperature thermogenic processes. The Thuryngian (Upper Permian) strata contain negligible amounts of organic matter (up to 0.07% wt. TOC). Apart from the dispersed organic matter, both the Lower Permian and Namurian A and Viséan strata most probably contain bigger carbonaceous intercalations up to 79.8% wt. TOC. Typical terrestrial gas-prone organic matter which already entered the initial stage of thermogenic processes dominates there. Small quantities of organic matter in the Tournaisian and Famenian carbonate strata to 0.27% wt. TOC are of algal character (marine and/or non-marine oil-prone type II kerogen) which reached the middle stage of low-temperature thermogenic processes.