Hydrocarbon potential of organic-rich sediments in the Ukrainian Outer Carpathians and its Foreland

Johannes Florian Rauball

Research output: ThesisDoctoral Thesis

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Abstract

Organic-rich rocks with widely varying ages occur throughout many parts of the Ukrainian Carpathians, some of which are proven hydrocarbon source rocks. For this study, two organic-rich successions in the Outer Carpathians, as well as one potential source rock horizon and three oil samples from the Mesozoic basement of the Carpathian Foredeep, were chosen for a detailed analysis. Within the Ukrainian Outer Carpathians, the Lower Cretaceous Shypot Formation and the Oligocene-Lower Miocene Menilite Formation contain significant source rock potential. The latter, approximately 1800 m thick in the studied section, is considered to be the primary source rock interval of the region. The Menilite Formation contains thermally immature (vitrinite reflectance: 0.24-0.34 %Rr; Tmax: 419-425°C), organic-matter-rich sediments (frequently up to 24 wt.% TOC) that can generate up to 74.5 tons of hydrocarbons per m², which is a significantly higher generation potential than other source rocks in the entire Paratethys realm. The studied rocks are dominated by a marine (Type II) organic matter input mixed with varying amounts of land-plant derived material, which is supported by maceral and biomarker data. In addition, varying redox and salinity conditions during deposition are supported by varying dibenzothiophene/phenanthrene (DBT/Phen) and pristane/phytane (Pr/Ph) ratios. In contrast, the Shypot Formation, roughly 400 m thick in the study area, is rich in organic-matter (average TOC: 2.83 wt.%), but the hydrogen index (88 mgHC/gTOC) and the remaining source potential (2 tHC/m²) are low, partly due to the advanced maturity (vitrinite reflectance: 0.82 %Rr; Tmax: 456°C) of the succession. The higher maturities observed in the Shypot Formation imply that some hydrocarbons must have already been generated. However, it is argued that these accumulations were likely lost during major uplift and/or erosion. Preservation of the organic matter was supported by an oxygen-deficient environment, but strictly anoxic conditions were rare, which is supported by low DBT/Phen ratios, moderate Pr/Ph ratios and relatively high TOC/S ratios. The Middle Jurassic rocks, which occur in the Mesozoic basement of the Ukrainian Carpathian Foredeep, display elevated amounts of organic-matter (4.19 wt.%; max 14.98 wt.%). However, HI values (max: 242 mgHC/gTOC) are low, and organic-matter is dominated by gas-prone, Type III kerogen (with rare transitions into type II kerogen), which is supported by a strong predominance of terrestrial macerals. The petroleum potential, classifies the succession as a fair source rock, with only few intervals displaying a good source rock potential. Maturity parameters (vitrinite reflectance: 0.69-0.90 %Rr; Tmax: 434°C-448°C) indicate a marginally mature to peak oil window maturity, suggesting that major hydrocarbon generation may be restricted to the more mature sediments. An oil-source rock correlation was performed on Middle Jurassic rocks to investigate a possible genetic link with oils in the overlying Upper Jurassic reservoirs. However, biomarker analysis identified significant differences in DBT/Phen ratios, Pr/Ph ratios, sterane distributions and in isotopic signatures. As a result, an alternative source was investigated, and the new data collected on the oils was compared to published data on Upper Jurassic rocks in the Mesozoic basement, which presented a better fit and revealed the likely source of these oil accumulations.
Translated title of the contributionKohlenwasserstoffpotenzial von organisch-reichen Sedimenten in den ukrainischen Karpaten und dem Karpatenvorland
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Wagreich, Michael, Assessor B (external), External person
  • Sachsenhofer, Reinhard, Assessor A (internal)
Publication statusPublished - 2020

Bibliographical note

embargoed until null

Keywords

  • Carpathians
  • hydrocarbon potential
  • source rocks
  • organic geochemistry

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