Depositional Environment and Hydrocarbon Potential of Coal and Oil Shale in the Miocene Aleksinac Basin (Serbia)

Klaus Oberauer

Research output: ThesisMaster's Thesis

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Numerous sedimentary basins with oil shale deposits occur in Serbia. Their formation and development was controlled by tectonic cycles, which also influenced the formation and development of the southern part of the Pannonian Basin. The most important oil shale deposit is located in the Aleksinac Basin and is assigned to the Lower Miocene. A lower and an upper oil shale horizon occur in the Aleksinac Basin, which are separated by the several meter thick “Aleksinac” coal seam. The lower oil shale horizon is 30 m thick and includes interlayered sandy rocks and thin coal layers. The upper oil shale horizon overlies the Aleksinac coal seam and is about 60 m thick. Intense faulting by the end of the Early Miocene divided the deposit into tectonic blocks with various dip angles. In this study the depositional environment of the Aleksinac coal seam and of the upper oil shale horizon was investigated. In addition, the hydrocarbon potential of the sedimentary succession in the Aleksinac Basin was quantified. The study outcomes are based on bulk geochemical, organic petrographical, organic geochemical as well as carbon-isotope data of samples taken from well BD-4, which was drilled near the village of Subotinac. Different biological markers, including n-alkanes, isoprenoids, steroids, hopanoids, di- and triterpenoids, were determined. Maturity parameters, such as vitrinite reflectance and temperature of maximal hydrocarbon generation (Tmax), indicate that the organic material is thermally immature. The Aleksinac coal seam in the well BD-4 is around 4 m thick and was deposited subaqueously in a low-lying mire. The plant input is dominated by angiosperms. The upper part displays an unusual high HI (> 500 mgHC/gTOC) for a coal seam. A relative rise in water level led to the drowning of the swamp and to the deposition of the 60-m-thick upper oil shale in a lacustrine environment. The organic material of the oil shale is dominated by algae and bacterial biomass and, therefore, is classified as type I kerogen. Biomarker data suggest a stratified water column which likely was formed due to differences in salinity. The stratified water column led to a strictly anoxic environment in a mesosalinar lake which enabled the accumulation of uncommon high amounts of organic material (average TOC: 18.0 wt.%) and excellent preservation (average HI: 743 mgHC/gTOC). TOC and Rock-Eval data show that the lower and upper oil shale layers are "excellent" source rocks and that they can generate 7.8 tons of hydrocarbon per m2 (t HC/m2, lower oil shale) and 14.2 t HC/m2 (upper oil shale), respectively. The oil yield is about 15 wt.% in the lower oil shale and about 12 wt.% in the upper oil shale.
Translated title of the contributionAblagerungsbedingungen und Kohlenwasserstoffpotential von Kohle und Ölschiefer im untermiozänen Aleksinac Becken (Serbien)
Original languageEnglish
  • Sachsenhofer, Reinhard, Supervisor (internal)
Award date7 Apr 2017
Publication statusPublished - 2017

Bibliographical note

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  • Serbia
  • Aleksinac Basin
  • source rock
  • oil shale
  • coal
  • Lower Miocene

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