Hydrocarbon Generation and Alteration in the Vienna Basin

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Abstract

The Vienna Basin, located in Central Europe, is a mature hydrocarbon province. It hosts hydrocarbons in autochthonous units, the Calcareous Alps, in turbiditic sandstones of the Flysch Zone, in a high number of Miocene sandstone reservoirs, as well as in sandstones of the Molasse zone. The most important source rocks are Upper Jurassic marlstones (Mikulov Fm.) and marly limestones (Falkenstein Fm.). They form part of the autochthonous succession underlying the Alpine nappes and the Miocene fill of the Vienna Basin. In addition, the Mikulov Formation has been considered a potential shale gas play. Study aims include the determination of the depositional environment of the main Upper Jurassic source rock, the evaluation of lateral and vertical variations of its source potential, the assessment of possible additional source rocks with a Middle Jurassic age, oil/gas-source rock correlations, and the description and quantification of hydrocarbon migration and alteration. In order to reach the aims, rock-, oil- and gas samples have been investigated. Borehole Staatz 1 has been selected as a key well for the study of the vertical variability of the source potential of the Upper Jurassic source rocks. Samples have been investigated using organic geochemical, petrographical and mineralogical techniques. Additional samples from other boreholes are used to evaluate lateral trends. Deltaic sediments (Lower Quartzarenite Member) and prodelta shales (Lower Shale Member) of the Middle Jurassic Gresten Formation are potential secondary sources and are therefore also included in the present study. The Falkenstein and Mikulov formations in Staatz 1 contain up to 2.5 wt.%TOC and a type III to II kerogen. The organic matter is dominated by algal material. Nevertheless, HI values are relative low, a result of organic matter degradation in a dysoxic environment. Both formations hold a fair to good petroleum potential. Limited data from the deep overmature samples suggest that the original TOC contents may have increased basinwards. Based on TOC contents and the very deep position of the maturity cut-off values for shale oil and shale gas production, the potential for the economic production of unconventional petroleum is limited. The Lower Quartzarenite Member of the Middle Jurassic Gresten Formation hosts a moderate oil potential, while the Lower Shale Member is a poor source rock. An active, but minor petroleum system could be identified within the Lower Quartzarenite Member (Lower Quartzarenite Member – Doggerian (.) PS). The majority of the investigated oils have been generated from the Mikulov and Falkenstein formations. Oil has been generated at peak oil maturity, gas was generated at higher maturity. Microbial gas prevails in fields located along the Southeastern High (east of Vienna) and in the Molasse zone. Biodegradation affects oil down to a depth of approximately 2000 m. Biodegradation reaches rank 4 of the Biomarker Biodegradation Scale. Apart from reservoir temperature, both the tectonic position of reservoirs and trap type, influence the degree of biodegradation. Anaerobic biodegradation results in the formation of isotopically heavy CO2 and isotopically light microbial methane. Hydrocarbons in deep reservoirs within the Calcareous Alps are affected by thermochemical sulphate reduction. While these gases are rich in H2S and CO2, oil is characterized by increased DBT/Ph ratios. In contact with clastic rocks, H2S is removed by pyrite precipitation, whereas DBT/Ph ratios remain high. Stable sulphur isotope signatures confirm Upper Triassic anhydrites as the main sulphur source for H2S. Oils contain different quantities of benzocarbazoles, which can be used to determine the migration distances from the active source rocks. Although a general agreement exists between estimates based on benzocarbazoles and geological evidence, more detailed information about the timin

Details

Translated title of the contributionKohlenwasserstoffgenese und -alteration im Wiener Becken
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
Publication statusPublished - 2017