Petroleum Systems in the Austrian Sector of the North Alpine Foreland Basin: An Overview

Abstract

Two separate petroleum systems have been identified in the Austrian sector of the North Alpine Foreland Basin: a lower Oligocene – Cenomanian/Eocene oil and thermogenic gas system; and an Oligocene‐Miocene microbial gas system. Recent studies by both academic and industry‐based research groups have resulted in an improved understanding of these petroleum systems, which are reviewed in this paper. Lower Oligocene organic‐rich intervals (up to 12 %TOC; HI: 400–600 mgHC/gTOC), capable of generating slightly more than 1 t of hydrocarbons/m2, are the source rocks for the thermogenic petroleum system in the Austrian sector of the North Alpine Foreland Basin. The present‐day distribution of this source rock is controlled by submarine mass movements which removed a large part of the organic‐rich interval from its depositional location during the late early Oligocene. The transported material was redeposited in locations to the south which are at the present day buried beneath Alpine thrust sheets. In addition, source rock units were incorporated into Molasse imbricates during Alpine deformation. Hydrocarbon generation began during the Miocene, and the oil kitchen was located to the south of the Alpine thrust front. Hence, lateral migration over distances of up to 50 km was required to charge the mainly Eocene and Cenomanian non‐ and shallow‐marine sandstone reservoir units. Hydrocarbons are in general trapped in structures related to east‐west trending normal faults, and differences in source rock facies resulted in the development of separate western and eastern oil families. Surprisingly, with the exception of some fields in the eastern part of the study area, associated gas contains varying (and sometimes very high) percentages of primary and secondary microbial methane. The composition of oil in some fields is influenced by both biodegradation and water washing. Post‐Miocene uplift in the Austrian sector of the basin had further effects on biodegradation and the consequent formation of secondary microbial gas, and also resulted in re‐migration. The upper Oligocene to lower Miocene succession (Puchkirchen Group, Hall Formation) provides both source and reservoir rocks for the microbial petroleum system in the Austrian sector of the North Alpine Foreland Basin. TOC contents (<1.0 %) and HI values (<140 mgHC/gTOC) of pelitic source rocks are typically low. Microbial gas was generated shortly after deposition during early diagenesis and was subsequently fixed in gas hydrates. Basin subsidence and high sedimentation rates resulted in decomposition of the hydrates below their stability zone, and reservoirs were filled during the early Miocene. Subsequent mixing of microbial gas with thermogenic gas and condensates is widespread. However, biodegradation has prevented precise determination of the fraction of thermogenic hydrocarbons present in gas samples. Reservoir sandstones were deposited within a deep‐marine channel belt along the axis of the North Alpine Foreland Basin, and reservoir quality depends on the precise posit...

Selective Recording of Tectonic Forcings in an Oligocene/Miocene Submarine Channel System: Insights From New Age Constraints and Sediment Volumes From the Austrian Northern Alpine Foreland Basin

“…The sediment-source area, the European Alps, form one of the most extensively studied orogens in the world with well-constrained phases of uplift and denudation, and relatively well understood tectonic drivers (e.g., Handy et al, 2015). Similarly, the Upper Austrian NAFB is one of the most thoroughly studied foreland-basin systems (Gross et al, 2018). During the deposition of the Oligocene to Miocene Zupfing Formation, Puchkirchen Group -consisting of the Lower (LPF) and Upper Puchkirchen (UPF) Formations -and the lower Hall Formation, sediment routing in the basin was largely controlled by a submarine channel system along the basin axis (Figures 2, 3) (De Ruig and Hubbard, 2006;Hubbard et al, 2009).…”

“…Simplified lithological section of Well Z (for position seeFigure 1) with FO and LO of index taxa [nannofossils and benthic foraminifera (Ćorić and Spezzaferri, 2009)], TOC-and S-values are high in the UPF and CaCO 3 -content is highly variable (A1-horizon afterGross et al, 2018). At 1125 m TOC-and S-contents show a decrease, increase again and finally decrease to low and stable levels until the end of the section.…”

New Opportunities for Oil and Gas Exploration in Poland—A Review

“…The majority of European hydrocarbon reserves (excluding Russia) is located in the North Sea region within the Northern Permian basin, where reservoirs ranging from Carboniferous to Tertiary are present, e.g., [8], although the Adriatic region also has a long exploration history concerning hydrocarbon potential, e.g., [9,10], France, e.g., [11,12], Spain, e.g., [13], Italy, e.g., [14,15], Vienna Basin, e.g., [16], the Carpathians and their foreland in Czech, Poland, Ukraine, and Romania, e.g., [17][18][19][20][21][22][23], Transylvania, e.g., [20,24], Eastern Ukraine, e.g., [25] and the Black Sea, e.g., [26]. In Poland, new small-or mediumsized gas and oil fields continue to be discovered (e.g., Brzyska Wola, Czarna Wieś, Olchowiec, Pniewy, Rogoźnica, Wielichowo W, Gnojnica gas fields with total reserves of ~5.8 BCM/206 BCF, and Połęcko oil and gas field of total reserves of gas ~2.3 MCM/81 MCF and oil ~12.3 kTOE/87.6 MBOE; all of them documented by the Polish Oil and Gas Company in 2019-2020 in the Carpathian Foredeep and Polish Lowland) [1,2], which suggests the existence of still-unexplored regions.…”