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The Alpine Molasse Basin : Review of Petroleum Geology and Remaining Potential

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The Alpine Molasse Basin : Review of Petroleum Geology and Remaining Potential The Alpine Molasse Basin : review of petroleum geology and remaining potential Autor(en): Véron, James Objekttyp: Article Zeitschrift: Bulletin für angewandte Geologie Band (Jahr): 10 (2005) Heft 1 PDF erstellt am: 27.09.2021 Persistenter Link: http://doi.org/10.5169/seals-225567 Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und den korrekten Herkunftsbezeichnungen weitergegeben werden. 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Vol. 10/1 Juti 2005 S.75-86 The Alpine Molasse Basin - Review of Petroleum Geology and Remaining Potential James Veron1 Keywords: Molasse Basin, Petroleum potential, Yet-to-Find, Austria, Germany Abstract Zusammenfassung Given the decades of exploration activities in the Die langjährigen Explorationstätigkeiten in den German and Austrian areas of the Molasse Basin, deutschen und österreichischen Teilen des Molasse new large discoveries in the basin may be rare. However, Beckens, lassen neue grosse Kohlenwasserstoff-Funde technical progress, new seismic interpretation als eher unwahrscheinlich erscheinen. and geological models generated new prospects and Neueste technologische Entwicklungen im Bereich increased exploration efficiency. The largest gas der Seismik sowie neue geologische Modelle field in Upper Austria, was discovered in 1997 and haben jedoch die Explorationserfolge erhöht. Das several small to medium discoveries were found in grösste Gasfeld Oberösterreichs wurde zum the Austrian Molasse Basin since. The presented Beispiel im Jahre 1997 entdeckt. Mehrere andere neue here Yet-to-Find analysis of the Molasse Basin Öl- und Gasfunde folgten danach. Die hier präsentierte indicates that up to several hundred (small to very «Yet-To-Find» Analyse des Beckens zeigt, small] fields can still be discovered, with the dass einige hundert kleine Kohlenwasserstoff-Felder, estimated total recoverable reserves exceeding 400 mit einem geschätzten förderbaren Reservevolumen MMboe (million barrels of oil equivalent]. von über 400 MMboe (million barrels of oil equivalent], noch zu entdecken sind. 1 Introduction The Molasse Basin is located to the north of companies are showing interest in the area the Alps and extends from France to the eastern as opportunities related to not yet fully border of Austria (Fig. 1). In its present explored specific plays might still exist in day configuration, the basin is about 900 km various types of prospects. For example, the long and up to 120 km wide in the German latest discoveries in the basin, Zaggling and sector. The Molasse Basin is a Cenozoic Foredeep Strass were made by RAG (Rohöl-Auf- Basin, the basin fill of which fundamentally suchungs AG/Österreich) in 2004 in the responded to flexural subsidence. Its southwestern corner of the Salzburg block, substratum comprises Mesozoic, locally Per- in Austria. Zaggling encountered gas in the mo-Carboniferous and crystalline/metamor- Oligocene series, while Strass in the phic basement rocks. Miocene series. After decades of exploration - over 1'200 exploratory wells have been documented - and with some 192 discoveries, the basin is considered mature in terms of hydrocarbon exploration. However, several oil and gas 1 Basin Specialist, IHS Energy, 24 Chemin de la Mairie, 1258 Perly-Geneva 75 6°E 7°E 8°E 9°E 10°E 1TE 12°E 13°E 14°E 15°E 16°E 49°N GERItfANY Bohemian Massif olasse Bas 48°N SF^chZone Waschberg Zone Austrides Folded Molasse AUSTRIA 47-N jg? eVBÒeS V^eW Z SWITZERLAND Zaggling discovery S Strass discovery O Tertiary age reservoirs *p Cretaceous age reservoirs £3 Jurassic age reservoirs £5 Triassic age reservoirs Fig. 1 : Basin Location and Generalised Distribution Map of the Reservoirs in Germany and Austria. 2 Regional Geology The Molasse Basin extends along the northern 1987). The shift from the epicontinental to front of the Alpine Mountain Range of the passive margin setting is being correlated Central Europe. Trending WSW-ENE, it covers with Jurassic extensional events (Roeder areas of France, Switzerland, Germany & Bachmann 1996), apparently falling into and Austria. Main areas of deposition are the time of Middle Jurassic crustal separation north-central Switzerland, southernmost in the western Tethys (Ziegler 1982). Germany and eastern Austria. The Late Cretaceous to Paleogene was dominated The Molasse Basin and its substratum underwent by primarily strike-slip movements four major evolutionary stages, termed along NW-SE directions. here as Syn-rift, Epicontinental, Passive Margin Deposition was resumed at basin-wide scale and Alpine Foredeep. During Permo-Car- during the Paleogene, reflecting the flexural boniferous times (Syn-rift phase), narrow basin development in response to Africa- troughs formed along the dominating Europe convergence and subduction of the ENE-WSW and WNW-ESE trends of the European Plate. Sediments were mainly Variscan wrench faults. In the Molasse Basin sourced from the south, onlapping progressively area, those are the Giftthal, Bodensee and to northwest and, in terms of facies Entlebuch troughs. Epicontinental deposits evolution, changed from marine, turbidité of Triassic-Middle Jurassic age progressively sedimentation to non-marine, freshwater overstep the Variscan Basement, or on Per- elastics. As a result of the flexural bending of mo-Carboniferous series, from NW to SE the crust, mainly extensional stress was (Boigk 1981), to the effect that neither the induced in an overall compressional setting, Landshut-Neuötting paleohigh of Eastern causing the formation of sets of synthetic Bavaria nor major parts of the Austria and antithetic normal faults which trend Molasse Basin area are covered. mainly parallel to the basin axis. The passive margin stage was accompanied Two geologically and geomorphologically by transpressional and transtensional differing entities are observed within the movements in Middle Jurassic to Early Cretaceous basin: the mainly undeformed part (Unfolded time (Maikovsky 1987; Nachtmann & Wagner Molasse) which makes up more than 90% 76 of the basin, and the deformed part, the Folded Waschberg Zone, the eastern equivalent of and thrusted (subalpine) Molasse, which the Folded Molasse. takes up the southernmost parts of the basin To the south, the Molasse Basin terminates area, being limited to the south by different along the various thrust fronts which delimit tectonic units of the Alpine mountain range. the Alpine system. Locally, particularly in the Upper Austria area, the fold belt is absent, overridden by the southerly Alpine thrusts. The division of 3 Petroleum Geology the Molasse Basin into deformed and unde- formed sub-units dates back to times of field 3.1 Petroleum Systems geological work, when the limit between the two domains was drawn along the northernmost Four petroleum systems are believed thrust fault with surface expression, controlling the occurrence of hydrocarbons in lacking seismic control. This definition is the basin (Fig. 2). However, due to the maintained here, although recent reviews of absence of unequivocal evidence, i.e. subsurface data indicated the presence of a supportive oil/gas - source correlations, an frontal triangular zone at regional scale, element of uncertainty is inherent in the separating both entities. identification of the petroleum systems. The Alpine Molasse Basin (Fig. 1) is limited along the northern margin, mainly on Swiss 1) The Permo/Carboniferous - Triassic/ terranes, by the mountain range of the Jura Jurassic/Neogene Petroleum System Fold Belt. Along the transition from the Molasse lowlands to the Jura Mountains, the Upper Carboniferous and Lower Permian Molasse sediments - although (Rotliegend) coal seams and bituminous unconformably resting on their substratum - depict shales provide the source rocks. The petroleum the structuration, i.e. folding and faulting, of system, as the distribution of source the Jura Fold Belt. This reflects the young rocks, is confined to narrow rift grabens. (Late Miocene to Pliocene) age of the fold belt Traps of those locally confined areas are deformation. The Mesozoic platform area of antithetic, tilted fault blocks (particularly in the Swabian and Franconian Jura adjoins to the German Western Molasse area), and the northeast, where youngest Molasse thrust sheets or subthrust fault blocks in the sediments onlap on that platform. The onlap Folded Molasse area, as is the case of the sediments are partially eroded, indicating an Entlebuch discovery.
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