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Geology

Regional Geology

RAG started crude oil exploration in 1935 after obtaining the first exploration rights in the Vienna Basin. Oil has been produced from Miocene and Pliocene sands and sandstones since 1937. RAG still holds production licenses in three old oil fields in the Vienna Basin.

RAG has evaluated the geology and the hydrocarbon potential of the Molasse Zone in Salzburg and Upper Austria since the late 1940‘s and, more recently, in Bavaria. The Molasse Zone largely corresponds to the North Alpine Foreland Basin extending from Switzerland in the West, through Germany and Austria into the Czech Republic in the East. The basin was filled by clastic sediments due to uplift and erosion of the Alpine Orogen.

Oil and gas fields in Upper Austria, Salzburg and Bavaria

The geological profile shows that the Molasse basin is an asymmetric basin dipping to the south and partly extending underneath the Alps. It consists of relatively thin Mesozoic formations overlain by several thousand of meters of Cenozoic sediments. These consist of sandstones, conglomerates and shales sourced from the uplifted Alps. Sediments from the Bohemian Massive were deposited only in the northern parts of the basin. The basin consists of 1) the Foreland Molasse, reaching from the crystalline rocks that outcrop as the Bohemian Massive in the north, down to the northernmost extension of the Alps, 2) the Imbricated Molasse associated with the syntectonic ”south slope facies” , a narrow zone along the Alpine Flysch front and 3) the Subalpine Molasse overlain by the Alpine nappes.


Geological cross section through the Molasse Basin

Today’s knowledge of the geology of the Molasse Basin and its hydrocarbon potential is based on the results of approximately 850 wells, 22,000 kilometers of 2D seismic lines and almost 3100 km² of 3D seismic coverage. In Bavaria we have another 900 wells and 700 km² of 3D seismic. These are supplemented by thousands of shallow wells and maps of the near-surface stratigraphy. Although these horizons do not bear hydrocarbons, they have substantial ground water resources.


Stratigraphic table

Es gilt als weitgehend gesichert, dass in Oberösterreich das Erdöl und Begleitgas durch die thermische Umwandlung der organischen Stoffe des unter-In Upper Austria, the crude oil and associated gas were formed by thermal maturation of organic matter of the Lower Oligocene Schöneck Formation (“Fischschiefer”). The oil was not generated in the immediate vicinity of today’s reservoirs. It formed within the Subalpine Molasse that was overthrust by the Alpine nappes at a time when the Schöneck Formation entered the “oil window” (experiencing higher temperatures and pressures).  It migrated northwards to its present position.

The generation of natural gas of the Foreland Molasse is different. The quick burial of large sediment masses into a reducing deep water environment during subsidence of the basin encouraged biogenic gas generation. Bacterial activity converted the organics dispersed within the sediment into methane.

Oil reservoirs are found mainly in Upper Eocene sandstones. Cretaceous and Jurassic sandstones can also contain oil.  Natural gas, however, is mainly restricted to sandstones and conglomerates of the Oligocene (Puchkirchen Formation) and the lower Miocene (Hall Formation).


Geological fields of activity

In petroleum geology, the main activities of geoscientists are exploration, development and optimum production of oil and gas fields in collaboration with various other disciplines. Four major fields of activity can be distinguished

  • Exploration - Searching for and mapping oil and gas reservoirs and accumulations
  • Operations – Supporting borehole planning and drilling activities and evaluation of results
  • Reservoir characterisation – Creating detailed reservoir attribute maps (depth, thickness, porosity, permeability, compartmentalisation, etc.)
  • Appraisal and Production – Appraising and exploiting hydrocarbon discoveries in an optimum way