Abstract: Alpine Overthrust Exploration in Austria

COLINS, ELMAR, OMV AG

Exploration for hydrocarbons in the Alpine overthrusted areas (Flysch Zone and Calcareous Alps) started in the late fifties with the drilling of Urmannsau 1. The two main targets were Triassic dolomites within the Alpine nappes and the Jurassic to Cretaceous autochthonous sediments below the Alps. The Triassic dolomites within the Alpine overthrust are comparable to the Triassic dolomites from below the Vienna basin which constitute a prolific exploration target.

The main source rocks east of the Crystalline Spur of the Bohemian Massif and in the most western part of Austria are marls and marly limestones of the autochthonous Malm. The Oligocene Molasse shales are the source rocks for the area between the western edge of the Spur and Innsbruck. Within the Calcareous Alps, only a few layers are considered to have potential to expel considerable amounts of hydrocarbons. Main oil and gas generation started during the Early to Middle Miocene of Alpine thrusting. Trapping in the Autochthonous is mainly basement related while highly complicated anticlinal structures have trapping potential within the Allochthonous.

Structural mapping, gravity and magnetics as well as seismic 2D surveys were carried out in the whole Overthrust area. The seismic results were sometimes unsatisfactory because of the extreme topography, deep valley infills and an irregular and coarse data grid.

The drilling of 32 wells in the Austrian Overthrust resulted in three HC-discoveries (Molln, Grunau and Hoflein) of which only one - the gas and condensate field Hoflein - is of economic importance.

Although exploration in the Austrian Overthrust is by no means economic at the moment, new technologies in geophysics and drilling together with a better oil and gas price scenario may change the situation considerably.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria