Technical Presentation: Geology – a real science?

Geology – a real science? Subsurface and surface images tell the story of the evolving Eastern Alps and the North Alpine Foreland Basin – the key to subsurface energy exploration

Development of subsurface energy projects – fossil energy accumulated as hydrocarbons and coal during the past hundreds million years as well as the subsurface energy storage facilities and geothermal plants, all depend on structure and reservoir prediction.

The presentation is focused on the North Alpine Foreland Basin (NAFB) and the northern margin of the Eastern Alps, which evolved since late Cretaceous times as part of the broader Alpine fold belt system. Beside the classical Alpine surface geology, hydrocarbon exploration activities during the last 100 years accumulated a huge amount of subsurface data of the North Alpine Foreland Basin (NAFB) and partly of the thrust belt. More than 1000 wells have been drilled in the Austrian part of the Molasse Basin, with its internal overthrusted part being still underexplored. Large parts of the foreland basin and the imbricated southern part of the NAFB and the Flysch zone were covered with a dense net of 2D and 3D seismic reflection surveys. The 3D seismic covered parts of the frontal thrust belt (imbricated foreland and flysch area), imaged several left-lateral, transpressional NE directed thrust structures which are linked to surface structure indicated on geological maps and high resolution laser-scan images of a digital elevation model. The latest thrusting involved Lower Miocene (Karpathian) sediments, displacing Lower Oligocene foreland imbricates with Upper Oligocene piggyback basin sequences on top (main foreland thrust phase). The orientation of the piggyback structures indicate NW directed thrusting, rooted in a common basal detachment horizon. The Early Oligocene (Rupelian) period was affected by sudden deepening of the foreland basin, due to flexural loading and deposition of source rocks. Eocene transgressional and shallow marine sequences cover a Late Cretaceous-Paleocene thick-skinned right-lateral transpressional thrust system along the western margin of the Bohemian Massif. The basement thrusts are visible on 3D seismic, where low-angle detachments could be traced deep into the crystalline basement of the Bohemian Massif. This Eo-Alpine basement thrusts of the European Platform form counterpart structures to the approaching collisional front and may be traced below the Eastern Alps along the Bohemian Spur. The continuous record of the structural evolution of the NAFB serves as a reference for reconstructing parts of the Alpine-Carpathian-Pannonian system. In this complex setting different play types evolved in the foreland basin: a variety of basement fault traps, axial channel systems and overbank deposits, at the basin flanks gully systems and ponded mini-basins. Proven plays in the thrust belt itself are imbricated channels and fractured carbonates.

Regional scale geologic features have to be downsized to field/reservoir scale to predict reservoir quality. Subsurface (reflection seismic) images show the field-size scale and may indicate some aspects of reservoir quality.

Dr. Hans-Gert Linzer graduated 1987 in geology, at the Karlsruhe Institute of Technology (KIT). After finishing his PhD in Karlsruhe 1989, he continued with several research projects in the Northern Calcareous Alps, the Western, Eastern and Southern Carpathians at Eberhard-Karls-University of Tübingen and Rice University Houston, partly supported by AMOCO and OMV. Since 1998, he worked in Vienna with RAG Austria AG in hydrocarbon exploration, field development and most recently in geothermal energy exploration.