PETROLEUM SYSTEMS IN THE AUSTRIAN SECTOR OF THE NORTH ALPINE FORELAND BASIN: AN OVERVIEW

PETROLEUM SYSTEMS IN THE AUSTRIAN SECTOR OF THE NORTH ALPINE FORELAND BASIN: AN OVERVIEW

Gas hydrates

Hydrocarbons

Gasoline

Deposition

Biodegradation

Hydration

Oils and fats

Gases

Petroleum geology

Sandstone

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: 400600 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 ( 2018 The Authors. Journal of Petroleum Geology 2018 Scientific Press Ltd

299-317

3

41

Journal of Petroleum Geology

2018

Gross, D.

Sachsenhofer, R.F.

Bechtel, A.

Gratzer, R.

Grundtner, M.-L.

Linzer, H.-G.

Misch, D.

Pytlak, L.

Scheucher, L.

journalArticle

1416421

10.1111/jpg.12704