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Gas in Imbricated Channel Systems of the Foreland Basin of the Eastern Alps

Linzer, Hans-Gert 1
1 RAG, Vienna, Austria.

The foreland basin of the Alps consists in the eastern part of a deeper marine segment which was dominated by an axial channel system. This channel system was discovered by 3D seismic volume visualization techniques (Linzer 2001, 2002). Detailed analysis of depositional processes was carried out by Hubbard et al. (2005) and Covault J.A. et al. (2008).

Now that nearly the complete channel system is covered by 3D seismic, its complex pattern has been made transparent. Whereas the lower part (Early Oligocene) is a broad linear feature, the upper part (Late Oligocene) consists of stacked meandering channels. The southern margin of the deeper marine foreland basin is imbricated in two areas. In the western area, thrusting started after the deposition of Early Oligocene sediments. The western imbricates were detached in Upper Cretaceous to Lower Eocene levels and contain Late Oligocene syn-thrust piggy-back basin succession. The imbricates of the eastern part were detached in Rupelian marls and claystones. The Late Oligocene sediments of the eastern imbricates which are partly layered parallel to the thrust planes contain parts of the axial channel system and were covered by Early Miocene sediments, thus indicating Late Oligocene to Early Miocene thrusting. Kinematics of thrusting can be derived from geometries of footwall and hangingwall cutoffs of the thrust sheets and are indicating a left-lateral transpressional contraction. The last channel system was formed in Lower Miocene times during the last thrust movements of the Molasse imbricates. This channel is only slightly deformed and runs along the northern thrust front of the Alps. The basin was finally filled up with Lower to Middle Miocene sediments.

Hydrocarbon exploration started in the mid-fifties with a first exploration well in the eastern imbricates based on single fold 2D lines on a proposed anticlinal structure. The second exploration well in the undeformed foreland basin was the beginning of a successful exploration history in this area. Major gas fields are situated in structural high positions within parts of the channel and levee systems.

With a recent exploration well in the imbricated channel successful in finding gas a new play type is being developed.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009