Turbidite-Reservoir Architecture in Complex Wedge-Top Depocenters, Tertiary Molasse Foreland Basin System, Austria

Jacob A. Covault¹, Stephen M. Hubbard², and Stephan A. Graham^1
1Geological and Environmental Sciences, Stanford University, Stanford, CA
²Geology and Geophysics, University of Calgary, Calgary, AB, Canada

We employ an integrated subsurface dataset, including >400 m (1300 ft) of drill cores and 3D seismic-reflection data from >530 sq km (200 sq mi) of the Tertiary Molasse foreland basin system in Austria, to characterize turbidite-reservoir architecture across structurally-complex wedge-top depocenters and to interpret the influence of submarine topography on hydrocarbon-reservoir quality and distribution. Reservoir architecture and depositional processes were correlated with associated wedge-top topographical features in order to identify zones of preferential sediment gravity-flow convergence or divergence. Zones of flow convergence facilitate flow acceleration and accumulative flow behavior, whereas zones of flow divergence facilitate deceleration and depletion. Zones of preferential flow convergence include narrow (<2 km [1 mi]) and steep (<15°; exaggerated by post-depositional deformation) foredeep-margin slope channels along thrust front-segmenting tear faults, and steep (<20°), unchannelized piggyback-basin and foredeep margins. Slope-channel topography facilitated deposition of relatively coarse-grained, amalgamated turbidite reservoirs, whereas unchannelized basin-margin topography facilitated deposition of fine-grained, chaotic non-reservoirs. Zones of preferential flow divergence are flat (<1°), unconfined (i.e., large in comparison to sediment gravity flows) piggyback-basin floors, which facilitated the development of relatively coarse-grained, non-amalgamated, upward fining turbidite reservoirs stratigraphically partitioned by fine-grained mass transport-complex deposits. The results of this study elucidate the influence of wedge-top submarine topography on turbidite-reservoir character and distribution across the classic Molasse foreland basin system in Austria, and can be applied to oil and gas exploration in analogous, structurally-complex settings.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas