A 3D HIGH-RESOLUTION MODEL OF BOUNDING SURFACES IN AEOLIAN-FLUVIAL DEPOSITS: AN OUTCROP ANALOGUE STUDY FROM THE PERMIAN ROTLIEGEND, NORTHERN GERMANY
C. Fischer1,*, R. Gaupp2, M. Dimke3 and O. Sill4
1 Geowissenschaftliches Zentrum der Universität Göttingen, Sedimentologie/ Umweltgeologie, Goldschmidtstr. 3, D-37077 Göttingen, Germany.
2 Institut für Geowissenschaften, Friedrich-Schiller-Universität, Burgweg 11, D-07749 Jena, Germany.
3 RWE Dea, Überseering 40, D-22297 Hamburg, Germany.
4 ExxonMobil Production Deutschland GmbH (EMPG), Riethorst 12, D-30659 Hannover, Germany.
* corresponding author, present address: Department of Earth Science, MS-126, Rice University, 6100 Main Street, Houston, TX 77005, USA. email: firstname.lastname@example.org
The fluvial-aeolian Rotliegend succession exposed in a quarry near Magdeburg (Flechtinger Höhenzug, Northern Germany) is an analogue for deeply-buried, gas-bearing Rotliegend sandstones in the Southern Permian Basin. The spatial configuration of bounding surfaces within this succession was reconstructed with reference to twelve profiles with 926 sample points. Generally sub-horizontal interdune migration surfaces were surveyed, and the areal extent of small-scale superimposition surfaces and the thicknesses of intervening strata were measured. Based on these observations and also on the extent of different lithofacies types and on corresponding porosity and permeability data, a 3D lithofacies model (including bounding surface configurations) incorporating porosity and radial permeability was created using PETREL™ software.
In the quarry, aeolian sandstones approximately 12 m thick (φ ~ 5-11 vol. %, kradial ~ 0.01-10 mD) are separated into a number of tabular bed sets by sub-horizontal interdune migration surfaces. The surfaces are often associated with thin pelitic intervals with low permeabilities which originate from deflation and sheet flood events. Aeolian deposits consist mainly of two lithotypes: low-angle cross-bedded, and steeply cross-bedded medium-grained sandstones. Superimposition surfaces occur at the base of the low-angle cross-bedded sandstone bodies. The highest porosities and permeabilities occur within the steeply cross-bedded sandstones, reflecting intense eodiagenetic calcite and quartz cementation with subsequent calcite dissolution. The low-angle cross-bedded sandstones may act as fluid flow baffles.
This outcrop-derived, high resolution model may contribute to a better understanding of the sub-surface architecture and reservoir properties of aeolian-fluvial successions. Taking into consideration the decimetre to metre-scaled inhomogeneities observed at outcrop, lithotype modelling with reference to the occurrence of bounding surfaces may help to predict how similar reservoir rocks are partitioned.