A 3D HIGH RESOLUTION MODEL OF BOUNDING SURFACES IN AEOLIAN‐FLUVIAL DEPOSITS: AN OUTCROP ANALOGUE STUDY FROM THE PERMIAN ROTLIEGEND, NORTHERN GERMANY

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Abstract
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 PETRELT™ software.In the quarry, aeolian sandstones approximately 12 m thick (φ∼ 5‐11 vol. %, κradial∼ 0.01‐10mD) 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 flow 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 flow baffles.This outcrop‐derived, high resolution model may contribute to a better understanding of the subsurface architecture and reservoir properties of aeolian‐fluvial successions. Taking into consideration the centimetre‐ 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.

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