The Rotliegend feather-edge area in the central part of the endorheic Southern Permian Basin in the Dutch offshore is characterized by a predominance of mud-prone, evaporite-bearing playa and lake deposits with a subordinate amount of interbedded, thin, fluvial sheet sandstones. The distribution and lateral facies changes of the sandstone bodies have been analyzed by generating a long-range, high-resolution chronostratigraphic correlation framework. The correlation technique of pattern matching of GR logs was applied, supported by calculating spectral trend curves. Flooding events are the primary near-synchronous correlation surfaces, which can be traced up to and over 100 km. The basin setting of the Southern Permian Basin, the studied sandstone depositional architecture (logs) and sedimentary characteristics (core) are analogous to the depositional setting of laterally-amalgamated terminal lobes of dryland-river systems in an endorheic basin, such as the Holocene Altiplano Basin in Bolivia, present-day Lake Eyre (Australia) and the Miocene Ebro Basin (Spain). The integrated approach has yielded a stratigraphic reservoir-architecture framework in which the reservoir sandstones, with net sand up to 10 m, have been identified as amalgamated terminal-splay sandstone sheets formed at the end of dryland-river pathways, alternating with lacustrine mudstone layers deposited during short-duration, high-magnitude flooding in intermittent wet climate periods.

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Rotliegend aeolian and fluvial sandstones are prolific gas reservoirs throughout the Southern Permian Basin (SPB). Exploration and research efforts concentrated on the sand-dominated southern flank of the SPB, where the major gas fields are located. The reservoir potential of the Rotliegend feather edge in the central part of the SPB, i.e. the area where the south-derived sands pinch out towards the Silver Pit salt lake, has long been underestimated. The sand-starved, claystone-dominated and evaporite-bearing lithology in the central part of the basin hampered the detectability of thin-bedded, potential reservoir sandstones with conventional well logs. The present study uses high-resolution well correlations in a sequence-stratigraphic framework. The employed methodology is a combination of pattern analysis (trends and trend changes) in gamma-ray (GR) logs, and maximum entropy-based (MEM-based) spectral trend curves of GR to graphically evaluate the validity of the pattern analysis. This allowed for the correlation of at least twelve individual thin-bedded sheets (1 – 2m thick) a 20-25m thick reservoir interval over distances larger than 20km. Core analysis has identified the sheets as unconfined fluvial terminal-splay sandstone. The facies characteristics and sedimentary architecture were corroborated in an outcrop analogue study of a present-day river system in the Altiplano Basin (Bolivia). @en