High-Resolution Reservoir Architecture Modelling of Thin- Bedded Fluvial Terminal-Splay Sandstone in the Rotliegend Feather-Edge Area

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).