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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Exploitation of unconventional resources could prolong the gas production in the North Sea. Low-net-togross fluvial intervals have tough-gas reservoir potential in thin-bedded crevasse splays. To assess economic risks associated to the development of these reservoirs, a reliable grain-size distribution model is required. Sparse areal data availability for reservoir models commonly results in the use of stochastic interpolation. Numerical models offer the possibility to support these methods with proven physical concepts.To this end, simulations were conducted with Delft3D process-based modelling software. Input parameters and the validation data sets for these models are derived from outcrop studies in the presentday Río Colorado fluvial system in the Altiplano Basin, Bolivia. The grain-size trends of the simulated surface sediments for a single flood event are consistent with the validation data. These trends were used to populate individual crevasses splays within a static model. This shows that process-based models are able to support sediment trends and depositional mechanisms of a crevasse splay. The combination of numerical models and discrete field data provides a solid case for sediment distribution predications. However, simulations still have a limited accuracy. @en

Thin-bedded crevasse splays in low-net-to-gross fluvial stratigraphy were previously not considered as potential reservoir targets. This paper focuses on the construction of a high-resolution static reservoirarchitecture model of crevasse splay deposits associated with meandering rivers on the low-gradient coastal plain of endorheic basins. Outcrops of the Miocene Huesca fluvial fan (Ebro Basin, Spain) display low-net-to-gross fluvial stratigraphy, bounded by two large sand-prone channel belts. A static model of the study area is constructed following a sequential macro-to-micro approach. The model shows connectivity between the channel belts through crevasse splays. Connections between separate crevasse splays are present through incisions of younger crevasse splays and channels. Without the connectivity between the channel belts, connectivity would still be present in vertical wells through the extensive crevasse splays originating from the channel belts. This makes the model suitable for reservoirs with less connections as well. Ongoing research on process-based modelling of crevasse splays will yield an improved understanding of the grain-size distribution and can be used to populate the static model. The model will be upscaled to allow for fluid flow simulations in which several production mechanisms will be evaluated in order to assess the economic potential of these secondary tough gas reservoirs. @en