Fluvial point‐bar architecture and facies heterogeneity and their influence on intra‐bar static connectivity in humid coastal‐plain and dryland fan systems

Many published studies detail the sedimentology and stratigraphic architecture of meandering fluvial systems and their preserved successions based on data from modern systems, outcrops or subsurface. However, the broader understanding of the behaviour of depositional systems and its role in determining the nature of the resultant depositional units remains limited due to difficulties associated with the collection of appropriate data on three‐dimensional sedimentary‐facies distributions and on the temporal evolution of the form of architectural elements. To overcome such limitations, numerical lithofacies and stratigraphic modelling approaches provide a valuable suite of tools to examine the sensitivity of intrinsic system behaviour to different controls that operate at varying spatial and temporal scales. This study utilises a three‐dimensional forward stratigraphic model, the ‘Point‐Bar Sedimentary Architecture Numerical Deduction’ (PB‐SAND), informed by data and relationships extracted from a sedimentological database, to model the facies architecture and heterogeneity of fluvial point‐bar elements in two contrasting environmental settings: humid coastal plains vs. dryland fluvial fans. This study demonstrates a workflow that uses high‐resolution seismic imagery to constrain the planform evolution of preserved point‐bar elements, in combination with data from appropriate geological analogues (five humid coastal‐plain and eight dryland fluvial‐fan systems) to constrain modelling parameters (i.e. bar thickness, facies proportion and mud‐drape geometry). The method applies a statistical analytical approach to constrain the ranges and types of sedimentary architectures and facies heterogeneity known for humid and dryland meandering fluvial depositional systems. Modelling results demonstrate the effects of increasing compartmentalisation of sand geo‐bodies by mud drapes, whose density increases vertically towards the bar top of point‐bar architectural elements. Modelling results also demonstrate how the compartmentalisation of point‐bar elements in the models constrained on humid coastal‐plain analogues, compared to those based on dryland‐fan analogues, exhibits a larger variation in response to the spatial distribution of mud drapes and their discontinuity in three dimensions. The modelling outputs are able to represent realistic architectural geometries, capture the three‐dimensional complexity of sedimentary architecture and incorporate styles of facies heterogeneity that can be employed in the quantitative analysis of connectivity. The PB‐SAND simulations can, therefore, be used to enhance conventional reservoir models and thereby to improve the realism of fluid‐flow models.