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Fluvial Systems: Scaling Relationships, Predictive Facies Models and Subsurface Application


Scaling relationships for fluvial systems such as width-thickness ratios are used to predict sandstone body lateral extent and to construct reservoir models. However, sandstone body widths can vary by up to 4 orders of magnitude for a given thickness, making selection of appropriate values and analogues difficult. We have constructed a database of dimensions for modern and rock record fluvial system examples where the basinal context is well constrained. We show that scaling relationships vary systematically depending on location within a basin e.g. whether the fluvial system is proximal, distal, axial or lateral to the basin margins. Within modern and ancient fluvial-dominated basin-fill successions we recognise 3 depositional systems: axial, valley-fill and distributive fluvial systems (DFS). We also recognise inter-DFS tributary river systems in modern basins where rivers come together between larger DFS, however these are rare and potentially difficult to identify in the rock record. These three principal depositional systems account for most fluvial sandstone bodies within fluvial-dominated basin-fill successions and comprise a range of architectural elements: including floodplain, single storey channels and multi-storey channel belts. Architectural elements and depositional systems are restricted to specific locations within present day sedimentary basins. Consequently scaling relationships and sandstone body width-thickness ratios will vary systematically with basin location. This approach links observations from modern basins including hydrological data, remotely sensed imagery and field data, with rock record observations to derive datasets that are constrained by depositional system, architectural element and basin location. We use this database together with net to gross and storey development to construct predictive models of sandstone body thickness, heterogeneity and lateral extent, and apply these to the subsurface.