The physical scale modelling of braided alluvial architecture and estimation of subsurface permeability D. J. Moreton,* À P. J. Ashworth Á and J. L. Best À *School of Geography and À School of Earth Sciences, University of Leeds, Leeds, LS29JT,UK Á DivisionofGeography,SchoolofEnvironment,University ofBrighton,Brighton,BN24GJ,UK ABSTRACT The quantitative modelling of fluvial reservoirs, especially in the stages of enhanced oil recovery, requires detailed three-dimensional data at both the scale of the channel belt and within-channel. Although studies from core, analogue outcrop and modern environments may partially meet these needs, they often cannot provide detail on the smaller-scale (i.e. channel-scale) heterogeneity, frequently suffer from limited three-dimensional exposure and cannot be used to examine the influence of different variables on the process±deposit relationship. Physical modelling offers a complementary technique that can address many of these quantitative requirements and holds great futurepotentialforintegrationwithreservoirmodelling.Physicalmodellingprovidesthepotentialto upscale results and derive reservoir information on three-dimensional facies geometry, connectivity and permeability. This paper describes the development and use of physical modelling, which employs generic Froude-scaling principles, in an experimental basin that permits aggradation in order to model the morphology and subsurface depositional stratigraphy of coarse-grained braided rivers. An example is presented of a 1:50 scale model based on the braided Ashburton River, Canterbury Plains, New Zealand and the adjacent late Quaternary braided alluvium exposed in the coastal cliffs. Critically, a full, bimodal grain size distribution (20% sand and 80% gravel) was used to replicate the prototype, which allows the realistic reproduction of the surface morphology and importantly permits grain size sorting during deposition. Uncertainties associated with the compression of time, sediment mass balanceandthehydrodynamicsofthefinestparticlesizesdonotappeartoaffectthereproducibilityof stratigraphy between experimental and natural environments. Sectioningofthepreservedsedimentarysequenceinthephysicalmodelallowsquantificationofthe geometry, shape, spatial distribution and internal sedimentary structure of the coarse- and fine- grainedfacies.Asix-foldfaciesschemeisproposedforthemodelbraidedalluviumandadirectlinkis establishedbetweenthegrainsizedistributionandfaciestype:thisallowspermeabilitytobeestimated for each facies, which can be mapped onto two-dimensional vertical cross-sections of the preserved stratigraphy. Results demonstrate the dominance of four facies based on permeability that range over threeordersofmagnitudeinhydraulicconductivity.Quantificationofsuchvariability,andlinkageto bothverticalproportioncurvesforfaciesdistributionandconnectivitypresentssignificantadvantages over other methodologies and offers great potential for the modelling of heterogeneous braided river sediments at the within channel-belt scale. This paper outlines how physical models may be used to develop high-resolution, geologically-accurate, object-based reservoir simulation models. INTRODUCTION One of the greatest challenges facing the reservoir geolo- gist and engineer is the prediction of hydrocarbon flow through heterogeneous fluvial sediments. The geologist usuallyhasaccesstofield-wideseismiclinesandboreholes Correspondence: D. J. Moreton, Exxon Mobil International Limited, St. Catherine's House, 2 Kingsway, London, WC2B 6HA, UK. E-mail: david.j.moreton@exxonmobil.com Present address: Mobil North Sea Limited, Grampian House, Union Row, Aberdeen, AB10 1SA, UK. Basin Research (2002) 14, 265±285 ß 2002 Blackwell Science Ltd 265