Modeling Hierarchical Aquifer Architecture From Centimeter to Kilometer Scales

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0510819RitziComplexity and uncertainty in ground water flow and transport are related to heterogeneity in the hydraulic properties of natural porous media. In deposits of sediment this heterogeneity is related to the sedimentary architecture, of which the important aspects are the proportions, geometry, and juxtapositioning relationships of sedimentary units. These are units created at different spatial scales under various processes of deposition and erosion and organized within a hierarchical framework. Realistic representations of aquifer architecture within hydrogeologic models must be achieved because the geologic structures reduce entropy in hydraulic properties from the maximally disordered state. At the same time, these structures can create greater entropy in transport statistics compared to those from a maximum entropy spatial field (e.g., models containing interconnected gravel units within a lower permeability background have greater variance in mass residence time statistics than models containing random, unconnected gravel patches).A digital representation of a sedimentary deposit will be created with realistic architecture from the scale of centimeters up to the scale of kilometers. A model with this range of scales is unprecedented. The digital deposit will represent the hierarchical sedimentary architecture of fluvial braid-belt deposits, common in both aquifers and in petroleum reservoirs. The digital deposit will be a synthetic but realistic data set for use in computational experiments in hydrogeology. As such, it will have a sedimentary architecture that is consistent with known depositional processes, with the shapes and scales of depositional bedforms, and with field measurements of stratification geometries and grain-size variations. Developing a digital deposit over this range of scales will require quantifying the three-dimensional architecture from a large amount of data collected within a modern river system, developing simulation algorithms tailored to those findings, and developing efficient means of computational storage. The model will be created with geometric simulation on a centimeter-spaced regular grid that facilitates its import into other types of numerical models (e.g., models for ground-water flow and transport). The digital deposit, together with its unique storage structure and generating algorithms, will be made freely available to the research community.