Modeling Hierarchical Aquifer Architecture From Centimeter to Kilometer Scales

地下水流动和输送的复杂性和不确定性与天然多孔介质水力特性的非均质性有关。在沉积物中，这种非均质性与沉积结构有关，其中重要的方面是沉积单元的比例、几何形状和并置关系。这些单位是在不同的沉积和侵蚀过程下以不同的空间尺度创建的，并在一个等级框架内组织起来。必须在水文地质模型中实现对含水层结构的真实表示，因为地质结构降低了最大无序状态下的水力特性的熵。同时，与最大熵空间场相比，这些结构可以在传输统计中创建更大的熵(例如，在较低渗透率背景中包含相互关联的砾石单元的模型在质量停留时间统计方面的差异比包含随机的、未连接的砾石块的模型更大)。沉积矿床的数字表示将使用从厘米尺度到公里尺度的真实建筑来创建。拥有这种规模范围的模型是史无前例的。数字矿床将代表河流辫带沉积的分层沉积结构，这种沉积在含水层和石油储集层中都很常见。数字沉积物将是一个合成但现实的数据集，用于水文地质学的计算实验。因此，它的沉积结构将与已知的沉积过程、沉积床的形状和规模以及分层几何和粒度变化的野外测量相一致。在这种范围内开发数字沉积物将需要从现代河流系统中收集的大量数据中量化三维结构，开发针对这些发现量身定做的模拟算法，以及开发高效的计算存储手段。该模型将在厘米间距的规则网格上进行几何模拟，以便于将其导入其他类型的数值模型(例如，地下水流动和传输模型)。数字存款及其独特的存储结构和生成算法将免费提供给研究界。

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.