Geostatistical Modeling of Heterogeneity in Glaciofluvial, Buried-Valley Aquifers
Geostatistical Modeling of Heterogeneity in Glaciofluvial, Buried-Valley Aquifers
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冰川河流、埋谷含水层异质性的地质统计模型
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
G. Fogg
中科院分区：
文献类型：
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作者：
R. Ritzi;Dale F. Jayne;A. Zahradnik;A. A. Field;G. Fogg
在北美西部和中部冰川平原的潜谷含水层中，可渗透的喷流相组合可能形成大型和多产的区域含水层系统。在冰川成因的含水层中，低渗透性相(如冰川或湖相粘土)与高渗透性相(如砂岩和砾石)并列分布是很常见的。以俄亥俄州西南部迈阿密潜谷含水层系统的非均质性为例进行了研究。在缺乏资料的地区，探索了评价岩性不确定性的实用方法。相类型用指示随机函数表示，表现出各向同性、指数协方差结构。采用三种不同的指示地统计学方法对相界面进行了定量的对比分析：(1)指示点克里格法和概率截止法的水文地层学分析；(2)条件指示符号法的水文地层学分析；(3)指示块克里格法和网格单元平均法的渗漏分区。在第一种方法中，理论分析表明，指示点克立格法计算的0.5概率水平可能对应于高渗透相和低渗透相之间的边界，也可能不对应，这取决于数据支持的水平。在迈阿密含水层系统的数据支持下，0.65概率等值线给出了低渗透相的区域分布，既考虑了原始数据，也考虑了原始指示数据的非聚集全局平均值。第一种和第三种方法产生了单一的模型，其中相分布在某种局部精度意义上是最好的。第二种方法产生了许多不同的模型，在这些模型中，相分布的全局纹理优先于对期望值的局部估计。前两种方法包括在创建地下水数值模型的网格之前评估相类型之间的边界的几何形状，以便网格单元边界可以与相边界相对应。第三种方法在更新现有地下水模型时非常有用，该模型的网格单元边界不一定对应于相边界。
In the buried-valley aquifers of the western and central glaciated plains of North America, assemblages of permeable outwash facies may form large and productive regional aquifer systems. In glacially derived aquifers it is common to have low-permeability facies (e.g., till or lacustrine clay) juxtaposed with high-permeability facies (e.g., sand and gravel outwash). The heterogeneity in the Miami buried-valley aquifer system in southwestern Ohio was examined as an example. Practical approaches for evaluating the lithological uncertainty were explored in the areas lacking data. The facies types were represented by an indicator random function, which exhibited an isotropic, exponential covariance structure. A comparative, quantitative analysis of the facies boundaries was accomplished using three different indicator geostatistical methodologies: (1) hydrostratigraphic analysis with indicator point kriging and probability cutoff, (2) hydrostratigraphic analysis with conditional indicator simulation, and (3) leakance zonation with indicator block kriging and grid-cell averaging. With the first method, it was shown in a theoretical analysis that the 0.5 probability level computed by indicator point kriging may or may not correspond to the boundary between high- and low-permeability facies, depending upon the level of data support. With the data support for the Miami aquifer system, the 0.65 probability contour gave an areal distribution of low-permeability facies that honored both the original data and the declustered global mean of the original indicator data. The first and third methods gave rise to a single model, in which the facies distribution was best in some local accuracy sense. The second method gave rise to many alternative models, in which the global texture of the facies distribution took precedence over local estimation of the expected value. The first two methods involved evaluating the geometry of the boundaries between the facies types in advance of creating the grid of the numerical ground-water model, so that grid cell boundaries could be made to correspond to facies boundaries. The third method was useful when updating an existing ground-water model that has grid cell boundaries not necessarily corresponding to facies boundaries.