UPSCALING HYDRAULIC CONDUCTIVITIES IN CROSS-BEDDED FORMATIONS

Modern geostatistical techniques allow the generation of high-resoluti on heterogeneous models of hydraulic conductivity containing millions to billions of cells. Selective upscaling is a numerical approach for the change of scale of fine-scale hydraulic conductivity models into c oarser scale models that are suitable for numerical simulations of gro undwater flow and mass transport. Selective upscaling uses an elastic gridding technique to selectively determine the geometry of the coarse grid by an iterative procedure. The geometry of the coarse grid is bu ilt so that the variances of flow velocities within the coarse blocks are minimum. Selective upscaling is able to handle complex geological formations and flow patterns, and provides full hydraulic conductivity tensor for each block. Selective upscaling is applied to a cross-bedd ed formation in which the fine-scale hydraulic conductivities are full tensors with principal directions nor parallel to the statistical ani sotropy of their spatial distribution. Mass transport results from thr ee coarse-scale models constructed by different upscaling techniques a re compared to the fine-scale results for different flow conditions. S elective upscaling provides coarse grids in which mass transport simul ation is in good agrement with the fine-scale simulations, and consist ently superior to simulations on traditional regular (equal-sized) gri ds or elastic grids built without accounting for flow velocities.