Recent Developments in Stochastic Modeling and Upscaling of Hydrologic Properties in Tuff

by Christopher A. Rautman, Sandia Natl Lab, Albuquerque, United States,
Thomas H. Robey, Sandia Natl Lab, Albuquerque, United States,

Abstract: A set of detailed geostatistical simulations of porosity has been produced for a layered stratigraphic sequence of welded and non-welded volcanic tuffs at Yucca Mountain, Nevada. The simulations are produced using a composite model of spatial continuity and they are highly conditioned to abundant drill hole (core) information. A set of derivative simulations of saturated hydraulic conductivity has been produced, in the absence of conditioning data, using a cross-variable relationship developed from similar data elsewhere. The detailed simulations reproduce both the major stratigraphic units and finer scale layering indicated by the drill hole data. These simulations have been scaled up several orders of magnitude to represent block-scale effective hydrologic properties suitable for use in numerical modeling of groundwater flow and transport. The upscaling process involves the reformulation of a previously reported method that iteratively adapts an initial arbitrary grid to 'homogenize' the detailed hydraulic properties contained within the adjusted cell limits and to minimize the size of cells in highly heterogeneous regions. Although the computation of the block-effective property involves simple numerical averaging, the blocks over which these averages are computed are relatively homogeneous, which reduces the numerical difficulties involved in averaging non-additive properties, such as permeability. The entire process of simulation and upscaling is rapid and computationally efficient compared with alternative techniques. It is thus suitable for the Monte Carlo evaluation of the uncertainty in site characterization as it affects the results of groundwater flow and transport calculations.

Subject Headings: Hydrologic models | Hydrologic properties | Stochastic processes | Groundwater flow | Flow simulation | Numerical models | Simulation models | Porosity | Stratigraphy | Europe | Monaco | Monte Carlo | Nevada | North America | United States

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