2001 Journal Articles
Theoretical estimation of free and entrapped nonwetting-wetting fluid interfacial areas in porous media
M. Oostrom
Pacific Northwest National Laboratory, Richland, Washington
M.D. White
Pacific Northwest National Laboratory, Richland, Washington
M.L. Brusseau
Department of Soil, Water, and Environmental Sciences & Department of Hydrology and Water Resources University of Arizona, Tucson, AZ
Advances in Water Resources 24: 887-898, (2001).
Abstract
Fluid-fluid interfacial areas play important roles in numerous subsurface processes such as dissolution, volatilization, and adsorption. Integral expressions have been derived to estimate both entrapped (discontinuous) and free (continuous) nonwetting fluid-wetting fluid specific interfacial areas in porous media. The expressions, compatible with widely used capillary head-saturation and entrapment models, require information on capillary head-saturation relation parameters, porosity, and fluid-pair interfacial tension. In addition, information on the maximum entrapped nonwetting fluid saturation as well as the main drainage branch reversal point for water and total liquid saturations is necessary to estimate entrapped fluid interfacial areas. Implementation of the interfacial area equations in continuum-based multifluid flow simulators is straightforward since no additional parameters are needed than those required by the simulators to complete the multifluid flow computations. A limited sensitivity analysis, based on experimentally obtained parameter values, showed that imposed variations resulted in logical and consistent changes in predicted specific interfacial areas for both entrapped and free nonwetting fluid-wetting fluid systems. A direct comparison with published experimental work to test the derived expressions was limited to free air-water systems and yielded reasonable results. Such comparisons are often not possible because of the lack of information given on retention parameters, and variables used to determine nonwetting fluid entrapment. This contribution is dedicated to John W. Cary. The experimental results show that zones with entrapped air, formed during the imbibition portions of the experiment, were instrumental in re-oxygenation of the water. The fluctuating water table system also caused significant amounts of dissolved oxygen to be transported deeper into the flow cell. The simulator was able to predict water and entrapped air saturations, as well as dissolved oxygen concentrations reasonably well.
Effective parameters for two-phase flow in a porous medium with periodic heterogeneities
B. Ataie-Ashtiani
Department of Civil Engineering, Sharif University of Technology, Iran
S.M. Hassanizadeh
Hydrology and Ecology Section, Faculty of Civil Engineering and Geosciences & Centre for Technical Geoscience, Delft University of Technology, Netherlands
M. Oostrom
Pacific Northwest National Laboratory, Richland, WA
M.A. Celia
Department of Civil Engineering, Princeton University, Princeton, NJ
M.D. White
Pacific Northwest National Laboratory, Richland, WA
Journal of Contaminant Hydrology 49: 87-109, (2001).
Abstract
Computational simulations of two-phase flow in porous media are used to investigate the feasibility of replacing a porous medium containing heterogeneities with an equivalent homogeneous medium. Simulations are performed for the case of infiltration of a dense nonaqueous phase liquid (DNAPL) in a water-saturated, heterogeneous porous medium. For two specific porous media, with periodic and rather simple heterogeneity patterns, the existence of a representative elementary volume (REV) is studied. Upscaled intrinsic permeabilities and upscaled nonlinear constitutive relationships for two-phase flow systems are numerically calculated and the effects of heterogeneities are evaluated. Upscaled capillary pressure-saturation curves for drainage are found to be distinctly different from the lower-scale curves for individual regions of heterogeneity. Irreducible water saturation for the homogenized medium is found to be much larger than the corresponding lower-scale values. Numerical simulations for both heterogeneous and homogeneous representations of the considered porous media are carried out. Although the homogenized model simulates the spreading behavior of DNAPL reasonably well, it still fails to match completely the results form the heterogeneous simulations. This seems to be due, in part, to the nonlinearities inherent to multiphase flow systems. Although we have focussed on a periodic heterogeneous medium in this study, our methodology is applicable to other forms of heterogeneous media. In particular, the procedure for identification of a REV, and associated upscaled constitutive relations, can be used for randomly heterogeneous or layered media as well.
Estimating soil hydraulic properties from field-scale experiments using the inverse model UCODE with the STOMP simulator
Z.F. Zhang, A.L. Ward, G.W. Gee.
Pacific Northwest National Laboratory, Richland, WA
EOS Transactions - American Geophysical Union 82(47), (2001).
Abstract
Direct measurement of soil hydraulic properties often require restrictive initial and boundary conditions and can be time consuming, of limited range and often very expensive. An indirect method of increasing popularity is inverse modeling, which uses nonlinear regression methods to estimate hydraulic parameters. A major advantage of this approach is the inherent statistical analysis, which can be used diagnostically to measure the amount of information provided by the data and to infer the uncertainty with which values are calculated. In this research, we used the inverse modeling program, UCODE, with the flow simulator, STOMP, to estimate soil hydraulic properties from unsaturated flow experiments. The optimized parameter values and their corresponding 95% linear confidence intervals were estimated, their uniqueness and sensitivity analyzed, and the overall model fit evaluated. Results show that the STOMP/UCODE combination provides a convenient way to obtain the desired information from field-scale flow and transport experiments at the Hanford Site, WA.