Saturation Function Options (W)
Saturation functions relate the aqueous capillary pressure to aqueous saturation. Model options and parameters for these functions are specified through the Saturation Function Card. Every rock/soil type defined on the Rock/Soil Zonation Card must be referenced. With the IJK Indexing option, node dependent parameters are entered via external files and node independent parameters are entered directly on the card. Functional forms for the saturation-capillary pressure functions are preferred; however, tabular input is acceptable. By default, tabular data will be interpolated using linear interpolation, whereas values beyond the table limits will be assigned either the table minimum or maximum values appropriately.
van Genuchten Function
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Brooks and Corey Function
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Haverkamp Function
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Tabular Input
This option accepts tabulated retention data. The default is the data of pressure head and saturation data pairs and linear interpolation is used between data points. Alternately, water content vs capillary head can be provided using the keyword "water content." Other interpolation schemes that can be specified are linear-log, cubic spline, or cubic-spline-log.
Sub-Options
Fractured (Dual porosity) Function
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Entrapment (with Gas Entrapment)
This option considers entrapped gas that is immobile and also reduces the pore fraction for the mobile fluid. A theoretical model for hysteretic saturation functions for aqueous-gas systems was developed by Parker and Lenhard [1987]. A simplified version of this model, analogous to Kaluarachchi and Parker [1992], has been implemented in the STOMP simulator. The model includes effects of gas entrapment during aqueous-phase imbibition paths. Gas entrapment during aqueous-phase imbibition will depend on the aqueous saturation and current saturation path. The amount of entrapped gas varies linearly between zero and the gas effective residual saturation with the apparent saturation, which varies between the reversal point from main drainage to one. Gas effective residual saturations are computed using an empirical relationship developed by Land [1968] for aqueous-NAPL systems. In this simplified hysteretic model for aqueous-gas systems, gas can be trapped or free, where free gas refers to continuous volumes which advect freely and trapped gas refers to discontinuous ganglia of gas occluded within the aqueous phase. Occluded gas is assumed to be immobile. The apparent aqueous saturation equals the effective aqueous saturation plus effective trapped gas saturation, as shown in equation (1) below. The effective gas saturation equals the effective trapped and free gas saturations, as shown in equation (3) below. In hysteretic systems, the residual saturation is independent of capillary pressure:
where
The saturation functions relate gas-aqueous capillary pressure to apparent aqueous saturations, according to equations (4) and (5), for the van Genuchten and Brooks and Corey functions, respectively. The effective trapped gas saturation is computed according to equation (7), which recognizes that entrapped gas cannot exceed the gas present. Land’s parameter for gas-aqueous interfaces is computed according to equation (8).
where
Symbols
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apparent aqueous liquid saturation |
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effective aqueous liquid saturation |
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effective gas saturation trapped by aqueous phase |
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actual aqueous liquid saturation |
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actual aqueous liquid residual saturation |
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effective gas saturation |
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effective free gas saturation |
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actual gas saturation |
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van Genuchten function parameter, 1/m |
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van Genuchten n parameter |
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van Genuchten m parameter |
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gas pressure, Pa |
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aqueous liquid pressure, Pa |
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reference aqueous density, kg/m3 |
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acceleration of gravity, m/s2 |
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Brooks and Corey function nonwetting fluid entry head, m |
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Brooks and Corey parameter |
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minimum effective aqueous liquid saturation |
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maximum effective residual gas saturation |
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Land's parameter for gas-aqueous interface |
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Triple Curve Function (Hysteresis)
This option considers the hysteresis of the saturation curve for the Van Genuchten or Brooks Corey model.
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IJK, JKI or KIJ Indexing
If IJK Indexing, JKI Indexing, or KIJ Indexing is specified as the Rock/Soil Name in the Rock/Soil Zonation Card, then this must also be specified as the Rock/Soil Name in the Saturation Function Card.
IJK Indexing If the IJK Indexing option is specified in the Rock/Soil Zonation Card, then the saturation functions and any or all associated parameters can be specified either as a single value that will be applied to each node in the domain, or in an external file with the values for every grid-cell ordered according to the IJK indexing scheme. Units shown in the input line will be applied to all parameters in the external file.
JKI Indexing If the JKI Indexing option is specified in the Rock/Soil Zonation Card, then the saturation functions and any or all associated parameters can be specified either as a single value that will be applied to each node in the domain, or in an external file with the values for every grid-cell ordered according to the JKI indexing scheme. Units shown in the input line will be applied to all parameters in the external file.
KIJ Indexing If the KIJ Indexing option is specified in the Rock/Soil Zonation Card, then the saturation functions and any or all associated parameters can be specified either as a single value that will be applied to each node in the domain, or in an external file with the values for every grid-cell ordered according to the KIJ indexing scheme. Units shown in the input line will be applied to all parameters in the external file.
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References:
Brooks, RH and AT Corey. 1966. "Hydraulic Properties of Porous Media Affecting Fluid Flow," Proc. ASCE J. Irrig. Drain. Div. , 92:61-68.
Haverkamp, R, M Vauclin, J Touma, PJ Wierenga, and G Vachaud. 1977. "A Comparison of Numerical Simulation Models for One-Dimensional Infiltration," Soil Sci. Soc. Am. J., 41:285-294.
Kaluarachchi, JJ and JC Parker. 1992. "Multiphase Flow with a Simplified Model for Oil Entrapment," Transport in Porous Media, 7:1-14.
Klavetter, EA and RR Peters. 1986. Estimation of Hydrologic Properties of Unsaturated Fractured Rock Mass, SAND84-2642, Sandia National Laboratories, Albuquerque, NM.
Land, CS. 1968. "Calculation of Imbibition Relative Permeability for Two- and Three-Phase Flow from Rock Properties," Trans. Am. Inst. Min. Metall. Pet. Eng., 243:149-156.
Nitao, JJ. 1988. Numerical Modeling of the Thermal and Hydrological Environment around a Nuclear Waste Package Using the Equivalent Continuum Approximation: Horizontal Emplacement, UCID-2144, Lawrence Livermore National Laboratory, Livermore, CA.
Parker, JC and RJ Lenhard. 1987. "A Model for Hysteretic Constitutive Relations Governing Multiphase Flow 1. Saturation-Pressure Relations," Water Resources Research, 23(12):2187-2196.
van Genuchten, MT. 1980. "A Closed-Form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils," Soil Science Society of America Journal, 44:892-898.