NESC1098 TOUGH2, TOUGH

TOUGH2, TOUGH. Last updated versions are available at http://esd.lbl.gov/TOUGH2/

A successor to the TOUGH program, TOUGH2 offers added capabilities and user features, including the flexibility to handle different fluid mixtures (water, water with tracer; water,CO2; water,air; water,air,with vapour pressure lowering, and water,hydrogen), facilities for processing of geometric data (computational grids), and an internal version control system to ensure referenceability of code applications.

TOUGH (Transport of Unsaturated Groundwater and Heat) is a multi-dimensional numerical model for simulating the coupled transport of water, vapor, air, and heat in porous and fractured media. The program provides options for specifying injection or withdrawal of heat and fluids. Although primarily designed for studies of high-level nuclear waste isolation in partially saturated geological media, it should also be useful for a wider range of problems in heat and moisture transfer, and in the drying of porous  materials. For example, geothermal reservoir simulation problems can be handled simply by setting the air mass function equal to zero on input. The TOUGH simulator was developed for problems involving strongly heat-driven flow. To describe these phenomena a multi-phase approach to fluid and heat flow is used, which fully accounts for the movement of gaseous and liquid phases, their transport of latent transitions between liquid and vapor. TOUGH takes account of fluid flow in both liquid and gaseous phases occurring under pressure, viscous, and gravity forces according to Darcy's law. Interference between the phases is represented by means of relative permeability  functions. The code handles binary, but not Knudsen, diffusion in the gas phase and capillary and phase absorption effects for the liquid phase. Heat transport occurs by means of conduction with thermal conductivity dependent on water saturation, convection, and  binary diffusion, which includes both sensible and latent heat.

All thermophysical properties of liquid water and vapor are obtained from steam table equations, as given by the International Formulation Committee, 1967. Air is treated as an ideal gas, and additivity of partial pressures is assumed for air/vapor mixtures. The viscosity of these mixtures is computed by a formulation given by Hirschfelder et al., but using steam table values instead of approximations from kinetic gas theory for vapor viscosity. Air dissolution in water is represented by Henry's law. The basic mass- and energy-balance equations are written in integral form for an arbitrary flow domain. The continuum equations are discretized in space using the "integral finite difference" method. Time is discretized fully implicitly as a first-order finite difference to obtain the needed numerical stability for an efficient calculation of multi-phase flow. The resulting set of algebraic equations are strongly coupled and highly nonlinear. A completely simultaneous solution of the discretized mass- and energy-balance equations is performed taking all coupling terms into account. The nonlinearities are handled by Newton-Raphson iteration. The discretized equations are valid for one-, two-, or three-dimensional regular and irregular geometries and for porous as well as fractured media.

Maxima of

• 500 grid blocks

• 27 reservoir domains

• 8 relative permeability functions

• 7 capillary pressure functions

No allowance is made for vapor pressure lowering or for hysteresis in either capillary pressure or relative permeability. TOUGH does not perform stress calculations for the solid skeleton, but does allow for porosity changes in response to changes in pore pressure (compressibility) and temperature (expansivity).

The longest running sample problem requires 3 CP minutes on a Cray X-MP/14 (TOUGH2), 2 CPU hours on a SUN3 (TOUGH) with SUN Floating-Point Accelerator, and 1.3 CPU hours on a DEC VAX6220.

A library of the most commonly used capillary pressure and relative permeability functions is provided in the TOUGH source; values are selected by means of input  data. Additional functions may be used by adding the necessary FORTRAN code to the appropriate subroutines.

TOUGH and TOUGH2 belong to the MULKOM family of multi-phase, multi-component codes, developed at Lawrence Berkeley Laboratory primarily for geothermal reservoir applications. TOUGH2 includes a number of fluid property modules (also referred to as equation-of-state or EOS modules). The formulation of the TOUGH governing equations is analogous to the multi-phase treatment customarily used in geothermal reservoir simulators, such as SHAFT79 (NESC 893).

• TOUGH, NESC No. 1098.SUN, TOUGH SUN Version Tape Description and Sample Problem Output NESC 91-01 (October 2, 1990).

1.3 Mwords of memory are required on a Cray X-MP/14 and 2 Mbytes on a DEC VAX6220.

UNICOS (Cray), UNIX 4.2 (SUN), VMS 4.6, 5.2 (DEC VAX).

TOUGH input files can be run with TOUGH2, so that existing TOUGH applications can be maintained.

  CRAX     K.A. Pruess
           Earth Sciences Division
           Lawrence Berkeley Laboratory

   SUN     C. Cooper
           Water Resources Center
           Desert Research Institute

   VAX     J.D. Osnes
           RE/SPEC Inc.