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TOUGH2 Software


TOUGH2 Model of geothermal reservoirTOUGH2 offers the flexibility to handle different fluid mixtures, the properties of which are described in separate Equation-of-State (EOS) modules. TOUGH2 uses an integral finite difference method for space discretization, and first-order fully implicit time differencing. A choice of a sparse direct solver or various preconditioned conjugate gradient algorithms is available for linear equation solution. Thermophysical properties of water are represented, within experimental accuracy, by steam table equations. The program provides options for specifying injection or withdrawal of heat and fluids. Double-porosity, dual-permeability, and multiple interacting continua (MINC) methods are available for modeling flow in fractured porous media.

Although primarily designed for geothermal reservoir studies and high-level nuclear waste isolation, TOUGH2 can be applied to a wider range of problems in heat and moisture transfer, and in the drying of porous materials. The TOUGH2 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 and sensible heat, and phase transitions between liquid and vapor. TOUGH2 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 includes Klinkenberg effects and binary diffusion in the gas phase, and capillary and phase adsorption 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.

Equation-of-State Modules

TOUGH2 provides multiple equation-of-state (EOS) modules, which define the components and phases and related thermophysical propeties (such as density, viscosity, enthalpy) of the fluid mixture being considered. The chosen EOS module is linked to the TOUGH2 core, which sets up the mass and energy balance equations, and solves the resulting strongly couples, nonlinear algebraic equations using Newton-Raphson iterations for each time step, which involves the calculation of a Jacobian matrix and the solution of a set of linear equations.

The following table lists the currently available EOS modules and the components and phases they handle.

Module Components PhasesManualSample
EOS1 water, water with tracer, heat aqueous, gas TOUGH2 User's Guide  r1q, rfp, rvf Basic module for geothermal applications; see also EOS7 and EWASG
EOS2 water, CO2, heat aqueous, gas TOUGH2 User's Guide rfp Basic module for near-surface, gaseous CO2 applications; see also ECO2N, ECO2M, EOS7C, EWASG and TMVOC
EOS3 water, air, heat aqueous, gas TOUGH2 User's Guide rhp, sam1 Basic module for vadose zone applications
EOS4 water, air, heat aqueous, gas TOUGH2 User's Guide rhp Same as EOS3, including vapor pressure lowering effects
EOS5 water, hydrogen, heat aqueous, gas TOUGH2 User's Guide n/a Applicable to corrosion-gas producing waste repositories 
EOS7 water, brine, air, heat aqueous, gas TOUGH2 User's Guide rf1 For multiphase, density-driven flows where salinity does not reach saturation levels; see also EOS7R, EWASG, ECO2N, and ECO2M
EOS7R water, brine , air, radionuclide1, radionuclide2, heat aqueous, gas TOUGH2 User's Guide rdica, rdif7 Same as EOS7, with parent-daughter radionuclides
EOS7C water, brine, NCG (CO2 or N2), tracer, CH4, heat aqueous, gas EOS7C User's Guide sam7c 1-3 Applicable to CO2 or N2 in natural gas (CH4) reservoirs; CO2 is gaseous or supercritical; real gas law; tracer
EOS7C-ECBM water, brine, NCG (CO2 or N2), tracer, CH4, heat, with ECBM isotherm and Dusty Gas Model
aqueous, gas EOS7C-ECBM User's Guide Law1A, Law1B, Law1C, HeAr, rdica Same as EOS7C, with extended Langmuire isotherm for simulating enhance coal-bed methane, and the Dusty Gas Model for gas-phase diffusion
EOS8 water, air, oil, heat aqueous, gas, NAPL TOUGH2 User's Guide rcol8 Oil component is not volatile nor soluble, i.e., it is present only in the NAPL phase (“dead oil”)
EOS9 water aqueous TOUGH2 User's Guide reos9a, rpm Richards equation; saturated-unsaturated flow
EOS9nT water, tracer, colloids aqueous EOS9nT User's Guide Test 1-6 Richards equation; saturated-unsaturated flow; transport of multiple, non-volatile solutes/colloids; radioactive decay (including ingrowth), adsorption, advection/diffusion/dispersion, filtration, colloid-assited tracer transport, first-order chemical reaction
EWASG water, NaCl, NCG (CO2, air, CH4, H2, N2), heat aqueous, gas, solid TOUGH2 User's Guide rhbc Applicable to geothermal reservoirs with saline fluids and a noncondensible gas; temperature-dependent NaCl solubility; includes sal precipitation and dissolution
ECO2N water, brine, CO2 aqueous, CO2-rich phase ECO2N User's Guide r1dv, rcc3, rtab, rtp7 Applicable for simulation of geologic CO2 sequestration in saline aquifers; CO2 in gaseous, liquid and supercritical phases; no crossing of saturation line; salt precipitation and dissolution; see also EOS2 and ECO2M
ECO2M water, brine, CO2 aqueous, gaseous/liquid/ supercritical CO2 ECO2M User's Guide r1d, rcc3, rtab, rwaf Multiphase version of ECO2N; includes transition between super and sub-critical conditions, and phase change between liquid and gaseous CO2
T2VOC water, air, VOC, heat aqueous, gas, NAPL T2VOC User's Guide r3d, rblev, rfs, rgdif, rtce Three-phase module for environmental applications; see also the TMVOC and the T2VOC web pages
TMVOC water, VOCs, NCGs aqueous, gas, NAPL TMVOC User's Guide r2dl, r7c, rad, rblm, rbt, rdif2, rh2l, rtcem, rz2d Three-phase module for simulating flow of multicomponent  mixtures of VOC and one or multiple NCGs; see also the T2VOC and the TMVOC web ages

NAPL:  nonaqueous phase liquid

NCG:   noncondensible gas

VOC:   volatile organic compound

Features & Capabilities

TOUGH2 is a general-purpose numerical simulation program for multi-dimensional fluid and heat flows of multiphase, multicomponent fluid mixtures in porous and fractured media. TOUGH2 solves mass and energy balance equations that describe fluid and heat flow in general multiphase, multicomponent systems. Fluid advection is described with a multiphase extension of Darcy’s law; in addition there is diffusive mass transport in all phases. Heat flow occurs by conduction and convection, the latter including sensible as well as latent heat effects. The description of thermodynamic conditions is based on the assumption of local equilibrium of all phases. Fluid and formation parameters can be arbitrary nonlinear functions of the primary thermodynamic variables.

For numerical simulation the continuous space and time variables must be discretized. Space discretization is made directly from the integral form of the basic conservation equations, without converting them into partial differential equations. This “integral finite difference” method (IFDM) avoids any reference to a global system of coordinates, and thus offers the advantage of being applicable to regular or irregular discretizations in one, two, and
three dimensions. The IFDM also makes it possible, by means of simple preprocessing of geometric data, to implement double- and multiple-porosity methods for fractured media. Time is discretized fully implicitly as a first-order backward finite difference. This together with upstream weighting of flux terms at interfaces is necessary to avoid impractical time step limitations in flow problems involving phase (dis-)appearances, and to achieve unconditional stability.


See TOUGH2 User's Guide and bibliography.

Licensing & Download

A short overview of the history of the TOUGH suite of models shows the TOUGH2 code as the main simulator based on which additional capabilities have been built. The most current version (V2.1) is released by the Berkeley Lab Software Center. This version is an upgrade from TOUGH2 V2.0, released by DOE's Energy Science and Technology Software Center since 1999. The most current version differs from the previous version in that (a) all known bugs have been fixed, (b) the core has been restructured to fully integrate the TMVOC and ECO2N modules, and (c) the new fluid property module ECO2M has been added to the suite. Due to this technical differences and changes in the licensing and distribution of the TOUGH2 codes, the V2.1 modules cannot be linked to the V2.0 core, and a new license for both the core and fluid property modules needs to be obtained.