TOUGH2

TOUGH2 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.

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 di