ZERT Task 2: Performance prediction for long-term fate and transport of injected CO2
ZERT Task 2 Goal
To develop reliable techniques to predict and model CO2 migration and trapping mechanisms.
ZERT Task 2 Overview
The TOUGH codes will be further developed to accurately simulate the fate and transport of CO2 in the subsurface. TOUGH2 and TOUGHREACT are available to the public through the Department of Energy’s National Energy Software Technology Center. The TOUGH2 simulator ("transport of unsaturated groundwater and heat") is a multi-dimensional numerical model for simulating the coupled transport of water, vapor, gas components, and heat in porous and fractured media. TOUGH2 offers added capabilities and user features, including the flexibility to handle different fluid mixtures through a wide variety of EOS (equation of state) modules. TOUGH2 uses an integral finite difference method for space discretization, and first-order fully implicit time stepping. Various preconditioned conjugate gradient and direct sparse matrix solvers are available for linear equation solution. Thermophysical properties of water are represented, within experimental accuracy, by steam table equations provided by the International Formulation Committee. 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. 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.
TOUGHREACT uses the same basic architecture as TOUGH2, but includes geochemical reactions between CO2, water, solutes and rock. Both equilibrium and kinetic calculations of mineral dissolution and precipitation can be carried out, thus allowing evaluation of mineral trapping.