TOUGHREACT

Technical Summary

Coupled modeling of subsurface multiphase fluid and heat flow, solute transport, and chemical reactions can be applied to many geologic systems and environmental problems, including geothermal systems, diagenetic and weathering processes, subsurface waste disposal, acid mine drainage remediation, contaminant transport, and groundwater quality. TOUGHREACT has been developed as a comprehensive non-isothermal multi-component reactive fluid flow and geochemical transport simulator to investigate these and other problems. A number of subsurface thermo-physical-chemical processes are considered under various thermohydrological and geochemical conditions of pressure, temperature, water saturation, and ionic strength. TOUGHREACT can be applied to one-, two- or three-dimensional porous and fractured media with physical and chemical heterogeneity. The code can accommodate any number of chemical species present in liquid, gas and solid phases. A variety of equilibrium chemical reactions are considered, such as aqueous complexation, gas dissolution/exsolution, and cation exchange. Mineral dissolution/precipitation can take place subject to either local equilibrium or kinetic controls, with coupling to changes in porosity and permeability and capillary pressure in unsaturated systems. Chemical components can also be treated by linear adsorption and radioactive decay.

TOUGHREACT has been applied to a wide variety of problems, some of which are included as examples, such as:

Supergene copper enrichment (Xu et al., 2001).
Mineral alteration in hydrothermal systems (Xu and Pruess, 2001b; Xu et al., 2004b; Dobson et al., 2004; Kiryukhin et al., 2004; Todaka et al., 2004).
Mineral trapping for CO₂ disposal in deep saline aquifers (Xu et al., 2003a and 2004b).
Coupled thermal, hydrological, and chemical processes in boiling unsaturated tuff for the proposed nuclear waste emplacement site at Yucca Mountain, Nevada (Sonnenthal and Spycher, 2000; Spycher et al., 2003; Xu et al., 2001).
Modeling of mineral precipitation/dissolution in plug-flow and fracture-flow experiments under boiling conditions (Dobson et al., 2003).
Calcite precipitation in the vadose zone as a function of net infiltration (Xu et al., 2003).
Stable isotope fractionation in unsaturated zone pore water and vapor (Singleton et al., 2004).
Coupled processes of fluid flow, solute transport, and geochemical reactions in reactive barriers (Kim et al., 2004).

The TOUGHREACT program makes use of “self-documenting” features. It is distributed with a number of input data files for sample problems. Besides providing benchmarks for proper code installation, these can serve as a self-teaching tutorial in the use of TOUGHREACT, and they provide templates to help jump-start new applications.

The present version of TOUGHREACT provides the following TOUGH2 fluid property or “EOS” (equation-of-state) modules: (1) EOS1 for water, or two waters with typical applications to hydrothermal problems, (2) EOS2 for multiphase mixtures of water and CO₂ also with typical applications to hydrothermal problems, (3) EOS3 for multiphase mixtures of water and air with typical applications to vadose zone and nuclear waste disposal problems, (4) EOS4, which has the same capabilities as EOS3 but with vapor pressure lowering effects due to capillary pressure, (5) EOS9 for single phase water (Richards’ equation) with typical applications to ambient temperature and pressure reactive geochemical transport problems, and (6) ECO2 for multiphase mixtures of water, CO₂ and NaCl with typical applications to CO₂ disposal in deep brine aquifers. Click here for more information on ECO2.