The TOUGH software was developed and continuing improved at Lawrence Berkeley National Lab by dozens of scientists. The first release of TOUGH was in 1987 (Pruess, 1987) for simulations of nonisothermal flow of water and air in aqueous and gaseous phase, which is based on the research software MULCOM (Pruess, 1983). In 1991, the second generation of TOUGH was released and named as TOUGH2 by including simulation of subsurface flow of different non-condense gases. The TOUGH2 was further improved in process modeling capabilities and formed the TOUGH2 V2 (Pruess et al., 1999). After the release of TOUGH2 V2, many process modeling modules had been developed, such as ECO2N (Pruess, 2005 ), TMVOC(, and EOS7C(Oldenburg et al. , 2004)). In 2008, the massively parallel version of TOUGH2, TOUGH2-MP, was released (Zhang et al., 2008). In 2018, The third generation of TOUGH, named TOUGH3 (J), was published. TOUGH3 incorporated more process modeling modules and consolidated the series and parallel version of the simulator. In 2008, Moridis et al. developed TOUGH+, which re-wrote TOUGH2 in modern Fortran and expanded it for the simulations of hydrate-bearing geologic media and mixed gases. In the past three decades, a series of satellite software of TOUGH has been developed, such as TOUGHREACT, ITOUGH, TOUGH-FLAC, and some specific-purpose EOS Modules (Figure 1).
