Two numerical codes, TOUGH2 with the EOS5 module and CODE_BRIGHT, were compared in a confidence building effort for multiphase flow problems in a geological repository in Boom Clay, Belgium. A model study comparison between two codes was carried out through three numerical examples, including a one-dimensional hydro-gas (HG) case, a two-dimensional (2-D) axisymmetrical HG case with a constant hydrogen production rate, and a 2-D axisymmetrical thermo-hydro-gas (THG) case with time-varying heat and gas production rate. This numerical study of modeling the gas-driven migration of pore water under constant or time-dependent thermal conditions in two dimensions is based on the current Belgian multibarrier repository design for geological disposal of high-level waste. Comparison between numerical results demonstrates that the two numerical tools give sufficiently similar results in all three cases, thus providing evidence for the consistency of these tools in solving HG and THG problems in Boom Clay. The differences in the results obtained by the two modeling tools were also discussed.