Numerical investigation on the impact of thermo-osmosis on fluid pressurisation and barrier integrity in Boom clay – a case study of the ATLAS in-situ full-scale heating experiment.

Existing literature suggests the importance of the thermo-osmosis (TO) for an accurate simulation of pore pressure evolution in heater tests for nuclear waste disposal in clay rock. However, there is limited consensus regarding the appropriate choice of parameters controlling TO and the extent of its physical impact. Uncertainty of parameters describing the host rock and their spatial variability further add to  both the complexity of this consideration. This study will use the ATLAS in-situ full-scale heating experiment from the HADES underground research laboratory in Mol, Belgium, to investigate the impact of TO on the thermal pressurisation in Boom Clay and its significance for the evaluation of barrier integrity.

The ATLAS experiment was simulated with an inelastic thermo-hydro-mechanical model implemented in OpenGeoSys. After comparison to published data, assisted-history-matching was performed to obtain a good representation of the in-situ measurements with and without taking into account TO. The comparison of both groups allows a clearer discussion of the influence of TO on temperature and pressure evolution in the studied system. The final step -- uncertainty quantification of the TO parameterisation -- puts the results in the context of the large parameter uncertainty documented in the literature. Subsequently, the impact of TO and said uncertainties on barrier integrity was estimated in terms of area and duration of potential integrity violation using statistical and geometrical methods.