Modelling the Mont Terri HE-D experiment for the Thermal–Hydraulic–Mechanical response of a bedded argillaceous formation to heating

Abstract

Coupled thermal-hydrological-mechanical (THM) processes in the near field of deep geological repositories can influence several safety features of the engineered and geological barriers. Among those features are: the possibility of damage in the host rock, the time for re-saturation of the bentonite, and the perturbations in the hydraulic regime in both the rock and engineered seals. Within the international cooperative code-validation project DECOVALEX-2015, eight research teams developed models to simulate an in situ heater experiment, called HE-D, in Opalinus Clay at the Mont Terri Underground Research Laboratory in Switzerland. The models were developed from the theory of poroelasticity in order to simulate the coupled THM processes that prevailed during the experiment and thereby to characterize the in situ THM properties of Opalinus Clay. The modelling results for the evolution of temperature, pore water pressure, and deformation at different points are consistent among the research teams and compare favourably with the experimental data in terms of trends and absolute values. The models were able to reproduce the main physical processes of the experiment. In particular, most teams simulated temperature and thermally induced pore water pressure well, including spatial variations caused by inherent anisotropy due to bedding.

Fault Stability Perturbation by Thermal Pressurization and Stress Transfer Around a Deep Geological Repository in a Clay Formation

“…Pore pressure and temperature were monitored at various boreholes drilled nearby the emplaced canisters (Wileveau, ). The sensors installed in the boreholes measured an increase in pore pressure with increasing temperature: Gens et al () clarified the coupling of thermal to hydraulic and mechanical effects, while Garitte et al () later provided a numerical benchmarking exercise to confirm the thermohydromechanical (THM) coupling effect. In a recent numerical reproduction of the experiment, Nguyen () noted that the maximum measured pressure of 4 MPa could be sufficient to create new tensile fractures in intact rock, given that the in situ minimum principal stress is estimated to be in the range of 2–3 MPa (Martin & Lanyon, ), while tensile strength of the Opalinus Clay is expected to be of the order of 1 MPa parallel to bedding and 0.5 MPa perpendicular to bedding (Bock, ).…”

Modeling Desiccation Cracks in Opalinus Clay at Field Scale with the Phase-Field Approach

“…For modeling the CD-A experiment, we collected the material properties corresponding to the sandy facies of the Opalinus Clay (6,7,24,79) where the niches are located (34,83). The properties are summarized in Table 1.…”

TOUGH3-FLAC3D: a modeling approach for parallel computing of fluid flow and geomechanics

“…Analytical solutions are only available for very simplified processes (e.g., only for fully saturated medium), and observations from lab and in situ experiments involve significant uncertainties. Benchmarking activities involving code-to-code comparison and validation against analytical solutions and experimental data are often in play for developing numerical models [17][18][19][20]. The TOUGH family of codes are commonly applied to model the coupling of fluid flow and heat transport in geological media [21,22], and have been extended to consider coupling to geomechanical processes.…”