A laboratory experiment for determining both the hydraulic and diffusive properties and the initial pore-water composition of an argillaceous rock sample: a test with the Opalinus clay (Mont Terri, Switzerland).

Argillaceous formations are thought to be suitable natural barriers to the release of radionuclides from a radioactive waste repository. However, the safety assessment of a waste repository hosted by an argillaceous rock requires knowledge of several properties of the host rock such as the hydraulic conductivity, diffusion properties and the pore water composition. This paper presents an experimental design that allows the determination of these three types of parameters on the same cylindrical rock sample. The reliability of this method was evaluated using a core sample from a well-investigated indurated argillaceous formation, the Opalinus Clay from the Mont Terri Underground Research Laboratory (URL) (Switzerland). In this test, deuterium- and oxygen-18-depleted water, bromide and caesium were injected as tracer pulses in a reservoir drilled in the centre of a cylindrical core sample. The evolution of these tracers was monitored by means of samplers included in a circulation circuit for a period of 204 days. Then, a hydraulic test (pulse-test type) was performed. Finally, the core sample was dismantled and analysed to determine tracer profiles. Diffusion parameters determined for the four tracers are consistent with those previously obtained from laboratory through-diffusion and in-situ diffusion experiments. The reconstructed initial pore-water composition (chloride and water stable-isotope concentrations) was also consistent with those previously reported. In addition, the hydraulic test led to an estimate of hydraulic conductivity in good agreement with that obtained from in-situ tests.

Estimating thermo-osmotic coefficients in clay-rocks: II. In situ experimental approach.

Water flow in compacted shales is expected to be modified by thermo-osmosis when a thermal gradient exists. However this coupled-flow process is poorly characterized since no experiments on non-remoulded clay-rocks are found in the literature. This paper presents a set of thermo-osmosis experiments carried out in an equipped borehole installed in the Liassic argillite at the Institut for Radiological protection and Nuclear Safety (IRSN) underground research laboratory (URL) of Tournemire (southeastern France). A numerical model - including coupled-flow equations, mass conservation laws, thermal expansion and changes of water properties with temperature - was developed for the interpretation of these experiments. A thermo-osmotic response was deduced from the pressure evolution in the test interval after temperature pulses (+2.5, +5.1, and +9 degrees C). The values of thermo-osmotic permeability determined during the experiments range between 6x10(-12) and 2x10(-10)m(2)K(-1)s(-1), depending on the pulse temperature and uncertainties on the model parameters. A sensitivity analysis on several model parameters was performed to constrain these uncertainties.