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 °C). The values of thermo-osmotic permeability determined during the experiments range between 6×10-126×10-12 and 2×10-10m2K-1s-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.

Graphical abstractMeasured and modelled pressure evolution after a temperature pulse of +2.5. performed in an equipped borehole. Two model cases are considered: only with thermal expansion and changes of water properties with temperature; and with thermo-osmosis added.Figure optionsDownload full-size imageDownload high-quality image (77 K)Download as PowerPoint slide