Thermo-osmosis coupled-flow characterization in clay-rocks: experiments and modeling
Abstract
Water flow in clay-rocks is not only driven by a hydraulic gradient but also by chemical, thermal or electrical gradients. It implies a re-evaluation of the Darcy law by considering all gradients occurring in the clay-rock and their associated coupling coefficients (e.g. the osmotic efficiency to link a chemical gradient to a water flow). The occurrence of such processes in clay-rocks is due to the low hydraulic conductivity of this media and because of electrical charges at the clay minerals surface. Here, we focused on the thermo-osmosis process, a water flow under a temperature gradient, which is poorly characterized in spite of its implications in nuclear waste storage in clay-rocks. A set of thermo-osmotic experiments was performed in an equipped borehole installed in a Toarcian compacted clay at the IRSN’s Underground Research Laboratory in the south of France. The water flow induced by a temperature gradient (from the hotter towards the colder zone) was reproduced by the help of a numerical model, including coupled-flow processes, mass conservation laws and hydro-thermo-mechanical changes (see Figure). A range of thermo-osmotic permeability (kT), between 6.10-12 and 2.10-10 m2.K-1.s-2, was obtained during the experiments depending on the temperature gradient and uncertainties on the model parameters. Values obtained for the Tournemire’s argillite are in the high range of thermo-osmotic permeabilities for argillaceous materials and suggest an effect of pore size on the thermo-osmotic permeability of a clay-rock (kT being higher with little pore size). Another dependence of thermo-osmotic permeability with temperature is observed, with kT decreasing when the temperature increases. These experiments and modeling indicate thermo-osmosis will have an influence on water flow in presence of a temperature gradient and this process is to consider in water flow studies in clay-rocks. Reference: Tremosa et al. Estimating thermo-osmotic coefficients in clay-rocks: II. In-situ experimental approach. Submitted to Journal of Colloid and Interface Science. Measured and modeled pressure evolution after a temperature pulse. Best fit considering both thermo-osmosis and hydro-thermo-mechanical effects.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.H12C..02T
- Keywords:
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- 1832 HYDROLOGY / Groundwater transport;
- 1859 HYDROLOGY / Rocks: physical properties;
- 5114 PHYSICAL PROPERTIES OF ROCKS / Permeability and porosity;
- 5134 PHYSICAL PROPERTIES OF ROCKS / Thermal properties