Marc Dzikowski

Relations entre réponses impulsionnelles et conditions hydrodynamiques des systèmes dans le cadre de traçages artificiels: Theorie et application sur colonne de laboratoire

Abstract In this paper, theoretical relationships are established between the impulse response to the injection of tracer and the steady state flow rate in a pipe. This approach is a step toward the analysis of non-linear systems. For different scales of transfer, the impulse responses were defined from short-time injection. Impulse responses were also calculated by representing mass transfer in porous media by the ‘random walk method’;, which enabled us to verify relationships in unsteady flow conditions. The validity of these relationships has been quantitatively assessed by applying it to tracer experiments in a column in the laboratory at different flow rates.

A new algorithm for representing transport in porous media in one dimension, including convection, dispersion, and interaction with the immobile phase with first-order kinetics

The model uses, in one-dimensional flow, the random-walk method on particles and integrates them into a discretized representation of space which eliminates the individual management of each particle. The method of computing allows a simulation of mass transfer in adsorbing media by dissociating the roles of convection, dispersion, and the exchange occurring between the mobile and immobile phases. This gives the parameters that have to be fitted, such as the dispersivity or the exchange rate, a meaning which is closer to their physical reality than that defined by global models (e.g., apparent dispersivity without considering exchange between phases). The model was tested first on analytical solutions and also on data from laboratory experiments on a double porosity chalk column and showed that, with the same limited set of parameters, it could fit concentration/time restitutions at different distances from the injection point. Because of its structure, the algorithm can easily be modified so as to simulate distributed injections and transfers in a regime of variable flow rates.

Thermal Influence of an Alpine Deep Hydrothermal Fault on the Surrounding Rocks

Major fault zones in mountain areas are often associated with cold-water circulations and hydrothermal pathways. Compared with the massif as a whole, the deep groundwater flows in these high hydraulic-conductivity zones modify the thermal state of the surrounding rock. This paper examines the thermal effects of groundwater flow in the area around the steeply dipping La Léchère deep fault zone (LFZ, French Alps) and associated shallow decompressed zone. We used a 3D numerical model drawn up from groundwater circulation data to investigate the La Léchère hydrothermal system and the thermal state of the rock in the valley sides. Hydrothermal simulations showed that convective flow into the LFZ cools the valley sides and creates a thermal upwelling under the valley floor. An unsteady thermal regime that continues for about 10,000 years is also needed to obtain the temperatures currently found under the valley floor in the LFZ. Temperature-depth profiles around the LFZ show disturbances in the thermal gradients in the valley sides and the valley floor. Convective heat transfer into the LFZ and the decompressed zone, and conductive heat transfer in the surrounding rocks produce an unsteady, asymmetric thermal state in the rock on both sides of the LFZ.