[1] We present a set of single-well injection withdrawal tracer tests in a paleoreef porous reservoir displaying important small-scale heterogeneity. An improved dual-packer probe was designed to perform dirac-like tracer injection and accurate downhole automatic measurements of the tracer concentration during the recovery phase. By flushing the tracer, at constant flow rate, for increasing time duration, we can probe distinctly different reservoir volumes and test the multiscale predictability of the (non-Fickian) dispersion models. First we describe the characteristics, from microscale to meter scale, of the reservoir rock. Second, the specificity of the tracer test setup and the results obtained using two different tracers and measurement methods (salinity-conductivity and fluorescent dye-optical measurement, respectively) are presented. All the tracer tests display strongly tailed breakthrough curves (BTC) consistent with diffusion in immobile regions. Conductivity results, measured over 3 orders of magnitude only, could have been easily interpreted by the conventional mobile-immobile (MIM) diffusive mass transfer model of asymptotic log-log slope of À2. However, the fluorescent dye sensor, which allows exploring much lower concentration values, shows that a change in the log-log slope occurs at larger time with an asymptotic value of À1.5, corresponding to the double-porosity model. These results suggest that the conventional, one-slope MIM transfer rate model is too simplistic to account for the real multiscale heterogeneity of the diffusion-dominant fraction of the reservoir.Citation: Gouze, P., T. Le Borgne, R. Leprovost, G. Lods, T. Poidras, and P. Pezard (2008), Non-Fickian dispersion in porous media: 1. Multiscale measurements using single-well injection withdrawal tracer tests, Water Resour. Res., 44, W06426,

21 pages, 17 figures.
Mis en ligne avec l'aimable autorisation de l'éditeurTiny basaltic samples containing finely grained titanomagnetite with Curie temperature less than 100°C were heated in air in weak field (25 to 100 microT) at temperatures between 400 and 560°C for times as long as 32 hours. Oxyexsolution of titanomagnetite resulted in the crystallization of interacting single domain particles with Curie point close to 540°C and the concomitant development of one of two types chemical remanence, depending upon thermal treatment: isothermal chemical remanence (CRM) or thermochemical remanence (TCRM), the latter acquired under the combined effects of chemical change and temperature decrease. CRM and TCRM acquired under various conditions were subjected to Thellier-type experiments. The CRM/TRM ratio is found to be less than one and increases rapidly with acquisition temperature (0.35 at 400°C, 0.65 at 450°C, and 0.90 at 500°C). Thus, very large underestimate of geomagnetic field paleostrength can occur when a natural CRM is not recognized as such and is believed to be a natural TRM. In an attempt to mimic deuteric oxyexsolution in cooling magma, TCRM was imparted from 560 to 400°C at a cooling rate of 0.1°C/mn. The TCRM/TRM is found to slightly exceed one (1.10), in agreement with the theoretically predicted effect of the difference in cooling rate

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