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Caractérisation hydrogéophysique des milieux fracturés : développement instrumental et modélisation des vitesses d’écoulement en forage

Abstract : The fractured media are characterized by a strong heterogeneity of the velocity field related to the localization of flow in the local permeable zones of the fracture network. In this context, predicting the flow or transport needs to provide enough constraints on the lithology and the flow velocity. We bring some information for this question through three complementary approaches: (i) a study of the relationship between fracturing and deformation zones and flow observed in the Ploemeur’s experimental site, (ii) implementation of a numerical flowmetry model for imaging hydraugeologic properties between boreholes, and (iii) the development of a new borehole tool for horizontal velocities measurement, in partnership with the Technical Division of INSU (Brest). A recurring issue raised in this manuscript is in what extent the data at the local scale can provide sufficient information on the overall behavior. The log analysis and core drilling Ploemeur’s site clearly shows that the main deformation zones are characterized by intense deformation and by fault breccia or gouge zones associated or not associated with very fractured pegmatites. Locally, the link between deformation zones or fracturing and flow is difficult to corelate because of the important variability of local properties. At the site scale, the intense fractured zone with fractured pegmatite is corelated to important connected zone. At the regional scale, it appears that the subvertical fracturing N110 ° and N20 ° associated with high strain zone, forms the contact between the Pouldu mica and Ploemeur granite, controls part of the flows. The numerical model allowed us to replicate these experiments of flowmetry interference tests to establish the standard answers that must be observed according to the wellbore storage and hydraulic properties of fractures. The characterization of the connectivity of the different structures connected to the wells is easily identified through the analysis of transient flows. The main difficultie related to the inversion is due to the presence of indirect pathsway, and deficiency of real pumping rate in each connected structures. We also showed that the fractures storage coefficient significantly controlled the response of vertical flow. Finally, we show how disconnected structures from the pumping well can influence the hydrogeological response. This work is illustrated by an field application. For the characterization of in situ velocities in fractured media, we have participated in the development of a new sensor (PIVEF) able to measure the velocity by particle tracking. This probe was calibrated and validated in the laboratory. With its large viewing window, we can characterize the velocity accurately. We can observe the velocity field in situ on a wide range (1.10-5 to 1.10-2 m/s). This velocity accuraty is allowed for both homogeneous and in fractured media, provided that the fracture dips is not too important. The velocity measurement can be done constinuously over the entire height of the measurement area. We observed in fractured media the precense of recirculation loops. This recirculation loops creating disturbances in the water column. Despite these inherent difficulties in this kind of measurement, a field application showed the full potential of the tool
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https://hal-insu.archives-ouvertes.fr/tel-01137326
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Submitted on : Monday, March 30, 2015 - 2:39:56 PM
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Sébastien Ruelleu. Caractérisation hydrogéophysique des milieux fracturés : développement instrumental et modélisation des vitesses d’écoulement en forage. Sciences de la Terre. Universite Rennes 1, 2010. Français. ⟨tel-01137326⟩

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