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Colmatage des réseaux de fractures, modèles et conséquences hydrologiques

Abstract : Fracture networks have a major impact on crystalline rocks' hydraulic properties because they constitute the only flowing paths. Field data often point out that a large proportion of the network is however sealed by physico-chemical processes and thus is impermeable. For example, at the Forsmark site (Sweden), future deep nuclear waste repository, the core-log data indicate that 75-80 % of fractures are sealed. The way sealed surfaces are distributed in fracture networks (in terms of fracture size, orientation, etc) is critical because it can drastically change the connectivity and the flow organization. In the first part, we study how the sealing distribution can be constrained by numerical models. The aim is to have models that are simple enough to be applied to large fracture networks. We show that a graph structure (made of nodes and edges) can be used to simplify fracture networks models (DFN) and to compute the flows directly. Then, we use it to model a sealing process coupled to the flows. The results demonstrate that the flow heterogeneity at the network scale creates correlations between sealing rates and fracture sizes. In the second part, we evaluate the sealing distribution from Forsmark core-log data. The statistical analyses show a strong correlation between the proportion of open fractures and the normal stress, indicating a mechanical control. This mechanical control is further deepened by an analysis of fluid pressures, which can cause fracture reactivation. The results reveal their significant role. Finally, we evaluate the hydrological consequences of the measured correlation with the normal stress, by using DFN models. We show that this correlation can not itself explain the flow organization measured in Forsmark boreholes and that a correlation with fracture sizes must be considered.
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Submitted on : Wednesday, February 23, 2022 - 3:19:08 PM
Last modification on : Thursday, June 2, 2022 - 2:48:17 PM
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  • HAL Id : tel-03586056, version 1

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Diane Doolaeghe Wehowsky. Colmatage des réseaux de fractures, modèles et conséquences hydrologiques. Sciences de la Terre. Université Rennes 1, 2021. Français. ⟨NNT : 2021REN1B026⟩. ⟨tel-03586056⟩

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