SAFT
Structural and hydrodynamic controls on fluid travel time distributions across fracture networks
Context
In the SAFT project, DFN-based models are used to study advective transport and breakthrough curves (BTC) in fractured crystalline rocks, with conditions relevant to the Forsmark site. The 2022 phase focused on advancing the paper draft, extending simulations, and developing a robust framework to analyze travel-time distributions and anomalous transport regimes. The work combines a broad set of DFN geometries with varied transmissivity structures to assess model sensitivity and calibrate transport indicators.
The objectives are to understand regimes of transport dispersion in DFNs and identify model relevance, quantify travel-time probability density functions from DFN.lab particle tracking, provide indicators for model calibration and sensitivity analysis and fit BTCs with a consistent theoretical framework.
Project Results
We analyzed solute transport in three-dimensional discrete fracture network (DFN) models spanning a range of fracture geometries and connectivity structures, including stochastic and Forsmark-based realizations. Fracture transmissivity was prescribed using simplified to highly heterogeneous representations to isolate the relative roles of network structure and hydraulic variability.
Most BTCs are characterized by a stretched inverse gamma regime at early times followed by a power-law tail at late times. The late-time power-law behavior dominates dispersivity and depends primarily on the underlying DFN structure. In contrast, early-time transport reflects both DFN geometry and transmissivity variability and departs from late-time scaling when transmissivity is relatively uniform.
Find out more
P. Davy, R. Le Goc, C. Darcel, B. Pinier, J. Selroos, & T. Le Borgne, Structural and hydrodynamic controls on fluid travel time distributions across fracture networks, Proc. Natl. Acad. Sci. U.S.A. 121 (47) e2414901121, https://doi.org/10.1073/pnas.2414901121 (2024).