Linking Structural and Transport Properties in Three‐Dimensional Fracture Networks

• Published in: Journal of geophysical research. Solid earth 2019-02, Vol.124 (2), p.1185-1204
• Main Authors: Hyman, J. D., Dentz, M., Hagberg, A., Kang, P. K.
• Format: Article
• Language: English
• Subjects: Conditioning; Distribution; Earth Sciences; Electric power distribution; flow and transport in fractured media; fractured media; Geophysics; GEOSCIENCES; graph theory; Mathematics; Particle motion; Percolation; Power law; Properties; Random walk; Random walk theory; solute transport; Solutes; Transport; Transport properties; Velocity; Velocity distribution
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2018JB016553

We investigate large‐scale particle motion and solute breakthrough in sparse three‐dimensional discrete fracture networks characterized by power law distributed fracture lengths. The three networks we consider have the same fracture intensity values but exhibit different percolation densities, geometric properties, and topological structures. We considered two different average transport models to predict solute breakthrough, a streamtube model and a Bernoulli continuous time random walk model, both of which provide insights into the flow fields within the networks. The streamtube model provides acceptable predictions at short distances in two of the networks but fails in all cases to predict breakthrough times at the outlet plane, which indicates that particle motion in such fracture networks cannot be characterized by a constant velocity between the inlet and control plane at which the breakthrough curve is detected. Rather, the structure of the network requires that frequent velocity transitions be made as particles move through the system. Despite the relatively broad distribution of fracture radii and relatively small number of independent velocity transitions, the continuous time random walk approach conditioned on the initial velocity distribution provides reasonable predictions for the breakthrough curves at different distances from the inlet. The application of these averaged transport models provides a richer understanding of the link from the fracture network structure to flow and transport properties. Key Points We investigate solute breakthrough in sparse three‐dimensional discrete fracture networks The network structure plays a key role in controlling velocity transitions along a particle pathline We uncover a link between structural properties of the network and observed hydrodynamic behavior