The role of advection and matrix diffusion in power-law scaling behavior of first passage times in three-dimensional discrete fracture networks

The relative impact of advection and matrix diffusion on transport behavior through fracture networks is explored using a using a time domain random walk method within three-dimensional discrete fracture networks (DFN). The high-fidelity DFN simulations are carried out using dfnWorks [Hyman et al. 2015], which allows for detailed investigation into how structural properties of the fracture network and matrix influence solute breakthrough times. We consider multiple DFN realizations generated with varying parameters and a wide range of matrix diffusion properties to investigate how the interplay of advection within the fracture network and retention of particles in the surrounding matrix influences late time behavior of first passage time distributions. Using these simulations, we provide new insights into power-law tailing behavior of transport based on the relative dominance of the decay rate of the advective travel time distribution versus matrix diffusion.

References: Hyman, Jeffrey D., Satish Karra, Nataliia Makedonska, Carl W. Gable, Scott L. Painter, and Hari S. Viswanathan. "dfnWorks: A discrete fracture network framework for modeling subsurface flow and transport." Computers & Geosciences 84 (2015): 10-19.