We study how the interplay between fracture aperture heterogeneity and tracer injection mode controls fluid flow and tracer transport in three-dimensional (3D) discrete fracture networks (DFNs). The direct 3-D DFN simulations show that tracer injection mode has substantial effects on tracer spreading across all levels of aperture heterogeneity. The key controlling factor for effective transport is the initial Lagrangian velocity distribution, which is determined by the interplay between injection mode and aperture heterogeneity. The fundamental difference between initial Lagrangian velocity distribution and domain-scale Eulerian velocity distribution plays a vital role in determining anomalous transport. We effectively capture the observed anomalous transport using an upscaled transport model that incorporates initial velocity distribution, stationary velocity distribution, velocity correlation length, and average advective tortuosity. With the upscaled transport model, we accurately capture the evolution of Lagrangian velocity distribution and predict longitudinal spreading in 3-D DFN.
Bibliographical noteFunding Information:
PKK acknowledges the College of Science & Engineering at the University of Minnesota and the George and Orpha Gibson Endowment for its generous support of Hydrogeology. PKK and WSH acknowledge a grant from Korea Environment Industry and Technology Institute (KEITI) through Subsurface Environmental Management (SEM) Project, funded by the Korea Ministry of Environment (MOE) (2018002440003). MD acknowledges the support of the European Research Council (ERC) through the project MHetScale (617511), and the support of the Spanish Ministry of Science and Innovation through a Severo Ochoa project (No. CEX2018324 000794‐S), and the project HydroPore (PID2019‐106887GB‐C31). JDH acknowledges support from the LANL LDRD program office Grant 20180621ECR and thanks to the Department of Energy (DOE) Basic Energy Sciences program (LANLE3W1) for support as well.