Characterizing the impact of finite matrix block size on conservative particle transport through three-dimensional fracture networks

Journal Article · Fri Dec 06 00:00:00 EST 2024 · Journal of Hydrology

DOI:https://doi.org/10.1016/j.jhydrol.2024.132462· OSTI ID:2481565

Volponi, Sabrina N. ^[1]; Pachalieva, Aleksandra A. ^[2]; Bolster, Diogo ^[1]; Sweeney, Matthew R. ^[2]; Stauffer, Philip H. ^[2]; Viswanathan, Hari S. ^[2]; Hyman, Jeffrey D. ^[2]

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1. University of Notre Dame, IN (United States)
2. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Mass transfer of solutes between fractures and the surrounding rock matrix exerts a noticeable signature on the tail of travel time distributions. When the width of the matrix is assumed to be infinite and advective transport through the fracture is sufficiently fast, the tails of the travel time distributions exhibit a classically expected slope of ψ(t) ∝ t ^-3/2. However, studies have yet to characterize how solute transfer between fractures via diffusion through finite matrix blocks influences the tail’s slope in three-dimensional fractured media. Here, in this study, we assess the impact of finite matrix block size on breakthrough curve shape at different spatio-temporal scales by con ducting particle tracking simulations in three-dimensional discrete fracture networks. We consider a variety of hydrodynamic and geostructural proper ties to determine their relative impact on the resulting travel time distributions. We observe that the impact of matrix diffusion through a finite block on travel time distributions is similar to that of an infinite matrix block when the fracture spacing is sufficiently large, matrix diffusion is relatively weak, or transport is considered at an early control plane distance. We observe that the converse of these conditions, results in deviations from the classical ψ(t) ∝ t ^-3/2 scaling. These results provide a first step toward developing a metric to assess when finite block size effects are expected to significantly influence transport.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA); USDOE Office of Nuclear Energy (NE), Office of Spent Fuel and Waste Disposition. Office of Spent Fuel and Waste Science and Technology; USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: 89233218CNA000001; SC0023429
• OSTI ID: 2481565
• Report Number(s): LA-UR--24-25519
• Journal Information: Journal of Hydrology, Journal Name: Journal of Hydrology Vol. 650; ISSN 0022-1694
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
Discrete fracture network
Earth Sciences
Fracture networks
Matrix diffusion
Time domain random walk