Evaluating the effect of internal aperture variability on transport in kilometer scale discrete fracture networks

• Published in: Advances in water resources Vol. 94; pp. 486 - 497
• Main Authors: Makedonska, Nataliia, Hyman, Jeffrey D., Karra, Satish, Painter, Scott L., Gable, Carl W., Viswanathan, Hari S.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01.08.2016; Elsevier
• Subjects: Advective transport; Aperture variability; Apertures; Correlation; Discrete fracture networks; Discrete Fracture Networks, Subsurface flow and transport, Heterogeneity, Advective Transport, High-performance Computing, Fractured rock; Earth Sciences; ENVIRONMENTAL SCIENCES; Fracture mechanics; Fractured rock; GEOSCIENCES; Heterogeneity; High-performance computing; Mathematical models; Networks; simulation; subsurface flow; Subsurface flow and transport; Transport; Transportation networks; Travel time; Heterogeneity; Advective transport; Discrete fracture networks; High-performance computing; Fractured rock; Subsurface flow and transport; Aperture variability
• ISSN: 0309-1708; 1872-9657
• DOI: 10.1016/j.advwatres.2016.06.010

•90% of injected contaminants are driven by fracture network geometry.•In-fracture variability shows effect on transport in large scale DFN at P<0.1•Spatial correlation length of in-fracture variability does not effect transport in DFNs.•High variance of transmissivity effects earlier breakthrough due to flow channeling. The apertures of natural fractures in fractured rock are highly heterogeneous. However, in-fracture aperture variability is often neglected in flow and transport modeling and individual fractures are assumed to have uniform aperture distribution. The relative importance of in-fracture variability in flow and transport modeling within kilometer-scale field–scale fracture networks has been under a matter of debate for a long time because the flow in each single fracture is controlled not only by in-fracture variability but also by boundary conditions. Computational limitations have previously prohibited researchers from investigating the relative importance of in-fracture variability in flow and transport modeling within large-scale fracture networks. We address this question by incorporating internal heterogeneity of individual fractures into flow simulations within kilometer scale three-dimensional fracture networks, where fracture intensity, P32 (ratio between total fracture area and domain volume) is between 0.027 and 0.031 [1/m]. A recently developed discrete fracture network (DFN) simulation capability, dfnWorks, is used to generate DFNs that include in-fracture aperture variability represented by a stationary log-normal stochastic field with various correlation lengths and variances. The Lagrangian transport parameters, non-reacting travel time and cumulative retention, are calculated along particles streamlines. It is observed that due to local flow channeling early particle travel times are more sensitive to in-fracture variability than the tails of travel time distributions, where no significant effect of the in-fracture transmissivity variations and spatial correlation length is observed.