Evaluating the effect of internal aperture variability on transport in kilometer scale discrete fracture networks. (August 2016)

• Record Type: Journal Article
• Authors: Makedonska, Nataliia; Hyman, Jeffrey D.; Karra, Satish; Painter, Scott L.; Gable, Carl W.; Viswanathan, Hari S.
• Is Part Of: Advances in water resources. Volume 94(2016)
• Page Start: 486
• Page End: 497
• Publication Date: 2016-08
• Subjects: Discrete fracture networks -- Subsurface flow and transport -- Heterogeneity -- Advective transport -- Aperture variability -- High-performance computing -- Fractured rock; Hydrology -- Periodicals; Hydrodynamics -- Periodicals; Hydraulic engineering -- Periodicals; 551.48
• DOI: 10.1016/j.advwatres.2016.06.010
• Languages: English
• ISSNs: 0309-1708

Abstract

Highlights: 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. Abstract: 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.