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Structural controls on anomalous transport in fractured porous rock
Author(s) -
Edery Yaniv,
Geiger Sebastian,
Berkowitz Brian
Publication year - 2016
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/2016wr018942
Subject(s) - continuous time random walk , tracer , probability density function , permeability (electromagnetism) , porous medium , geology , flow (mathematics) , outcrop , histogram , statistical physics , porosity , random walk , physics , mechanics , mathematics , geotechnical engineering , statistics , chemistry , geomorphology , computer science , image (mathematics) , nuclear physics , biochemistry , artificial intelligence , membrane
Anomalous transport is ubiquitous in a wide range of disordered systems, notably in fractured porous formations. We quantitatively identify the structural controls on anomalous tracer transport in a model of a real fractured geological formation that was mapped in an outcrop. The transport, determined by a continuum scale mathematical model, is characterized by breakthrough curves (BTCs) that document anomalous (or “non‐Fickian”) transport, which is accounted for by a power law distribution of local transition times ψ ( t ) within the framework of a continuous time random walk (CTRW). We show that the determination of ψ ( t ) is related to fractures aligned approximately with the macroscopic direction of flow. We establish the dominant role of fracture alignment and assess the statistics of these fractures by determining a concentration‐visitation weighted residence time histogram. We then convert the histogram to a probability density function (pdf) that coincides with the CTRW ψ ( t ) and hence anomalous transport. We show that the permeability of the geological formation hosting the fracture network has a limited effect on the anomalous nature of the transport; rather, it is the fractures transverse to the flow direction that play the major role in forming the long BTC tail associated with anomalous transport. This is a remarkable result, given the complexity of the flow field statistics as captured by concentration transitions.