 |
| Titel |
Origins of Anomalous Transport in Heterogeneous Media: Structural and Dynamic Controls |
| VerfasserIn |
Yaniv Edery, Alberto Guadagnini, Harvey Scher, Brian Berkowitz |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250087609
|
| Publikation (Nr.) |
 EGU/EGU2014-1667.pdf |
|
|
|
|
|
| Zusammenfassung |
| Anomalous (or “non-Fickian”) transport is ubiquitous in the context of tracer migration in
geological formations. We quantitatively identify the origin of anomalous transport in a
representative model of a heterogeneous porous medium under uniform (in the mean) flow
conditions; we focus on anomalous transport which arises in the complex flow patterns of
lognormally distributed hydraulic conductivity (K) fields, with several decades of K values.
Transport in the domains is determined by a particle tracking technique and characterized by
breakthrough curves (BTCs). The BTC averaged over multiple realizations demonstrates
anomalous transport in all cases, which is accounted for entirely by a power-law distribution
~ t-1-β of local transition times, contained in the probability density function Ï(t) of
transition times, using the framework of a continuous time random walk (CTRW). A
unique feature of our analysis is the derivation of Ï(t) as a function of parameters
quantifying the heterogeneity of the domain. In this context, we first establish the
dominance of preferential pathways across each domain, and characterize the statistics
of these pathways by forming a particle-visitation weighted histogram Hw(K).
By converting the ln(K) dependence of Hw(K) into time, we demonstrate the
equivalence of Hw(K) and Ï(t), and delineate the region of Hw(K) that forms the
power law of Ï(t). This thus defines the origin of anomalous transport. Analysis
of the preferential pathways clearly demonstrates the limitations of critical path
analysis and percolation theory as a basis for determining the origin of anomalous
transport. Furthermore, we derive an expression defining the power law exponent β in
terms of the Hw(K) parameters. The equivalence between Hw(K) and Ï(t) is a
remarkable result, particularly given the nature of the K heterogeneity, the complexity of
the flow field within each realization, and the statistics of the particle transitions. |
|
|
|
|
|
|