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Effects of single-fracture aperture statistics on entrapment, dissolution and source depletion behavior of dense non-aqueous phase liquids
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2012 (English)In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 133, 1-16 p.Article in journal (Refereed) Published
Abstract [en]

Understanding of the entrapment and dissolution behavior of dense non-aqueous phase liquids (DNAPLs) in single fractures is important for modeling contaminant flux generation from fractured sites. Here a systematic numerical study is presented to investigate the effect of fracture aperture statistics on DNAPL migration, entrapment and dissolution within individual, variable-aperture fractures. Both fractures with open and closed bottom boundaries were considered. For the simulation a continuum-based two-phase model was used with a capillary pressure function which calculates the entry pressure based on the local aperture. Prior to application the model was compared against the invasion percolation approach and found more suitable for the present study, in particular as it allows a more versatile presentation of boundary conditions. The results showed that increasing aperture standard deviation and/or decreasing correlation length lead to larger amounts of entrapped DNAPL (due to the fact that larger standard deviation produces more distinct contrast between small and large aperture regions and the fact that longer correlation length provides more possible channels through the fracture) as well as larger maximum and average sizes of DNAPL blobs, and subsequently lead to longer times for complete dissolution. To understand the relationship between the solute flux and the remaining mass, a simplified source depletion function which links the outflow concentration to the DNAPL saturation was found adequate to describe the dissolution process for the case where the bottom boundary is open for DNAPL migration and thus the DNAPL does not accumulate to form a pool. The parameters in this function were not very sensitive to variations in correlation length but were sensitive to aperture standard deviation. The same average entrapped DNAPL saturation produced considerably smaller solute concentrations in cases with larger aperture variability due to the larger average size of DNAPL blobs (i.e., smaller contact area for DNAPL dissolution). Boundary conditions had a significant impact on DNAPL entrapment and dissolution. A closed boundary at the bottom led to DNAPL pooling (i.e., large continuous blobs) which causes significant tailing in the dissolution breakthrough curve due to water bypassing.

Place, publisher, year, edition, pages
2012. Vol. 133, 1-16 p.
Keyword [en]
Fracture, Two-phase flow, Aperture variation, Dense non-aqueous phase liquid, Mass transfer, Source depletion
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-178877DOI: 10.1016/j.jconhyd.2012.03.002ISI: 000304634500001OAI: oai:DiVA.org:uu-178877DiVA: diva2:542915
Available from: 2012-08-06 Created: 2012-08-02 Last updated: 2013-02-11Bibliographically approved
In thesis
1. Multiphase Contamination in Rock Fractures: Fluid Displacement and Interphase Mass Transfer
Open this publication in new window or tab >>Multiphase Contamination in Rock Fractures: Fluid Displacement and Interphase Mass Transfer
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Flerfasföroreningar i sprickigt berg : Utbredning och massöverföring mellan faser
Abstract [en]

Multiphase flow and transport in fractured rock is of importance to many practical and engineering applications. In the field of groundwater hydrology an issue of significant environmental concern is the release of dense non-aqueous phase liquids (DNAPLs) which can cause long-term groundwater contamination in fractured aquifers. This study deals with two fundamental processes – fluid displacement and interphase mass transfer – concerning the behavior of the multiphase contaminants in fractured media. The focus of this work has been placed on improving the current understanding of small-scale (single fracture) physics by a combined effort of numerical modeling analysis, laboratory experiments and model development. This thesis contributes to the improved understanding through several aspects. Firstly, the effect of aperture variability, as characterized by geostatistical parameters such as standard deviation and correlation length, on the DNAPL entrapment, dissolution and source-depletion behaviors in single fractures was revealed. Secondly, a novel, generalized approach (adaptive circle fitting approach) to account for the effect of in-plane curvature of fluid-fluid interfaces on immiscible fluid displacement was developed; the new approach has demonstrated good performance when applied to simulate previously published experimental data. Thirdly, the performance of a continuum-based two-phase flow model and an invasion percolation model was compared for modeling fluid displacement in a variable-aperture fracture and the dependence of fracture-scale capillary pressure – saturation relationships on aperture variability was studied. Lastly, through experimental studies and mechanistic numerical modeling of DNAPL dissolution, kinetic mass transfer characteristics of two different entrapment configurations (residual blobs and dead-end pools) were investigated. The obtained understanding from this thesis will be useful for predictive modeling of multiphase contaminant behavior at a larger (fracture network) scale.

Abstract [sv]

Flerfasflöde och ämnestransport i sprickigt berg är av betydelse för många praktiska och tekniska problem. Tunga, svårlösliga organiska vätskor (engelska: dense non-aqueous phase liquids: DNAPLs; t.ex. klorerade lösningsmedel) kan orsaka långvarig förorening av vattenresurser, inklusive akviferer i sprickigt berg, och utgör ett viktigt miljöproblem inom grundvattenhydrologin. Denna studie behandlar två fundamentala processer för spridning av flerfasföroreningar i sprickiga medier – utbredning av den organiska vätskan och massöverföring mellan organisk vätska och vatten. Arbetet har fokuserat på att förbättra nuvarande kunskap om de fysikaliska processerna på liten skala (enskilda sprickor) genom en kombination av numerisk modellering, laboratorieexperiment och modellutveckling. Avhandlingen har bidragit till utökad processförståelse i flera avseenden. För det första har arbetet belyst effekterna av sprickaperturens variabilitet, uttryckt med geostatistiska parametrar som standardavvikelse och rumslig korrelationslängd, på fastläggning och lösning av organiska vätskor i enskilda sprickor, samt utmattningsbeteendet hos dessa källor till grundvattenförorening. För det andra har en ny, generell metod (adaptiva cirkelpassningsmetoden) för att ta hänsyn till effekten av krökningen av gränsytan mellan organisk vätska och vatten i sprickplanet utvecklats; denna metod har visats fungera väl i simuleringar av tidigare publicerade experimentella data. För det tredje, har en jämförelse gjorts mellan en kontinuumbaserad tvåfasflödesmodell och en invasions-perkolationsmodell med avseende på hur väl de kan simulera tvåfasflöde i en spricka med varierande apertur. Här studerades även hur relationen mellan kapillärtryck och mättnadsgrad på sprickplansskala beror av variabiliteten i sprickapertur. Till sist undersöktes lösning av den organiska vätskan i grundvatten för två fastläggningsscenarier (fastläggning i immobila droppar och ansamling i fällor – ”återvändssprickor”) både genom experiment och mekanistisk numerisk modellering. Kunskapen som tagits fram i denna avhandling bedöms vara användbar även för att modellera spridningen av flerfasföroreningar på större (spricknätverks-) skalor.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 75 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 994
multiphase flow; dissolution; mass transfer; invasion percolation; immiscible displacement; fractured media; groundwater contamination; non-aqueous phase liquid; curvature
National Category
Oceanography, Hydrology, Water Resources Environmental Sciences
Research subject
urn:nbn:se:uu:diva-183720 (URN)978-91-554-8531-3 (ISBN)
Public defence
2012-12-14, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Swedish Research Council
Available from: 2012-11-23 Created: 2012-10-31 Last updated: 2013-02-11Bibliographically approved

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