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Dissolution of dense non-aqueous phase liquids in vertical fractures: Effect of finger residuals and dead-end pools
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.
Center for Experimental Study of Subsurface Environmental Processes, Colorado School of Mines, Golden, CO, USA.
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2013 (English)In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 149, 88-99 p.Article in journal (Refereed) Published
Abstract [en]

Understanding the dissolution behavior of dense non-aqueous phase liquids (DNAPLs) in rock fractures under different entrapment conditions is important for remediation activities and any related predictive modeling. This study investigates DNAPL dissolution in variable aperture fractures under two important entrapment configurations, namely, entrapped residual blobs from gravity fingering and pooling in a dead-end fracture. We performed a physical dissolution experiment of residual DNAPL blobs in a vertical analog fracture using light transmission techniques. A high-resolution mechanistic (physically-based) numerical model has been developed which is shown to excellently reproduce the experimentally observed DNAPL dissolution. We subsequently applied the model to simulate dissolution of the residual blobs under different water flushing velocities. The simulated relationship between the Sherwood number Sh and Peclet number Pe could be well fitted with a simple power-law function (Sh = 1.43Pe0.43). To investigate mass transfer from dead-end pools, another type of trapping in rock fractures, entrapment and dissolution of DNAPL in a vertical dead-end fracture was simulated. As the entrapped pool dissolves, the depth of the interface between the DNAPL and the flowing water increases linearly with decreasing DNAPL saturation. The interfacial area remains more or less constant as DNAPL saturation decreases, unlike in the case of residual DNAPL blobs. The decreasing depth of the contact interface changes the flow field and causes decreasing water flow velocity above the top of the DNAPL pool, suggesting the dependence of the mass transfer rate on the depth of the interface, or alternatively, the remaining mass percentage in the fracture. Simulation results show that the resultant Sherwood number Sh is significantly smaller than in the case of residual blobs for any given Peclet number, indicating slower mass transfer. The results also show that the Sh can be well fitted with a power-law function of Pe and remaining mass percentage. The obtained relationships of dimensionless groups concerning the mass transfer characteristics at the level of individual fractures can be further used in predictive modeling of dissolution at a larger (fracture network) scale.

Place, publisher, year, edition, pages
2013. Vol. 149, 88-99 p.
Keyword [en]
fracture, fingering, mass transfer, entrapment configuration, source depletion, contaminant flux, modeling.
National Category
Oceanography, Hydrology, Water Resources
Research subject
Hydrology
Identifiers
URN: urn:nbn:se:uu:diva-183719DOI: 10.1016/j.jconhyd.2013.03.006ISI: 000319550400007OAI: oai:DiVA.org:uu-183719DiVA: diva2:563918
Funder
Swedish Research Council
Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2017-12-07Bibliographically 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.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 994
Keyword
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
Hydrology
Identifiers
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)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2012-11-23 Created: 2012-10-31 Last updated: 2013-02-11Bibliographically approved

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