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Two-phase flow in rough-walled fractures: Comparison of continuum and invasion-percolation models
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (geohydrologi)
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.
2013 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 2, 993-1002 p.Article in journal (Refereed) Published
Abstract [en]

We present a systematic comparison study of simulating two-phase flow (drainage) in single heterogeneous fractures by using two fundamentally different approaches, namely a continuum-based two-phase flow model and an invasion percolation (IP) model. We analyze both gravity neutral and gravity destabilized cases. In the continuum model, the two-phase mass conservation equations for the two-dimensional fracture plane are solved, based on a modified TOUGH2 model. A specific capillary pressure-liquid saturation function is used to account for the sudden drainage of a local aperture location in the fracture once its local aperture-dependent non-wetting phase fluid entry pressure is exceeded. Results from the continuum model are compared to those from an invasion percolation model that includes trapping. We consider cases where the contribution of aperture-induced curvature in the capillary pressure term dominates over that of the in-plane curvature. The comparison shows that the presented continuum model can well reproduce the IP model results at low-capillary number conditions and, furthermore, can also produce meaningful results in the high capillary number regimes where IP models are not valid. Taking into account the viscous forces in the fluid displacement process, the continuum model is used to examine the effect of capillary number (reflecting the injection rate) on the phase invasion. When the injection rate varies from low to high, simulations using the continuum model show that the invasion pattern changes from single dominant fingers to more homogeneous spreading and/or clusters with numerous tortuous fingers. This trend is comparable to results from previous experimental observations in the literature. The continuum model is also used to numerically construct the upscaled (fracture-scale) capillary pressure-saturation relationship. The upscaled relationship can be well fitted to the van Genuchten and the Brook-Corey porous-medium-type models. Fracture capillary behavior depends on the aperture field heterogeneity. Simulation results indicate that increasing the aperture standard deviation leads to smaller entry pressure and larger residual water saturation.

Place, publisher, year, edition, pages
2013. Vol. 49, no 2, 993-1002 p.
Keyword [en]
variable-aperture fracture, continuum model, invasion percolation, immiscible displacement, high-capillary number flow, numerical modeling
National Category
Oceanography, Hydrology, Water Resources
Research subject
Hydrology
Identifiers
URN: urn:nbn:se:uu:diva-183717DOI: 10.1002/wrcr.20111ISI: 000317828600023OAI: oai:DiVA.org:uu-183717DiVA: diva2:563916
Funder
Swedish Research Council
Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2017-05-08
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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Yang, ZhibingNiemi, AuliFagerlund, Fritjof

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