Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Multiphase Contamination in Rock Fractures: Fluid Displacement and Interphase Mass Transfer
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Flerfasföroreningar i sprickigt berg : Utbredning och massöverföring mellan faser (Swedish)
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 [en]
multiphase flow; dissolution; mass transfer; invasion percolation; immiscible displacement; fractured media; groundwater contamination; non-aqueous phase liquid; curvature
National Category
Oceanography, Hydrology and Water Resources Environmental Sciences
Research subject
Hydrology
Identifiers
URN: urn:nbn:se:uu:diva-183720ISBN: 978-91-554-8531-3 (print)OAI: oai:DiVA.org:uu-183720DiVA: diva2:563925
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: 2018-01-12Bibliographically approved
List of papers
1. Effects of single-fracture aperture statistics on entrapment, dissolution and source depletion behavior of dense non-aqueous phase liquids
Open this publication in new window or tab >>Effects of single-fracture aperture statistics on entrapment, dissolution and source depletion behavior of dense non-aqueous phase liquids
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.

Keyword
Fracture, Two-phase flow, Aperture variation, Dense non-aqueous phase liquid, Mass transfer, Source depletion
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-178877 (URN)10.1016/j.jconhyd.2012.03.002 (DOI)000304634500001 ()
Available from: 2012-08-06 Created: 2012-08-02 Last updated: 2017-12-07Bibliographically approved
2. A generalized approach for estimation of in-plane curvature in invasion percolation models for drainage in fractures
Open this publication in new window or tab >>A generalized approach for estimation of in-plane curvature in invasion percolation models for drainage in fractures
2012 (English)In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 48, no 9, W09507- p.Article in journal (Refereed) Published
Abstract [en]

In-plane interfacial curvature plays an important role in shaping the phase structure during quasi-static immiscible displacement in horizontal rough-walled fractures. Existing approaches used in percolation modeling require the use of a pre-defined globally representative length scale for calculating the in-plane curvature. This length scale is typically estimated using the geostatistics of fracture aperture variability. However, there has not been any rigorous and general derivation on how to obtain this length scale in the literature. This paper presents a general method referred to as adaptive circle fitting (ACF) approach to estimate in-plane curvature, recognizing that in some fractures the in-plane curvature along the fluid-fluid interface may exhibit various length scales due to the variability both in the locally averaged aperture and in the fracture wall roughness. The ACF involves nonlinear fitting of the interface to an osculating circle whose radius geometrically defines the inverse of the local curvature. This approach does not require pre-defining an empirical representative length scale. The influence length of the interface to which the circle is fitted is determined adaptively based on an acceptable threshold error.  We have implemented the ACF approach to an invasion percolation model and performed numerical simulations against experimental data on drainage processes in two horizontal rough-walled fractures. The observed invasion phase structures can be well reproduced using this generalized approach. In comparison to the previous approaches, it also demonstrates better performance in matching the experimental results of invasion phase distributions and fractal dimensions of the invasion clusters.

Keyword
fracture, two-phase flow, curvature, invasion percolation, immiscible displacement
National Category
Oceanography, Hydrology and Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-180902 (URN)10.1029/2012WR011829 (DOI)000310541400002 ()
Funder
Swedish Research Council
Available from: 2012-09-12 Created: 2012-09-12 Last updated: 2018-01-12Bibliographically approved
3. Two-phase flow in rough-walled fractures: Comparison of continuum and invasion-percolation models
Open this publication in new window or tab >>Two-phase flow in rough-walled fractures: Comparison of continuum and invasion-percolation models
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.

Keyword
variable-aperture fracture, continuum model, invasion percolation, immiscible displacement, high-capillary number flow, numerical modeling
National Category
Oceanography, Hydrology and Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-183717 (URN)10.1002/wrcr.20111 (DOI)000317828600023 ()
Funder
Swedish Research Council
Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2018-01-12
4. Dissolution of dense non-aqueous phase liquids in vertical fractures: Effect of finger residuals and dead-end pools
Open this publication in new window or tab >>Dissolution of dense non-aqueous phase liquids in vertical fractures: Effect of finger residuals and dead-end pools
Show others...
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.

Keyword
fracture, fingering, mass transfer, entrapment configuration, source depletion, contaminant flux, modeling.
National Category
Oceanography, Hydrology and Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-183719 (URN)10.1016/j.jconhyd.2013.03.006 (DOI)000319550400007 ()
Funder
Swedish Research Council
Available from: 2012-10-31 Created: 2012-10-31 Last updated: 2018-01-12Bibliographically approved

Open Access in DiVA

fulltext(5485 kB)1151 downloads
File information
File name FULLTEXT01.pdfFile size 5485 kBChecksum SHA-512
5da3e8c235ad3f489888fdc29c455da788ce93b60bd6cadbc73e383c60716633330a2ea2e5c2177283188dbe06d41286130b8df7ed099caf8022d3f4993d5af7
Type fulltextMimetype application/pdf
Buy this publication >>

Search in DiVA

By author/editor
Yang, Zhibing
By organisation
LUVAL
Oceanography, Hydrology and Water ResourcesEnvironmental Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 1151 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 1736 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf