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Understanding the effect of single fracture heterogeneity from single well injection withdrawal (SWIW) tests
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Lawrence Berkeley National Laboratory, CA, USA.
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.
2013 (English)In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 21, no 8, 1691-1700 p.Article in journal (Refereed) Published
Abstract [en]

The single well injection withdrawal (SWIW) tracer test on a fracture or fracture zone is a method used to estimate its tracer retardation properties.  In this study, the effects of single fracture aperture heterogeneity on SWIW test tracer breakthrough curves are examined by numerical modelling. The effects of the matrix diffusion and sorption is accounted for by using a particle tracking method through the addition of a time delay added to the advective transport time. For a given diffusion and sorption property value (Pm) and for a heterogeneous fracture, the peak concentration is larger compared to a homogeneous fracture. The cumulative breakthrough curve for a heterogeneous fracture is similar to that for a homogeneous fracture and a less sorptive/diffusive tracer. It is demonstrated that the fracture area that meets the flowing water, the so-called specific flow-wetted surface (sFWS) of the fracture, can be determined by comparing the observed breakthrough curve for a heterogeneous fracture with that for a homogeneous fracture. SWIW tests are also simulated with a regional pressure gradient present. The results point to the possibility of distinguishing the effect of the regional pressure gradient from that of diffusion through the use of multiple tracers with different Pm-values. 

Place, publisher, year, edition, pages
New York: Springer-Verlag New York, 2013. Vol. 21, no 8, 1691-1700 p.
Keyword [en]
tracer test, SWIW test, flow channelling, flow-wetted surface, fractured rock, aperture heterogeneity
National Category
Oceanography, Hydrology, Water Resources
Research subject
Hydrology
Identifiers
URN: urn:nbn:se:uu:diva-180408DOI: 10.1007/s10040-013-0988-xISI: 000327391000002OAI: oai:DiVA.org:uu-180408DiVA: diva2:550047
Funder
Formas, 245-2006-1152
Available from: 2012-09-06 Created: 2012-09-06 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Heterogeneity-Induced Channelling, Flow-Wetted Surface, and Modelling of Transport in Fractured Rock
Open this publication in new window or tab >>Heterogeneity-Induced Channelling, Flow-Wetted Surface, and Modelling of Transport in Fractured Rock
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Heterogeneities in fractured rock are found at all scales; from the scale of individual fractures, to the scale of fracture networks, and to the largest regional scales. These heterogeneities cause challenges for modelling and parameter estimation of flow and solute transport. The heterogeneities in fracture aperture, characterization of the flow channelling they are causing, and implementation of this information into numerical simulation models of the solute transport in fractured media are the subjects of this thesis.

Aperture variability within a fracture causes the flow channelling, where the water flow is focused in a few channels and other areas of the fracture have practically stagnant water. The flow-wetted surface is the area where the flowing water is in contact to the fracture area. Contaminants are transported with the flowing water and therefore the flow-wetted surface is an important parameter that influences the diffusion into the rock matrix and sorption to the fracture rock surface. The specific flow-wetted surface (sFWS) is the flow-wetted surface divided by the total fracture area. The sFWS is systematically analyzed for different fracture aperture distribution characteristics. The local aperture is linked to the local hydraulic conductivity K. Increasing standard deviation of the hydraulic conductivity K field (σln K) leads to decreased sFWS. The sFWS is found to be independent of the correlation length (λ) of the field. An empirical relationship is developed, which describes the sFWS as a function of the σln K. A method is also introduced to determine this key parameter by analysis of the breakthrough curve from a single-well injection-withdrawal (SWIW) test. Further, an approach is presented to incorporate the effect of fracture level heterogeneity into fracture network models and to analyze the effect on sorption and matrix diffusion, by including the sFWS parameter into the transport calculations. The results show that the median transport time is proportional to the square of the sFWS-value. The results also suggest that there are an averaging behaviour in the fracture network, the sFWS-value of each individual fracture is not important for the transport over the domain, but a mean-value can be utilized in the numerical model.

Abstract [sv]

Heterogeniteter i sprickigt berg finns i alla skalor, från millimeterskala till en skala på hundratals kilometer. Dessa heterogeniteter orsakar problem vid beräkning av vattenflöde och ämnestransport. Aperturen i en spricka är öppningen mellan de två omslutande bergsidorna, den varierar både inom och mellan olika sprickor. Ämnet för denna avhandling är heterogeniteter i aperturerna inom enskilda sprickor, karaktärisering av den flödeskanalisering som uppstår på grund av dessa heterogeniteter och hur man kan använda denna information till en numerisk modell.Variabilitet av aperturen i en enskild spricka gör att vattenflödet blir fokuserat i ett fåtal kanaler, medan andra områden av sprickan kan ha praktiskt taget stillastående vatten. Den flödesvätta ytan är det område där det strömmande vattnet kommer i kontakt med sprickytan. Den flödesvätta ytan som påverkar diffusionen in i bergmatrisen och sorptionen till sprickytan är en viktig parameter eftersom föroreningar transporteras med det strömmande vattnet. Den specifika flödesvätta ytan (sFWS) är den flödesvätta ytan dividerad med den totala sprickarean. I avhandlingen analyserades sFWS systematiskt för olika statistik över sprickaperturen. Den lokala aperturen är kopplad till den lokala hydrauliska konduktiviteten K. En ökad standardavvikelse för det hydrauliska konduktivitetsfältet (σln K) ledde till minskad sFWS. sFWS visades vara oberoende av konduktivitetsfältets korrelationslängd (λ). En empirisk relation utvecklades som beskriver sFWS som en funktion av σln K. Ett SWIW-test är en typ av spårämnesförsök, där ett spårämne injiceras i en brunn följt av vatten i en bestämd tidsperiod, innan flödet vänds och en genombrottskurva registreras. Testet används traditionellt för att bestämma bergets diffusions- och sorptionsegenskaper. En metod presenterades för att bestämma den specifika flödesvätta ytan genom analys av genombrottskurvan för ett SWIW-test. Ett tillvägagångssätt introducerades för att analysera effekterna av sorption och matrisdiffusion i heterogena sprickor i en spricknätverksmodell genom att inkludera sFWS-parametern i transportberäkningar. Resultaten visade att medianvärdet för transporttiden är proportionell mot kvadraten på sFWS-värdet. Resultaten visade också att transporten genom spricknätverket inte är beroende av sFWS-värdet i de individuella sprickorna, utan att medelvärdet kan användas för modellering.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 76 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 971
Keyword
channelling, flow-wetted surface, fractured rock, solute transport, groundwater modelling, groundwater
National Category
Oceanography, Hydrology, Water Resources
Research subject
Hydrology
Identifiers
urn:nbn:se:uu:diva-180409 (URN)978-91-554-8468-2 (ISBN)
Public defence
2012-10-19, Hambergsalen, Geocentrum, Uppsala Universitet, Villavägen 16, 75236 Uppsala, Uppsala, 13:00 (English)
Opponent
Supervisors
Funder
Formas, 245-2006-1152
Available from: 2012-09-28 Created: 2012-09-06 Last updated: 2013-01-23

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