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Upscaling of Flow, Transport, and Stress-effects in Fractured Rock / Uppskalning av flöde och ämnestransport i sprickigt berg samt bergspänningens inverkan

One of many applications of geohydraulic modelling is assessing the suitability of a site to host a nuclear waste repository. This modelling task is complicated by scale-dependent heterogeneity and coupled thermo-hydro-mechanical (THM) processes. The objective here was to develop methods for (i) upscaling flow and transport in fractured media from detailed-scale data and (ii) accounting for THM-induced effects on regional-scale transport. An example field data set was used for demonstration. A systematic framework was developed where equivalent properties of flow, transport, and stress-effects were estimated with discrete fracture network (DFN) modelling, at some block scale, and then transferred to a regional-scale stochastic continuum (SC) model. The selected block scale allowed a continuum approximation of flow, but not of transport. Instead, block-scale transport was quantified by transit time distributions and modelled with a particle random walk method at the regional scale. An enhanced SC-upscaling approach was developed to reproduce the DFN flow results more simply. This required: (i) weighting of the input well-test data by their conductivity-dependent test volumes and (ii) conductivity-dependent correlation structure. Interestingly, the best-fitting correlation structure resembled the density function of DFN transmissivities. Channelized transport, over distances exceeding the block scale, was modelled with a transport persistence length. A linear relationship was found between this persistence length and the macroscale dispersion coefficient, with a slope equal to a representative mean block-scale dispersion coefficient. A method was also developed to combine well-test data and rock-mechanical data in estimating fracture transmissivities, and its application was demonstrated. Finally, an overall sequential THM analysis was introduced allowing the estimation of the significance of waste-related thermo-mechanical (TM) effects on regional transport; here TM effects are calculated separately and their impact on fracture transmissivities were incorporated into the hybrid framework. For the particular case, their effects on regional-scale transport were small.

Identiferoai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-5739
Date January 2005
CreatorsÖhman, Johan
PublisherUppsala universitet, Institutionen för geovetenskaper, Uppsala : Acta Universitatis Upsaliensis
Source SetsDiVA Archive at Upsalla University
LanguageEnglish
Detected LanguageEnglish
TypeDoctoral thesis, comprehensive summary, info:eu-repo/semantics/doctoralThesis, text
Formatapplication/pdf
Rightsinfo:eu-repo/semantics/openAccess
RelationDigital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 35

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