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Solute transport through fractured rock: Radial diffusion into the rock matrix with several geological layers for an arbitrary length decay chain
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.ORCID iD: 0000-0003-2353-6505
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.ORCID iD: 0000-0001-8241-2225
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
2016 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 536, 133-146 p.Article in journal (Refereed) Published
Abstract [sv]

The paper presents a model development to derive a semi-analytical solution to describe reactive solute transport through a single channel in a fracture with cylindrical geometry. The model accounts for advection through the channel, radial diffusion into the adjacent heterogeneous rock matrix comprising different geological layers, adsorption on both the channel surface, and the geological layers of the rock matrix and radioactive decay chain. Not only an arbitrary-length decay chain, but also as many number of the rock matrix layers with different properties as observed in the field can be handled. The solution, which is analytical in the Laplace domain, is transformed back to the time domain numerically e.g. by use of de Hoog algorithm. The solution is verified against experimental data and analytical solutions of limiting cases of solute transport through porous media. More importantly, the relative importance and contribution of different processes on solute transport retardation in fractured rocks are investigated by simulating several cases of varying complexity. The simulation results are compared with those obtained from rectangular model with linear matrix diffusion. It is found that the impact of channel geometry on breakthrough curves increases markedly as the transport distance along the flow channel and away into the rock matrix increase. The effect of geometry is more pronounced for transport of a decay chain when the rock matrix consists of a porous altered layer.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 536, 133-146 p.
Keyword [en]
Analytical solution, Radial matrix diffusion, Geological rock layers, Fractured rock, Radionuclide decay chain
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-183591DOI: 10.1016/j.jhydrol.2016.02.046ISI: 000374811200011ScopusID: 2-s2.0-84959564763OAI: oai:DiVA.org:kth-183591DiVA: diva2:912762
Note

QC 20160318

Available from: 2016-03-17 Created: 2016-03-17 Last updated: 2016-05-31Bibliographically approved
In thesis
1. Solute transport through fractured rocks: the influence of geological heterogeneities and stagnant water zones
Open this publication in new window or tab >>Solute transport through fractured rocks: the influence of geological heterogeneities and stagnant water zones
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

To describe reactive solute transport and retardation through fractured rocks, three models are developed in the study with different focuses on the physical processes involved and different simplifications of the basic building block of the heterogeneous rock domain. The first model evaluates the effects of the heterogeneity of the rock matrix and the stagnant water zones in part of the fracture plane. The second and the third models are dedicated to different simplifications of the flow channels. Both account for radioactive decay chain, but consider either a rectangular channel with linear matrix diffusion or a cylindrical channel with radial matrix diffusion. Not only an arbitrary-length decay chain, but also as many rock matrix layers with different geological properties as observed in the field experiments can be handled.

The analytical solutions thus obtained from these three models for the Laplace-transformed concentration in the flow channel can all be conveniently transformed back to the time domain by use of e.g. de Hoog algorithm. This allows one to readily include the results into a fracture network model or a channel network model to predict nuclide transport through flow channels in heterogeneous fractured media consisting of an arbitrary number of rock units with piecewise constant properties. The relative impacts and contributions of different processes in retarding solute transport in fractured rocks can easily be evaluated by simulating several cases of varying complexity.

Additionally, a model is developed to study the evolution of fracture aperture in crystalline rocks mediated by pressure dissolution and precipitation. It accounts for not only advective flow that can carry in or away dissolved minerals but also the fact that dissolved minerals in the fracture plane, in both the flow channel and the stagnant water zone, can diffuse into the adjacent porous rocks. The analytical solution obtained in the Laplace space is then used to evaluate the evolution of the fracture aperture under combined influence of stress and flow, in a pseudo-steady-state procedure. The simulation results give insights into the most important processes and mechanisms that dominate the fracture closure or opening under different circumstances.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. x, 53 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2016:15
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-183592 (URN)978-91-7595-906-1 (ISBN)
Public defence
2016-04-26, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160318

Available from: 2016-03-18 Created: 2016-03-17 Last updated: 2016-03-18Bibliographically approved

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