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Evolution of fracture aperture mediated by dissolution in a coupled flow channel–rock matrix–stagnant zone system
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.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.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Fracture aperture is an important entity controlling fluid flow in natural fractures in rocks. The aperture of fractures in crystalline rocks may decrease or increase by different mechanical and chemical mechanisms. A model to describe the evolution of fracture aperture mediated by dissolution and precipitation is presented in this study. It includes advective flow in the fracture that can carry in or away dissolved minerals. The model also accounts for the fact that dissolved minerals in the fracture plane, in both flow channel and stagnant water zone, can diffuse into the adjacent porous rock matrix. The analytical solution obtained in the Laplace space is then used to study 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. It is found that the times involved for any changes in fracture aperture are very much larger than the times needed for concentrations of dissolved minerals to reach steady state in the rock matrix, the stagnant water zone and the flow channel. This suggests that the steady state model can be used to assess the evolution of concentration of dissolved minerals in the rock fracture. Moreover, it is shown that diffusion into the rock matrix, which acts as a strong sink or source for dissolved minerals, clearly dominates the rate of concentration change and consequently the rate of evolution of the fracture aperture.

Keyword [en]
Fracture aperture, Dissolution, Rock matrix diffusion, Fluid flow, Channeling, Modeling
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-183773OAI: oai:DiVA.org:kth-183773DiVA: diva2:913009
Note

QS 2017

Available from: 2016-03-18 Created: 2016-03-18 Last updated: 2016-03-18Bibliographically 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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Mahmoudzadeh, BatoulLiu, LongchengMoreno, LuisNeretnieks, Ivars
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