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Numerical modeling of stress effects on solute transport in fractured rocks
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
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
2011 (English)In: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 38, no 2, p. 113-126Article in journal (Refereed) Published
Abstract [en]

The effects of stress/deformation on fluid flow and contaminant transport in fractured rocks is one of the major concerns for performance and safety assessments of many subsurface engineering problems, especially radioactive waste disposal and oil/gas reservoir fields. However, very little progress has been made to study this issue due to difficulties in both experiments and numerical modeling. The objective of this study is to systematically investigate the influence of stress on solute transport in fractured rocks for the first time, considering different stress and hydraulic pressure conditions. A hybrid approach combining discrete element method (DEM) for stress-flow simulations and a particle tracking algorithm is developed. The impact of matrix diffusion (diffusion of molecular size solutes in and out of the rock matrix, and sorption onto the surface of micropores in rock matrix) is also included. The numerical results show that stress not only significantly changes the solute residence time through the fracture networks, but also changes the solute travel paths. Matrix diffusion plays a dominant role in solute transport when the hydraulic gradient is small, which is often encountered in practice.

Place, publisher, year, edition, pages
2011. Vol. 38, no 2, p. 113-126
Keyword [en]
Stress effects, Solute transport, Coupled stress-flow-transport processes, Matrix diffusion, Discrete fracture network, Fractured rocks
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:kth:diva-31356DOI: 10.1016/j.compgeo.2010.10.001ISI: 000287633700002Scopus ID: 2-s2.0-79551479285OAI: oai:DiVA.org:kth-31356DiVA, id: diva2:404400
Note
QC 20110317Available from: 2011-03-17 Created: 2011-03-14 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Stress Effects on Solute Transport in Fractured rocks
Open this publication in new window or tab >>Stress Effects on Solute Transport in Fractured rocks
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The effect of in-situ or redistributed stress on solute transport in fractured rocks is one of the major concerns for many subsurface engineering problems. However, it remains poorly understood due to the difficulties in experiments and numerical modeling. The main aim of this thesis is to systematically investigate the influences of stress on solute transport in fractured rocks, at scales of single fractures and fracture networks, respectively.

For a single fracture embedded in a porous rock matrix, a closed-form solution was derived for modeling the coupled stress-flow-transport processes without considering damage on the fracture surfaces. Afterwards, a retardation coefficient model was developed to consider the influences of damage of the fracture surfaces during shear processes on the solute sorption. Integrated with particle mechanics models, a numerical procedure was proposed to investigate the effects of gouge generation and microcrack development in the damaged zones of fracture on the solute retardation in single fractures. The results show that fracture aperture changes have a significant influence on the solute concentration distribution and residence time. Under compression, the decreasing matrix porosity can slightly increase the solute concentration. The shear process can increase the solute retardation coefficient by offering more sorption surfaces in the fracture due to gouge generation, microcracking and gouge crushing.

To study the stress effects on solute transport in fracture systems, a hybrid approach combing the discrete element method for stress-flow simulations and a particle tracking algorithm for solute transport was developed for two-dimensional irregular discrete fracture network models. Advection, hydrodynamic dispersion and matrix diffusion in single fractures were considered. The particle migration paths were tracked first by following the flowing fluid (advection), and then the hydrodynamic dispersion and matrix diffusion were considered using statistic methods. The numerical results show an important impact of stress on the solute transport, by changing the solute residence time, distribution and travel paths. The equivalent dispersion coefficient is scale dependent in an asymptotic or exponential form without stress applied or under isotropic compression conditions. Matrix diffusion plays a dominant role in solute transport when the hydraulic gradient is small.

Outstanding issues and main scientific achievements are also discussed.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. p. x, 108
Series
Trita-LWR. PHD, ISSN 1650-8602
Keyword
Fractured rocks, Solute transport; Stress effects, Coupled stress-flow-transport processes; Analytical solution; Particle mechanics model; Fracture surface damage; Discrete element method; Particle tracking method
National Category
Civil Engineering
Identifiers
urn:nbn:se:kth:diva-42361 (URN)978-91-7501-099-1 (ISBN)
Public defence
2011-11-04, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20111011Available from: 2011-10-11 Created: 2011-10-10 Last updated: 2011-10-11Bibliographically approved

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