Experimental and numerical study of fluid flow, solute transport, and mineral precipitation in fractured porous media

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Author
Date
2020Type
- Doctoral Thesis
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Abstract
Geothermal energy can replace fossil fuels, thus reducing CO$_2$ emissions and
mitigating greenhouse effects. Similar to other subsurface reservoirs,
geothermal reservoirs often consist of fractures,i.e. high-permeable conduits,
and porous rock materials, i.e. low-permeable matrices. In such a fractured
porous medium, mass and energy are considered to be transported mainly through
the open fracture networks, while the rock matrices often serve as the source of
mass and energy. With the aim of filling the knowledge gap in fluid flow, solute
transport, and mineral precipitation, this thesis reports on an integrated
experimental-numerical study of pore-scale flow and transport properties in a
fractured porous medium.
For our experimental studies, we use a well-defined, reproducible, 3D-printed
medium which consists of two (i.e., high- and low-permeability) matrices, each containing one flow-through and one dead-end fracture.
To conduct experimental measurements of fluid flow and solute transport, we
employ Particle Image Velocimetry (PIV), Laser-induced Fluorescence (LIF), and
Magnetic Resonance Imaging (MRI). In this context, an image analysis framework
and a novel PIV method, i.e., temporo-ensemble method, have been developed to
substantially increase the spatial resolution of velocity vectors per unit
area/volume. We compare the velocity measurements obtained with PIV and MRI,
and use the PIV measurements to calculate fluid exchange, and the dimensionless
Beavers-Joseph velocity-slip ($\alpha$) and Whitaker stress-jump ($\beta$) coefficients
at the fracture-matrix interfaces. Under the current definition of the
boundaries at the physical fracture-matrix interfaces, the coefficients $\alpha$
and $\beta$ are incapable of explaining and predicting the fluid exchange
between fractures and matrices. Consequently, a new quantity is proposed to
relate the shear rates inside the fractures and inside the matrices around the
fracture-matrix interfaces. LIF experiments are conducted to monitor the
transport of tracer dyes during the progression and depletion processes. Based
on the LIF measurements, the temporal and spatial evolution of the displacement
front, moments of the concentration field, and solute mass fractions are
elucidated. We explore the non-Fickian behavior of tracer dyes and associate it
to the evolution of relative concentration in different regions of the medium.
In our numerical work, we use Lattice-Boltzmann Methods (LBMs) to simulate
fluid flow, solute transport, and mineral precipitation in the 3D-printed porous medium. We focus on the feedback loop of fluid flow, solute transport, mineral precipitation, pore-space geometry changes, and permeability. Our simulations are carried out over a wide range of species diffusivity and reaction rates from advection- to diffusion-dominated, and from transport- to reaction-limited, respectively. Using the ratio of Damköhler (Da) and the Peclet number (Pe) , the numerical results exhibit four distinct precipitation patterns, namely (1) no precipitation (Da/Pe $<1$), (2) near-inlet clogging (Da/Pe $>100$), (3) fracture isolation ($1<$ Da/Pe $<100$ and Pe $>1$), and (4) diffusive precipitation ($1<$ Da/Pe $<100$ and Pe $<0.1$). Finally, this thesis establish a general relationship among mineral precipitation pattern, porosity, and permeability using statistical and spatial distribution.
This doctoral thesis deepens the understanding of pore-scale processes using
numerical simulations and experimental measurements in fractured porous media.
In particular, this thesis has developed a novel experimental approach for validation of numerical and theoretical
models. These results are of upmost importance to a wide range of
scientific and industrial applications such as, but not limited to, geological
CO$_2$ sequestration, hydrogeology, geothermal energy utilization, geochemistry,
groundwater supply, subsurface contaminant migration, hydrometallurgical
recovery, and evaporation from soil matrices. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000465063Publication status
publishedExternal links
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Contributors
Examiner: Saar, Martin O.
Examiner: Kong, Xiang-Zhao

Examiner: Hassanizadeh, S. Majid
Examiner: Singh, Kamaljit
Publisher
ETH ZurichSubject
fractured porous media; Particle image velocimetry (PIV); MRI (magnetic resonance imaging); Lattice Boltzmann method; Mineral precipitation patterns; laser induced fluorescenceOrganisational unit
09494 - Saar, Martin O. / Saar, Martin O.
Funding
ETH-12 15-2 - Simultaneous visualization of fluid flow and mineral precipitation in fractured porous media - a novel method with implication for geothermal energy use and carbon storage (ETHZ)
Related publications and datasets
Is supplement to: http://hdl.handle.net/20.500.11850/386605
Is supplement to: http://hdl.handle.net/20.500.11850/316588
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ETH Bibliography
yes
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