Comparison of Surface Roughness and Transport Processes of Sawed, Split and Natural Sandstone Fractures

In single fractures, dispersion is often linked to the roughness of the fracture surfaces and the resulting local aperture distribution. To experimentally investigate the effects of diverse fracture types and surface morphologies in sandstones, three fractures were considered: those generated by sawing and splitting, and a natural sedimentary fracture. The fracture surface morphologies were digitally analyzed and the hydraulic and transport parameters of the fractures were determined from Darcy and the tracer tests using a fit of a continuous time random walk (CTRW) and a classical advection–dispersion equation (ADE). While the sawed specimen with the smoothest surface had the smallest dispersivity, the natural fracture has the largest dispersivity due to strong anisotropy and non-matching fracture surfaces, although its surface roughness is comparable to the split specimen. The parameterization of the CTRW and of the ADE agree well for β > 4 of the truncated power law. For smaller values of β, non-Fickian transport processes are dominant. Channeling effects are observable in the tracer breakthrough curves. The transport behavior in the fractures is controlled by multiple constraints such as several surface roughness parameters and the equivalent hydraulic aperture.

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Preselection of a sorption model based on a column test: the algorithm and an example of its application

Hydrogeology Journal ◽

10.1007/s10040-021-02338-8 ◽

2021 ◽

Author(s):

Marek Marciniak ◽

Monika Okońska ◽

Mariusz Kaczmarek

Keyword(s):

Mathematical Model ◽

Breakthrough Curve ◽

Breakthrough Curves ◽

Transport Processes ◽

Column Experiments ◽

Transport Parameters ◽

Sorption Model ◽

Advection Dispersion ◽

Conservative Tracer ◽

Reactive Tracer

AbstractIn order to describe the contamination of saturated porous media, it is necessary to find an appropriate mathematical model that includes processes occurring in aquifers, such as advection, dispersion, diffusion, and various kinds of sorption. The identification of parameters of those processes is possible through laboratory column experiments, which result in records of breakthrough curves for a conservative tracer and a reactive tracer. An algorithm leading to the preliminary selection of the mathematical model that best describes transport processes of the reactive tracer in the experimental column is proposed in this article. A study published previously presented a sensitivity analysis for an arbitrarily adopted variability of the transport parameters. The analysis involved examining changes in the shape of breakthrough curves caused by the alteration of each parameter value. Specially defined indicators called descriptors were proposed to quantitatively describe the breakthrough curves. Then, formulas were proposed to determine the percentage deviations of descriptors of the breakthrough curve obtained for the reactive tracer in relation to the descriptors of the breakthrough curve of the conservative tracer. In the work described in this article, the deviations are analyzed and an algorithm is proposed that allows the preselection of the most suitable sorption model out of the five discussed simple (one-site) and six hybrid (two-site) models. The algorithm can facilitate and accelerate the interpretation of column experiments of contaminant transport in a porous medium. An example is provided to illustrate the usability of the proposed algorithm.

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Use of close-range photogrammetry to characterize fracture surfaces

BSGF - Earth Sciences Bulletin ◽

10.2113/175.5.481 ◽

2004 ◽

Vol 175 (5) ◽

pp. 481-490 ◽

Cited By ~ 1

Author(s):

Frédéric Filipe ◽

Judith Sausse

Keyword(s):

Surface Roughness ◽

Natural Fracture ◽

Fracture Plane ◽

Natural Fractures ◽

Fracture Surfaces ◽

Close Range Photogrammetry ◽

Contact Points ◽

Close Range ◽

Void Geometry ◽

Non Destructive

Abstract Natural fractures are characterized by rough surfaces and complex fluid flows. A large distribution of apertures (residual voids) within their walls and the presence of contact points produce heterogeneous flows (channelling). The resulting permeabilities, porosities or fluid-rock exchange surfaces cannot be realistically modelled by parallel and smooth plate models. It is therefore very important to better constrain models of the fracture planes : asperity heights and aperture distribution to be able to fix specific models of permeability in specific fracture void geometry. In this approach, a precise description of the fracture surface planes is given by providing some new quantitative data of surface roughness in the case of natural fractures. Studied fractures are sampled in a granite and a sandstone in the deep basement of the Hot Dry Rock site of Soultzsous-Forêts (Bas-Rhin, France). An original use of close-range photogrammetry is performed to quantify XYZ data on fracture walls. This methodology is presented as a non destructive, precise and accurate technology to quantify some digital terrain models (DTM) of the fracture plane topography. XYZ results are statistically treated in terms of surface roughness and tortuosity and are compared for different rocks to previous data obtained by mechanical profilometry. The results shows that the photogrammetric approach gives same order of asperity heights magnitudes as profilometry despite a shift towards more important values of roughness when close range photogrammetry uses relative autocorrelation models. The advantage of photogrammetry is that this technique gives very quick results and is non destructive when thin alteration or pulverulent deposits are present within fracture walls or in the rock matrix. The disadvantage is that a slight smoothing of data is inherent to an absolute model calibration. Finally only relative 300*300 DTM are finally chosen to match profilometry data because of their higher precision in terms of micro roughness description to compare natural fracture surfaces. In the objective of a classification of fracture roughness in specific geological contexts, the photogrammetric approach gives a good estimation of different classes of roughness in function of rock alteration and type.

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Determination of rock transport parameters using short-term radionuclides and nanoparticles

10.5194/egusphere-egu2020-18967 ◽

2020 ◽

Author(s):

Milan Zuna ◽

David Dobrev ◽

Václava Havlová ◽

Pavel Kůs ◽

Daniela Doubravová ◽

...

Keyword(s):

3D Visualization ◽

Tracer Tests ◽

Transport Processes ◽

Detection Methods ◽

Transport Parameters ◽

Detection Techniques ◽

Rock Samples ◽

Radionuclide Distribution ◽

On Line ◽

Computational Analyses

The aim of the project is to develop and test the short-lived radionuclides in order to describe the contaminant transport processes radionuclides, tracer metals and nanoparticles in the environment. Furthermore, the aim is also to develop on-line detection methods to quantify the processes that influence their movement towards the biosphere. Use of short lived radionuclide in tracer tests brings an advantage of excellent detection and avoids contamination of rock samples/environment during experiments.The research is focused predominantly on radio-tracers in various forms (solute/nanoparticles) and on development of advanced detection techniques for their monitoring and display. The following pre-selected radionuclides were considered for potential &#160;irradiation (24Na, 42K, 64Cu, 72Ga, 76As, 82Br, 99Mo, 140La, 142Pr, 198Au, 166Ho, 188Re, 153Sm). After thorough evaluation, holmium and rhenium compounds were selected for irradiation in the LVR- 15 reactor (CV&#344; &#344;e&#382;), namely holmium oxide (Ho2O3) and ammonium perphenate (NH4ReO4). Those compounds were selected based on the computational analyses. Solutions of 50, 200, 300 MBq (188Re) and 300 MBq (166Ho) were finally prepared for detection tests. Paralelly, a method for the preparation of chromium oxide nanoparticles was introduced and tested.A miniaturized spectral camera MiniPIX TPX3 has been developed for radionuclide detection. It is similar to the MiniPIX with a Timepix3 chip, a new generation of chips developed by the collaboration Medipix3. The camera has a resolution of 256 x 256 pixels with a pixel size of 55 x 55 &#181;m (2 mm CdTe sensor).The developed measurement system enables on-line monitoring and 3D visualization of the radioactivity distribution in the studied rock samples with respect to radionuclide distribution within the rock. Various measurement configurations were tested with respect to source activity, detector/collimator distance, and rock thickness to find optimal measurement parameters.<ul><li>The work described herein was funded by the project of the Ministry of Industry and Trade in the TRIO program (FV30430)</li> </ul>

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Experimental Study and Models Comparison for Solute Transport through Riparian Zones

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1073-1076.1604 ◽

2014 ◽

Vol 1073-1076 ◽

pp. 1604-1608

Author(s):

Zhou Chen ◽

Jin Guo Wang ◽

Wen Zhang Zhang ◽

Jia Hui Shi

Keyword(s):

Solute Transport ◽

Riparian Zone ◽

Tracer Tests ◽

Breakthrough Curves ◽

Advection Dispersion ◽

Early Arrival ◽

Models Comparison ◽

Silt Layer ◽

Better Than ◽

Peak Value

Solute transport through riparian zone was studied experimentally and numerically with the consideration of silt layer. The silt layer had markable change on flow field and lead to a significant variation of the breakthrough curves (BTCs). BTCs of solute tracer tests show non-Fickian features as early arrival of peak value and long tailings. BTCs were fitted by advection dispersion equation (ADE), mobile and immobile model (MIM) and the continuous time random walk (CTRW) models. MIM and CTRW can fit BTCs better than ADE and MIM fit better on the capture of the peak value and CTRW fit better in description of the long tailing.

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Experimental Reproducibility and Natural Variability of Hydraulic Transport Properties of Fractured Sandstone Samples

Geosciences ◽

10.3390/geosciences10110458 ◽

2020 ◽

Vol 10 (11) ◽

pp. 458

Author(s):

Sascha Frank ◽

Thomas Heinze ◽

Mona Ribbers ◽

Stefan Wohnlich

Keyword(s):

Fracture Surface ◽

Surface Morphology ◽

Transport Properties ◽

Natural Variability ◽

Transport Processes ◽

Fracture Aperture ◽

Hydraulic Transport ◽

Fracture Surface Morphology ◽

Transport Parameters ◽

Hydraulic Aperture

Flow and transport processes in fractured systems are not yet fully understood, and it is challenging to determine the respective parameters experimentally. Studies on 10 samples of 2 different sandstones were used to evaluate the reproducibility of tracer tests and the calculation of hydraulic transport properties under identical boundary conditions. The transport parameters were determined using the advection–dispersion equation (ADE) and the continuous time random walk (CTRW) method. In addition, the fracture surface morphology and the effective fracture aperture width was quantified. The hydraulic parameters and their variations were studied for samples within one rock type and between both rock types to quantify the natural variability of transport parameters as well as their experimental reproducibility. Transport processes dominated by the influence of fracture surface morphology experienced a larger spread in the determined transport parameters between repeated measurements. Grain size, effective hydraulic aperture and dispersivity were identified as the most important parameters to evaluate this effect, as with increasing fracture aperture the effect of surface roughness vanishes and the experimental reproducibility increases. Increasing roughness is often associated with the larger effective hydraulic aperture canceling out the expected increased influence of the fracture surface morphology.

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Use of column experiments to investigate the fate of organic micropollutants – a review

10.5194/hess-2016-196 ◽

2016 ◽

Cited By ~ 4

Author(s):

Stefan Banzhaf ◽

Klaus H. Hebig

Keyword(s):

Boundary Conditions ◽

Field Experiments ◽

Breakthrough Curves ◽

Transport Processes ◽

Column Experiments ◽

Organic Micropollutants ◽

Transport Parameters ◽

Column Studies ◽

Set Up ◽

The Individual

Abstract. Although column experiments are frequently used to investigate the transport of organic micropollutants, little guidance is available on what they can be used for, how they should be set up, and how the experiments should be carried out. This review covers the use of column experiments to investigate the fate of organic micropollutants. Alternative setups are discussed together with their respective advantages and limitations. An overview is presented of published column experiments investigating the transport of organic micropollutants, and suggestions are offered on how to improve the comparability of future results from different experiments. The main purpose of column experiments is to investigate the transport and attenuation of a specific compound within a specific sediment or substrate. The transport of (organic) solutes in groundwater is influenced by the chemical and physical properties of the compounds, the solvent (i.e. the groundwater, including all solutes), and the substrate (the aquifer material). By adjusting these boundary conditions a multitude of different processes and related research questions can be investigated using a variety of experimental setups. Apart from the ability to effectively control the individual boundary conditions, the main advantage of column experiments compared to other experimental setups (such as those used in field experiments, or in batch microcosm experiments) is that conservative and reactive solute breakthrough curves can be derived, which represent the sum of the transport processes. There are well-established methods for analyzing these curves. The effects observed in column studies are often a result of dynamic, non-equilibrium processes. Time (or flow velocity) is an important factor, in contrast to batch experiments where all processes are observed until equilibrium is reached in the substrate-solution system. Slight variations in the boundary conditions of different experiments can have a marked influence on the transport and degradation of organic micropollutants. This is of critical importance when comparing general results from different column experiments investigating the transport behavior of a specific organic compound. Such variations unfortunately mean that the results from most column experiments are not transferable to other hydrogeochemical environments but are only valid for the specific experimental setup used. Column experiments are fast, flexible, and easy to manage; their boundary conditions can be controlled and they are cheap compared to extensive field experiments. They can provide good estimates of all relevant transport parameters. However, the obtained results will almost always be limited to the scale of the experiment and not directly transferrable to field scales as too many parameters are exclusive to the column setup. The challenge for the future is to develop standardized column experiments on organic micropollutants in order to overcome these issues.

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Breakthrough Investigation of Advective and Diffusive Transport in a Porous Matrix with a Crack

Fluids ◽

10.3390/fluids6100358 ◽

2021 ◽

Vol 6 (10) ◽

pp. 358

Author(s):

Ekkehard Holzbecher

Keyword(s):

Flow Direction ◽

Porous Matrix ◽

Systematic Investigation ◽

Breakthrough Curves ◽

Transport Processes ◽

Free Fluid ◽

Transport Parameters ◽

Transport Patterns ◽

Set Up ◽

Application Fields

Fluid flow and transport processes in fractured porous media are of particular interest for geologists and in the material sciences. Here a systematic investigation is presented, dealing with a generic geometric set-up of a porous matrix with a crack. In such a combined porous medium/free fluid system flow patterns have been examined frequently, while the resulting transport patterns have attracted less attention. Using numerical modeling with finite elements the problem is approached using a dimensionless formulation. With a reduced number of dimensionless parameter combinations (Darcy-, Peclet- and Reynolds-numbers) solution dependencies are examined in parametric sweeps. Breakthrough curves are fitted in comparison to those of 1D model approaches, yielding effective diffusivities and velocities. The computations reveal highest sensitivity concerning the angle between crack axis and flow direction, followed by the Peclet number and the crack axes ratio. As a dimensionless representation is used the results are scale independent. Thus, they deliver estimations concerning effective heat and solute transport parameters that can be relevant in all application fields.

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Solute transport in dual conduit structure: experiment and modelling

10.5194/egusphere-egu2020-21513 ◽

2020 ◽

Author(s):

Chaoqi Wang ◽

Xiaoguang Wang ◽

Samer Majdalani ◽

Vincent Guinot ◽

Hervé Jourde

Keyword(s):

Solute Transport ◽

Peak Concentration ◽

Dispersion Model ◽

Tracer Tests ◽

Breakthrough Curves ◽

Physical Models ◽

Length Ratio ◽

Tracer Transport ◽

Transport Parameters ◽

Total Length

An important phenomenon often encountered when interpreting tracer tests in karst aquifers is the occurrence of dual-peaked breakthrough curves (BTCs). The dual-peaked BTCs are usually attributed to tracer transport through a conduit system consisting of a dual-conduit structure: an auxiliary conduit that deviates from the main conduit at the upstream and converges back at the downstream. In order to understand how the geometric configuration of the dual-conduit structure influences the BTCs, laboratory experiments utilizing plastic tubes were conducted. The physical models were constructed by varying: 1) the total length of the conduits, while fixing the length ratio; 2) length ratio between the two conduits, while fixing the length of the main conduit; and 3) conduits connection angle. The tracer experiments are then fitted by a Multi-Region Advection Dispersion model and a Transfer Function model to derive effective transport parameters. This allows us to quantitatively compare the experimental results, and thus to analyse the conduit geometry effects on solute transport and to compare the performance of the two models.Results show that the dual-conduit structure causes the double peaks of BTCs. Keeping the length ratio of the two conduits and increasing their total length leads to a larger separation of the two peaks of the BTCs. Keeping the length of main conduit while increasing the length of the secondary conduit causes similar effects. As (&#952;1-&#952;2) increases, the first peak concentration value decreases, the second peak concentration value increases.Keywords: karst, lab experiment, dual-peaked BTCs, modelling

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Investigating surface morphology and transport parameters of single fractures

10.5194/egusphere-egu2020-5229 ◽

2020 ◽

Author(s):

Sascha Frank ◽

Thomas Heinze ◽

Mona Ribbers ◽

Stefan Wohnlich

Keyword(s):

Fracture Surface ◽

Surface Morphology ◽

Transport Processes ◽

Coarse Grained ◽

Hydraulic Permeability ◽

Transport Parameters ◽

Flow And Transport ◽

Fracture Surfaces ◽

Depth Analysis ◽

Surface Images

In order to obtain a deeper understanding of flow and transport processes in fractures, experimental investigations and numerical modelling have been carried out focusing on the effects of fracture surface morphology. To determine a possible relationship between the roughness of fracture surfaces and hydraulic and transport parameters, two different types of sandstones has been investigated. The sandstones were a coarse-grained, inhomogeneous and strongly anisotropic Flechtinger sandstone (Bebertal, Germany) and a fine-grained, rather homogeneous, isotropic Remlinger sandstone (W&#252;rzburg, Germany).The sandstones were first cored with a diameter of 100 mm and a height of 150 mm and split into individual fissures. The resulting fracture surfaces were scanned using a 3D scan and surface images were generated. These surface images were used to determine the Joint Roughness Coefficient (JRC) and other measures of roughness. The roughness has been characterized along 1D profiles in each direction. Mean values and spread have been calculated for each surface. The fracture surfaces are self-affine so that little variation along both surfaces has been determined. Both sandstone halves were then joined together and the reassembled fractured rock core was examined experimentally. Darcy and tracer tests were carried out for the investigations and hydraulic (permeability, fracture opening width) and transport parameters (flow velocity, dispersivity, dispersion coefficient) were derived from the results and compared with each other and with the surface roughness. For the Darcy experiments, the cores were clamped in a specially designed Darcy cell and calculations were done based on equations for the cubic law. The transport parameters were determined using a salt tracer and by evaluating the breakthrough curves, recorded by measuring the electrical conductivity, with the moment analysis.First results show a very clear separation between Remlinger and Flechtinger sandstone. Thus, the finer-grained Remlinger cores show lower JRC than the coarser-grained Flechtinger, as expected. Further, the Flechtinger cores have larger aperture opening widths than the Remlinger cores. First comparisons show a tendency to higher dispersivity with higher JRC, and thus with the Flechtinger than in the case of the Remlinger cores. Though, in-depth analysis reveals that the JRC alone might not be sufficient to characterize transport processes along fractures, as anisotropy, as well as roughness variability along the fracture surface can influence flow and transport. Numerical modeling of flow paths across the fracture surface are used to relate experimental results with the flow pattern across the rough surface.

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Spatially resolved information on karst conduit flow from in-cave dye tracing

Hydrology and Earth System Sciences ◽

10.5194/hess-18-435-2014 ◽

2014 ◽

Vol 18 (2) ◽

pp. 435-445 ◽

Cited By ~ 19

Author(s):

U. Lauber ◽

W. Ufrecht ◽

N. Goldscheider

Keyword(s):

Land Surface ◽

Karst Aquifer ◽

Tracer Tests ◽

Breakthrough Curves ◽

Transport Parameters ◽

Mean Flow ◽

Dye Tracing ◽

Flow And Transport ◽

Spatially Resolved ◽

Order Of Magnitude

Abstract. Artificial tracers are powerful tools for investigating karst systems. Tracers are commonly injected into sinking streams or dolines, while springs serve as monitoring sites. The obtained flow and transport parameters represent mixed information from the vadose, epiphreatic and phreatic zones (that is, the aquifer remains a black box). Accessible active caves constitute valuable but underexploited natural laboratories to gain detailed insights into the hydrologic functioning of the aquifer. Two multi-tracer tests in the catchment of a major karst spring (Blautopf, Germany) with injections and monitoring in two associated water caves aimed at obtaining spatially and temporally resolved information on groundwater flow in different compartments of the system. Two tracers were injected into the caves to characterize the hydraulic connections between them and with the spring. Two injections at the land surface, far from the spring, aimed at resolving the aquifer's internal drainage structure. Tracer breakthrough curves were monitored by field fluorimeters in caves and at the spring. Results demonstrate the dendritic drainage structure of the aquifer. It was possible to obtain relevant flow and transport parameters for different sections of this system. The highest mean flow velocities (275 m h−1) were observed in the near-spring epiphreatic section (open-channel flow), while velocities in the phreatic zone (pressurized flow) were one order of magnitude lower. Determined conduit water volumes confirm results of water balances and hydrograph analyses. In conclusion, experiments and monitoring in caves can deliver spatially resolved information on karst aquifer heterogeneity and dynamics that cannot be obtained by traditional investigative methods.

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