Abstract: Spectral induced polarization of calcite precipitation in a porous media

Event: AGU Fall Meeting, Washington DC (USA), December 2018
Abstract by Satoshi Izumoto , Johan Alexander Huisman, Egon Zimmermann, Yves Méheust, Francesco Gomez, Joris Heyman, Wu Yuxin, Harry Verecken, Tanguy Le Borgne


Abstract

Induced calcite precipitation is used in a range of in-situ geotechnical applications to modify the mechanical and hydrological properties of soils and fractured rocks. It is also a model process for mixing-induced biogeochemical reactions that occur naturally in a broad range of hydrological systems. Laboratory experiments have shown that spectral induced polarization (SIP) measurements can be used to monitor calcite precipitation. However, the results of the limited number of previous studies investigating the SIP response of calcite precipitation were not fully consistent.

This study aims to investigate how the SIP response of calcite depends on solute composition, since this may explain the differences in SIP response observed in previous studies. For this, a five-phase experiment with SIP measurements on a column filled with sand was performed.

In phase I, calcite precipitation was generated for a period of 12 days by injecting Na2CO3 and CaCl2 solutions through two different ports. This resulted in a well-defined calcite precipitation front, which was associated with an increase in the imaginary conductivity in the kHz frequency range.

In phase II, the injected solutions were stepwise diluted. This resulted in a clear decrease in the imaginary conductivity.

In phase III, the injection of the two solutions was stopped. Nevertheless, calcite precipitation continued and solute concentrations in the mixing zone decreased. As in phase II, this led to a decrease in the imaginary conductivity.

In phase IV, the injection rate of the Na2CO3 solution was reduced to shift the mixing zone away from the calcite precipitation front, which also decreased the imaginary conductivity.

Finally, the column was flushed with a solution in equilibrium with calcite in phase V, which led to a very small SIP signal.

These results imply that the SIP response of calcite is very sensitive to the solution composition near the precipitates, which may explain the previously reported conflicting results. In a next step, the relationship between SIP response, volume of calcite, and solute composition will be quantitatively investigated using SIP measurements on a 2D milifluidic cell with an artificial porous media that allows visualizing the temporal dynamics of calcite precipitation.


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Abstract: Updating structural uncertainty through dimension reduction of geophysical data

Event: AGU Fall Meeting, Washington DC (USA), 2018
Abstract by Frédéric Nguyen, Jorge Lopez-Alvis, Thomas Hermans


Abstract

When studying uncertainty in geosciences we usually have to deal with: (1) very high dimensionality in both data and parameters, (2) complex models to describe the subsurface, and (3) nonlinear forward models to simulate data.

All these facts hinder the quantification of uncertainty as the estimation of thecorresponding joint probability distribution is not straightforward. In this study, we follow a Bayesian approach to obtain the marginal probability distribution of structural parameters given the geophysical data. We approximate this distribution with a combination of Monte Carlo sampling, data dimension reduction and kernel density estimation. We use synthetic GPR cross-borehole traveltime data with added noise and consider two structural parameters: (1) geological scenario, a discrete parameter, and(2) preferential orientation, a continuous parameter.

The focus of this work is in comparing different dimension reduction techniques to assess which one gives the most accurate estimation of structuraluncertainty. We generate the Monte Carlo samples starting with the structural parameter, then applyingmultiple-point geostatistics to obtain the subsurface realization and finally simulating traveltime data with the geophysics forward model. We follow four different strategies: (1) apply multidimensionalscaling directly on traveltime data (2) use histograms of traveltime data as features and then apply multidimensional scaling to further reduce dimensions, (3) transform data into geophysical images bymeans of regularized inversion and then apply multidimensional scaling, and (4) obtain connectivityfeatures from these geophysical images and then apply multidimensional scaling.

Using defined features results in the most accurate estimations of structural uncertainty as measured through cross-validation, both for the histogram and the connectivity, but working with the former is computationallymore efficient since it does not require obtaining the geophysical image. Data dimension reduction is useful when approximating the marginal probability distribution of structural parameters but the accuracy of this distribution depends on the ability of the dimension reduction technique to retain themost informative part of the data with respect to the parameter of interest.


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Abstract: Spectral induced polarization response of calcite precipitation

Event: 5th International Workshop on Induced Polarization, Newark (USA), October 2018
Abstract by Satoshi Izumoto, Johan Alexander Huiman, Egon Zimmermann, Odilia Esser, Franz-Hubert Haegel, Harry Vereecken


Abstract

Induced calcite precipitation is used in a range of geotechnical applications to improve the mechanical properties of porous media. It has been shown that spectral induced polarization (SIP) allows to monitor calcite precipitation, although results were partly inconsistent. Therefore, this study aims to investigate how the SIP response of calcite depends on solute composition, since this may explain the differences in previous studies. SIP measurements were made on a column filled with sand while calcite precipitation was created by injecting Na2CO3 and CaCl2 solutions through two different ports. The experiment consisted of five phases. In phase I, calcite precipitation was generated for a period of 12 days. This resulted in a well-defined calcite precipitation front, which was associated with an increase in the imaginary conductivity. In phase II, the injected solutions were increasingly diluted. This resulted in a clear decrease in imaginary conductivity. In phase III, the injection of the two solutions was stopped. Nevertheless, calcite precipitation continued and solute concentrations in the mixing zone decreased. As in phase II, this led to a decrease in the imaginary conductivity. In phase IV, the injection rate of the Na2CO3 solution was reduced to shift the mixing zone, which also decreased the imaginary conductivity. Finally, the column was flushed with a solution in equilibrium with calcite in phase V, which led to a very small SIP signal. These results imply that calcite only generates a SIP response when it is in contact with solution which is strongly oversaturated with respect to calcite.


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Presentation: Fractured aquifer heterogeneity characterization for advanced transport modelling based on multiple single fracture tracer tests

Event: 45th IAH – Korea (International Association of Hydrogeologists), 2018
Presentation by Richard Hoffmann, Pascal Goderniaux, Angélique Poulain, Alain Dassargues


Abstract

Assessing fractured rocks, like a complex double porosity chalk, requires an advanced heterogeneity characterization and preferential pathway quantification. This contributes for reducing the uncertainty of transport predictions for protecting this excellent drinking water suppliers. With flowmeter tests and optical imaging, a horizontal main fracture between two adjacent 7.55 m distant wells is figured out. Injecting jointly 70 h heat and two solute pulses in a dipole configuration shows a strong heat delay and temperature rebound due to matrix reactions. Using dissolved gases jointly with a solute show, that the higher the tracer diffusivity the higher the confronted flow heterogeneity.

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Presentation: The double porosity of the chalk and its influence on solute and heat transport

Event: 6th International Geologica Belgica Meeting 2018
Presentation by Richard Hoffmann, Pascal Goderniaux, Pierre Jamin, Alain Dassargues


Abstract

Fractured rock aquifers like the Belgium chalk can act as important drinking water suppliers and for protection an advanced imaging of double porosity effects is important for transport predictions with reduced uncertainty. Between two adjacent 50 m-deep 7.55 m distant boreholes a with flowmeter tests and optical imagining figured out open main fracture is for multiple tracer tests isolated using an inflatable double packer system. Injecting in a dipole configuration continuously 50 °C hot water for 70 h jointly with two pulse fluorescent dye tracer (uranine) shows a 12.5 hours arrival delay of the heat compared to the solute. Stopping heat injection shows a strong direct temperature decrease followed by slow temperature rebound over several days. Stored heat around the injection well is pulled and the matrix reacts slowly by contribute stored heat to the colder water drawn from the surroundings.


ESR11_Abstract_GB2018_DoublePorChalk


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