Time‐domain electromagnetic imaging of a clayey confining bed in a brackish environment: A case study in the Kairouan Plain Aquifer (Kelbia salt lake, Tunisia)

Finco, Cécile; Pontoreau, Coralie; Schamper, Cyril; Massuel, Sylvain; Hovhannissian, Gaghik; Réjiba, Fayçal

doi:10.1002/hyp.13303

Cited by 8 publications

(5 citation statements)

References 33 publications

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“…In geophysics, the most common methods to identify the presence of clay minerals non‐intrusively in the field are electrical and electromagnetic methods (e.g., Auken et al., 2017): direct current electrical resistivity tomography (ERT) (e.g., Batayneh, 2006), induced polarization (IP) (e.g., Lévy, Maurya, et al., 2019; Okay et al., 2013), time‐domain electromagnetics (TDEM) (e.g., Finco et al., 2018), frequency domain (FDEM) electromagnetics (e.g., Spichak & Manzella, 2009), and ground penetrating radar (GPR) (e.g., Looms et al., 2018). However, if clays are usually associated to high electrical conductivity zones, they can be mistaken with highly mineralized pore water when only the real electrical conductivity is considered.…”

Section: Introductionmentioning

confidence: 99%

Spectral Induced Polarization Characterization of Non‐Consolidated Clays for Varying Salinities—An Experimental Study

et al. 2021

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Clay material characterization is of importance for many geo‐engineering and environmental applications, and geo‐electrical methods are often used to detect them in the subsurface. Spectral induced polarization (SIP) is a geo‐electric method that nonintrusively measures the frequency‐dependent complex electrical conductivity of a material, in the mHz to the kHz range. We present a new SIP data set of four different types of clay (a red montmorillonite sample, a green montmorillonite sample, a kaolinite sample, and an illite sample) at five different salinities (initially de‐ionized water, 10−3, 10−2, 10−1, and 1 mol/L of NaCl). We propose a new laboratory protocol that allows the repeatable characterization of clay samples. The complex conductivity spectra are interpreted with the widely used phenomenological double‐Pelton model. We observe an increase of the real part of the conductivity with salinity for all types of clay, while the imaginary part presents a nonmonotonous behavior. The decrease of polarization over conduction with salinity is interpreted as evidence that conduction increases with salinity faster than polarization. We test the empirical petrophysical relationship between σsurf″ and σsurf′ and validate this approach based on our experimental data and two other datasets from the literature. With this data set we can better understand the frequency‐dependent electrical response of different types of clay. This unique data set of complex conductivity spectra for different types of clay samples is a step forward toward better characterization of clay formations in situ.

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Section: Introductionmentioning

confidence: 99%

Spectral Induced Polarization Characterization of Non‐Consolidated Clays for Varying Salinities—An Experimental Study

et al. 2021

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“…Further additional parameters such as the duration of the current injection or the acquisition geometry can also cause distortion at the early times. However, as these parameters are defined by the user, they can be more accurately considered during the inversion process; for example, the turn‐off time can be measured or inverted (Finco et al ., 2018). Moreover, the estimation of the acquisition device filter can be modelled when considering equivalent RLC electrical circuits, as shown in Figure 2.…”

Section: Discussionmentioning

confidence: 99%

“…The time‐domain electromagnetics (TDEM) method is commonly used for hydrogeological application under all latitudes and therefore can be utilized in all hydrogeological contexts, such as cold environments (Guérin et al ., 2001), watersheds in temperate (Mouhri et al ., 2013), tropical or semi‐arid zones (Finco et al ., 2018). Such applications are based on the interpretation of the response in time gates, which allow a depth of investigation on the order of tens of metres (reaching up to 100 m), with transmission coils (Tx) of decametric size.…”

Section: Introductionmentioning

confidence: 99%

Full‐wave modelling of early‐time measurements in time‐domain electromagnetics: Consideration of coupling between Tx–Rx antennas and the ground

Finco

Schamper

Réjiba

et al. 2021

Geophysical Prospecting

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Early‐time measurements of time‐domain electromagnetics carry information of the near surface, and therefore, the interpretation of such measurements is important, particularly when utilizing small‐loop acquisition devices. However, these early‐time gates are often distorted by responses from the acquisition system itself, primarily caused by self‐transients associated with the transmission link composed of the transmitter and receiver loops and with the investigated medium electrical properties. Estimating all such potential couplings is crucial for interpreting early‐time measurements and gathering information on the near surface. In this study, a receptor loop made of 20 turns was built for this purpose. Field results and simulations were then compared, which shows how full‐wave finite‐difference method in the time‐domain simulations can be used to accurately calculate the impedance characteristics of time‐domain electromagnetics systems. All simulations were performed using finite‐difference time‐domain software based on a fully explicit three‐dimensional solver. First and second sets of simulations, respectively, were carried out in free space to compare the results to an alternate simulation method with equivalent lumped electrical circuits and on a homogeneous half‐space with varying electrical resistivities. The results were then used to improve the inversion of field data acquired on a test site in Garchy, France.

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“…Examples would include applications in geological prospection, based on electromagnetic and seismic measurements (e.g. Bauer et al, 2010;Finco et al, 2018;Hsu et al, 2010), earthen embankment diagnosis and monitoring using electrical measurements to detect possible leakages or weakened areas (e.g. Bièvre et al, 2017;Fargier et al, 2014;Johansson & Dahlin, 1996;Ling et al, 2019), archaeological prospection by means of electromagnetic sounding (e.g.…”

Section: Introductionmentioning

confidence: 99%

A data mining approach for improved interpretation of ERT inverted sections using the DBSCAN clustering algorithm

Sabor

Jougnot

Guérin

et al. 2021

Geophysical Journal International

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Summary Geophysical imaging using the inversion procedure is a powerful tool for the exploration of the Earth's subsurface. However, the interpretation of inverted images can sometimes be difficult, due to the inherent limitations of existing inversion algorithms, which produce smoothed sections. In order to improve and automate the processing and interpretation of inverted geophysical models, we propose an approach inspired from data mining. We selected an algorithm known as DBSCAN (Density-Based Spatial Clustering of Applications with Noise) to perform clustering of inverted geophysical sections. The methodology relies on the automatic sorting and clustering of data. DBSCAN detects clusters in the inverted electrical resistivity values, with no prior knowledge of the number of clusters. This algorithm has the advantage of being defined by only two parameters: the neighbourhood of a point in the data space, and the minimum number of data points in this neighbourhood. We propose an objective procedure for the determination of these two parameters. The proof of concept described here is applied to simulated ERT (Electrical Resistivity Tomography) sections, for the following three cases: two layers with a step, two layers with a rebound, and two layers with an anomaly embedded in the upper layer. To validate this approach, sensitivity studies were carried out on both of the above parameters, as well as to assess the influence of noise on the algorithm's performance. Finally, this methodology was tested on real field data. DBSCAN detects clusters in the inverted electrical resistivity models, and the former are then associated with various types of earth materials, thus allowing the structure of the prospected area to be determined. The proposed data-mining algorithm is shown to be effective, and to improve the interpretation of the inverted ERT sections. This new approach has considerable potential, as it can be applied to any geophysical data represented in the form of sections or maps.

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Time‐domain electromagnetic imaging of a clayey confining bed in a brackish environment: A case study in the Kairouan Plain Aquifer (Kelbia salt lake, Tunisia)

Cited by 8 publications

References 33 publications

Spectral Induced Polarization Characterization of Non‐Consolidated Clays for Varying Salinities—An Experimental Study

Spectral Induced Polarization Characterization of Non‐Consolidated Clays for Varying Salinities—An Experimental Study

Full‐wave modelling of early‐time measurements in time‐domain electromagnetics: Consideration of coupling between Tx–Rx antennas and the ground

A data mining approach for improved interpretation of ERT inverted sections using the DBSCAN clustering algorithm

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