- Home
- Conferences
- Conference Proceedings
- Conferences
23rd European Meeting of Environmental and Engineering Geophysics
- Conference date: September 3-7, 2017
- Location: Malmö, Sweden
- Published: 03 September 2017
61 - 80 of 157 results
-
-
Re-parameterization of the Cole-Cole Model for Improved Spectral Inversion of Induced Polarization Data
Authors G. Fiandaca, L.M. Madsen and P.K. MauryaSummaryThe induced polarization phenomenon, both in time-domain (TD) and frequency-domain (FD), is often parameterized using the empirical Cole-Cole model. We here suggest three re-parametrizations of the Cole-Cole model, namely the maximum phase angle (MPA) model, the maximum imaginary conductivity (MIC) model and the minimum imaginary resistivity (MIR) model. We test these new parameterizations against the classic Cole-Cole model using a Markov Chain Monte Carlo (MCMC) inversion algorithm. The MCMC method allows us to study the probability distributions of each model parameter and gives us direct information on the parameter uncertainty. We show that models that are poorly resolved from inversion with the Cole-Cole model, e.g. due to low C values or strongly correlated parameters, can be resolved well with the new parameterizations and that the parameterizations work equally well for TDIP and FDIP data.
-
-
-
A Network Model of Membrane Polarization to Simulate the Induced Polarization Response of Sandstone Samples
Authors H. Stebner, M. Halisch and A. HördtSummaryThe hydraulic conductivity of sediments is an essential parameter for many applications, and thus its estimation from induced polarization (IP) measurements is an important aim of current research. For this purpose, a comprehensive understanding of the processes at the pore scale is necessary. We suggest a membrane polarization model based on a sequence of two cylinders with different size. To account for the complexity of real rock, we combine many impedances calculated for such a 2-cylinder model into a network. We define global network parameters, which we tune in such a way that macroscopic properties, such as specific internal surface area, porosity, and fractal dimension, match those measured for real sandstone samples. Using remaining degrees of freedom of the network we are able to simulate the IP parameters, namely maximum phase shift and relaxation time, of the measured samples. Matching the IP parameters gets more difficult if we also try to constrain the network by data from µ-CT measurements. We conclude that the impedance network has a great potential to connect bulk electrical properties with microscopic geometry.
-
-
-
The Potential of X-ray Tomography and Image Analysis for Interpretation of Spectral Induced Polarization Measurements
Authors S. Johansson, M. Rossi and T. DahlinSummaryThe spectral induced polarization (SIP) method is a promising method for many near surface applications, including characterization of contaminated soil. In this study, SIP measurements, high-resolution X-ray tomography and image analysis are combined to investigate clean and tetrachloroethylene (PCE) contaminated sand. This is the first known combination of these methods and the aim of this paper is to demonstrate some powerful possibilities of using X-ray tomography in SIP research. X-ray tomography enables a direct visual control of the sample conditions and quantification of relevant sample properties via image analysis techniques. The image stacks from were processed with image analysis techniques, so that individual grains and PCE phases could be extracted from the sample volume. This enabled calculations of relevant sample properties such as PCE blob volumes, grain diameter, -surface area and —eccentricity as well as bulk porosity, specific surface area to pore volume and proportion of high-density grains. We conclude that the combination of SIP measurements and X-ray tomography have a great potential of increasing the understanding of SIP mechanisms in geological materials. The tomography results can be used both to calculate properties relevant for SIP interpretation as well as 3D modelling of the pore space.
-
-
-
Contribution of Stern Layer and Membrane Polarization to the Spectral Induced Polarization of Porous Media
Authors M. Rossi, A. Brovelli, G. Cassiani, S. Johansson and T. DahlinSummaryRecently there is an increasing interest in the understanding of the Spectral Induced Polarization (SIP) phenomenon in porous media. The complex electrical conductivity of porous geological materials has a frequency dependent behavior than can be associated to three main mechanisms: Maxwell-Wagner (MW) polarization, Membrane polarization, Electrical double layer (EDL) polarization.
This paper aims to develop a mechanistic model for induced polarization in frequency domain, that incorporates both grain and membrane polarization and uses a non-linear mixing rule to combine the contribution of water, air and solid grains.
The model is tested on two different lab experimental datasets. Different spectra characteristics can be understood and described by distinguished porous media behaviors.
-
-
-
Simulated Time-lapse DC-IP Monitoring of Dense Non-aqueous Phase Liquids (DNAPLs) - An Initial Approach
Authors C. Power, P. Tsourlos, J.I. Gerhard and T. DahlinSummaryGeoelectrical techniques have long standing potential for imaging sites contaminated by dense non-aqueous phase liquids (DNAPLs). Recent work explored the effectiveness of time-lapse DC resistivity to monitor DNAPL source zone remediation. A fundamental component of the work was the development of a unique and comprehensive linkage between well-established DNAPL and DC resistivity models, with the coupled model serving as a cost-effective and valuable investigative tool. The objective of this current study is to evaluate the application of integrated time-lapse DC resistivity and induced polarization (DC-IP) for monitoring DNAPL contamination. This paper introduces the various modelling tools and presents an initial simplistic approach to extend the established DNAPL-DC resistivity modelling framework to incorporate time-lapse IP. Preliminary results are encouraging and ongoing work is focused on developing an advanced hydraulic-electric linkage between the DNAPL and DC-IP models to produce more realistic IP responses from DNAPL spills.
-
-
-
Mapping Possible Flowpaths of Contaminants through Surface and Cross-borehole Spectral Time-domain Induced Polarization
Authors T. Bording, G. Fiandaca, P.K. Maurya and E. AukenSummaryTraditional methods for mapping possible flowpaths of contaminants in sedimentary environments by boreholes may often be insufficient. Additional information may be acquired by geophysical methods. In the present study, cross-borehole and surface measurements were performed using time-domain induced polarization (TDIP). After measurements the entire test site was dug out, and the geology was described. Despite of being above the groundwater table, it was possible to retrieve exceptionally well the distribution of sand lenses/layers at the site, with clear signature in both the DC conductivity and the IP parameters, as confirmed by the excavations carried out for verifying the geophysical results. Consequently, cross-hole TDIP imaging is a valuable tool for characterizing possible flowpaths of contaminants in in clayey moraines.
-
-
-
Resolution of DC Resistivity-thickness Equivalences by Inclusion of Induced Polarization Data
Authors L.M. Madsen, G. Fiandaca, E. Auken and A.V. ChristiansenSummaryThe principle of equivalence is known to cause non-uniqueness in interpretations of direct current (DC) resistivity data. Here, we show that these equivalences can be significantly reduced by combining DC data with time-domain induced polarization (IP) measurements. An understanding of model equivalences requires a comprehensive investigation for each model when using gradient-based inversion methods. Instead, we apply a 1D Monte Carlo inversion that makes it possible to investigate the space of equivalent models. We invert synthetic DC data of a model with low-resistivity equivalences. We then include a contrast in chargeability, modelled in terms of spectral Cole-Cole IP parameters, and invert the DC and IP data together. The results show that the inclusion of IP data resolves the equivalences. The degree of resolution depends on the contrast in the chargeability and/or the other IP parameters. The contrasts required are easily expected in the field, which is justified with a field example where DC and IP data are measured on a sand formation with an embedded clay layer. Inversion results show that the resistivity data alone does not resolve the clay layer due to equivalence problems, but by adding the IP data to the inversion, the layer is resolved.
-
-
-
Series Expansion Based Inversion to Process Laboratory TD Induced Polarization Data
Authors A. Kiss and M. DobrókaSummaryThe Induced Polarization (IP) method is often used in ore exploration, since the electrode polarizability provides a good basis for distinguishing the ore-rich zones from the waste rock. Several successful field applications confirmed the effectiveness of the method. Previous studies proved that the series expansion based inversion is a well applicable data processing method in case of field TDIP data. In this paper laboratory apparent polarizability data measured on core samples with Time Domain Induced Polarization method are processed in a new inversion procedure, where the time constant spectrum containing the polarization effects is determined with series expansion approximation.
-
-
-
Generalized Relative and Cumulative Response Functions for Conductivity Meters Operating at Low Induction Numbers
Authors F.C.M. Andrade and T. FischerSummaryRelative and cumulative analytical response functions have been widely used as a powerful tool for forward modelling and interpretation of measurements obtained by electromagnetic induction conductivity meters operating at low induction numbers for one-dimensional layered earth models. These well-known functions were derived and should be used for the instruments laid on the surface of the earth. In this paper we extended these functions and obtained new generalized analytical expressions which can be used for instruments carried at any height from the surface. The proposed new equations were compared with numerically constructed functions, obtained using the full solution of the electromagnetic equations, and proved to be in very good agreement at low induction numbers.
-
-
-
Practical Inversion of Electric Resistivity in 3D from Frequency-domain Land CSEM Data
Authors F. Bretaudeau, S. Penz, N. Coppo, P. Wawrzyniak and M. DarnetSummaryEM prospection are methods of choice for many applications such as deep water or geothermal prospection because of their sensitivity to electrical resistivity and their potential to investigate at depths of 500m or even more. However, the investigated areas in Europe are usually urbanised and industrialised so high level of cultural noise prevents from the use of MT. Land CSEM is an alternative. But cost and logistical constrains limits to the use of a small number of transmiter positions. The inversion of CSEM data in the near field using a single transmiter position suffers from critical sensitivity singularities due to the unsymmetric illumination. To overcome this problem we proposed an inversion framework adapted to this ill-conditioned inversion problem. The framework relies specificaly on a robust Gauss-Newton solver, on model parameter transformations and data reformulation under the form of pseudo-MT tensors. We describe here the modeling and inversion approach implemented in our code POLYEM3D and describe the framework proposed for its practical application. We illustrate its application on synthetic cases and then show the application of the process to a real CSEM dataset acquired for thermal water prospection at a few kilometer from a nuclear power plant in France.
-
-
-
A Case-study for Comparing a Mobile DC System and a Multi-configuration EMI Sensor for Depth-to-Soil Mapping
Authors E. Lück, J. Guillemoteau and J. KloseSummaryIn the past, different types of mobile sensors were used to image the lateral heterogeneity of the subsurface electrical conductivity. Later, the development of DC (direct current) and EMI (electromagnetic induction) multi-configuration instruments permitted to get also information about the soil layering. In this study, we report a case study, which shows a good agreement between the inversion of DUALEM-21 data and the inversion of DC data for imaging lateral and vertical conductivity variations.
-
-
-
GPR and Geoelectical Studies in a Historical Site in Buenos Aires, Argentina, for Locating an Old Cistern and Evaluating
Authors V. Grunhut, H.P. Martinelli, N.E. Bonomo, M.V. Bongiovanni, A. Pinio and A.M. OsellaSummaryWe performed a geophysical study in a historical site. The main objective was to localize and characterize an old water cistern, no longer in use. Considering its expected dimensions, high density GPR data and geoelectrical dipole-dipole profiles were acquired. This allowed achieving very good resolution of the subsurface structures.
We could localize the cistern and determine that it would not be risk of collapse. While a very resistive electrical anomaly related to this structure was identified (with a diameter of approximately 1.5 m and extending up to a depth of about 0.9 m), considering the GPR results, this anomaly was associated to resistive filling material and not to the presence of a void. Below that depth, the structure seems to be filled with compacted material similar to the surrounding soil. Two other anomalous zones were detected that could correspond to structures with historical lineage. Exploratory excavations are being carried out.
Regarding the geoelectrical data, first, conventional 2D inversions were done. Then, a pseudo-3D model was built by transversally interpolating those results, and also a fully 3D inversion was performed. This aided to further improve the delineation of the anomalies.
-
-
-
Lake Baikal - A Unique Site for Testing and Calibration of Near-surface TEM Systems
Authors M.V. Sharlov, N.O. Kozhevnikov and R.V. SharlovSummaryThe paper discusses using Lake Baikal as a site for testing a near-surface TEM system. The water column of Lake Baikal forms a natural geoelectric model with precisely known parameters. Because of this, it has been possible to identify and assess the differences between the transient voltage responses measured with different arrays, and the corresponding modeled ones. It follows, from the field experiments conducted that the smaller the transmitter loop employed (central loop mode) the greater the difference between measured and modeled TEM responses. Since the geoelectrical model is known, this difference gives an objective assessment of the effect that the TEM system has on the overall measured response. It is notable that measured and calculated responses coincide when TEM soundings are done using separate loops (loop-loop mode).
-
-
-
Increasing the Signal-to-noise Ratio of Field NMR (SNMR) Measurements by Means of Pre-polarization
By T. RadicSummaryThe Surface Nuclear Magnetic Resonance (SNMR) Method allows direct quantification and characterization of free pore-water in the soil. SNMR measurements in densely populated areas, often cause S/R ratios of less than 1. This situation is made additionally worse when the SNMR method is used to investigate the Vadose Zone. Because the magnitude of the SNMR signal is also dependent on the strength of the magnetic field, we have build and tested an SNMR Instrument which uses the Pre-Polarization technique to improve the Data quality by up to one order.
-
-
-
Removal of Co-frequency Powerline Harmonics from Multichannel Surface NMR Data
Authors J.J. Larsen, L. Liu, D. Grombacher and E. AukenSummaryPowerline harmonics is often the dominant noise source in surface NMR data and can completely overwhelm the NMR signal. Several methods have been successfully implemented for removal of powerline harmonics including notch filtering, multichannel filtering and model-based subtraction. However, the performance of these methods can be problematic when one of the powerline harmonic components has a frequency close to or coincident with the Larmor frequency, referred to as a co-frequency harmonic. Removal of the co-frequency harmonic can distort the NMR signal causing erroneous estimates of water content and relaxation rates. To solve this problem we propose an extended method of multichannel model-based subtraction of powerline harmonics. In this method, the co-frequency component is modeled in the primary coil and a reference coil on noise-only data recorded immediately prior to the NMR excitation. The phase and amplitude relationships between the components measured in the two coils are calculated. The relationships are used to predict the co-frequency harmonic component parameters in the primary coil during the NMR decay based on NMR signal free, synchronously recorded reference coil data. The mathematical framework is developed and we give examples of the efficiency of the method based on synthetic NMR signals embedded in noise-only data.
-
-
-
Application of Magnetic Resonance Soundings and ERT Measurement to Characterize the Transition Between Sediment and Crys
Authors C. Jodry, J.-F. Girard, J. Porté, J.-R. Dujardin and P.-D. MattheySummaryCrystalline basement rocks at the surface are both surface water resources and an analogue of deep reservoir used for geothermal exploitation. We present here a geophysical survey realized in the East of France, at an outcrop in a quarry allowing to characterize the transition zone between sediments and basement. We applied electrical resistivity measurements and magnetic resonance soundings and highlighted water-bearing structures in the sandstone and in the basement, showing lateral variations.
-
-
-
Analysis of Severely Aliased Surface Waves from a 2D Seismic Reflection Line
More LessSummarySurface wave analysis was performed on a 2D seismic reflection line acquired in the context of paleo-environmental research of the Llancanelo Lake region (Mendoza, Argentina). The line consisted of 96 receivers with 10 m spacing. During reflection processing the surface waves were muted due to their severe aliasing. The current analysis aimed to use them to derive complementary information about the shallow subsurface, by inverting their dispersion curves to obtain S-wave velocity profiles.
The analysis was restricted to a 190 m segment, due to hints of strong lateral variations along the rest of the line which would violate the 1D inversion hypothesis. The dispersion curves were picked in f-k domain. This required correcting the wavenumber values to account for the aliasing. Dispersion curves of the Rayleigh fundamental and first higher modes where obtained from the spectra of 4 records, allowing the computation of average curves and statistical errors. They were inverted by means of the Nearest Neighbour global inversion algorithm.
Inverted Vs profiles are reasonably well resolved up to around 30 m deep, and show a strong contrast around 6–8 m, which is consistent with results from other geophysical methods used in the region.
-
-
-
Radiomagnetotelluric Studies of Landfills of Industrial Wastes on the Karelian Isthmus
Authors A.K. Saraev, A.E. Simakov, B. Tezkan, I.V. Tokarev and A.A. ShlykovSummaryResults of radiomagnetotelluric (RMT) soundings with use of various modifications of this method (foot, mobile and controlled source ones) on landfills of industrial wastes on the Karelian Isthmus are considered. A landfill in the settlement Morozova near St. Petersburg was formed as a result of a long-term warehousing of toxic wastes by the sulfuric acid manufacture. In the adjacent to the landfill territory investigations by the foot and mobile modifications of the RMT method were conducted and a polluted zone was contoured. Another landfill of debris in a former sandy
career is located in the Vyborg area. A survey by the controlled source modification of the RMT method was fulfilled. As a result the contouring of the wastes was realized and the structure of the landfill was studied.
-
-
-
Geoelectric Surveys in Handling Urban Environmental and Geotechnical Problems
More LessSummaryThe termination of industrial activities may have side effects with harmful impact on civil infrastructure. The drastic increase of ground water level may endanger the quality of the fresh water resources and the basement stabilities of the surface infrastructures. Geoelecric survey is an effective method in solving environmental or geotechnical problems in urban areas.
This study introduces two case histories on geophysical characterization of sites that are endangered with the reappearance of karstic water. Validated with drill hole data the subsurface structures were reliably imaged. Extended with laboratory analysis of water and mud samples the source of water contamination was identified. The successful designation of subsurface aquifers and flow directions gave useful information for mitigation planning.
-
-
-
High-resolution Geophysics in the Investigation of the Inner Structure of Walls and Columns of Batalha Abbey
Authors M.J. Senos Matias, F. Almeida, R. Moura and N. BarracaSummaryKnowledge of walls and other structural elements construction characteristics and techniques is mandatory in the maintenance and restoration of historical buildings.
Such information is obtained from documents or by comparing with monuments of the same period. Documents are difficult to obtain and comparison with other buildings can be inaccurate. The use of direct invasive techniques may be considered but they are likely to damage structures or compromise buildings stability. Thus, indirect high-resolution methods are adapted to these investigations.
This work describes a GPR and a Seismic Transmission Tomography survey to investigate the walls and columns of the 14th century Batalha Abbey (UNESCO heritage site).
High-resolution GRP data revealed the dimensions and thicknesses of different walls and the structure and nature of materials inside them.
The Seismic Transmission Tomography survey, supported by high-resolution photogrammetry scanning for accurate positioning of sources and geophones, was carried out to investigate the Abbey columns. Seismic velocities distribution inside the columns characterized their interior and clarified the nature of the materials used. Columns construction followed the same technique and used the same materials. However, each column depicts a different velocity zonation that could correspond to different stages of deterioration for each one.
-