- Home
- Conferences
- Conference Proceedings
- Conferences
Near Surface Geoscience 2014 - 20th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 14-18, 2014
- Location: Athens, Greece
- Published: 08 September 2014
61 - 80 of 185 results
-
-
Contribution of Geophysics to Geochemical Study
Authors S. Barhoum, R. Guérin, D. Valdès, L. Bodet, P. Gombert and Q. VitaleSummaryA study of spatial heterogeneity of groundwater geochemistry is conducted within an abandoned underground quarry of chalk.
An associated geophysical study (electromagnetic mapping at low induction number, and electrical resistivity tomography) is carried out on the surface.
It allows to determine the structural geometry of superficial formations, in order to understand the link between the geochemical spatial variability of the lakes and the properties of the environmental medium.
-
-
-
Water in Karst Hydrosystems Unsaturated Zone; MRS Evidences within an Integrated Hydrogeophysical Approach
Authors K. Chalikakis, S.D. Carrière, N. Mazzilli, C. Danquigny, A. Legchenko and C. EmblanchSummaryKarst unsaturated zone (UZ) is recognized to play a key role in karst hydrosystems recharge and contaminant attenuation processes. Its characteristics are identified as an important factor for karst groundwater vulnerability assessment and resource management. A large scale hydrogeophysical experiment was undertaken over the last 4 years combining several surface-based geophysical methods and measuring techniques in a unique experimental site within the Fontaine de Vaucluse (FDV) hydrosystem in southern France. The aim was to apprehend the UZ structure and functioning of typical urgonian karstified mediterranean limestone. Geological structure is being well recognized by electrical, electromagnetic and seismic measurements. Magnetic Resonance Sounding (MRS) results clearly identify water presence and evidence seasonal variations within the karst UZ. Due to these results a conceptual hydrogeological model is proposed. On May–June 2014 a drilling campaign is being programmed and a cross-validation of the MRS results is also planned.
-
-
-
Geo-electrical Characterization and Monitoring of a Waste Landfill for Its Future Exploitation as a Bioreactor
Authors A. Arato, E. Agostini and A. GodioSummaryThis work deals with the geoeletrical characterization of a municipal solid waste landfill, and with the time-lapse monitoring of an infiltration test within the waste mass. The main objective is to understand the hydraulic behaviour of the wastes under a controlled water supply from the surface, in order to delineate the paths through which the water flows.
In fact, the landfill will be exploited as a bioreactor, in order to speed up the biodegradation of the organic fraction of the waste. Then, ensuring the adequate moisture content, through re-circulation of water or leachate, is essential to enhance the bacterial activity, and therefore the biogas production.
Geoelectrical characterization helped to locally understand the water infiltration processes, supplying useful knowledge for future plans of leachate re-circulation system.
-
-
-
Sensitivity Analysis of a Light Fixed-wing Airborne TDEM System for the Characterization of Karstic Environments
Authors G.-A. Sab, C. Schamper, F. Rejiba and A. TabbaghSummaryDetailed mapping of karstic aquifers is of prime importance for water resources management. To achieve these surveys objectives, airborne measurements are the only methods which allow both large and dense coverage. Electromagnetic induction methods such as time-domain electromagnetic (TDEM) help to map conductors like clayey accumulations surrounding karstic conduits. Fixed-wing TDEM systems using light aircrafts do not exist on the market, despite being able to offer higher cost effectiveness and performance close to that reached with helicopter-borne EM systems in hydrogeological surveys. A sensitivity analysis of key acquisition parameters is undertaken to evaluate the capabilities of this kind of system for mapping karstic environments. Despite a flight altitude of 50m, higher than the average altitude of 30m reached with helicopter-borne systems, the results are encouraging and indicate a good capacity for investigation from 10m to about 150m depth.
-
-
-
Geoelectrical Studies by VES/TDEM Joint Inversion in the Parana Sedimentary Basin, Brazil
Authors J.L. Porsani, D.N. Leite, C.A. Bortolozo, M.A. Couto Jr. and J.D.R. CampanãSummaryIn this work the authors shows results of VES/TDEM joint inversion for Urupês region, located in Paraná basin, São Paulo State, Brazil. The objectives were to map the sedimentary and crystalline aquifers. The sedimentary aquifer is characterized by Adamantina Formation (Bauru aquifer) and the crystalline aquifer is characterized by fractures zones in the basalt layers of the Serra Geral Formation. The joint inversion results are promising and they permit to map the tick of the Adamantina Formation, as well as locate a fracture zones inside of the basalt layer of the Serra Geral Formation.
-
-
-
Application of Cross-hole Seismic Tomography in Characterization of Heterogeneous Aquifers
Authors S.I Ehosioke and T. FechnerSummaryDetailed characterization of subsurface geological heterogeneities which control fluid flow and transport is still an unresolved challenge in the geoscience community. While surface geophysical methods have helped in obtaining large scale parameter distributions, the decrease of resolution with depth limits their application for delineating heterogeneities at high resolution. This limitation has encouraged the use of cross-hole geophysical techniques such as cross-hole seismic tomography. Cross-hole seismic tomography which involves measuring travel times of seismic ray paths between two or more boreholes in order to derive an image of seismic velocities between the wells offers an approach for characterizing geological heterogeneities at a high resolution. Its application range from near surface aquifer studies, geothermal, to deep oil and gas reservoirs (Sainkov et al 2005; Tselentis et al 2011). Becht et al., (2007), evaluated the use of cross-hole seismic tomography for high resolution aquifer characterization. In this study, we present a case application of cross-hole seismic tomography for a high resolution characterization of the Prakla-Seismos field test site. Detailed velocity distributions are correlated with available borehole geological data to better delineate subsurface heterogeneity which provide useful information for an improved groundwater flow and contaminant transport modeling in the area.
-
-
-
Effectiveness of the Reciprocity Principle for Dipole-dipole Electrical Resistivity Survey in Field
More LessSummaryThe reciprocity principle of source and receiver array holds in dipole-dipole electrical resistivity survey. To examine the aspects of source voltage and current and of the potential difference of reception electrodes for heterogeneous medium, a vertically contacted half space model involving high and low-resistivity medium is defined, and the numerical simulation is carried out in the case of dipole-dipole electrode array configuration. And to examine the effectiveness of the electrode optimization based on the reciprocity principle in actual field situations, the numerical experiments for the model involving high and low resistivity with random noise are performed and analyzed.
-
-
-
Effective Array of Electrical Survey for Detection of Piping Zone of Embankment
Authors S.H. Oh, H. Lee, W.Y. KIM, E.S. IM and H.J. CHUNGSummaryPiping through embankment or foundation of concrete dam has been issued as a main factor of various menaces for safe maintenance of the water facility structure. In this study, a new approach to find the location of the piping point by geoelectrical method is proposed.
Our approach is to install the current line source in the water of upstream and downstream, and then let the current flow from upstream to downstream area. The potential will be measured at downstream to find any electrical anomalies due to piping condition.
Numerical study made it possible to adjust various conditions to configure optimal configuration for successful locating of the piping point. And lab test was successfully performed and the result implied a new way of electrical application for safety assessment of water facility structure for the piping problem.
-
-
-
How Calculate DOI Index to Assess Inverted ERT model?
Authors S. D. Carrière, K. Chalikakis, C. Danquigny and L. Torrès-RondonSummaryAssessing Electrical Resistivity Tomography (ERT) reliability is critical for interpretation step and decisions making. Scientists try to provide solutions with several quality indicators: Depth of Investigation (DOI) index, sensitivity, uncertainty and resolution matrix. Each indicator, presenting strengths and weaknesses, has to be cross-validated with others. Most of these indicators are already included in the commercialized inversion softwares.
This paper deals with DOI index calculation. Two calculation methods appear/exist in the Literature: the one uses inverted resistivity and the other uses logarithm of inverted resistivity. Both solutions are compared in this paper with several synthetic models and field data set. In general, DOI index calculated using inverted resistivity point out systematically a less reliability in resistive zone of the model. DOI index map calculated using logarithm of inverted resistivity appears more robust in various configurations. This calculation method highlights quite accurately inversion artifacts.
-
-
-
Near Surface Ore Exploration Using TAU-transformation of Time-domain IP Data
Authors E. Turai, M. Dobroka, A. Kiss, G. Petho and M.K. BaraczaSummaryThe so-called critical elements can be connected to polimetallic ores therefore geophysical measurements were carried out in the area to explore and describe ore bodies in volcanic geological environment.
Geoelectric, especially the Induced Polarization (IP) method yields good results. For the interpretation of IP curves the TAU-transformation was developed, which provide the spectral information of polarization with the spectrum of time-constants. With introducing the Weighted Amplitude Value (WAV) it was possible to give quantitative characterization of the ore. With the application of these processing methods, two different type of mineralization could be distinguished: a stock-vein type ore which is mainly affected by redox processes in the western part and primary porphyritic mineralization on the northern part of the exploration area. The results proved the applicability of TAU-transformation and WAV in case of ore exploration. Based on the WAV, corrected apparent specific conductivity metallic and redox polarization maps, three points were marked out for drilling.
-
-
-
Geophysical Exploration of a Complex Metavolcanic Environment
Authors G. Petho, E. Turai, N.P. Szabo, N. Nemeth, M.K. Baracza, D. Bulla and K. KormosSummaryThe Triassic stratovolcanic complex of the East Bükk Mts. in North Hungary was the target of our geophysical exploration because of its previously known REE and critical element occurrence. There is no direct geophysical survey to locate these elements, for this reason complex geophysical survey including magnetic, very low frequency (VLF) electromagnetic, spectral radiometry, multielectrode resistivity and multielectrode induced polarization measurements were made along profiles to gain more knowledge about the possible host rocks of REE and critical elements being relatively close (5–30m) to the surface. In the course of interpretation the core description and well logs of the boreholes drilled earlier were also taken into account. It was experienced that the ore zones were overlying mainly high resistivity and low chargeability metarhyolites. The combination of the magnetic and VLF measurements were used to locate a covered boundary separating limestone and metarhyolite. Among the applied geophysical methods the simultaneous interpretation of the multielectrode resistiviy and induced polarization measurements provided the best geological image.
-
-
-
Developing a Near Surface Electrical Resistivity Model of Great Britain
Authors J.C. White, D.C. Entwisle, J.P. Busby, R. Lawley and I.L. CookeSummaryA model of the near surface electrical resistivity of Great Britain is presented. The first geological unit beneath the base of soil layer is attributed with electrical resistivity.
Geotechnical data are used to derive modeled resistivity distributions for each of the lithostratigraphic units described in the near surface geological model of Great Britain. Resistivities are calculated using an effective medium methodology and these values are tested against electrical resistivity sounding data and apparent resistivity estimates from the airborne electromagnetic surveys. The central moments of the statistical distributions are coupled to the geological map and the resulting resistivity distribution shows a general increase in resistivity from SE England to NW Scotland. This pattern reflects the age of the bedrock geology of Great Britain.
The methodology described in this paper can be applied to other regions where suitable geotechnical information and geological mapping is available.
-
-
-
Application of Geoelectrical Techniques in the Investigation of a Coastal Sand Dune Field
Authors J.D. Alexopoulos, S. Dilalos, S.E. Poulos, G. Ghionis and S. MavroulisSummaryA geophysical research was carried out to investigate the lithostarigraphic substratum characteristics of the dune field of the central Kyparissiakos Gulf (W. Peloponnese, Greece), which is characterised by the presence of four dune lines. For this purpose, the geophysical techniques of Electrical Resistivity Tomography (ERT) and Vertical Electrical Soundings (VES) were applied, along with detailed morphological mapping and the collection of geological and geomorphological information. The processing of the geophysical data that were collected from two ERT soundings, perpendicular to the general direction of the dune lines, and seven geoelectrical soundings revealed four geoelectrical layers with the two surficial resistive layers adumbrating the extent and thickness of the four sand dune ridges and the associated slags. The third layer, corresponding to the underlying geoelectrical formation of 50–75 Ohm.m, is interpreted as a layer of transgressive Holocene deposits saturated with fresh water, while the deepest geoelectrically identified layer seems to correspond to the “Neda” formation, which consists of marls, sandy marls and conglomerates. It is concluded that the combined application of the aforementioned techniques has the potential to provide valuable data for the investigation of complex coastal depositional environments.
-
-
-
Describing the Pressure Dependence of Lamé Coefficients on Coal Samples
Authors J. Somogyi Molnar, A. Kiss and M. DobrokaSummaryUnderstanding the relationship between pressure and rock physical parameters, such as acoustic velocity, elastic moduli, porosity is essential for exploring and exploiting of natural reserves. Therefore a petrophysical model for describing the pressure dependence of P and S wave velocities was developed. The advance of the model is that it provides the required physical explanation of the pressure dependence with its three-parameter exponential function. On the basis of the model the pressure dependent Lamé coefficients were deduced. To prove the applicability of our method laboratory data of coal specimen was inverted to estimate the model parameters. Since the model valid for P and S wave velocity has a common parameter a joint inversion technique was applied. The velocity data were measured under varying confining pressure with pulse transmission technique on dry samples. A very good fitting between measured and calculated data was found thus inversion results strengthened the applicability of the petrophysical model.
-
-
-
High Resolution 3D Seismic Reflection Investigation in Urban Environment for Assessment of a Sinkhole Feature
Authors C. Hartmann and U. SwobodaSummaryIt is well known that full spatial information about the underground geology generally can be retrieved by 3D seismic investigations. The advantage of recording multidirectional data information allows imaging of complex underground features, such as fault systems, sinkholes or dome structures.
The downside of a 3D seismic investigation is the operational requirement of laterally free access to the investigation site at the surface to lay out the seismic recording equipment and deploy the seismic source. This is typically no problem, for example, for large scale operations in desert-like areas for the oil and gas industries. In urban areas, though, access is limited due to building structures or transport infrastructure. Moreover, other constraints such like the public interests require significant considerations during all stages of a seismic operation.
This work summarizes the possibilities and limitations of carrying out a detailed 3D seismic reflection investigation in urban environment by presenting a case study investigation program which has been carried out across a small community in Germany.
-
-
-
Correlation between S-wave Velocities and Building Damage Distribution in Bolu (Turkey) During the 1999 Düzce Earthquake
By A.T. BasokurSummaryThe ‘Düzce Earthquake’ of magnitude Mw= 7.2 took place on 12th November 1999 in the northeast of Turkey. Besides the effect of earthquake parameters such as epicentre distance, magnitude, duration, source mechanism and frequency content of earthquake waves, this large earthquake indicated the importance of the local soil conditions on building damage especially for incorrectly designed and improperly constructed structures.
In order to examine the connection between damage and the local subsoil condition, the two-dimensional inversion of shear-wave refraction arrival times performed on 149 profiles having a total length of 10370 meters. A strong correlation was found between the local shear-wave velocity and building damage distributions that also comparable with the geology of the studied area. The consistency between seismic velocities and building damages shows the importance of seismic refraction survey to estimate the local site effects that extracted from the transmission properties of shear waves.
-
-
-
Applying Time-frequency Analysis in Borehole Seismic Travel-time Picking
More LessSummaryThe data reductions of existing borehole seismic methods are currently based on travel-time analysis in which first-arrival times of the seismogram are manually picked. However, manual picking is not efficient and depends heavily on the data quality and analyst’s experience. Besides the difficulty of picking first arrivals in the time domain, no information is obtained regarding the effective frequency of the analysis. Data reduction method based on the time-frequency domain was proposed in the study. The aim of the study was to propose a semi-automatic procedure for more objective first-arrival time picking. Evaluation using field data shows that the semi-automatic time-frequency spectrum analysis works well in PS-Log testing. The picked first arrival times from the proposed method agree well with the manually-picked results. The procedure is stable and yields reasonable results. But it should be noted that the method inherit the tradeoff between frequency and time resolution from the time-frequency spectrum analysis. The parameters used in the time-frequency analysis should be optimized for different source types.
-
-
-
Proving the Applicability of the Petrophysical Model Describing Acoustic Hysteresis of P and S Wave Velocities
Authors J. Somogyi Molnar, A. Kiss, H. Szegedi and M. DobrokaSummaryDue to the increasing demand for hydrocarbons and the depletion of the known hydrocarbon fields there is a growing claim to predict rock physical parameters more accurate at non-conventional conditions also. It is well known that acoustic velocity in rocks strongly depends on pressure which influences the mechanical, transport and elastic properties of rocks as well as wave propagation under pressure is very nonlinear and the quasistatic elastic properties of rocks are hysteretic. Characterization of hysteretic behavior is important for mechanical understanding of reservoirs during depletion. Therefore a quantitative model - which provides the physical explanation - of the mechanism of pressure dependence is required. In this paper a petrophysical model is presented which provides the connection between the propagation velocity of acoustic waves (both P and S) and rock pressure both in case of pressurization and depressurization phases as well as explains the mechanism of acoustic hysteresis. The developed model is based on the idea that the pores in rocks close under loading and reopen during unloading. The model was applied with success to acoustic P and S wave velocity data sets.
-
-
-
Development of a Prototype 3-Component Borehole Electromagnetic Receiver
More LessSummaryA proto-type borehole electromagnetic receiver has been developed and compared the response to the commercial audio-frequency magnetotelluric receiver BF6. The proto-type showed comparable sensitivity and decay of magnetic field to BF6. The purpose of the receiver development is for wide application of electromagnetic tomography techniques, that is readily developed the interpretation software in last two decades. The barrier of the EM tomography is that appropriate hard-ware or measurement system cannot be found in the market. Once developed, the system can be applied to monitoring the fluid migration in EOR and CO2 sequestration and various engineering purpose. In the presentation, we expect to show more advanced version of system and test results as well.
-
-
-
Three-dimensional Modeling of GREATEM Data
Authors T. Mogi, S. Abdallah and E. FomenkoSummaryThe GREATEM (GRounded Electrical source Airborne Transient ElectroMagnetics) survey uses a grounded electrical dipole source of 2∼3 km length as a transmitter and a three-component magneto-meter in the bird towed from a helicopter as a detector. The GREATEM system is considered to be an airborne version of the Long Offset Transient ElectroMagnetics (LOTEM) system ( Strack, 1992 ). We developed a numerical forward modelling scheme using a staggered-grid finite-difference method (SFD, Fomenko and Mogi, 2002 ) adding a finite-length electrical dipole source routine. To construct a three dimensional (3D) resistivity model for GREATEM data, we have to overcome to compute a model composed of huge number of grid at wide frequency ranges because GREATEM has obtained resistivity data in time domain at a large number of sites.
In order to verify the validity of the code, we compare the results with those obtained by the 2D numerical code of the LOTEM case developed by Mitsuhata (2000) for a 2D quarter space model and a trapezoidal hill model. Finally, we simulate GREATEM responses for 3D modeling with a conductor placed at coast-land boundary and a topography model.
-