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Near Surface 2007 - 13th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 03 Sep 2007 - 05 Sep 2007
- Location: Istanbul, Turkey
- ISBN: 978-90-73781-81-8
- Published: 03 September 2007
81 - 100 of 144 results
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Flow Zone Index for Improving Permeability and Porosity Relation and Facies Description
Authors E. Puskarczyk, J. Jarzyna, J. Krawiec and M. BalaA well-defined relation between permeabilty and effective porosity is a way for calculating permeability in all cases where direct lab measurements are impossible. In homogeneous rock formations, correlations between discussed reservoir parameters are always high. In the group of lab data from the Rotliegendes formation from the Polish Lowland, correlations between permeablity and porosity showed not very good R coefficients and a great dispersion. The data originated from 78 wells, over a dozen of them was chosen for analysis. The whole research area was divided into smaller ones. We assumed the smaller data groups would be more homogeneous than the whole data set as regards lithology and facies composition. The relations permeability vs. porosity were determined for them and the results were better than those obtained for the whole data set, but still they were not satisfied. The Flow Zone Indexes were calculated for the units of the same hydraulic parameters and relations permeability vs. porosity were separately calculated for each such unit. The correlation coefficients were good and the prediction equations for permeability were constructed. The obtained formulas can be applied to calculating the continuous permeability log in the borehole profile on the basis of the porosity curve.
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On the Reduction of Noise-sensitivity in Seismic Tomography
Authors M. Dobroka, T. Ormos and A. GyulaiThe Iteratively Reweighted Least Squares (IRLS) procedure is combined with the Conjugate Gradient method in defining a robust tomography method (W-CGRAD). In order to make the Simulated Annealing (SA)-based tomography algorithm more robust, a generalized weighted norm is introduced, as generalized energy function. Robustified versions of the SIRT method are also introduced. The generalization is made both in the data space (weighted average using Cauchy weights) and in the model space. A robust SIRT algorithm can also be defined by introducing alpha-trimmed mean instead of the arithmetic mean in the well-known updating formula of the traditional SIRT method. Using synthetic traveltime data the generalized (robust) tomography algorithms are tested in a medium sized tomography example. It is proved that the weighted tomography methods are more robust and less sensitive for noise (especially outliers) then their original versions.
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Application of Well Logging Data to Determine a Model of Elastic Parameters for the Ksiezpol Gas Reservoir
By M.J. BalaThis paper presents effects of gas- and water saturation on elastic parameters of rocks. Gas present in the pore space of rocks significantly decreases velocity of P-wave propagation whereas it is much smaller on S-wave velocity. Hence, a small VP/VS ratio can be an indicator of gaseous hydrocarbons in the deposit. The analysis was based on theoretical relationships for porous media, known as the Biot-Gassmann’s and Kuster and Toksöz’s models, and on well-logging data and results of the quantitative interpretation of wells logs. The relationships between P-wave and S-wave velocities and reservoir parameters may contribute to solving some problems associated with seismic interpretation of wave forms in autochthonous Miocene deposits.
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Improving the Data Quality of Earth’s Magnetic Field NMR Measurements in a Noisy Laboratory Environment
By T. RadicNMR (Nuclear Magnetic Resonance) measurements on rock samples provide important information about the structure and the fluids of the pore space. Normally these measurements are done in fields of strong permanent magnets. However, in some cases it is important to do this in the weak earth’s magnetic field. Unfortunately the high laboratory noise level in combination with the very low NMR signal amplitudes complicates the NMR measurement and reduces the data quality. For this reason we have updated a former NMR instrument. The new hardware concept considers three unwanted noise signal types: 1) Mains noise (50/60 Hz), railway traffic (162/3 Hz) and harmonics, 2) wideband noise from switched power supply and electronic instruments, 3) low-frequency magnetic fields (1 Hz) from DC motors. Three noise reduction techniques were implemented for routinely use: a) Gradiometric receiver coils to suppress up to 97-99% of the lab noise, b) Remote Reference Receiver Loops to predict and eliminate residual noise in the time series, c) Method for compensating the influence of rapidly changing Larmor frequency while stacking. As long as the lab noise is moderate, these three methods provide a good NMR data quality as tests at different locations have demonstrated.
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International Cooperation for the Mapping of Buried Valley Aquifer Systems – The Project BurVal
Authors H. Wiederhold and The BurVal Working GroupThe project BurVal has been established to study systematically buried Pleistocene subglacial channels valleys - or in short buried valleys - of the North Sea Region. The aim of the project BurVal is to develop tools for the mapping of buried valleys under the aspect of groundwater exploration and protection, to test and demonstrate these tools at selected Pilot project areas, and to show how these mapping results can contribute to a sustainable use of the water resources. Nine partners from Denmark, Germany and the Netherlands cooperated in this project.
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Integrating Multi-scale Geophysical Data for the 3D Characterization of an Alluvial Aquifer
Authors H. Paasche, T. Günther, J. Tronicke, A.G. Green, H.R. Maurer and K. HolligerUnderstanding groundwater flow and contaminant transport within alluvial aquifers requires the detection and detailed characterization of preferential flow paths. We present an integrated interpretation of a 3D geoelectric data set, 2D crosshole radar and seismic tomograms and the results of sparse direct-push slug tests that allows us to identify potential preferential flow paths within an alluvial aquifer in northwest Switzerland. The 3D electrical resistivity model is divided into clusters of high and low electrical resistivity using a fuzzy c-means cluster analysis technique. Despite significant differences in resolution, dominant structures identified in a 2D cross-section extracted from the clustered 3D resistivity model largely coincide with those obtained from an independent fuzzy c-means cluster analysis of crosshole radar and seismic tomograms. By linking the 3D electrical resistivity clusters to hydraulic conductivity measurements obtained from a limited number of slug tests, we derive a 3D aquifer model distinguished by zones of increased hydraulic conductivity that may act as preferential flow paths.
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The Role of Geophysical Methods in Salt-water Intrusion Mapping for Strongly Karst Formations, a Case Study at Stylos, Crete
Authors H.A. Hamdan, G. Kritikakis, A. Vafidis and E. ManoutsoglouGeophysical methods are useful tools for mapping the boundary between fresh and saline water. A geophysical survey was conducted in order to study the mechanisms of saltwater contamination in a strongly karstic coastal area. The region of interest is located in Western Crete about 3 Κm from the seashore. Seismic and electrical resistivity methods, along with detailed geological mapping have been employed to study the complex geological structure of the area under investigation. Electrical tomography detected a low resistivity zone which is attributed to a saline water layer. From the combination of the geophysical and geological data, a depicted major normal NE-SW fault zone mainly causes the groundwater salinization.
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Characterization of Electrical Anisotropy for Cuttability of Rocks Using Geophysical Resistivity Measurements
More LessThe rock hardness, strength, fracturing and anisotropy property parameters are the main factors controlling cuttability of the rocks. The orientations of elongated grains cause considerable variations in hardness, anisotropy and layering parameters of the rocks. The resistivity sounding technique (DES) is used to determine anisotropy resulted by the rock's fracturing, pressure and metamorphism properties. We calculated typical polar diagrams by modelling using various anisotropy values and electrode arrays for comparing with field measurements. Based on the synthetic data it is clearly seen that dipole azimuthal sounding was most determined electrical anisotropy. To understand the reason of these effects and to estimate suitable direction for easily cuttability of the rock, resistivity soundings using dipole azimuthal array were applied on karstified limestones covered with alluvial units around Kozyatağı quarry, Istanbul. Dipole azimuthal soundings were made on 10°, 55°, 100°, 140° azimuths with spacing r=10-90 meters. The azimuthal diagrams in the ranges of 88-950 ohm-m were indicated characteristic orientations as the anisotrophy indicator at various depth levels within limestone. Based on the azimuthal diagrams, the direction ~120° (from north) where apparent resistivit considerably decreased to lower values towards deep levels (>15 m) within limestone is interpreted as more suitable extension for easy cuttability.
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Assessment of Silicified Wood Potentiality Using Geoelectrics and GPR Applications in New Cairo City, Egypt
More LessNew Cairo City is a new urban area which has been developed on the periphery of Cairo. A natural protectorate area of Silicified woods is located inside this city. Accordingly, a Conflict between the Ministries of Tourism and Buildings about this protectorate area is arisen. As an attempt to assess the existence of silicified wood in this natural protectorate area, 2D and 3D electrical resistivity and GPR measurements have been conducted. The survey has been conducted at two sites in the percorate area. At site 1, in which there are no traces of silicified wood on the surface but in site 2, there are traces of silicified wood on the subsurface. The data of geoelectric in show accumulation of burden traces of silicified wood. The data obtained from Geolectric are well in range and fits with those from GPR data. This survey approves that the study area should be maintained as protectorate area and should not be used for further constructions.
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Magnetic Detection of Buried Oil and Gas Metallic Pipes
Authors D. Ioane, F. Chitea and M. MezincescuMagnetic detection of burried metallic pipes is a well-known application of this geophysical method, the “pipe” magnetic anomaly being easily recognised. Recent applications carried out in Romania aimed at locating abbandoned oil transportation pipes or gas transportation network in view of land “clearing” for new industrial or commercial facilities. The Ploiesti city area, hosting refineries and dense networks of oil trasportation pipes, enabled the authors to find processing methods for separating the “pipe” magnetic effects from other magnetic noises due to neighboring industrial facilities and electric lines. The Sibiu city area hosting buried gas transportation network at its limits offered good possibilities for a clear location of the pipelines, but also information on the subsequent modifications of the buried pipe network.
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Gravity Effects of Deformation Zones Induced by Tunnelling in Soft and Stiff Clays
More LessWe calculated gravity response of geotechnical models of deformation zones induced by tunnelling in two environments - soft clays and stiff clays. Approximately elliptic zones of deformation above the tunnels arise in both cases, but internal structures of the zones are different, and different are also theirs gravity effects. In soft clays, the deformation zone above the tunnel is actually zone of compaction and causes decrease of amplitude of gravity anomaly over the tunnel. In stiff clays a zone of dilatancy occurs next to the tunnel, but an overall gravity effect of deformation zone is insignificant and doesn’t affect the amplitude of gravity anomaly measured above the tunnel at the surface.
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Liquefaction Risk Assessment by the Use of Seismic Techniques – The Test Area of Nafplion City, Peloponnesus, Greece
Combined seismic surveys of P and S waves (seismic reflection, refraction, modelling, MASW and crosshole investigations) with geotechnical borehole testing effectively evaluated the land where the Nafplion city, Greece is expanding. Since the area was suspected for high liquefaction potential, a study was performed using all the modern tools for this evaluation. The study area was too large to be examined by the standard laboratory and borehole testing, therefore the aid of geophysics was proved to be valuable. We present the methodology we followed and the main results of the study for the test area of Nafplion city. Evidence was found indicating a low factor of safety against liquefaction at specific sites within the area of interest.
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New Results of High Resolution Seismic Measurements at Lake Balaton
Authors Z. Pronay, T. Cserny and R. MiskolcziInvestigations of Lake Balaton by the Geological Institute of Hungary started in 1981. Between 1987 and 1989 within the framework of Cuban–Hungarian cooperation a total of 373 km boomer seismic section was registered covering the entire lake in a quasi uniform network. As a result of the profiles’ evaluation a picture was drown up about the spatial distribution of lacustrine sediments, the mud structure as well as the variable morphology and geological setting, till 30 m depth from the lake bottom. During 2003 and 2004, in the cooperation of Geophysical and Geological Institutes the original thermo-paper records were digitally archived, re-evaluated and the recent records were integrated as well. The re-evaluation gave the opportunity for a more detailed spatial determination of the geological structure of the bed (layers, faults). This gave an opportunity to plan the research of Pleistocene sediments, deposited before the lake formation.
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Shallow Reflection Seismic Shear-wave Velocity Analysis on Paved Soils Using a Land Streamer Unit
Authors I. Arsyad, U. Polom and S.T. WiyonoAs part of the Project “Management of Georisk” of the Federal Institute for Geosciences and Natural Resources (BGR), Hannover, high resolution shear-wave reflection seismic was applied in the Indonesian province Nanggroe Aceh Darussalam in cooperation with the Government of Indonesia and local counterparts. Target was earthquake site effect classification in the city of Banda Aceh and the surrounding region of Aceh Besar. Using a land streamer system was advantageous in the populated area and for an easy recording operation. Additionally, paved roads, compacted dirt roads or concrete surfaces suppress Love waves and refracted waves, if the soil layer below the surface is of lower seismic velocity. The recorded wave field of single records often includes direct and reflected SH shear-waves only in such cases, allowing RMS-velocity-depth determination on site. Because RMS-velocity is higher than mean velocity, this gives a good estimation of the mean shear-wave velocity-depth function. Results show that shear-wave reflection seismic in combination with Land Streamer is a useful tool to evaluate the soil stiffness in populated urban areas. The specialized seismic system for compacted soil surfaces allows a wide range of applications within cities, industrial sites, paved roads and also on small dirt roads.
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The Influence of the Surface Conditions on Reflection Seismic Data – A Joint Study of Reflection Seismic Data in Denmark
Authors E. Nørmark, H. Lykke-Andersen and K.H. EsbensenIn Denmark reflection seismic data are intensively used for mapping ground water resources. However, due to variations in the near surface layers, significant variations in the data quality are encountered. Seismic modelling may be carried out, in order to understand the influence of the surface layers. However, in lack of reliable geological models of the surface layers, this will normally not be feasible. In this context we seek another approach, where the seismic data quality is evaluated and compared to borehole information, ground water potentials and other kinds of surface information. By use of multivariate data analysis, a regression model has been established, which reasonably well predicts the seismic data quality. By using this approach up to 60 % of the variations in the data quality can be predicted. The model is only valid in the region where it is estimated or in regions with the same acoustic properties. However, the procedure can be applied anywhere and is also believed to be relevant in other similar cases.
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Joint Interpretation of P and SH Refraction Data
Authors T. Ormos, M. Dobróka and A. DaragóIn this paper we propose the use of a fast kinematic refraction inversion method for P and SH arrivals for interpretation near surface structures. The basic aim for this method is that lateral changes both in layer thicknesses and propagation velocities in the media are described by adequately chosen functions expanded in series.With the method we can estimate the lateral changes of the P and S velocities and layer thicknesses. With the joint interpretation of both inversion results we can recognize in near surface structures the water table and low velocity contrast too. In the paper we show a practical example.
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Comparison between Inversion Algorithms of Surface Refraction Tomography for Cavities Detection
Authors M. Dwornik and A. LesniakThe analysis of popular algorithms of the inverse problem dedicated to surface refraction tomography is discussed in the paper. Surface refraction tomography is a method, which is able to estimate a velocity of elastic wave on a layer boundary. This work presents comparison between popular methods of inversion of seismic data: Singular Value Decomposition (SVD), genetic algorithm and ART and SIRT iterative methods. Stability of results and error of estimated solution were analysed. Numerical experiments show, that the most effective method is SVD (it gives acceptable solution in shortest time). Genetic algorithm, which is one of the basic methods for non-linear inversion, gives the best inversion result, but its computation time is the longest one. Significant improvement of convergence was obtained by using some iterations of SIRT in single iteration.
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Numerical Simulations of NMR Responses in Fractal Pore-space with the Finite Element Method
Authors J. Lehmann-Horn, S. Strehl and U. YaramanciA finite element technique for simulating NMR responses in a complex porous media is developed to investigate the effects of rough inner surfaces to the NMR response of fluids in rocks. The influence on the NMR response (i.e. decay times and intensities) by changing physical and geometrical parameters of the inner surface is investigated. Attention is focused to the effect of increasing inner surface whereas volume maintains constant. The finite element program allows to investigate the NMR response of any complex two-dimensional pore-space. Simulations are designed and conducted for fully water saturated rocks. It shows that roughness shifts the T2 (distribution) to lower values and the intensities of higher modes are not negligible in rough, high surface relaxivity but still fast diffusion condition. A multi-exponential function describes the decay. Commonly used permeability vs. T2 (distribution) relationships vary in rough inner surface conditions. Estimations with the logarithmic mean of T2 (distribution) give a realistic trend for the permeability. The NMR response of fluids in a pore with rough inner surface in the fast diffusion regime between 0.1 and 1 is adequately described only by a multi-exponential function.
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The Strategy of Joint Inversion Using Function Series
Authors Á. Gyulai, T. Ormos, M. Dobróka and R. KavandaThe paper presents the results of investigations on the choosing of the optimal number of coefficients (unknown) in the function inversion. Using synthetic noisy geoelectric data we show, that it can be find an optimum number of these coefficient using in the joint inversion. The method can be used also in case of field data the optimum of the coefficient’s number is at the minimum of the main model parameter estimation error and the relative data distance as a function of the number of expansion coefficients.
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Geophysical Application of Power Lines EM Fields
More LessAs it has been shown by using numerical forward modelling and experimental field measurements, the electromagnetic fields due to power lines can give geological information even in the vicinity of powerlines. For the localisation of relatively near-surface lateral inhomogeneities, we recommend to construct a map about the ratio of electric field components measured in two neighbouring sites, along profiles parallel to the power line. Such a survey can be carried out easily, quickly and cheaply, and by means of a very simple instrumentation. This method may become a useful complementary tool of traditional geoelectric soundings. The stratigraphic identification and the depth position of the inhomogeneities are given from related traditional measurements. It is possible to obtain a vertical resolution from several upper harmonics of the fifty hertz, too. For such a frequency-sounding a simultaneous measurement of the electric and magnetic field components is suggested, which requires multichannel, frequency-selective voltmeters of higher sensitivity -possibly with digital recording - as well as additional theoretical and field examinations.
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