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Near Surface 2010 - 16th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 06 Sep 2010 - 08 Sep 2010
- Location: Zurich, Switzerland
- ISBN: 978-90-73781-88-7
- Published: 06 September 2010
61 - 80 of 153 results
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Geophysical Survey for Crypt Detection in the Church of Virgin St. Mary’s Birth in Horné Krškany, Slovakia
Authors J. Panisova, R. Pasteka, W. Rabbel, M. Bielik, T. Wunderlich and J. PapcoGeophysical methods are an essential part of non-destructive prospecting methods in archaeology. Geophysical measurements for crypt detection were performed in the interior of the Church of Virgin St. Mary’s Birth in Horné Krškany during the International course on ArchaeoGeophysics INCA 2009 (European Union LLP-Erasmus programme). The church is a valuable representative of Slovak historical heritage. Ground-penetrating radar (GPR) and microgravity techniques independently confirmed the presence of two crypts in the nave. Obtained results are very expressive by the character of the deformation of geophysical fields. Recommendations for video inspection or archaeological opening were also given to the archaeological site-excavators.
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Restoration of the Historico-architectural Plan of the Voskresensky New-Jerusalem Monastery by Geophysical Methods
Authors A.V. Urusova, A.A. Ivanov, V.V. Monakhov, N.G. Pudova and M.P. ShirobokovToday different geophysical methods are often applied in related fields of science. Thus application of geophysics in archeological exploration has actually separated into an individual branch characterized by specific methods of observations and data interpretation. Search and identification of archeological objects, especially those not distinguished in the relief of the daylight surface, is the issue of the day. Despite the fact that application of geophysical methods in archeology is half-century old, the surveyors are adding new effective methods and technologies to their stock. First of all we should mention GPR-position. However, it is good to remember well-behaved methods of resistance and magnetic exploration known since the middle of the last century. Russia as the rest of the world is currently favoring an integrated approach involving various geophysical methods which are jointly used for exploration of archeological monuments. Integration allows significant expansion of the circle of the tasks solved and increase in reliability of the results. In this report the authors intend to turn the searchlight on the matters related to geophysical mapping and data processing, and to demonstrate some results obtained during exploration of the archeological objects.
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Integration of Satellite Imagery, Airborne Radiometric and Regional Geochemical Data Sets for Mineral Exploration
Authors D.G. Eberle and H. PaascheCluster analysis algorithms enable the rapid and objective integration of multi-method data bases with unknown parameter relationship between the individual data types present in the data base. We are employing the fuzzy Gustafson-Kessel (GK) cluster algorithm to integrate a data base comprising 2D information from Landsat satellite imagery, airborne radiometric and regional geochemical data acquired over a survey area in the Northern Cape Province of South Africa. We are combining the structural information provided by satellite and airborne radiometric data with regional geochemical soil sample data to obtain an objective 2D classified zoned map reflecting sub-surface lithology. Ground truth control supports to ascribe the various clusters to lithology and generate mineral exploration target areas.
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Noise Sources for a Fixed Wing Airborne EM System, Quantified by Means of 3D Finite Element Modelling
Authors L. Rabenstein, S. Hendricks and C. HaasWith a 3D finite element model study the authors quantified noise occuring during aeroplane based electromagnetic measurements for the purpose of sea ice thickness determination. Namely, these are pitch and roll of the aircraft, electromagnetic coupling between aeroplane and ocean, and wing flexure. All effects are significantly amplified by the presence of the conducting sea water and for flight heights of 30 m over the ocean these effects can change the signal by about 10 percent or, in the case of wing flexure, by 100 percent. Roll, pitch and wing flexure signals have an inductive and a geometric contribution. For highly quantitative measurements such as sea-ice thickness, where a vertical resolution of 0.1 m is desired, all these effects must be taken into account. Most of the strong wing flexure signal appears on the in-phase component only, henceforth the quadrature component should be taken for sea ice thickness retrieval even when it encounters a weaker ocean response signal than the in-phase component.
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Validating SkyTEM Data Against Ground-based TEM Data at the Danish National Test Site by Upward Continuation
Authors N. Foged, A.V. Christiansen and E. AukenIn this abstract we show the results from a comparison of models from the SkyTEM-system with the ground based models at the extended test site. The comparison will also be carried out in data space by an upward continuation of the reference models to a SkyTEM-system response at nominal height. Furthermore, the repeatability of the SkyTEM-system at different heights is demonstrated. The national TEM test site was established to ensure that any TEM system used in the ongoing Danish groundwater mapping campaign can reproduce the reference models and match the upward continued responses of the reference model. The site was established in 2001. In 2009 the test site was extended from a point location with a known reference response and resistivity model to two crossing lines. This makes calibration and validation possible for airborne TEM-systems that cannot make hovering spot measurements. SkyTEM and VTEM have been on the new test lines so far. For the SkyTEM system we can conclude that it reproduces the ground-based TEM data and models very good and that SkyTEM data shows consistent results for different altitudes. In the data space we calculate an upward-continued dataset to perform the comparisons.
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Airborne EM Surveys Applied to Industrial Land-use Legacy Assessments in the UK
By D. BeamishRecent high-resolution airborne EM surveys in the UK have identified previously unknown, non geological, highly conductive environments in the near-surface. The surveys have covered a wide range of land-use contexts many of which have several centuries of industrial activities. Two case studies from southern Scotland are used to demonstrate the magnitude and scale of the high conductivity zones that may be encountered. The examples indicate that some of the most complex subsurface flow paths arise in the case of areas associated with coal extraction; here near-surface shafts and adits connect with shallow worked seams many of which are ancient and lost from modern records.
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Determination of Ground Thermal Properties for Dimensioning Large-scale Geothermal Heat Pump Systems
By L. RybachThe energetic performance of geothermal heat pump systems depends strongly on the local ground conditions. The key property dominating the performance is the ground thermal conductivity. Reliable values are needed for the design of large-scale systems. These can be determined in-situ. Site investigations, by specific equipment and procedures (wireless temperature logger, repeated measurements, numerical model simulations), provide the vertical thermal conductivity profile, along with the temperature profile. These are especially needed for systems foreseen for space heating and cooling.
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Estimation of Geothermal Reservoir Properties Using an Ensemble Kalman Filter Approach
Authors C. Vogt, C. Kosack and G. MarquartFor the assessment of a geothermal reservoir reliable knowledge of the physical rock properties as permeability, porosity and thermal conductivity are of primary concern. In our study the Ensemble Kalman Filter (EnKF) is used to estimate the permeability distribution in a geothermal reservoir. The EnKF is a stochastic technique based on a forward propagation of an ensemble of realizations. At successive instants in time, different kinds of data measured at various drill holes are collected in one data vector and used to update the system variables to improve the match between observation and simulation leading to a convergence of the ensemble. To demonstrate the method we studied a pumping test of a chemical tracer injected in one borehole and retrieved at a few others. As observation data we used bottom hole pressure and tracer concentration. We applied the method to a synthetic 2D test case and to the European EGS test site Soultz-sous-Forêts, France. We investigated the quality of the estimation depending on the data noise, the system error, a damping parameter and repeated application of the filter. Correct tuning of the filter allows a satisfying recovery of the permeability field with reliable error estimate.
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Microseismic Monitoring for Observation of Reservoir Processes – A Case study of the EGS Project Basel
Authors O. Genoni, A. Ebert and M.O. HäringDevelopment of the EGS reservoir in Basel was monitored by an array of six downhole geophone. An additional geophone was installed at 4422 m.b.s.l. depth for the initial phase of the stimulation. The calibration of the required velocity model was a crucial task prior to localization of events. The velocity model was derived directly from the microseismic data set. During a ten-days stimulation period, approximately 13’500 events were recorded, of which about 3’000 could be located in real-time with great spatial precision, allowing for a detailed study of the evolving reservoir. The event rate decreased within few months reaching a recent rate of approximately one event every two weeks. The monitoring network is still working with 4 stations.
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Pedophysical Study of Electrical Properties and Water Content, Laboratory and Field Experiments
Authors T. Wunderlich, S.A. al Hagrey, H. Petersen and W. RabbelWithin the iSOIL project we are developing a mobile multisensor platform to gain fast, accurate areal information of soils at the field scale. The measured geophysical attributes (e.g. electric, electromagnetic) need to be linked to soil parameters (e.g. clay and water content) via geophysical pedotransfer functions, GPTFs. These could either be empirical (e.g. Archie and Topp et al. Equations) or physically-based (e.g. mixing and effective medium models). Our interdisciplinary activities aim to develop robust GPTFs using diverse laboratory and in situ experiments. In laboratory experiments we investigated the influence of water content on di-/electrical measurements. The dried samples collected from different sites and depths were uniformly saturated with rain water in steps of ~2% pore volume. For each step we measured georadar reflections and geoelectrical resistivity as well as water content and temperature. Also independent permittivity measurements were conducted to validate GPTFs results. The geophysical results were complemented by a suite of standard soil parameters determined on the samples. From these lab and field data the relationship of water content with respect to both the dielectric permittivity and electric resistivity are established. Different empirical and mixing models are fitted to the data and discussed.
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Influence of Pore Fluid Conductivity and Water Content on the Complex Conductivity of Peat
Authors M. Ponziani, H. Vanhala, E.C. Slob and D.J.M. Ngan-TillardThis paper presents a new prototype cell that can perform simultaneous electrical and compression tests on peaty soils. Two different set-ups for measurements at high and low frequency are used. Results on the complex conductivity response of peat samples for different pore fluid salinities and degrees of compression are presented. This work presents reproducible results that can be utilized to improve interpretation of field measurements on peat.
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Bedrock Interface Detection for Sand and Gravel Mineral Reserve Assessment Using 3D ERT
Authors J.E. Chambers, P.B. Wilkinson, S. Penn, A.L. Weller, R.D. Ogilvy, O. Kuras, P.I. Meldrum and S.G. PearsonA study describing the use of 3D ERT to determine depth to bedrock, and hence mineral thickness, at a sand and gravel extraction site within river terrace deposits is presented. Two approaches are considered which automatically extract interface depths from 3D ERT models. The first assumes that the interface is located at the maximum slope of the resistivity-depth curve, and is therefore referred to as the ‘steepest gradient method’ (SGM). The second uses an intrusive sample point to calibrate the model by identifying the resistivity iso-surface associated with the interface, and is referred to here as the ‘known interface method’ (KIM). The results of these two approaches have been tested against direct GPS observations of the interface position that were made after the bedrock had been exposed by quarrying of the river terrace deposits. In this case, the use of intrusive data for model calibration (i.e. the KIM) was essential for recovering accurate depth information from the 3D ERT model. Reliance upon using the steepest resistivity gradient as an indicator of a geological boundary (i.e. the SGM) produced a severe overestimate of interface elevation.
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Prospecting Bauxite Horizons with GPR on Laterite Deposits at the Amazon Basin, Brazil
Authors M.A. Barsottelli-Botelho and J.L.G. GouveiaThe GPR was applied on areas with bauxite occurrences to see its capability of discriminate the different weathered horizons and, mainly, to detect the presence of bauxite horizon and also measure its width. The GPR was tested on two bauxite occurrences in Amazon Bazin, Brazil. The good quality of the radargrams was expected since the electric resistivity of the soil, evaluated by Vertical Electrical Sounding (VES) reveals a near surface resistivity varying from 450 to 1600 Ohm.m. The GPR data acquisition with constant-antenna-offset results in clear GPR sections where it was possible to separate four zones or horizons as well as its thicknesses. Each zone shows a different reflection pattern or radarfacies, which helps to differentiate them. The first horizon corresponds to the Belterra Clay, which is the most superficial layer, (AT); below, there is the laterite sequence composed by more three horizons, where the second one is a diffractions zone, which corresponds to a clay with concretionary laterites (ND); the third zone shows a homogeneous pattern and it corresponds to a massive ferruginous horizon (LT); an fourth zone shows discontinuous and small reflectors and/or chaotic pattern which corresponds to the main bauxite horizon (BX).
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Effective Dynamic Permeability for Seismic Waves in Inhomogeneous, Porous Media Using White's Patchy Saturation Model
Authors S.A. Greenhalgh, X. Liu and B. ZhouWe obtain an effective dynamic permeability model for a porous acoustic medium having mesoscopic heterogeneities of spherical inclusions by applying the non-self consistent theory to the scattered wavefield from a single spherical inclusion. At low frequency, our dynamic permeability tends to the real value of the effective static permeability, which depends on the host medium for small inclusion concentrations. This result is compared with the effective hydraulic permeability by replacing the permeability of the components with their dynamic values as determined from the JKD model For frequencies lower than the resonance frequency, these simple dynamic permeability models are very similar to those determined from the scattering model of this paper. However, the model which uses the arithmetic mean of the constituent phase permeabilities is not valid for inclusions having higher permeability than the host phase, and the model which uses the harmonic mean of the constituent phases is not valid for inclusions having lower permeability than that of the host material. In both cases, the effective dynamic permeability calculated from the static model of random spherical inclusions is in good agreement with our scattering model.
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Extraction of Permeability Variations from P-Wave Velocity Dispersion Data
Authors B. Milkereit, W. Pun and B. HarrisPermeability is a key parameter for the evaluation of subsurface formations in groundwater and hydrocarbon exploration. We utilize broadband full-waveform sonic data to exploit Pride's relationship between P-wave velocity dispersion and permeability for porous, fluid-filled media. Frequency dependent P-wave velocities are extracted from multi-channel sonic data during a two-step process: computation of semblance-based velocity spectra at two or more center frequencies followed by a 2D cross-correlation of the velocity spectra. A comparison with MRI-derived permeability logs confirm that P-wave velocity dispersion logs can be used to map permeability variations.
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Grounded Ice-sheets and Glacial Deposits within the Aberdeen Ground Formation of the Central North Sea
By F.A. BuckleyExploration and site survey seismic data from the Central North Sea have been analysed in a re-appraisal of the lithological characteristics of the Early to Middle Pleistocene Aberdeen Ground Formation. Several features, interpreted to result from grounded ice-sheets, are described and the implications for encountering a variety of geo-hazards in the top-hole sections of North Sea wells are considered. A regional seismic event, interpreted to represent near-base Quaternary is also described.
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Volumetric, Multi-fold Acoustic Interrogations of Complex Sub-seabeds
Authors J. Guigne, J.K. Welford and I. McDermottFor many marine applications in the offshore renewable energy and oil and gas industries, high resolution images of the shallow structures beneath the seabed are crucial for minimizing risks to infrastructure, personnel and investments. For both the emplacement and maintenance of piles and caissons for offshore wind turbines and oil platform supports, knowledge of drilling impediments like boulders and of the stratigraphic layering in which these supports are anchored can be invaluable to safe operations. We introduce a tandem approach of applying synthetic aperture sonar and high-resolution multi-fold seismic reflection techniques for obtaining such images in challenging marine site investigations.
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Evaluation of Properties of Morainic Soils Based on Shallow Seismic, Electrical Imaging Surveys and CPT Data
By V. LisinsThe evaluation of physical and mechanical properties of morainic soils based on shallow seismic, electrical imaging surveys, cone penetration testing (CPT) and standard penetration testing (SPT) data is considered. Shallow seismic investigations include the utilisation of reflected, refracted and surface wave techniques. The obtained correlation dependences were used for the prediction of the properties of morainic soils at a hardly accessible site of the river bed downstream the reservoir dam, drained during short-term stoppages of the operation of a hydroelectric power plant.
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Robust Weighted-mean Approach for the Evaluation of Ground Improvement Columns Using Surface Wave Analysis
Authors A. Madun, I. Jefferson, K.Y. Foo, P.R. Atkins, D.N. Chapman and M. CulshawThis paper demonstrates the application of surface wave analysis specifically for the evaluation of ground improvement columns, and considers the susceptibility of phase measurements to noise associated with this technique. This is addressed by introducing a robust approach of calculating the phase velocity based upon a weighted-mean approach that uses the signal-to-noise ratio (SNR) of the signal as a variable cost function to obtain an optimal phase velocity estimation. Experimental data was collected from a laboratory scale setup of a 0.1 m diameter x 0.15 m depth gravelly-sand column installed within a 0.6 m x 0.3 m x 0.3 m block of homogenous kaolinite-clay. Results from the measurements indicated Rayleigh-wave phase velocities of 59 m/s and 110 m/s for the clay and column respectively. The weighted-mean approach demonstrated consistently more accurate phase estimation as compared to the case of a rigid threshold approach.
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Difference in Resistivity Explained by Initial Stage of Weathering
Authors B.E. Danielsen and H.B. MadsenTwo core drilled boreholes in Southern Sweden were logged and the cores were inspected in order to correlate the results with the geological features. The resistivity log showed that the amphibolites in the two boreholes had very different resistivity. In one borehole the resistivity was high, whereas it was lower in the other. The visual inspection of the cores could not give an explanation as the amphibolites appeared similar. However, microscopy of the low resistivity amphibolites showed weathered pyroxenes, probably caused by introduction of water along the lithological contact between the amphibolites and the regional gneiss. The resistivity logs can thus detect even low grades of weathering of amphibolites which can be important for the mechanical properties of the rock.
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