1.2 FINITE ELEMENT MODELING OF BOREHOLE INDUCTION TYPE LOGGING USING GAUGED ELECTROMAGNETIC POTENTIALS Authors: Eugene Badea(1), Mark Everett(2), Greg Newman(3) (1)Halliburton Energy Services, 2135 Hwy.6 South, Houston, Texas, 77077, USA e-mail:ebadea@halnet.com (2)Geophysics Department, Texas A&M University, College Station, Texas, 77843-3115, USA (3)Geophysics Department, Sandia National Laboratories, P.O.Box 5800, Albuquerque, New Mexico, 87185-0750, USA The paper describes the implementation of the finite element method to solve Maxwell's equations for 3D contolled-source electromagnetic problems. The electromagnetic field is described by the magnetic vector and electric scalar potentials. The uniqueness of the potentials and elimination of any spurious solutions is ensured by the inclusion of either the Coulomb or Lorentz gauge conditions. The enhanced sparsity of the Galerkin weak form matrices balances the extra coupling effort generated by the incorporation of a fouth degree of freedom per node, compared to the direct E solution. The test problem of a filamentary circular coil located in a homogeneous formation was considered using the analytical solution as a reference. Several other examples of induction-type oil-reservoir well-logging data in different 3D environments are presented. 1.3 3D MODELLING OF BOREHOLE ELECTROMAGNETIC INDUCTION LOGGING: PROGRESS AND COMPARISON Authors: Eugene Badea(1), Greg Newman(2), Mark Everett(3) (1)Halliburton Energy Services, 2135 Hwy.6 South, Houston, Texas, 77077, USA (2)Geophysics Department, Sandia National Laboratories, P.O.Box 5800, Albuquerque, New Mexico, 87185-0750, USA (3)Geophysics Department, Texas A&M University, College Station, Texas, 77843-3115, USA The paper presents a comparison between numerical techniques such as finite differences of finite elements against an available semi- analytical model. When using finite differences, the vector Helmholtz equation for the electric field strength E is considered. The vector equation is approximated using second order schemes on a staggered grid. A sparse complex-symmetric system is assembled and solved using iterative Krylov solvers such as the biconjugate gradient or the quasi-minimum residual (QMR) algorithms. "We are currently studying decomposing the electric field into curl free and divergence free projections and preconditioning by the inverse of the real part of the Helmholtz operator to reduce solution run times and eliminate spurious modes". When using finite elements, the electromagnetic field is described by the magnetic vector and electric scalar potentials. Either the Coulomb or Lorentz gauge conditions are considered to eliminate any artificial spurious solutions. The sparse complex-symmetric system is solved by using the incomplete lower-upper (ILU) factorization technique. Both numerical solutions were tested against a hybrid semi-analytical model which combines the mode concept in waveguide theory with the finite element method. The test problem of a vertical borehole placed in two horizontal semi-infinite beds, with the transmitting coil located at the intersection between the symmetry axis and the bed boundary, was considered. 1.4 AN APPLICATION OF MODERN TEM-FAST TECHNOLOGY FOR ENVIRONMENTAL INVESTIGATIONS Authors: Barsukov P.O., Fainberg E.B. Institute of geoelectromagnetic investigations of Russian Academy of Sciences, 142092, Troitsk, Moscow region, e-mail:fain@geo.igemi.troitsk.ru TEM-FAST instrument has been designed for Martian electromagnetic sounding. After some modifications it was applied for environmental and engineering applications. TEM-FAST instrument and original software provide efficient operation in any conditions, including industrial city zones with limited space to lay out sounding loops. TEM-FAST system operates with any notebook using standard interface. Control of operations and visualization of measurements is related with computer's terminal. Cases of history 1. Hydrogeological applications (investigation of brine contamination). 2. Soundings in bad accessible regions (Himalayas). 3. Static shift correction of deep MT soundings (Byelorussia). 3. Detailed investigations in archaeology (Great Egyptian pyramids) 4. Search of unique, small size targets (Vorontsov's Palace-museum) 5. Rock sample property measurements (Superparamagnetic analysis) 6. Automatic monitoring of electromagnetic properties of electrical state of rocks (monitoring of IP effect),and many others. These cases of history are presented in the report. The research were supported by Russian Foundation for Basic Research, project 97-05-64338 1.5 PETROLEUM EXPLORATION USING THE MARINE MAGNETOTELLURIC METHOD Authors: Steven Constable(1), Mike Hoversten(2), Frank Morrison(2), and Arnold Orange(3). (1) Scripps Institution of Oceanography, La Jolla, CA 92093-0225 USA e-mail:sconstable@ucsd.edu (2) University of California, Berkeley, Berkeley, CA 94720 USA e-mail:mhovers@socrates.berkeley.edu (3) AOA Geophysics, Austin, TX 78759 USA e-mail:73321.3045@CompuServe.COM During the past 3 years we have developed equipment and techniques to extend the frequency range of the marine MT method up to 1-10 Hz, allowing MT to be used for the first time for exploration of the continental shelf at depths of 10 m to 10 km. The instruments include AC-coupled electric field amplifiers adapted from our controlled source EM program and induction coil magnetometers. Electrical methods are particularly useful in sub-salt, sub-carbonate, and sub-basalt exploration, where the seismic method performs poorly due to reflection and reverberation. In a test over a 3-D salt body beneath 1000 m water in the Gulf of Mexico, we are able to map base of salt buried 1.5 km to 5 km deep to within a few percent of the depth determined independently from 3-D seismic surveying. We have carried out commercial surveys in carbonate regimes, and during the summer of 1998 will conduct a survey in the sub-basalt plays in the Faroes/Shetland basin. Modelling shows that sedimentary structure beneath the basalt can be well recovered from MT data in the 1 s to 1000 s period range. 1.6 2D INVERSION OF VES DATA IN SAQQARA ARCHEOLOGICAL AREA, EGYPT Authors: Gad El-Qady(1), Chika Sakamoto(1) and Keisuke Ushijima(2) (1)Graduate Course Student, Faculty of Engineering, Kyushu University (2)Professor, Faculty of Eng., Kyushu University 36, Hakozaki, Fukuoka 812, Japan The interpretation of actual field data still have a problem for obtaining a unique solution. In order to investigate groundwater contamination in Saqquara archaeological area, vertical electric soundings with Schlumberger array has been carried out. 1D inversion was performed based on a horizontally layered earth model. However, some results of the 1D inversion are not fully understood for 3D geological structure such as archaeological tombs. Therefore, we have carried out 2D inversion based on ABIC least squares method for Schlumberger VES data obtained in Saqqara area. Although the resultant 2D cross sections was correlated with the previous interpretation, the 2D models derived from 2D inversion showed a rough spatial resistivity distribution which is the resistivity changes abruptly between two neighboring blocks. It is concluded that 3D interpretation is an essential tool for visualizing ground water distribution with depth in the Saqqara area. 1.7 INDUSTRIAL APPLICATIONS OF MT ROBUST PROCESSING AND SIGNAL SEPARATION Author: Jimmy C. Larsen National Oceanic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle, WA 98115, USA e-mail: larsen@pmel.noaa.gov MT data collected in industrialized regions for oil, geothermal and mining exploration have severe noise problems that lead to seriously distorted MT transfer functions using conventional processing methods. The noise problem is mainly due to the presence of correlated noise, that is, noise signals that occur in both the magnetic and electric time series with transfer functions that differ from the MT transfer function. Correlated noise can be caused by, spikes due to lightning, spectral lines at the power grid frequencies and its harmonics, and signals due to electrified railways and pipelines. A method has been developed for dealing with correlated noise that involves the rejection of spikes and power grid frequencies and the removal of railway noise using a clean remote site for signal separation. Over 2000 sites have been processed using this robust code. The robust code has been modified to improve the speed of computation, reduce the memory requirements, simplify the output and make the code run nearly automatically. An important improvement is a method for rejecting noisy data sections. Examples for various types of noise will be presented. 1.8 ELECTRICAL PROPERTIES OF SATURATED AND PARTIALLY SATURATED POROUS MEDIA: IMPLICATIONS FOR NEAR-SURFACE GEOPHYSICS Author: Jeffery J. Roberts Box 808, L-201, Lawrence Livermore National Laboratory, Livermore, CA, 94551, USA We have performed laboratory electrical measurements on a variety of materials including fused glass bead samples, low porosity graywacke and metashales, sandstones, volcanic tuffs, and mixed sand/clay samples. Measurements have been performed with confining pressures up to 50 bars and temperatures up to 160 0C, with a variety of saturating fluids, and as a function of saturation. These measurements, along with frequency dependent impedance measurements, have revealed some insight to physical properties and processes occurring in porous materials. The results are useful for the interpretation of well-logs, ground penetrating radar, cross-borehole resistance tomography, etc. Other applications include evaluation of vapor pressure lowering, development of relationships between electrical properties and other transport properties. Frequency dependent electrical measurements of partially saturated porous materials indicate a change in response style at distinct saturation levels. The change in response may relate to changes in fluid distribution. Measurements of saturated electrical properties of fused glass bead samples and rocks with carefully characterized microstructures allows evaluation of dominant conduction mechanisms and various methods of estimating permeability and other transport properties. Partial support for this work was provided by the Geosciences Program of the OBES. Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract W-7405-ENG-48. 1.9 APPLICATION AIR-BORN AND GROUND-BASED FDEM FOR GEOLOGICAL ENGINEERING AND ENVIRONMENTAL RESEARCHES Authors: Vlasov Y.T.(1),Ingerov A.I.(1), Soldatenko V.P.(2), Lozovoj A.L.(2) (1) GRL Slavuta Co.,Ltd,33,K.Marx Ave, Dnipropetrovsk,320044,Ukraine, Fax (380562) 476777 (2)National Mining Academy of Ukraine, 19, K.Marx Ave, Dnipropetrovsk,320027, Ukraine e-mail:root@slavuta.dnepropetrovsk.ua Air-born FDEM, the technology of which is created in a Kharkov Centor of Radiophysical Sounding of the Earth, are based on various reflecting ability of the earth`s surface in relation to electromagnetic waves of various length, as well as on various depth of a penetration of these waves into ground. The plane variant of a multifrequent equipment "Mars" functioning in a range of lengths of waves 0.8-0.3 m, can be installed on light planes TBM-700 of the French company "Socata". At enviromentel investigation, the method allows to inspect large territories, including water areas,the condition of pipelines, canels, dambs etc., to determine the places of flood and thickness of a film of petroleum waste, to reveal on water areas the infringers making unauthorized dumping of polluted products in water, and to determine their coordinates, to investigate ice conditions in Artic and Antartic regions, to estimate age and thickness of ice. The special field observations by ground-based FDEM and original interpretation techniques permit to achieve the exactitude in the mapping of the boundaries at near 1-5% of their depth. One more component of successful solution of a broad circle of problem by ground-based FDEM is the possibility to study, alongside with the electrical resistivity the induced polarization of section. FDEM using a set with an earthed source is integrated with the method of circular electromagnetic profiling (CEMP). This method has high sensitivity to anisotropy of a geoelectrical section. High conformation of our conclusions has been obtained at tectonical mapping, study of landslides and karst, ancient mining working, conditions of dams, embancments etc. 1.10 2D RADIOMAGNETOTELLURIC (RMT) RESULTS OF A CAVE SYSTEM NEAR ATTENDOM (GERMANY) Author: Dipl.-Geophys. Gerhard Zacher, Institute of Geophysics, University of Cologne, Albertus-Magnus-Platz, 50923 Cologne, Germany Radiomagnetotellurics (RMT) has been tested successfully for the investigation ofwaste sites and hydrological purposes. For the first time, the location of a cave system in a carstic area has been investigated by the RMT method including a twodimensional (2D) interpretation. This relatively new electromagnetic method uses radio signals in the frequency range 10 - 300 kHz and measures the electric and magnetic field. Like in MT a frequency sounding can be made at every measuring point. By choosing transmitters parallel and perpendicular to the mean strike direction in the survery area a 2D interpretation of TE and TM data can be obtained. The survey area is located near Attendorn (100 km to the East of Cologne) and is mainly characterized by a perpendicular cave and fissure system. A 1 day test measurement was carried out on 3 profiles mainly to see the prolongation of a known cave in 10 - 20m depth. The 2D inversion results show a strong dependence on the clay content in the caves and fissures. High and low resistive areas could be correlated with either empty caves or caves with some amount of clay. Model calculations stress these results and show significant differences on different polarization modes. The RMT method seams to be a powerful tool for the investigation of cave systems. 1.11 ELECTROMAGNETIC SOUNDING AND MONITORING OF THE EARTH CRUST WITH THE USE OF THE EXTRA LOW FREQUENCY ANTENNA WITH TAKING INTO ACCOUNT THE INFLUENCE FROM THE IONOSPHERE AND DISPLACEMENT CURRENTS Authors: Abdoulkhay A. Zhamaletdinov(1), Alexander A. Shevtsov(1), Michael I.Pertel(2) (1)Geological Institute of the Kola Science Centre of RAS, Apatity, RUSSIA). (2)Earth Crust Institute of Saint Petersburg University, Saint Petersburg, RUSSIA) New possibilities in the Earth Crust electromagnetic sounding and monitoring was opened due to use of the powerful ELF antenna ZEVS (frequency range 31-166 Hz), situated on the north of the Kola Peninsula. Experimental research illustrate high resolution of signals measured at distances up to several thousand kilometers from the source. The problem of relevant data analysis and interpretation needs in estimation of the influence from ionosphere and displacement currents (Velikhov, Zhamaletdinov et. al., 1994). Results of the soundings at distances more then 500 km from the source showed that apparent resistivity curves, obtained from normalization by electric and magnetic components happened to be strongly diverged from those ones obtained by normalization through effective impedance. For to explain the phenomena theoretical calculations were made with the use of the program for EM field for electrical dipole over horizontal layered model in presence of conductive ionosphere in the upper half-space. The solution of the problem was made on the basis of algorithm presented in [Boerner, West, 1989]. The calculations were made without quasistatic restrictions. Both approximations have been studied - the wave type and the diffusion type. Results of calculations gave possibility to explain experimental results by common influence from ionosphere (at moderate and high frequencies, 31-166 Hz) and displacement currents (at relatively more high frequencies, 83-166 Hz). On the basis of theoretical research the behavior of electromagnetic field was investigated in frequency range 1-1000 Hz and at distances from 100 till 3000 km in approximation of horizontally layered Earth and flat wave-guide "Earth - Ionosphere". 1.12p CONTROLLED-SOURCE ELECTROMAGNETIC STUDIES FOR NEAR-SURFACE HYDROGEOPHYSICAL CHARACTERIZATION OF CLAY-BEARING AQUIFERS Authors: M.E. Everett(1), E.M. Gorman(1), K. Sananikone(1), B. Johnson, C.L. Munster(2) (1)Dept of Geology and Geophysics Texas A&M University College Station TX USA (2)Dept of Agricultural Engineering Texas A&M University College Station TX USA Controlled--source electromagnetic (CSEM) methods are growing in importance for environmental site assessment and rapid non-invasive aquifer characterization. A reliable hydrogeophysical interpretation of CSEM data in terms of permeability, clay content and fault distribution depends on understanding how these parameters shape Earth's ac and transient response. Results of two CSEM experiments over clay--bearing aquifers in central Texas are described. The first was conducted as part of a larger, interdisciplinary effort to predict the fate of agricultural chemicals applied to river floodplains. A regularized inversion of the electromagnetic data enabled an estimate of aquifer heterogeneity over the resolving length--scale of the CSEM data. The information assists agricultural engineers to model the subsurface transport routes of nonpoint source pollutants into the watershed. A second CSEM experiment was performed to identify lateral variations in electrical conductivity associated with faults and lithological contacts in a shallow sandstone aquifer. Faulting often plays a significant role in affecting groundwater flow as faults can act as barriers or conduits to flow. Based on variations in clay content, the CSEM data identified several faults and facies contacts juxtaposing different units of the sandstone. CSEM data can be used to constrain hydrological models for local water resources management and conservation. 1.13p INTEGRATED TELLURIC AND MAGNETOTELLURIC RESEARCHES FOR SEDIMENTARY BASINS ( THE CENTRAL PART OF MOESIAN PLATFORM) Authors: Furnica Cornelia, Stanica Maria, Stanica D., Ivanov Ana, Nistor H., Asimopolos L. Geological Institute of Romania, 78344 1, Caransebes Str, Bucharest 32 e-mail : stanica@igr.sfos.ro, anaiv@igr.sfos.ro The studied area is situated between South-Carpathians and Danube.The main geological units are Moesian Platform and the Carpathian Foredeep. The area is dominated by basement faults with a general East-West trend and the main geological feature is the Bals-Optas uplift. The data used in this work are provided by telluric and magnetotelluric surveys carried out in this region. Some telluric and magnetotelluric parameters are obtained for describing the deep structure of investigated area. The results obtained by quantitative methods allow an improvement of depth estimation at the basement level obtained according to magnetotelluric data. The maximum depth estimation ranges between 11 and 13 km. The approaches have a structural nature being useful in oil prospecting areas. 1.14p RAPID INVERSION OF INDUCTION LOGGING DATA Author: Catherine deGroot-Hedlin, Scripps Institution of Oceanography IGPP - University of California, San Diego, 9500 Gilman Drive - Dept. 0225 La Jolla, California, 92093-0225 e-mail: cdh@eos.ucsd.edu Electromagnetic induction logging is used to define the conductivity, as well as porosity and permeability, of subsurface formations. Mud used in the process of drilling often invades the porous rock up to a radius of several metres, resulting in EM induction measurements that are a combination of both the disturbed and undisturbed formations. The conductivity of the undisturbed formation can be estimated by two- dimensional inversion of the induction log data. In this study, the physical model is parameterized in terms of a large number of thin layers, each with three radial zones representing the conductivities of the borehole, the invaded zone, and the original subsurface formation, respectively. For rock formations with low conductivity contrasts, the functional relationship between the measured voltages and the formation conductivity is nearly linear. To speed up the inverse algorithm, this linearity is exploited by regularizing the inverse problem such that conductivity contrasts are minimized; thus geometrical factor theory may be used to provide sufficiently accurate Jacobean derivatives. The algorithm alternately solves for conductivities and the depth of the mud infiltration zone, from which the oil saturation and permeability can be inferred. Title: 1.15p The Exploration of the Groundwater Aquifer by Using TEM & VES Methods in the Southern Part of the Nile Delta Authors: Hassaneen A.Gh.*,Al-sayed E.A.*,Osman S.Sh.* National Research Institute of Astronomy and Geophysics(NRIAG) Helwan,Cairo,Egypt. (Laboratory for geoelectrics and geothermics) Fax: 002-02-554820 E-mail: Arghareeb@Frcu.Eun.eg Qualitative and quantitative interpretation of the available geophysical data (particulary Transient Electromagnetic Method TEM and Vertical Electric sounding VES data) are achieved in the area under study. The area concerned in this study occupies the southern part of the Nile Delta region, Egypt. It lies between Lat. 30 deg.8min.& 30 deg. 25 min.N and Long. 30 deg. 48 min. & 31 deg. 27 min.E. It takes the form of a triangle enclosed between the two Nils branches, Damietta to the east and Rossetta to the west, and extended in the eastern and western desert of Egypt. This shallow geophysical methods in the form of VES and TEM survey are carried out in the area of study. This survey is achieved for exploring the groundwater potentialities and prospecting the geologic capabilities of water bearing sequence and to determine the more suitable technique for exploring groundwater. However the vertical distribution of the produced resistivities, as have been concluded from the interpretation of five profiles of TEM soundings in different places in the area of study. The longest profile consists of fifty two soundings and the shortest one consists of nine soundings using Rassian instrument (TEM_Fast Pro-System) in addion to ninety five VESes distributed in the area of study. From the interpretation of TEM and VES measurements, the layers in the area are classified electrically and hydrologically into four main zones. The upper high resistivity zone is devoid from water. The second low resistivity zone shows the aquiclude of the aquifer. The third zone exhibits the main aquifer, while the fourth zone represents the barren section. From the interpretation and comparing the results with the wells, which are present in area of study we can deduce that, the TEM technique is considered as the more suitable one for exploring of groundwater at least in the conditions of the studied area. Title: 1.16p Accordinative Study Between the Vertical Electrical Sounding and TEM Methods for Exploring Groundwater Along Cairo-Alexandria Road Authors: Hassaneen A.Gh.*,Al-sayed E.A.*,Osman S.Sh.* National Research Institute of Astronomy and Geophysics(NRIAG) Helwan,Cairo,Egypt. (Laboratory for geoelectrics and geothermics) Fax: 002-02-554820 E-mail: Arghareeb@Frcu.Eun.eg A shallow geophysical methods in the form of VES and TEM survey are carried out along Cairo-Alexandria Road. This survey achieved for exploring the groundwater potentialities and prospecting the geologic capabilities of water bearing sequence and to determine the more suitable technique for exploring groundwater which is considered as the main aim of this work. However the vertical distribution of the produced resistivities, as have been concluded from the interpretation of fifty two TEM soundings and thirteen VESes carried out in the studied area, investigated shallow sections into nearly four layers. These layers are classified electrically and hydrogically into four main zones. The upper high resistivity zone is devoid from water. The second low resistivity zone shows the aquiclude of the aquifer. The thirt zone exhibis the main aquifer, and the fourth zone represents the barren section. From the interpretation of the VESes and TEM data and comparing the results with the wells, which are present in the area of study we can deduce that, the TEM technique is considered the more suitable one for the exploring of groundwater at least in the conditions of the area of study. 1.17p TEM DETECTION OF THE FRESH TO SALINE-WATER INTERFACE IN THE CANADIAN PRECAMBRIAN SHIELD Authors: V. Maris, I. Ferguson, X. Wu Geological Sciences, University of Manitoba P. Street, G. Lodha, Whiteshell Laboratories, Atomic Energy of Canada Limited Atomic Energy of Canada Ltd. (AECL) has conducted detailed geotechnical site investigations on two granite bodies at the Whiteshell Research Area (WRA) in southeastern, Manitoba and at the Atikokan Research Area in northwestern Ontario. These studies revealed that extremely saline groundwaters exist in the rocks of the Canadian Shield at depths of few hundred meters depending on the distribution of fracturing and the groundwater flow conditions (Davison et.al 1994). Time-domain electromagnetic (TEM) soundings were completed at four sites in the granitic Lac du Bonnet Batholith at the WRA, to examine the resolution of a PROTEM47 system for detecting the fresh to saline water interface. Review of the measurements, made using 100 m square transmitter loops shows the early-time response (<30 us) from resistive near-surface rocks is near the detection limit. Inversion of central-loop data gives depths to the fresh/saline groundwater interface ranging from 145 to 540 m. The resistivity is typically >5000 above the interface and <1000 Ohm.m below it. Comparison of these TEM depths with borehole resistivity logs indicated good resolution where the interface was shallower than 200 m and had a simple geometry. The TEM estimates were less definitive in the areas of deeper and complex interface. 1.18p SOME CONSIDERATIONS ON THE INVESTIGATION RAY OF INDUCTION, ELECTROMAGNETIC PROPAGATION, AND CLASSICAL ELECTRIC DEVICES ON THE ROCKS WHERE THE BOREHOLE DRILLING-FLUID INVASION IS EXTREMELY DEEP Author: Victor Negoita Institute of Geodynamics, 19-21 J.L. Calderon Str., Bucharest, Romania, e-mail:crisan@geodin.ro Nowadays, the customary well logging techniques used to know the true rock electric conductivity are carried out on the basis of induction log measurements. In a shallow to moderately deep invaded rock by the drilling fluid filtrate (diameter of invasion less than 100 inches) the induction tool measurements affords values very close to true rock electric conductivity. But, when the rocks are more deeply invaded, the apparent electric conductivity recorded by the induction tool deviates from the true electric conductivity of the rock as invasion increases. The amount of deviation depends upon the depth of invasion and the contrast between the electric conductivities of flushing and in situ-rock fluids. Such a case is represented in Romania by the Kliwa Sandstone Formation whose thickness in the Moldavian Oligocene is about 400 ft. The invasion diameters in Kliwa sandstones exceeding 160 inches makes induction type-measurements less adequate for true electric conductivity knowledge and require, by all means, the long spacing recordings of the Romanian electric log site of DRR (Determination of Rock Resistivity). That is the reason why in the electric multi-devices suite of DRR the large-sized spacing for lateral investigation was established to be 340 inches. The Electromagnetic Propagation Tool measuring the dielectric permitivity of the rock located not more than 6 inches from the borehole wall enable to prove the existence of non-electric conductive fluids whose dielectric constants are generally less than 40 times the fresh water dielectric constant. Field measurements exemplifications as well as the charts that have been elaborated for improving data processing and interpretation are presented in the last part of this work. 1.19p INDUCTION EFFECTS OF 2D STRUCTURES ON BURIED PIPELINES Authors: Ana Osella, Ernesto L<=pez, Patricia Martinelli and Alicia Favetto Departamento de Fysica - Universidad de Buenos Aires - Conicet Ciudad Universitaria - Pab. 1 - 1428 - Buenos Aires -Argentina A theoretical method developed in order to model the currents induced in pipelines due to external natural fields has proved the dependence of the induced currents on the resistivity of the host media, predicting a drainage of current from the pipeline to the soil in zones of electrical resistivity contrasts. We have verified experimentally the validity of these predictions performing a study along the Tierra del Fuego pipeline system. The electrical resistivity map obtained from the inversion of the geoelectrical data showed the presence of two zones characterized by strong electrical resistivity contrasts. Analyzing the measurements of currents flowing from the pipeline, low values were detected in more conductive zones while a clear increase was found along more resistive host media. These results indicated a current drainage through the pipeline to the soil, in the zone of resistivity contrast, which can reach up to 60 to 70 mA.Then, in the present work the theoretical method is modified in order to consider a host media with lateral electrical discontinuities. Different 2D structures are modeled and the currents induced in pipelines embedded in such terrains are quantified in order to have a more reliable estimation of this kind of effects. 1.20p DEVELOPMENT OF PETROPHYSICAL RELATIONSHIPS NECESSARY TO ESTIMATE MOISTURE MIGRATION WITH TIME-LAPSE TOMOGRAPHIC RADAR DATA Authors: John E. Peterson, Jr., Susan S. Hubbard, Kenneth H. Williams, Yvonne Tsang; Lawrence Berkeley National Laboratory, Earth Sciences Division, phone: (510) 486-4267 e-mail: JEPeterson@lbl.gov Jeff Roberts; Lawrence Livermore National Laboratory A borehole radar tomography experiment was conducted at the Yucca Mountain potential nuclear waste storage facility in Nevada. The intent of this experiment was to investigate the use of high resolution, time-lapse tomographic radar data for studying moisture migration that occurs within the rock mass as a result of the dramatic increase in rock temperature during a heater test. The extreme sensitivity of the radar response to even very slight changes in water saturation suggested the suitability of this technique. However, temperature also affects the radar response. Petrophysical relationships developed using laboratory measurements and calibrations of field data were necessary to separate out the effects of saturation and temperature on the radar response prior to saturation estimation. These relationships were developed using three different approaches including: 1) linear regression and 2) artificial neural network techniques on laboratory measurements, as well as 3) regression techniques on field tomographic radar data and borehole logs. We will present the three different methodologies used to develop the petrophysical relationships, as well as the saturation estimates obtained using time-lapse tomographic radar data together with these relationships. The information supplied by these data are necessary for understanding and predicting the influence of the stored radioactive waste at the potential nuclear waste facility. 1.21p DETECTION OF HYDROCARBON CONTAMINATED SOIL WITH RADIOMAGNETOTELLURICS Authors: Stephan Recher Institute of Geophysics, University of Cologne,Albertus-Magnus-Platz D-50923 Cologne, Germany e-mail: recher@geo.uni-koeln.de Recher, S., Tezkan, B., Hoerdt, A. (University of Cologne) Soil contamination caused by hydrocarbons is a problem for the reorganisation of closed factories and tank farms. It is necessary to determine the kind and content of the contaminants. Soil samples lead to reliable results but the detailed investigation of an area requires a large number of boreholes, which are usually quite expensive. Radiomagnetotellurics (RMT) is comparable to the known VLF-R method but uses a broader frequency range (10-240 kHz). RMT is well-tried in the exploration of former waste dumps. In a research project sponsored by the EU, the applicability of RMT for the detection of hydrocarbon contaminated soil is being tested. The test area is a former tank farm near the airport of Strasbourg/France. It is known from previous boreholes that the soil near the water-table is contaminated by kerosine. A second test area is chosen as a reference site to explore the undisturbed geology. By considering the effects of pipes in the 2D inversion of the data a resistive layer in 9m depth is found. According to the results of the soil samples the layer may correspond to the contaminated soil near the water-table. 1.22p AMT AND GEOELECTRICAL SOUNDINGS FOR GROUNDWATER PROSPECTING AT PERGAMINO BASIN, (BUENOS AIRES PROVINCE, ARGENTINA) Authors: C. Sainato(1), C. Pomposiello(2), G. Galindo(3) y H. Malleville1. (1) Facultad de Agronomia. University of Buenos Aires. Argentina. (2)CIRGEO. CONICET. Argentina (3) Facultad de Ciencias Exactas y Naturales. University of Buenos Aires. Dra. Claudia Sainato Catedra de Fisica. Facultad de Agronomia.UBA, Av. San Martin 4453. C.P.1417. Buenos Aires. Argentina. e-mail:postmast@fissai.agro.uba.ar cpomposi@mail.retina.ar The demand of complementary irrigation at the zone of Pergamino (Buenos Air es Province, Argentina) because of drought cycles makes necessary to invest igate the underground aquifers, determining their location and water qualit y. The hydrogeology of Buenos Aires Province is much difficult by the fact that its smooth topography does not allow to observe outcropings, having to analyse the drilling profiles interpolating information from great distanc es. Therefore, it is necessary to carry out geophysical prospecting, partic ularly at located zones where there is no previous studies. At this work ge olectrical and AMT studies were performed at the basin of the Pergamino river and the results were compared with geological, geochemical and hydroge ological antecedents. The most important results are: a) the phreatic level is placed at shallow depth, from 2 m to 7 m, with thickness between 5 m and 25 m depth. The values of electrical resistivity of this layer varies from 3ohm-m to 12 ohm-m. b) Below this stratum a more resistive layer is found which might contain s ands with water with moderate saline values (resistivity between 10 ohm-m to 60 ohm-m). The thickness of the formation along the Pergamino river has a constant value between 20 m and 25 m. In a transversal profile its thickne ss increases towards the sorroundings of the river getting thinner at the l imits of the basin. Beneath this stratum, a highly conductive layer is plac ed with resistivities between 0.4 ohm-n and 4 ohm-m, which deepens in the direction of the river bed and coincides with the course of groundwater flow in the basin. This layer might correpond to a saturated stratum whose water quality deteriorates towards the west. 1.23p GEOELECTRIC MODELS OF UKRAINIAN CARPATHIANS AND POTENTIALS OF THEIR MATHEMATICAL INVESTIGATION Authors: Sapuzhak Yaroslav S., Prof., Dr., Leader Zhuravchak Ljubov M., Dr., Scientific Researcher Sapuzhak Oleg Ya., eng. Carpathian Branch of Subbotin Institute of Geophysics of National Academy of Sciences of Ukraine Standardization of sections and development of geoelectric models of their separate zones which specify both methods and scope of geoelectrometry for solving deep, structural or prospecting problems is a paramount request for electrometric investigations of all geotectonic regions. Geotraverses of transcarpathian direction along localities Gorohiv - Sambir - Chop and Vyshnevets - Dolyna - Beregove are typical of the Carpathian region which together with Folded Carpathians surrounded by Transcarpathian and Precarpathian Troughs is formed by the adjoining Eastern-European Platform. The Earth's crust geoelectric models for further investigations using methods of mathematical (or physical) modelling have been developed along geotraverses mentioned. The models mentioned present basic regularities for changes of generalized electric parameters of total longitudinal conductance and average resistivity of sedimentary cover as well as their connection with peculiarities of geotectonic regional structure. Values of total longitudinal conductance are directly proportional to thickness of basic formation and range from the first tens to thousand and more simences within the Platform boundary and Precarpathian and Transcarpathian Troughs. The boundaries of geotectonic units are easily recognized as zones of high gradients. Influence of different elements of a model and efficiency of different systems of electrometric observations for further natural geoelectric investigations have been examined using original methods including boundary element techniques. The results obtained testify to expediency of such approach as well as possible optimization of additional electric prospecting methods and making them cheaper significantly. 1.24p INVESTIGATIONS OF WASTE SITES BY ELECTROMAGNETIC METHODS WITH THE USE OF RADIO STATIONS AND ELECTROTRANSFER LINES FIELDS Authors: Alexander K. Saraev, Mikhail I. Pertel, Viktor G. Ivochkin, Petr A. Parfentjev, Jaroslav S. Nikiforov St. Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg, 199034, Russia. e-mail: aks@aks.usr.pu.ru For study a waste sites St. Petersburg University applies a complex of radioelectromagnetic profiling in frequency range of 10-1000 kHz and extremely low frequency profiling on industrial frequency of 50 Hz. The devices, accordingly IPI-1000 and ssFIPP-1 are used. The amplitude and phase of a surface impedance of an electromagnetic field are determined with use of magnetic and grounded electrical antennaes. For IPI-1000 device the measurements with ungrounded electrical antennas is realized too. The use of extremely low frequency of 50 Hz and several frequencies from range 10-1000 kHz enables to receive the information at several various depth levels. The primary field in these methods is approximated by a plane wave, that allows to use the unified scheme of data interpretation. Because of theoretical calculations of an electromagnetic field of electrotransfer lines was found, that in a distant zone the horizontal component of a magnetic field should exceed five times the vertical component. This criterion is used for an evaluation of a capability of approximating of industrial frequency field by a plane wave. Practical examples of application of the complex are obtained. The work was performed with the support of the program "Effective technologies of waste utilizations". 1.25p ROLE OF "A PRIORI" INFORMATION IN SUBMARINE CABLE STUDIES OF SEA OF JAPAN Authors: L.L.Vanyan and V.A.Kouznetsov, Shirshov Institute of Oceanology, Moscow Due to induction nature of MT field it gives the greater information about well-conductive layers. TM mode generated asic by the electric charges that appear at conductivity change areas present a good possibilty for study of the resistive layers (e.g. sea lithosphere) by means of submarine cables. Since the sea/land conductivity contrast is quite large, the B-pol electric field along the cable is srongly reduced. However the electric field decrease is to some extent compensated by the electric currents flowing from the asthenosphere through the lithosphere towards the water layer. Comparison of the resulting MT impedance with the thin-sheet modelling data can be used for the estimation of the integral resistivity of the lithosphere . The "a priori" information needed for the modelling is first of all the on-land sediments conductance and the asthenosphere conductance. We have studied the influence of the limited "a priori" information on the accuracy of the TM mode interpretation of the Sea of Japan cable (JASC). The results of modelling are as follows: 1. If the on-land conductance changes from 15 to 150S the impedance modulus for periods > 2 days changes only at 5%. 2. If the asthenosphere conductance changes from 5000 to 10000 S the impedance modulus change for periods > 1 day is negligible. Thus the long-period study of the Sea of Japan lithosphere using JASC is possible with rather soft requirement to the "a priori" information. This work was supported by the Russian Basic Research Foundation (project 96-05-66183) 1.26p ELECTROMAGNETIC RADIATION: AN EFFICIENT TOOL FOR ENVIRONMENT MONITORING BY REMOTE SENSING V. Vajdea, C.Nitica, Anca-Marina Vijdea, Cristina Dumitrica Geological Institute of Romania, 1 Caransebes St., 78344 Bucharest e-mail: remosens@igr.sfos.ro ; remosens @igr.ro After a synoptic presentation of the electromagnetic spectrum, emphasizing the spectral bands in which the sensors of the main satellites for Earth observations operate, as well as the systems from the endowment for automatic image processing and GIS integration, there are shown for exemplification some important results related to applying remote sensing in solving some problems referring to environment monitoring and protection, which prove both the efficiency of this summit technology, and the consistency of the delivered data. Thus it is presented the CORINE Land Cover (CLC) map of Romania made up by computer-assisted photointerpretation of Landsat - TM images (band combination 4,5,3 assigned to red, green and blue), and for a test zone located in the North-Western part of the country the map and statistics of changes which occurred in biophysical land occupation in the period 1989 - 1993. Another example is given by the results obtained by studying the eutrophycation of waters in the Upper Arges catchment, materialized in the mean summer in-river phosphorus concentration map, satellite data playing an important role in the elaboration of this map. It should be emphasized that all examples previously mentioned were obtained within the framework of some projects of the PHARE programme, financed by the Commission of the European Union. There are also presented the results obtained by using remote sensing data in assessing the impact of some antropic activities upon the environment factors, as for example, the modifications in time of the landscape and the categories of biophysical land occupation in Rovinari mining district as an effect of lignite extraction in quarries or the pollution produced by atmospheric emissions (gases, heavy metals, black carbon) or residual waters from two industrial units in Copsa Mica zone. 1.27p Marine Electrosounding Complex (MEC) Based on the MHD generator. Authors: Ye.P.Velikhov, V.V.Yevstigneyev, A.S.Lisin, O.G.Matveenko, V.P.Panchenco, A.A.Yakushev (Troitsk Institute for Innovation and Fusion Research (TRINITI), 142092, Troitsk, Moscow Reg., Russia). The main facilities and technical parameters of the Marine Electrosounding Complex, that is being developed on the base of the MHD generator, are presented. Application of the MEC seems to be very important in hydrocarbon searching on the sea shelf, becouse it permits to obtain some additional independent information on sedimental rock structures of the sea bottom. This information allows to reduce by a factor of ~(1.5-2) the probability of errors in chosing boring objects defined according seismic investigetions. The technico-technological parameters of MEC also allow to realise any traditional methods for obtaining a deep and profile distributions of electrical characteristics of shelf bottom sedimental rocks. 1.28p SHALLOW TRANSIENT EM SOUNDING Author: V.Yu.Zadorozhnaya Nizhnevolzhsky Geology and Geophysics Research Institute 70, Moskovskaya Str., 410600, Saratov, Russia e-mail: ccvg@mail.saratov.ru Nizhnevolzhsky Geology and Geophysics Research Institute ac- cumulated a great experience of TEM usage for different geologi- cal problems solution. A survey was carried out for the sake of fresh water sources discovery available for village Novosergievka water supply (Orenburg region). Sandy formations were revealed in the intervals of 30-50 m and 70-90 m, which porosity factors had been calculeted. The results of recommended well drilling confirmed the primary forecast. A TEM survey was undertaken in Saratov Municipal Park for the sake of ground waters level determination in order to prevent its invasion to the area of unique oak grove. A survey was conducted in the mines of Bereznikovskoye po- tassium salts deposit for waterproof separation and salt formati- ons structure and conditions studying. Those works were carried out on the depth of 300 m, using the units of different dimenti- ons, which enabled to increase the scope of investigations and to improve the cross-section specification. A geological shelf survey was performed for the first time in the world on Taimir peninsula in the region of Cheluskin cape on the scale equal to 1:200000, using TEM investigations condacted from the ice surface. The method of sampling for the objects containing the polarizing layers was tested in the different regions of the former USSR for the following problems solution: discovery of oil bearing signs for the sediments containing oil resources, for overburden sediments and the sediments contouring oil deposit.