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54th EAEG Meeting
- Conference date: 01 Jun 1992 - 05 Jun 1992
- Location: Paris, France
- ISBN: 978-90-73781-04-7
- Published: 01 June 1992
341 - 360 of 405 results
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Basic considerations for processing high-resolution marine seismic data
Authors P. Brussaard and T. M. McGeeAs faster and cheaper electronics have become available, the marine geophysics group at Utrecht have become increasingly active in the digital recording and processing of high-resolution marine seismic data. The ultimate goal is to invert the data and thereby estimate physical parameters of the sea-floor sediment. Prior to applying any inversion scheme, however, some basic "preprocessing" must be dove to remove artifacts of the recording technique employed. Some problems encountered while doing this "preprocessing" are discussed.
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Lithological parameters from shallow marine seismic surveys
Authors H. Steentoft, P. Gimpel and F. TheilenDevelopment of marine seismic instrumentation has been concentrated on generation and registration of compressional waves (p-waves). Successful applications of combined pand s-wave investigations on land surveys clearly demonstrated the advantages of these techniques (e.g . Helbig and Mesdag, 1982). In this paper survey techniques and instrumentations are presented for the generation, registration and interpretation of p -, and horizontally as well as vertically polarized s - waves in marine shallow water environments .
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Combined use of ELLOG data and borehole-to-surface DC measurements in environmental problems in Denmark
By P. M. DuchStainless steel electrodes were placed in 3 borings at and near a waste deposit located in the city of Aarhus, eastern Jutland, Denmark. The waste deposit is situated in a glacial river valley. Drinking water for the city of Aarhus is extracted from a lower aquifer consisting of fluvial deposits of varying composition with high permeable land/gravel formations interchanging with love permeable clay, silt and fine grained sand. The aquifer is covered by 20-30m thick moraine clay that is locally disturbed by the ice. The locations of the deposit areas and borings are shown on the opposite page .
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Non-destructive testing methods for scanning the near environment of buried sewer pips
By C. SchwarzeAt the present time, sewer systems are the most degraded urban infra-structure. In France, we estimate that the proportion of deteriorated sewers needing renovation is about 5% of the total linear, which represents 8000 km of non-visitable canalizations. The costs of reparation can be estimated between 50 and 100 billion francs.
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Integrated geophysical measurement on the Hallstatter glacier (Austria)
Study of glaciers may contribute to the solution of some scientific problems which have become important recently. More accurate determination of the size and geometry of glaciers may result in a more accurate estimation of the potential fresh water reserves and of impacts of climatic changes. In valleys endangered by ice-slide the preventive measures can be better arranged after heaving investigated the glacier and the ice-covered rock surface. In certain cases the glaciers are proper analogies for other geologic structures. Thus, obtained information from studying the structure of ice can be used in the interpretation of other tectonic phenomena as well.
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The power of reflection seismics for mapping of shallow layers
Authors H. Steentoft, W. Goedde and M. ThielA vast portion of shallow exploration requires non destructive methods with high resolution. For prospecting waste disposals it is necessary to map permeable and impermeable beds in a depth range of 10 to 100 m without any destruction of the impermeable layers to avoid a contamination of the ground water. The object of this paper is to show the power of high resolution reflection seismics in Quarternary ice-borne sediments in Northern Germany.
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Determination of permeability at shallow depth
More LessLandfills and hazardous waste sites are a major threat to the environment if pollutants are spreading towards groundwater reservoirs. A detailed investigation of the geological conditions on the ground and in the surroundings of landfills and waste sites is necessary to predict the potential danger. The key question is the determination of the permeability of the subsurface layering.
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An application of high resolution reflection seismics and some aspects on encountering problems arising from the particularities of the method
Authors V. Karastathis and J. LouisIn the last decade, we attend a rapid increase of the applications of shallow reflection, especially with engineering and hydrological targets. The developments in electronics, hardware and software computer technology helped the transferring of the most powerful and complex method of seismic reflection onto shallow situations doing so the method competitive in the cost and the results with the other conventional engineering geophysical methods.
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An integrated approach to the stability evaluation of prospective offshore sites
Authors D. Huws, M. Verschuren, A. Davis, M. de Batist, J. Bennell and J. -P. HenrietOffshore foundations can fail from one or a number of causes for example slope instability, reactivation of preexisting failure planes, or spontaneous liquefaction. In any seafloor site investigation for the erection of an offshore structure, the assessment of the potential failure mechanisme usually requires extensive geotechnical investigations with a close drilling programme. Such programmes are expensive and may still overlook major hazards. There is consequently a need for some other foren of site investigation, as a forerunner to and as an implementation of the traditional geotechnical reconnaissance techniques.
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Spatial sampling of cross-well wavefields
Authors J. Rector, J. Harris, S. Lazaratos and M. van SchaakRecently cross-well reflection surveys have been used to provide high resolution images between boreholes (Lazaratos, et al, 1991). Cross-well reflection imaging provider an advantage over traveltim tomography, allowing imaging of reservoir interval at and below the base of wells. With traveltime tomography, reliable images can only be produced for zones far above the well TD depth.
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Possibility for monitoring seismic sources in boreholes
Authors P. Carrion, J. Carcione and G. SerianiIn this work, we report a feasibility study for monitoring seismic sources in boreholes. We compute the radiation patterns of borehole sources for different frequency ranges and the load directions. A study of radiation patterns is certainly important and not only to predict all possible seismic events but also to analize the source performance itself. This study has several practical applications: for example, if a source of seismic energy corresponds to a rotational load (as in a drill-bit experiment), the measured three component displacement field can be an indicator to conclude whether the source drilling performance is satisfactory or not.
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Moving point mechanism representation for low frewuency monopole borehole sensors
Authors A. L. Kurkjian, B. de Hon, J. E. White, A. T. de Hoop and T. L. MarzettaIn this paper we derive the equivalent line mechanism for the case of low frequency monopole sources and receivers in boreholes. This line mechanism is equal to a point mechanism which propagates at the speed of tube waves. This was first recognized and treated in White and Sengbush (Geophysics, 28, p. 1001-1019). The resulting far-field radiation (or receptivity) pattern is a generalization of that published by Lee and Balch (Geophysics, 47, p 1308-1314) in that it addresses the case where the shear velocity is close to or slower than the tube wave speed. The equivalent moving point representation can be incorporated into existing modeling codes, thereby avoiding the need to directly model the borehole. Furthermore, realistic borehole environments (such as casing, caliper logs, curved welk, anisotropic formations, etc) can be incorporated into the equivalent representation.
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Backus averaging, scattering and drift
Authors M. S. Sams and P. R. WilliamsonIn certain kinds of finely-layered media seismic waves propagate as if the medium was replaced by its homogeneous transversely isotropic equilivant whose elastic constants are given by the averaging formulae of Backus (1962). These formulae were obtained under the assumtion that the distrubution of the properties of the layers is statistically stationary on the scale of the averaging length, 1, which must itself be much less than a wavelength.
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Inelastic absorption effects on the integration of borehole and subface seismic data
Authors T. S. Jackson and T. J. O‘RourkeTiming and character mismatches between borehole and surface seismic are often encountered when correlating and calibrating seismic data. Even after block shifts are applied, a good match at shallow depths can gradually deteriorate into a mis-tie of up to 20 msec in the target area. Once events have been correlated in a single well this mis-tie is often at tributed to well deviation or poor migration of the surface data. These time variant misdes pose a critical problem when a large number of wells are examined in a workstation environment. For example, wavelet matches appear to be time variant and the translation of physical parameters from one data set to the other will be wrong: In a number of cases inelastic absorption has proved to be the cause; compensation of this Q effect has provided a solution, often with the added benefit of improved vertical resolution.
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The two-level wavefield separation method applied to walkaway VSP data
Authors J. P. Kvarstein, T. Hilton and L. E. BergMany of the different methods for separation of VSP data into downgoing and upgoing wave modes are based on the assumption that there is a difference in moveout between the two wave modes. Examples are the approaches that involve alignment of the desired signal followed by median filtering, and the approaches that involve velocity filtering. These methods can, even when they are implemented as data adaptive, cause significant errors on the result in cases with large offsets or steep dips.
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Automater airborne EM anomaly picking and interpretation
By J. MacnaeAirborne electromagnetic (AEM) systems can collect very significant quantities of data on a daily basis. Traditional methods of data interpretation for urineral prospecting involve the visual scanning of 20 or more wiggle traces on rolls of paper, looking for local "anomalies" , from each of which a few characteristic parameters are estimated such as amplitudes on a few channels, anomaly width and shape. These extracted parameters are then compiled onto a map for subsequent ground follow-up. In conductive areas alternative presentations such as contours of individual channels or channel ratios are commonly attempted. Only the "best" anomalies are usually looked at in detail or quantitatively interpreted, and experience has shown that economically significant responses may at times be misinterpreted or even completely missed, patticularly if the source is deep and its anomaly small and broad .
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Case study: mapping of groundwater conditions at Olkiluoto site with electrical and electromagnetic soundings
Authors P. Saksa and M. PaananenTeollisuuden Voima Oy (TVO) carries out site investigations for the selection of the site for disposal of spent nuclear fuel. One of the five candidate areas is Olkiluoto island on the western coast, and where TVO's nuclear power plant is located. The bedrock at Olkiluoto is 1800 Ma old highly metamorphosed fractured gneiss. The characterization program comprises a sequence of investigations focussing on the modelleng and evaluation of groundwater flow conditions. One of the studies is the mapping of the existence of chemically different water bodies or layers down to the depth of 1000 meters
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Clarification of structural problems of a lignite bed near Soma (Turkey) using gravity and geoelectric methods
Authors Z. Szorenyi, P. Kardevan and L. VertesyA case history on the methodology applied in an integrated geophysical survey for lignite prospecting performed near Soma is presented. The tanks of geophysics were to describe tectonic features of the study area located in the vicinity of a lignite mine under production, to determine the depth and the orientation of the sequence containing lignite seams, moreover to delineate the lignite bed accurately. The lignite seams are embedded in Miocene marl-limestone sequence overlying high resistivity Triassic basement.
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Electromagnetic response of a discretely grounded circuit: an integral equation modelling approach
Authors W. Qian and D. E. BoernerIn this paper we will develop an integral equation approach to model the electromagnetic response of a discretely grounded circuit. This approach, unlike those developed Barlier (Nelson, 1977 ; Wait, 1984), takes into account the electromagnetic (EM) induction coupling between the discretely grounded circuit and the conductive earth.
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Case histories of interpreting LOTEM sign reversals
Authors A. Hordt, B. Kriegshauser and K. -M. StrackDue to the rapid development of technology and interpretation techniques, transient electromagnetic (TEM) methods are nowadays available for a wide range of applications, such as hydrocarbon exploration, geothermal resarch and Jeep crustal studies. The long-offset transient electromagnetic (LOTEM) method is one of those methods with a large depth of investigation (a few kilometers). In many cases, LOTEM can yield complementary information to seismics and thus contributes to exploration problems.
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