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53rd EAEG Meeting
- Conference date: 26 May 1991 - 30 May 1991
- Location: Florence, Italy
- ISBN: 978-90-73781-03-0
- Published: 28 May 1991
241 - 260 of 315 results
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Depth determination from gravity gradients
Authors M. M. Gobashy, E. M. Abdelrahman and A. I. BayoumiEstimation of the depth to a buried structure from the horizontal or vertical gravity gradients (Hammer and Anzoleaga, 1975; and Stanley and Green, 1976) has drawn considerable attention. The simplest and most widely used method to determine the depth of a buried structure from gravity gradients is the Xe-rule (Piek et al., 1973).
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An efficient 2D resistivity inversion technique and its application
By H. ShimaFor two-dimensional (2-D) resistivity analysis, a number of inversion techniques have already been proposed (e.g., Shima,1990). However when underground is close to a horizontally layered structure, an one-dimensional (1-D) assumption is considered to be more effective in arriving a further accurate solution. To make the 1-D assumption more useful, I propose a filtering procedure that improves the sensitivity characteristics of the potenrial data obtained by a pole-pole array.
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Regional tectonics derived from gravity gradients
Authors E. Kilenyi and Z. SzaboTwo-dimensional filtering of Bouguer anomaly maps enhances different 'wavelengths' according to the applied parameters. The meaning of wavelength in gravity can be interpreted in a more familiar way: long waves - regional anomalies, short waves residual anomalies, very short waves - derivatives.
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Magnetic-anomaly map of the Republic of Yemen
More LessA standardised composite magnetic-anomaly map of the Republic of Yemen is presented. This has been compiled from 23 airborne surveys of widely differing specifications undertaken between 1975 and 1985. The airborne magnetic surveys flown on behalf of the Natural Resources Project of the Ministry of Oil and Mineral Resources over the central parts of the Republic of Yemen in 1985, which included a high altitude regional coarse grid survey, completed the magnetic coverage of the Republic. The magnetic-anomaly map of the Republic of Yemen has been produced by The Robertson Group plc for the Natural Resorces Project. The surveying and compilation was primarily financed by loans from the Arab Fund for Economic and Social Development with technical assistance from the United Nations Department of Technical Co-operation and Development (UN/DTCD).
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A new view of the gravity and aeromagnetic fields in the UK
Authors I. F. Smith, M. K. Lee, C. A. Green, A. J. W. McDonald and K. E. RollinPublished maps showing the regional coverage of both gravity and aeromagnetic data for the land and parts of the sea areas of the UK have been available for a number of years. These data are now available in digital form, which allow the geophysicist to take advantage of advanced analytical and imaging techniques. Horizontal and vertical derivatives, inversions, grey-scale and colour shaded relief plots are startlingly effective in defining structural trends and characteristic anomaly pattems.
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Integrated interpretation of borehole investigations for structural modelling of crystalline bedrock
By P. PitkanenThe poster presents an integrated approach to use various borehole investigation methods in order to analyze structural and hydrological properties of crystalline bedrock. Geological and geophysical borehole data are interpreted to obtain engineering geological structures of the rock mass. The results are applied for the creation of three-dimensional bedrock models. The structural interpretations are also used as a basis for geohydrological modelling.
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Integrated presentation of all data from well
More LessThe goal of this paper is to illustrate what can be achieved by using all available information in integrated form with the help of composite log, for correlation, formation evaluation and documentation.
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Multiple offset VSP and multiple component VSP data processing to improve structural definition
Authors E. del Pino and E. RamirezA flower structure with two prospective blocks was drilled in the northem central part of Lake Maracaibo. In order to define the structural position of the fault plane separating the two blocks and its distance from a well driIled into the upper block, a multi offset 3 component VSP was acquired immediately upon penetration of the top of the structure.
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VSP and steep reflectors: A case history of data processing and interpretative modelling
Authors F. Ogliani and J. MullerIn the presence of dipping reflectors, a zero-offset VSP allows a lateral investigation far from the well. In data processing, such property is routinely exploited when reflectors are gently dipping or involved in salt tectonics. Some aspects, however, may become not familiar or problematic, when structural dips exceed 45 degrees.
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Evaluation of the VSP technique in the northern part of the Oseberg Field - A case history
Authors H. Rutledal, S. E. Johnstad and V. DanielsenThe Oseberg Field was discovered in 1979 and is located in the North Sea Norwegian Blocks 30/6 and 30/9 about 140 km west-northwest of Bergen. The field is a fault trap reservoir with about 600 m of structural relief at top reservoir level, and consists of three major eastwardly rotated fault blocks: Alpha, Gamma and Alpha North.
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Use of walkaway VSP in imaging a pre-zechstein reservoir in the UK Southern Gas Basin
Authors J. M. Smidt, P. Conn and M. LappinThe results of many VSPs are disappointing because they have not been planned in detail, and processing has not been optimised to achieve the prime objectives due to lack of communication between the specialists involved in planning, acquiring, processing and interpreting the data. In the case study reported here the close co-operation between interpreter, technical advisor and VSP processing geophysicist resulted in a carefully designed survey and an optimised processing sequence which fulfilled the planned objective and yielded further information.
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Some characteristics of coupled wave propagation
More LessCoupled wave propagation describes propagating wavefields of different physical quantities; hereby it is possible that all those fields interact with each other. In exploration geophysics coupling effects are generally believed to be small enough to be neglegable. Comparing different material relevant to exploration, however, shows that coupling can contribute to noticable propagation effects.
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Effects of processing on three-component shear-wave data
Authors P. K. Schruth and I. BushRecent developments in seismology have led to an increase recording of three-component (3-C) data, in particular for the study of seismic anisotropy where shear-waves have vector polarizations in three dimensions. By carrying information about the symmetry structure along the raypath the polarization of shear-waves can be used to evaluate the parameters of the anisotropy and hence provide information about the internal structure of the rock (S. Crampin, 1985). Crampin has shown in numerous papers that shear-waves are particularly sensitive to changes in crack- and pore-geometry caused by changes in pore-pressure, pore-fluid properties and the orientation of the stress field that aligned the cracks.
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Seismic velocities of marine sediments in box cores with concentration on the relationship between shear strenght and shear wavevelocity
Authors I. A. Pecher, Fr. Theilen and S. NebenThe determination of geotechnical parameters at the sea floor is of growing importance for engineering purposes. The measurement of compressional (P-) and especially shear (S-) wave velocities seems to he an appropriate method for the estimation of other physical properties in marine sediments.
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P-S waveseparation using parametric inversion: An offset VSP case study
Authors D. Belaud and W. S. LeaneyThe separation of interfering compressional and shear wavefields is an important problem in the processing of three-component offset VSPs,where, because of the raypath obliquity, the amount of converted shear energy may be significant compared to the P energy.
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S-Wave velocities and shallow layering in a Campi Flegrei site (Naples) through R-wave spectral analysis
Authors F. M. Guadagno and C. NunziataThe Spectral Analysis of Surface Waves (SASW) method is a nondistructive seismic testing aimed to determine shear wave velocities and layering from surface measurements of artificially generated Rayleigh waves (R-Waves). The SASW method has been mostly employed in the evaluation of the elastic properties of pavements (Heysey et al. 1982; Nazarian and Stokoe, 1983) and was also experimented for determining shear wave velocity profiles in a liquefaction susceptible site.
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Images of rock properties estimated from a crosswell seismic velocity tomogram
More LessMethods for obtaining an accurate image of the upper crust in terms of seismic velocities have evolved rapidly during the last decade, especially with well-to-well tomography techniques: well-to- well tomography allows us to constrain velocities more than with classical reftection seismology methods. At the same time, laboratory experiments have increased our knowledge of the influence of rock properties, such as porosity, saturation or clay content, on acoustic measurements. Our goal is to use results obtained in the laboratory for the interpretation in terms of porosity of an actual cross-well survey. Three different approaches are used: applying (1) geostatistical techniques, (2) rock physics relations obtained in the laboratory, and (3) a combination of geostatistics and rock physics.
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Direct estimation of lithology or compaction from seismic and well log data
Authors O. Sylta and J. HelgesenTraditionally, compaction has been determined from seismic stacking velocities or sonic logs. The use of stacking velocities requires a considerable human effort, since consistent velocity picks must be obtained. We propose to fit a depth dependant velocity function to seismic travel time information using the semblance criterion, and thereby obtain estimates of important parameters describing lithology and compaction. The need for human interaction is thus reduced, and more reliable estimates are obtained. Furthermore, the method uses all available travel time information in the depth interval to be analyzed, including zones of weak reflections.
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A comparison of petrophysical equations for extrapolation of lithilogy beyond well locations using seismic data
Authors S. H. Archer and R. D. MartinezSeveral alternative petrophysical models exist for relating the seismic properties of rocks to the elastic parameters of the rock constituents. This paper shows the effect of some alternative petrophysical models on the extrapolation of lithology using seismic data.
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Rock samples microcracks produced by temperature, hydrostatic pressure and fluid pressure stresses: electrical responses and acoustic emissions
Authors G. Losito, M. Muschietti, A. Trova and E. BiagiDuring the last years, many laboratory experiments have been carried out to study electrical properties of rock samples subjected to temperature, hydrostatic pressure and internal pore fluid pressure cycles. For the experiments an "ad hoc" apparatus has been designed at Applied Geophysical Laboratory of University of Florence, that can condition temperature (up to 300 ·C), hydrostatic pressure (up to 40 MPa) and internal pore fluid pressure (up to 40 MPa).
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