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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
301 - 315 of 315 results
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Transmission and reflection tomography using Gaussian beams
By B. LehmannSince over seven years DMT - Institut für Angewandte Geophysik has developed soft-and hardware to perfom tomgraphic surveys in mines and between boreholes and tunnels (Gelbke, 1985; Gelbke et al., 1988; Krajewski et al., 1989). The new development of a program package to invert traveltime and amplitude data wil! be presented. For the inversion not only the first arriving traveltimes or amplitude onsets but also the later arrivals from refracted and reflected waves are used.
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Anisotropic tomography: part II, algorithm and examples
Authors R. Michelena, F. Muir and J. HarrisAs discussed in Part I of this paper, we believe it is often useful to model the elastic properties of reservoir and associated rocks as anisotropic, and, in particular, we have argued in favor of a monoclinic model with horizontal symmetry plane. For simplicity, we choose a subset model for this paper, transversely isotropic with vertical symmetry axis.
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Radon and Kirchhoff migration
By M. NovotnyHigh-frequency asymptotics of Radon and Kirchhoff wavefield extrapolators are studied. Using the stationary phase method it is found that the Radon extrapolator degenerates into the Rayleigh-Sommerfeld solution of the Oirichlet problem in the far-field zone. The derivation is done for the 3-D and 2-D cases.
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EOS - Exploration oriented seismic modelling
Authors A. Bhele, P. Berg, J. Carcione, F. If, C. Jastrami, D. Kosloff, P. Nielsen, E. Priolo, G. Seriani, O. Skovgaard, E. Tessmer and G. TessmerAn objective of the EOS project is to develop advanced 3D seismic forward modelling methods and algorithms, resulting in computer program prototypes, which can handle economically seismic wave field simulations in laterally inhomogeneous full scale modeIs, in special situations (surface layers, offshore, VSP) or in special rheologies (viscoelastic, anisotropic).
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Acoustic modelling on a grid of vertically varying spacing
Authors C. Jastram and A. BehleIn many cases the efficiency of high-order finite differencing schemes and the Fourier method for the acoustic wave equation is limited as the differencing operators are applied to a uniform grid. To improve this a differencing scheme is introduced in which the grid spacings can be extended or reduced by any integer factor at a given depth. This scheme adds more flexibility and efficiency to the acoustic modelling as the grid spacings can be changed according to the material properties and the model geometry. The time integration is done by the Rapid Expansion Method (REM). The only additional computational effort of the modelling scheme is eaused by the requirement to interpolate the pressure on a strip of the computational mesh where the grid spacings change.
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Seismic modelling of a near-surface structure by the Chebyshev method
Authors P. Krajeweski, E. Tessmer and G. TessmerThe weathered zone is usually composed of unconsolidated soil, the seismic properties of which can be highly variable, especially in the vicinity of the earth's surface. The weathered zone and the free surface have a large influence on the generation and the recording of seismic energy, especially in horizontal seismic profiling where both, the source and the receivers are located near to or at the surface.
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Modelling guided waves in thin-layer sedimentary reservoirs in cross-hole surveys
Authors M. Lou and S. CrampinIn enhanced oil recovery (EOR) operations, reservoir engineers require high resolution (of the order of 1 m) to exploit the resources by optimal techniques. This resolution is unlikely to be achieved in thin layers in sedimentary reservoirs by conventional techniques (reflection profiles or VSP), where only a small proportion of the travel path is in the zone of interest, and crosshole surveys appear increasing attractive in production geophysics.
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Calculation of spherical wave reflection and transmission coefficients and their application to shallow seismic exploration
More LessThe reflection and transmission coefficients of spherical waves vary strongly and in a more complicated manner to changing layer parameters than do the plane wave coefficients (figures 1 and 2). The difference between both types of coefficients increases when the radius of curvature of the wavefront approaches the order of the seismic wave Length. This is often the case in shallow seismic prospecting where the depth of exploration is between somet tens and a hundred meters.
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Attenuation in random medial amplitude effects from phase fluctuations
More LessTwo main approaches have been used to describe the attenuation due to scattering by random inhomogeneities. One approach describes the attenuation as the fractional energy 1055 due to scattering (Chernov 1960, Wu 1989). The other approach derives the attenuation of the mean field by ensemble-averaging of stochastic wavefield realizations (Keller 1964). In this paper, we will concentrate on the latter approach. We discuss some conceptional differences to the energy approach and point out important consequences for its application in an exploration seismic environment.
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Seismic raytracing using linear traveltime interpolation
Authors E. Asakawa and T. KawanakaWe propose a new raytracing method which can compute traveltimes and raypaths in a two-dimensional velocity structure more rapidly and accurately than conventional methods. Our method is formulated as a raytracing for a cell structure, whereas the finite difference method of the eikonal equation is formulated on a regular grid. Therefore our method is more appropriate for cell ray tomography analysis.
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Accurate and efficient seismic modelling in random media
Authors G. Kneib, R. Pestana and C. KernerNumerical modelling techniques are increasingly applied to study scattering phenomena of wave propagation in random media. Frankel and Clayton (1984) and other authors (see Frankel, A., 1989) successfully used explicit finite difference (FD) schemes solving the heterogeneous wave equation with second or fourth order approximations of the differentlal operator. In this paper the potential of using higher order FD schemes in random media problems is investigated. Increasing the order leads in the limit to the pseudospectral method (Fornberg, B., 1987). The various FD schemes and the pseudospectral method are compared with respect to accuracy and efficiency.
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Electric investigations in sulphide mineralisation in the Majdanpek copper mine area, Yugoslavia
Authors S. Kostic and S. KomatinaThe results obtained by application of the electric investigations methodology in the region Vlaole-Jasikovo near Majdanpek are presented. The possibilities of electric methods and detailed investigations of copper and polimetallic mineralisations are given. In the paper the examples which illustrate phases in the investigation with the results which contributed to the discovery of the two hidden ore bodies in Coka Marin locality, are cited.
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Controlled seismic illumination of hydrocarbon reservoirs
Authors W. E. A. Rietveld, A. J. Berkhout and C. P. A. WapenaarThe purpose of redatuming is to transform surface data in such a way that the acquisition level is transported from the surface to another level ('datum') somewhere in the subsurface. This can be done by removing the propagation effects at the source and at the receiver side (Berryhill, 1984).
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Common offset depth migration using finite difference raytracing
More LessIn the last few years pre-stack depth migration has come to be routinely used to solve problems in complex geological areas. Two methods to accomplish pre-stack depth migration that have been widely publicised are shotrecord migration (SRM), and alternate shot and receiver downward continuation, of ten referred to as full pre-stack migration (FPM).
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Tutorial: Expert systems in oil exploration and production
By L. MatteiniThis tutorial is addressed to all geoscientists who are seeking an introduction to the advantages,
problems and opportunities involved in using expert systems technology in geophysics and
geology for oil exploration and production.
Recently, many successful applications in several areas, including the petroleum industry, have
transformed expert systems from lab technology into real world applications. In fact, because
expert systems are able to process and distribute knowledge, they play a fundamental role in
this field.
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