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- Volume 29, Issue 5, 1981
Geophysical Prospecting - Volume 29, Issue 5, 1981
Volume 29, Issue 5, 1981
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NON‐LINEAR ESTIMATION OF REFLECTION COEFFICIENTS FROM SEISMIC DATA*
Authors D. BILGERI and A. CARLINIAbstractFor years, reflection coefficients have been the main aim of traditional deconvolution methods for their significant informational content.
A method to estimate seismic reflection coefficients has been derived by searching for their amplitude and their time positions without any other limitating assumption. The input data have to satisfy certain quality constraints like amplitude and almost zero phase noise—ghosts, reverberations, long period multiples, and diffracted waves should be rejected by traditional processing. The proposed algorithm minimizes a functional of the difference between the spectra of trace and reflectivity in the frequency domain. The estimation of reflection coefficients together with the consistent “wavelet’ is reached iteratively with a multidimensional Newton‐Raphson technique. The residual error trace shows the behavior of the process. Several advantages are then obtainable from these reflection coefficients, like conversion to interval velocities with an optimum calibration either to the well logs or to the velocity analysis curves. The procedure can be applied for detailed stratigraphic interpretations or to improve the resolution of a conventional velocity analysis.
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DETERMINATION OF THE NATURE OF RESERVOIRS BY USE OF PATTERN RECOGNITION ALGORITHM WITH PRIOR LEARNING*
By P. BOISAbstractThe determination of the nature of reservoirs containing hydrocarbons is approached via a pattern‐recognition method with prior learning. This method consists of comparing the nature of a reservoir that has been drilled into with an unknown reservoir. The known reservoir plays the part of a monitor for the learning process. To this end an algorithm is compiled using the Burg method of the features represented by different portions of traces contained in the reservoirs. An analysis of the dots representing these different features serves as a criterion for deciding whether the two reservoirs have identical or different natures.
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OPTIMUM HYPERBOLIC MOVEOUT FILTERS WITH APPLICATIONS TO SEISMIC DATA*
By H. ÖZDEMIRAbstractOptimum multichannel filters can be designed to process seismic events falling on hyperbolic moveout curves using the conventional least‐squares method. Contrary to the linear moveout filters, autocorrelation and crosscorrelation functions inherent in the normal equations have to be computed numerically. However, computation times of filter coefficients are comparable to linear moveout operators.
For a given source‐receiver geometry and assuming straight ray‐path, relative moveout of a seismic reflection event is dependent on the two way arrival time and rms velocity. Consequently, to avoid overlapping of pass and reject moveout windows, hyperbolic moveout filters have to be designed over time gates rather than for the whole record lengths. Hyperbolic and hyperbolic‐linear moveout filters applied to synthetic and field seismic reflection traces show good signal‐to‐noise (S/N) ratio improvements. Results of some combined synthetic and field data examples are presented.
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SOIL CONSOLIDATION BEHAVIOR ASSESSED BY SEISMIC VELOCITY MEASUREMENTS*
Authors FALAH A.I. HAMDI and D. TAYLOR SMITHAbstractLarge gravity platforms are often used as alternatives to the more conventional pilesupported structures in hydrocarbon exploitation. A gravity structure, as opposed to the piled structure, is sitting on the sea floor by virtue of its weight and base width; as such it poses considerable problems for the site investigation engineer. One such problem is the calculation of the settlement of the structure and its time history; these depend upon the permeability and compressibility of the soil and its drainage conditions. The required data are usually obtained by sampling for subsequent laboratory testing. The collection of an undisturbed sample is beset by problems so that the consolidation behavior of the foundation material can only be inadequately assessed by laboratory testing. However, a series of laboratory consolidation experiments during which seismic velocities have been measured on the sample as consolidation proceeds shows that it is possible to reconstruct the stress‐strain and time‐dependent curves from the seismic data, once the initial void ratio and permeability of the soil are known. This leads the way to an in situ technique for predicting settlement using a combination of geophysical techniques (electrical resistivity and seismic velocities) to obtain the required engineering properties.
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LOW‐FREQUENCY STANDARD HYDROPHONE * FOR CALIBRATING LINE HYDROPHONE ARRAYS (SEISMIC STREAMERS) AND MARINE SEISMIC SOURCES **
Authors M.H. SAFAR and P. NEWMANAbstractThe design of a standard hydrophone with a maximally flat (Butterworth) response in the frequency range 8.0 Hz‐1.0 kHz is described. The standard hydrophone has been developed primarily for calibrating line hydrophone arrays (seismic streamers) and marine seismic sources.
The standard hydrophone has been used successfully during the past eight years for monitoring the output of a single air gun. It can be used for the calibration of a marine seismic streamer.
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A TIME‐DOMAIN APPROACH TO THE NORMAL‐INCIDENCE INVERSE PROBLEM*
More LessAbstractThis tutorial paper presents a time‐domain derivation of the Normal equations which are associated with the normal‐incidence inverse problem. Connections are made between our time‐domain derivation and the more familiar z‐transform transfer function derivation.
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RECURSIVE MIGRATION IN THREE DIMENSIONS*
Authors A.J. BERKHOUT and B.A. DE JONGAbstractA simple theory is presented to derive explicit recursive migration schemes in three dimensions which are suitable for situations with lateral velocity variations. The proposed schemes can be realized by one‐dimensional convolutions along the x‐axis and y‐axis. An investigation is made on the errors of each scheme. For each frequency component the amplitude error and the phase error are computed as a function of the immergence angle (dip). Based on the error analysis a critical discussion is given on the stability of explicit schemes.
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TECHNIQUE DE MESURE ET D'INTERPRETATION MINIMISANT LES ERREURS DE MESURES EN MICROGRAVIMETRIE*
Authors M. BICHARA, J.C. ERLING and J. LAKSHMANANAbstractDifferent sources of error influence gavity surveys, particularly shallow “micrograuity” sur‐veys. Experiments show that. the most frequent source of error in gravimetric prospecting is bad estimation of drift. Better control of drift exists with the field procedure and interpretation technique developed by the authors, as can be shown theoretically as well as experimentally. The method implies a random or semi‐random spatial sequence of measurement points. A real case of field prospecting is described.
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COMPUTATION OF THE ELECTRIC POTENTIAL IN THREE‐DIMENSIONAL STRUCTURES*
By H. SCRIBAAbstractA method has been developed for computation of the electrical DC potential of an arbitrary three‐dimensional resistivity structure using a finite difference method. The threedimensionality is necessary for interpretation of geoelectrical soundings with controlled point sources over a laterally inhomogeneous medium. Lateral inhomogeneities should be considered in resistivity soundings with large layouts. The results obtained with the described method permit a more realistic representation of geological features.
The resolution of the method is determined by the number of elements in the resistivity network. The problem of core memory space has been resolved by using random access disc files. The results computed using a Fortran program are in good agreement with analytically obtained solutions.
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ELECTROMAGNETIC FIELD OF SOURCES AT THE SURFACE OF A HOMOGENEOUS CONDUCTING HALFSPACE WITH HORIZONTAL ANISOTROPY: APPLICATION TO FISSURED MEDIA*
Authors D. LE MASNE and G. VASSEURAbstractThe electric and magnetic fields generated by horizontal electric and vertical magnetic dipoles lying on the surface of a conducting medium with horizontal anisotropy are investigated. Full expressions of their Fourier transforms are given, and the fields for a vertical magnetic dipole are calculated numerically. The radial and vertical magnetic components are found to be independent of the receiver‐transmitter direction, whereas the other magnetic and electric components strongly vary with this direction. These results give useful criteria for defining the direction and amplitude of anisotropy from ground data; a ground experiment on fissured limestone was found to confirm the expected variations of the various field components. It is believed that this electromagnetic method can be used in order to provide information about the direction and amplitude of electric anisotropy.
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Volumes & issues
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Volume 72 (2023 - 2024)
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Volume 71 (2022 - 2023)
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Volume 70 (2021 - 2022)
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Volume 69 (2021)
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Volume 68 (2020)
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Volume 67 (2019)
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Volume 66 (2018)
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Volume 65 (2017)
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Volume 64 (2015 - 2016)
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Volume 63 (2015)
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Volume 62 (2014)
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Volume 61 (2013)
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Volume 60 (2012)
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Volume 59 (2011)
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Volume 58 (2010)
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Volume 57 (2009)
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Volume 56 (2008)
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Volume 55 (2007)
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Volume 54 (2006)
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Volume 53 (2005)
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Volume 52 (2004)
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Volume 51 (2003)
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Volume 50 (2002)
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Volume 49 (2001)
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Volume 48 (2000)
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Volume 47 (1999)
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Volume 46 (1998)
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Volume 45 (1997)
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Volume 44 (1996)
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Volume 43 (1995)
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Volume 42 (1994)
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Volume 41 (1993)
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Volume 40 (1992)
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Volume 39 (1991)
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Volume 38 (1990)
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Volume 37 (1989)
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Volume 36 (1988)
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Volume 35 (1987)
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Volume 34 (1986)
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Volume 33 (1985)
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Volume 32 (1984)
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Volume 31 (1983)
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Volume 30 (1982)
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Volume 29 (1981)
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Volume 28 (1980)
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Volume 27 (1979)
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Volume 26 (1978)
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Volume 25 (1977)
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Volume 24 (1976)
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Volume 23 (1975)
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Volume 22 (1974)
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Volume 21 (1973)
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Volume 20 (1972)
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Volume 19 (1971)
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Volume 18 (1970)
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Volume 17 (1969)
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Volume 16 (1968)
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Volume 15 (1967)
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Volume 14 (1966)
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Volume 13 (1965)
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Volume 12 (1964)
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Volume 11 (1963)
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Volume 10 (1962)
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Volume 9 (1961)
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Volume 8 (1960)
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Volume 7 (1959)
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Volume 6 (1958)
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Volume 5 (1957)
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Volume 4 (1956)
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Volume 3 (1955)
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Volume 2 (1954)
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Volume 1 (1953)