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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Geophysics and Geophysical Exploration
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Journal DOI :
Korean Society of Earth and Exploration Geophysicists
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Volume & Issues
Volume 1, Issue 3 - Nov 1998
Volume 1, Issue 2 - Aug 1998
Volume 1, Issue 1 - May 1998
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EM Tomography by Extended Born Approximations
Cho In-Ky ; Sim Hyun-Mi ;
Geophysics and Geophysical Exploration, volume 1, issue 3, 1998, Pages 155~160
EM tomography technique has been developed. The algorithm used the extended Born approximations for forward modeling and reconstructed a conductivity image by a smoothness constraint least squares inversion method. Observed data, the vertical components of secondary magnetic fields, were simulated with the 3-D integral equation code. The results showed that the location of anomalous body could be imaged very well, but conductivity of the body was lower than real one and the vertical resolution was much higher than the horizontal resolution.
Optimum Quality Control of Seismic Data of Kunsan Basin in Offshore Korea
Kim, Kun-Deuk ;
Geophysics and Geophysical Exploration, volume 1, issue 3, 1998, Pages 161~169
The Kunsan basin is a pull-apart basin which was formed during Tertiary. The pre-Tertiary section consists of various rock types, such as meta-sediments, igneous rocks, carbonates, clastics, and volcanics. Tertiary sections are the main targets for the petroleum exploration. In order to determine the optimum processing parameters of the basin, about 12 kinds of test processings were performed. The first main steps for the quality control is to determine the noisy or bad traces by examining the near trace section and shot gathers. The true amplitude recovery was applied to account for the amplitude losses due to spherical divergence and inelastic attenuation. Source designature and predictive deconvolution test were conducted to determine the optimum wavelet parameters and to remove the multiples. Velocity analysis was performed at 1km intervals. The optimum mute function was picked by locating the range of offsets which gives the best stacking response for any particular reflections. Post-stack deconvolution was tested to see if the quality of stacked data improved. The stacked data was migrated using a finite difference algorithm. The migration velocity was obtained from the stacking velocities using the time varying percentages. The AGC sections were provided for the structural interpretation. The RAP sections were used for DHI analysis and for the detection of volcanics.
Automatic Electrofacies Classification from Well Logs Using Multivariate Statistical Techniques
Lim Jong-Se ; Kim Jungwhan ; Kang Joo-Myung ;
Geophysics and Geophysical Exploration, volume 1, issue 3, 1998, Pages 170~175
A systematic methodology is developed for the prediction of the lithology using electrofacies classification from wireline log data. Multivariate statistical techniques are adopted to segment well log measurements and group the segments into electrofacies types. To consider corresponding contribution of each log and reduce the computational dimension, multivariate logs are transformed into a single variable through principal components analysis. Resultant principal components logs are segmented using the statistical zonation method to enhance the quality and efficiency of the interpreted results. Hierarchical cluster analysis is then used to group the segments into electrofacies. Optimal number of groups is determined on the basis of the ratio of within-group variance to total variance and core data. This technique is applied to the wells in the Korea Continental Shelf. The results of field application demonstrate that the prediction of lithology based on the electrofacies classification works well with reliability to the core and cutting data. This methodology for electrofacies determination can be used to define reservoir characterization which is helpful to the reservoir management.
Automatic Determination of the Azimuth Angle of Reflectors in Borehole Radar Reflection Data Using Direction-finding Antenna
Kim Jung-Ho ; Cho Seong-Jun ; Yi Myeong-Jong ; Chung Seung-Hwan ;
Geophysics and Geophysical Exploration, volume 1, issue 3, 1998, Pages 176~182
The borehole radar reflection survey can image the underground structure with high resolution, however, we cannot get any information on the orientation of the reflectors with dipole antenna alone. The direction-finding antenna system is commonly used to give the solution to the problem. However, the interpretation of the data from direction- finding antenna may be time-consuming, and sometimes have ambiguities in the sense of precise determination of the azimuth. To solve the problem, we developed the automatic azimuth finding scheme of reflectors in borehole radar reflection data using direction-finding antenna. The algorithm is based on finding the azimuthal angle possibly showing the maximum reflection amplitude in the least-squared error sense. The developed algorithm was applied to the field data acquired in quarry mine. It was possible to locate nearly all of the reflectors in three dimensional fashion, which coincide with the known geological structures and man-made discontinuities.
Waveform Estimation from Seismic Records
Lee, Doo-Sung ;
Geophysics and Geophysical Exploration, volume 1, issue 3, 1998, Pages 183~187
Seismic waveform estimation is based on the assumption that the seismic trace tying a well is one dimensional convolution of the propagating seismic waveform and the reflectivity series derived from well logs (sonic and density). With this assumption, the waveform embedded in a seismic trace can be estimated using a Wiener match filter. In this paper, I experimented a preprocessing procedure that applies both on the seismic trace and on the reflectivity series. The procedure is based on the assumption that the travel time can be estimated better from the seismic trace and that the instantaneous reflectivity values can be measured better on the well log. Thus the procedure is, 1) start-time adjustment and dynamic differential stretches are applied on the sonic log, and 2) seismic amplitudes are balanced such that the low frequency part of the seismic are matched to that of the reflectivities derived from well logs.