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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Geophysics and Geophysical Exploration
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Korean Society of Earth and Exploration Geophysicists
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Volume & Issues
Volume 17, Issue 4 - Nov 2014
Volume 17, Issue 3 - Aug 2014
Volume 17, Issue 2 - May 2014
Volume 17, Issue 1 - Feb 2014
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A Suggested Method for Predicting Permeability of Porous Sandstone Using Porosity and Drying Rate
Ko, Eunji ; Kim, Jinhoo ;
Geophysics and Geophysical Exploration, volume 17, issue 3, 2014, Pages 121~128
DOI : 10.7582/GGE.2014.17.3.121
As the permeability is an important parameter to characterize the ease with which a porous medium transmits fluids, it is usually obtained by fluid flow experiment using core samples. In order to measure the permeability, however, an experimental apparatus is required and it might take long measurement time, especially for tight samples. In this study, the relationship between permeability and porosity as well as drying rate has been investigated to predict the permeability without a series of measuring experiments. Porosity is measured by drying monitoring method, which measures weight variation continuously while drying surface-dried saturated sample, and drying rate is obtained from weight variation ratio with respect to the water saturation. The total of 6 Berea sandstone samples, which have a permeability range of 70 to 670 mD, were used in this work, and a new and empirical equation which could predict permeability of porous sandstone by using porosity and drying rate were obtained through regression analysis.
Frequency-to-time Transformation by a Diffusion Expansion Method
Cho, In-Ky ; Kim, Rae-Yeong ; Ko, Kwang-Beom ; You, Young-June ;
Geophysics and Geophysical Exploration, volume 17, issue 3, 2014, Pages 129~136
DOI : 10.7582/GGE.2014.17.3.129
Electromagnetic (EM) methods are generally divided into frequency-domain EM (FDEM) and time-domain EM (TDEM) methods, depending on the source waveform. The FDEM and TDEM fields are mathematically related by the Fourier transformation, and the TDEM field can thus be obtained as the Fourier transformation of FDEM data. For modeling in time-domain, we can use fast frequency-domain modeling codes and then convert the results to the time domain with a suitable numerical method. Thus, frequency-to-time transformations are of interest to EM methods, which is generally attained through fast Fourier transform. However, faster frequency-to-time transformation is required for the 3D inversion of TDEM data or for the processing of vast air-borne TDEM data. The diffusion expansion method (DEM) is one of smart frequency-to-time transformation methods. In DEM, the EM field is expanded into a sequence of diffusion functions with a known frequency dependence, but with unknown diffusion-times that must be chosen based on the data to be transformed. Especially, accuracy of DEM is sensitive to the diffusion-time. In this study, we developed a method to determine the optimum range of diffusion-time values, minimizing the RMS error of the frequency-domain data approximated by the diffusion expansion. We confirmed that this method produces accurate results over a wider time range for a homogeneous half-space and two-layered model.
Discrimination between Earthquakes and Explosions Recorded by the KSRS Seismic Array in Wonju, Korea
Jeong, Seong Ju ; Che, Il-Young ; Kang, Tae-Seob ;
Geophysics and Geophysical Exploration, volume 17, issue 3, 2014, Pages 137~146
DOI : 10.7582/GGE.2014.17.3.137
This study presents a procedure for discrimination of artificial events from earthquakes occurred in and around the Korean Peninsula using data set in the Wonju KSRS seismograph network, Korea. Two training sets representing natural and artificial earthquakes were constructed with 150 and 56 events, respectively, with high signal to noise ratio. A frequency band, Pg(4-6 Hz)/Lg(5-7 Hz), which is optimal for the discrimination of seismic sources was derived from the two-dimensional grid of Pg/Lg spectral amplitude ratio. The corrections for the effects of earthquake magnitude and hypocentral distance were carried out for improvement of discrimination capability. For correcting the effect of magnitude dependence due to the inverse proportionality of corner frequency to seismic moment, the Brune`s source spectrum was subtracted from the observation spectrum. The spectrum was corrected using the optimal damping coefficient to remove damping effect with the hypocentral distance. The effect of locally varying spectrum ratio was cancelled correcting variation of wave propagation along the ray path. The performance in discrimination between training sets of natural and artificial events was compared using the Mahalanobis distance in each step of correction. The procedure of magnitude, distance, and path corrections show clear improvements of the discrimination results with increasing Mahalanobis distance, from 1.98 to 3.01, between two training sets.
Magnetic Data Analysis of the Chromium Mineralized Belt in Bophi Vum area, Northwestern Myanmar
Park, Gyesoon ; Heo, Chul-Ho ;
Geophysics and Geophysical Exploration, volume 17, issue 3, 2014, Pages 147~154
DOI : 10.7582/GGE.2014.17.3.147
For analyzing the distribution of chromite, magnetic survey was carried out on the chromium mineralized belt in Bophi Vum area, northwestern Myanmar. As a result, the magnetic susceptibility of chromite is lower than those of dunite and harzburgite, which are background rocks of chromite. Also, the locations of low magnetic anomaly zone and low magnetic susceptibility models of 3D magnetic inversion result are spatially well matched with those of chromite occurrences confirmed by the surface geological survey and trench survey. Some of low magnetic effects are expanded to the periphery area of chromite occurrences. Considering the magnetic susceptibility characteristics of various rocks in this area, the expanded low magnetic anomaly zones are estimated as the high potential areas bearing chromite. For confirming the potential area of chromite pointed by coarse magnetic survey, the additional detail exploration need to be carried out in future.
Response characterization of slim-hole density sonde using Monte Carlo method
Won, Byeongho ; Hwang, Seho ; Shin, Jehyun ; Park, Chang Je ; Kim, Jongman ; Hamm, Se-Yeong ;
Geophysics and Geophysical Exploration, volume 17, issue 3, 2014, Pages 155~162
DOI : 10.7582/GGE.2014.17.3.155
We performed MCNP modeling for density log, and examined its reliability and validity comparing the correction curves from physical borehole model. Based on the constructed numerical model, numerical modelings of density sonde in three-inch borehole were carried out under the various conditions such as the existence and type of casing or fluid, and also the stand-off between the sonde and borehole wall. These results of numerical modeling quantitatively reflect effects of casing and fluid in borehole, and moreover, demonstrate constant patterns with interval change from borehole wall. From this study, numerical modeling using MCNP shows a good applicability for well logging, and therefore, can be efficiently used for the calibration of well logging data under the various borehole conditions.
Three-dimensional Electromagnetic Modeling in Frequency Domain
Jang, Hannuree ; Kim, Hee Joon ;
Geophysics and Geophysical Exploration, volume 17, issue 3, 2014, Pages 163~170
DOI : 10.7582/GGE.2014.17.3.163
Development of a modeling technique for accurately interpreting electromagnetic (EM) data is increasingly required. We introduce finite difference (FD) and finite-element (FE) methods for three-dimensional (3D) frequency-domain EM modeling. In the controlled-source EM methods, formulating the governing equations into a secondary electric field enables us to avoid a singularity problem at the source point. The secondary electric field is discretized using the FD or FE methods for the model region. We represent iterative and direct methods to solve the system of equations resulting from the FD or FE schemes. By applying the static divergence correction in the iterative method, the rate of convergence is dramatically improved, and it is particularly useful to compute a model including surface topography in the FD method. Finally, as an example of an airborne EM survey, we present 3D modeling using the FD method.
Aeromagnetic Pre-processing Software Based on Graphic User Interface, KMagLevelling
Ko, Kwang-Beom ; Jung, Sang-Won ;
Geophysics and Geophysical Exploration, volume 17, issue 3, 2014, Pages 171~178
DOI : 10.7582/GGE.2014.17.3.171
Aeromagnetic survey generally require much more pre-processing steps than that of common land survey due to several complex and cumbersome steps included in pre-processing stage. Therefore it is desirable to use specific processing tool especially based on graphic user interface. For this purpose, aeromagnetic pre-processing software based on graphic user interface under the Windows environment, called
was developed and briefly introduced. In an aspect of its user-friendliness and originality, three noticeable features of
are summarized as the following (1) function of representation and handling for large amount of aeromagnetic data set as a visualization in the form of flight-path (2) function of selective exclusion of unwanted data by using survey area information expressed as polygon, and (3) function of selective removal processing for the irregular flight-path data acquired within the entire survey area by implementing the segmentation of flight-path technique.