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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 15, Issue 4 - Nov 2012
Volume 15, Issue 3 - Aug 2012
Volume 15, Issue 2 - May 2012
Volume 15, Issue 1 - Feb 2012
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Rayleigh-wave Phase Velocities and Spectral Amplitudes Affected by Insertion of an Anomalous Velocity Layer in the Overburden
Kim, Ki Young ; Jung, Jinhoon ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 155~162
DOI : 10.7582/GGE.2012.15.4.155
The Thomsen-Haskell method was used to determine sensitivities of the Rayleigh-wave phase velocities and spectral amplitude of vertical ground motion to insertion of a single velocity-anomaly layer into overburden underlain by a basement. The reference model comprised a 9-m thick overburden with shear-wave velocity (
of 300 m/s above a half-space with
Effective Porosity Variation of Cement Samples According to Vacuum Pressure and Time
Lee, Sang Kyu ; Lee, Tae Jong ; Kim, Hyoung Chan ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 163~176
DOI : 10.7582/GGE.2012.15.4.163
Effective porosity has been measured for cement specimen as a function of vacuum time and pressure in the vacuum saturation process. Six cement specimen are used; three of them are made of the same ratio of cement and sand, the other three are 100% cement mortar, of which average porosity is about 25% and 40%, respectively. Using the 6 samples, measured effective porosities are compared and examined with 5 different vacuum pressures (2, 4, 6, 8, 10 torr) and times (20, 40, 60, 80, 100 minute), respectively. Comparing measured effective porosity from experiments when vacuum time varies from 100 minute to 20 minute with 20 minute step and vacuum pressure is fixed to 10, 6, and 2 torr, average deviation decreases as 0.6, 0.5, and 0.2% respectively. Comparing measured effective porosity from experiments when vacuum pressure varies from 2 torr to 10 torr with 2 torr step and vacuum time is fixed to 100, 60, and 20 minute, average deviation increases as vacuum time decreases. These results can be a background of suggested method of ISRM that describes the vacuum time longer than 60 minute and vacuum pressure higher than 6 torr. In this study, only qualitative discussion can be possible for the effects on the effective porosity by decreasing 20 minute vacuuming time at the same pressure or by decreasing 2 torr of vacuum pressure at the same vacuum time. This is because the sample could not reached to perfectly dried condition even though the sample were dried at
and following the ISRM suggested method, so that initial water content could not be the same at each experiment.
Geostatistical Approach to Integrated Modeling of Iron Mine for Evaluation of Ore Body
Ahn, Taegyu ; Oh, Seokhoon ; Kim, Kiyeon ; Suh, Baeksoo ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 177~189
DOI : 10.7582/GGE.2012.15.4.177
Evaluation of three-dimensional ore body modeling has been performed by applying the geostatistical integration technique to multiple geophysical (electrical resistivity, MT) and geological (borehole data, physical properties of core) information. It was available to analyze the resistivity range in borehole and other area through multiple geophysical data. A correlation between resistivity and density from physical properties test of core was also analyzed. In the case study results, the resistivity value of ore body is decreased contrast to increase of the density, which seems to be related to a reason that the ore body (magnetite) includes heavy conductive component (Fe) in itself. Based on the lab test of physical properties in iron mine region, various geophysical, geological and borehole data were used to provide ore body modeling, that is electrical resistivity, MT, physical properties data, borehole data and grade data obtained from borehole data. Of the various geostatistical techniques for the integrated data analysis, in this study, the SGS (sequential Gaussian simulation) method was applied to describe the varying non-homogeneity depending on region through the realization that maintains the mean and variance. With the geostatistical simulation results of geophysical, geological and grade data, the location of residual ore body and ore body which is previously reported was confirmed. In addition, another highly probable region of iron ore bodies was estimated deeper depth in study area through integrated modeling.
A Study on Spine and Rib Properties for Standoff Compensation, Density Log
Kim, Yeonghwa ; Kim, Jongman ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 190~198
DOI : 10.7582/GGE.2012.15.4.190
A series of density log data were obtained from the standoff experiments made in the four physical model boreholes of different densities, and the properties of spine and rib curves have been derived by the analysis of the gamma-gamma data. Particularly, the shape of gamma ray propagation path between source and detector, the geometrical property of spine and rib curves, the influence of borehole density and the detector combination on the properties of the curves, and the adequate detector combination for standoff compensation could be discussed. It was also confirmed that spine and rib slopes can be expressed as proportional to source-to-detector distance ratio between far and near detectors. The result of this experiment was also effectively applied for understanding the basic concept of spine and rib slopes.
Swell Noise Attenuation Using a Cascade of F-X Filter and Median Filter
Kim, Sookwan ; Hong, Jong Kuk ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 199~208
DOI : 10.7582/GGE.2012.15.4.199
High-amplitude swell noises (HASN) are very difficult to eliminate from the marine seismic data. In this paper, we applied F-X filter and median filter in order to suppress HASN. Test data have been acquired on the northern offshore of the South Shetland Islands in December, 2010. Parts of data have been contaminated by HASN caused by bad weather during the cruise. We applied F-X filter and median filter to test data with HASN. After F-X filtering, most of non-coherent noises and small-amplitude swell noises are eliminated effectively but HASN are still remained significantly. With median filter, HASN was suppressed better than F-X filter, however some of non-coherent noises are still remains. We applied a cascade of two filters and results show HASN and non-coherent noises are suppressed effectively. After the cascade of two filtering, it is possible to define reflection layers clearly on the velocity spectrum and to produce better stacked section with a good signal-to-noise ratio.
Repeatability and Reproducibility in Effective Porosity Measurements of Rock Samples
Lee, Tae Jong ; Lee, Sang Kyu ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 209~218
DOI : 10.7582/GGE.2012.15.4.209
Repeatability and reproducibility in solid weight and effective porosity measurements have been discussed using 8 core samples with different diameters, lengths, rock types, and effective porosities. Further, the effect of temperature on the effective porosity measurement has been discussed as well. Effective porosity of each sample has been measured 7 times with vacuum saturation method with vacuum pressure of 1 torr and vacuum time of 80 minutes. Firstly, effective porosity of each sample is measured one by one, so that it can provide a reference value. Then for reproducibility check, effective porosity measurements with vacuum saturation of 2, 4, and 8 samples simultaneously have been performed. And finally, repeated measurements for 3 times for each sample are made for repeatability check. Average deviation from the reference set in solid weight showed 0.00
, which means perfect repeatability and reproducibility. For effective porosity, average deviations are less than 0.07% and 0.05% in repeatability and reproducibility test sets, respectively, which are in good agreement too. Most of porosities measured in reproducibility test lies within the deviation range in repeatability test sets. Thus, simultaneous vacuum saturation of several samples has little impact on the effective porosity measurement when high vacuum pressure of 1 torr is used. Air temperature can cause errors on submerged weight read and even effective porosity, because it is closely related to the temperature, density, and buoyancy of water. Consequently, for accurate measurement of effective porosity in a laboratory, efforts for maintaining air or water temperature constant during the experiment, or a temperature correction from other information are needed.
A study on slim-hole neutron logging based on numerical simulation
Ku, Bonjin ; Nam, Myung Jin ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 219~226
DOI : 10.7582/GGE.2012.15.4.219
This study provides an analysis on results of neutron logging for various borehole environments through numerical simulation based on a Monte Carlo N-Particle (MCNP) code developed and maintained by Los Alamos National Laboratory. MCNP is suitable for the simulation of neutron logging since the algorithm can simulate transport of nuclear particles in three-dimensional geometry. Rather than simulating a specific tool of a particular service company between many commercial neutron tools, we have constructed a generic thermal neutron tool characterizing commercial tools. This study makes calibration chart of the neutron logging tool for materials (e.g., limestone, sandstone and dolomite) with various porosities. Further, we provides correction charts for the generic neutron logging tool to analyze responses of the tool under various borehole conditions by considering brine-filled borehole fluid and void water, and presence of borehole fluid.
A study on slim-hole density logging based on numerical simulation
Ku, Bonjin ; Nam, Myung Jin ; Hwang, Seho ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 227~234
DOI : 10.7582/GGE.2012.15.4.227
In this study, we make simulation of density log using a Monte Carlo N-Particle (MCNP) algorithm to make an analysis on density logging under different borehole environments, since density logging is affected by various borehole conditions like borehole size, density of borehole fluid, thickness and type of casing, and so on. MCNP algorithm has been widely used for simulation of problems of nuclear particle transportation. In the simulation, we consider the specific configuration of a tool (Robertson Geologging Co. Ltd) that Korea institute of geoscience and mineral resources (KIGAM) has used. In order to measure accurate bulk density of a formation, it is essential to make a calibration and correction chart for the tool under considerations. Through numerical simulation, this study makes calibration plot of the density tool in material with several known bulk densities and with boreholes of several different diameters. In order to make correction charts for the density logging, we simulate and analyze measurements of density logging under different borehole conditions by considering borehole size, density of borehole fluid, and presence of casing.
A Review on nuclear magnetic resonance logging: fundamental theory and measurements
Jang, Jae Hwa ; Nam, Myung Jin ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 235~244
DOI : 10.7582/GGE.2012.15.4.235
Nuclear magnetic resonance (NMR) logging has been considered one of the most complicated nevertheless, one of the most powerful logging methods for the characterization on of both rocks and natural fluids in formation. NMR measures magnetized signals (polarization and relaxation) between the properties of hydrogen nucleus called magnetic moment and applied magnetic fields. The measured data set contains two important petrophysical properties such as density of hydrogen in the fluids inside the pore space and the distinct decay rate for fluid type. Therefore, after the proper data processing, key petrophysical information, not only the quantities and properties of fluids but also supplies of rock characterization in a porous medium, could be archived. Thus, based on this information, several ongoing researches are being developed in estimating aspects of reservoir productivity information, permeability and wettability since it is the key to having correct interpretation. This study goes through the basic theory of NMR at first, and then reviews NMR logging tools as well as their technical characteristics. This paper also briefly discusses the basic knowledge of NMR simulation algorithm by using Random walk.
Upward Continuation of Potential Field on Spherical Patch Area
Na, Sung-Ho ; Chung, Tae Woong ; Shin, Young Hong ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 245~248
DOI : 10.7582/GGE.2012.15.4.245
Two dimensional Fourier transform can be used for the upward continuation of gravity or magnetic field data acquired at given altitude over a rectangular area. Earth`s curvature is often neglected in most potential field continuations, however, it should be considered over several hundred kilometer field area. In this study, we developed a new method retaining terms of Earth`s curvature to better perform the continuation of potential field on spherical patch area.
The Presence of the Breakup Unconformity in the Korea Plateau in the East Sea and its Tectonic Implications
Kim, Han-Joon ; Lee, Gwang Hoon ; Jou, Hyeong-Tae ;
Geophysics and Geophysical Exploration, volume 15, issue 4, 2012, Pages 249~251
DOI : 10.7582/GGE.2012.15.4.249