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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 18, Issue 4 - Nov 2015
Volume 18, Issue 3 - Aug 2015
Volume 18, Issue 2 - May 2015
Volume 18, Issue 1 - Feb 2015
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Electrical Resistivity at Room Temperature and Relation between Physical Properties of Core Samples from Ulleung Island
Lee, Tae Jong ; Lee, Sang Kyu ; Yun, Kwan-Hee ;
Geophysics and Geophysical Exploration, volume 18, issue 4, 2015, Pages 171~180
DOI : 10.7582/GGE.2015.18.4.171
Electrical resistivity of 23 core samples from Ulleung Island at dry or saturated condition has been measured along with dry density and effective porosity, and the relations between the properties has also been discussed. Upper and lower bounds of electrical resistivity at room temperature can be provided by the dry- and saturated-resistivity, respectively. Injecting nitrogen gas to the pore space at the very end of drying process can prevent humid air from getting into the pore space, so that measurement of dry-resistivity can be less affected by humidity in the air. Dry density and porosity have very close correlation; the ratio between increase of porosity and the decrease of density showed distinct relation to the rock types, such that basaltic rocks showed higher ratio while trachytic rocks showed lower. Saturated resistivity showed close correlation to density and effective porosity of the rock sample, while dry resistivity didn't.
Swell Effect Correction of Sub-bottom Profiler Data with Weak Sea Bottom Signal
Lee, Ho-Young ; Koo, Nam-Hyung ; Kim, Wonsik ; Kim, Byoung-Yeop ; Cheong, Snons ; Kim, Young-Jun ; Son, Woohyun ;
Geophysics and Geophysical Exploration, volume 18, issue 4, 2015, Pages 181~196
DOI : 10.7582/GGE.2015.18.4.181
A 3.5 kHz or chirp sub-bottom profiling survey is widely used in the marine geological and engineering purpose exploration. However, swells in the sea degrade the quality of the survey data. The horizontal continuity of profiler data can be enhanced and the quality can be improved by correcting the influence of the swell. Accurate detection of sea bottom location is important in correcting the swell effect. In this study, we tried to pick sea bottom locations by finding the position of crossing a threshold of the maximum value for the raw data and transformed data of envelope or energy ratio. However, in case of the low-quality data where the sea bottom signals are not clear due to sea wave noise, automatic sea bottom detection at the individual traces was not successful. We corrected the mispicks for the low quality data and obtained satisfactory results by picking a sea bottom within a range considering the previous average of sea bottom, and excluding unreliable big-difference picks. In case of trace by trace picking, fewest mispicks were found when using energy ratio data. In case of picking considering the previous average, the correction result was relatively satisfactory when using raw data.
Study on Microseismic Data Acquisition and Survey Design through Field Experiments of Hydraulic Fracturing and Artificial Blasting
Kim, Jungyul ; Kim, Yoosung ; Yun, Jeum-Dong ; Kwon, Sungil ; Kwon, Hyongil ; Shim, Yonsik ; Park, Juhyun ;
Geophysics and Geophysical Exploration, volume 18, issue 4, 2015, Pages 197~206
DOI : 10.7582/GGE.2015.18.4.197
The purpose of this study is to ensure microseismic data acquisition technique for hydraulic fracturing imaging at the site of shale gas development. For this, microseismic data acquisition was performed during hydraulic fracturing and artificial blasting at a site bearing shale layers. Measured microseismic event data during the hydraulic fracturing have the very small amplitude of 0.001 mm/sec ~ 0.003 mm/sec and the frequency contents of 5 Hz ~ 20 Hz range. Meanwhile microseismic event data acquired during artificial blasting have the bigger amplitude (0.011 mm/sec ~ 0.302 mm/sec) than hydraulic fracturing event data and their frequency contents have the range of 5 Hz ~ 2 kHz. For microseismic data acquisition design, the selection of appropriate instrumentation including sensors and the recording system, the determination of sensor array and the deployment range were investigated based on the theoretical data and field application experiences.
A Geophysical Survey of Subsidence area around Limestone Mine Sites
Hong, Jinpyo ; Ji, Yoonsoo ; Oh, Seokhoon ; Choi, Sungoong ;
Geophysics and Geophysical Exploration, volume 18, issue 4, 2015, Pages 207~215
DOI : 10.7582/GGE.2015.18.4.207
Electrical resistivity surveys were conducted at two subsidence areas near and at limestone mine sites, respectively, in order to estimate their causes of subsidence and the regions of potential occurrence. In addition, the linkages of mine development with these subsidences were investigated by the rock engineering analysis. Two study areas have different geological setting. One study site is the land subsidence area, which contains clay and sandy soil near the limestone mine, The other study site is the land subsidence area located just above the mine, which is expected to be relevant to the limestone mine. As results of two-dimensional (2D) electrical resistivity surveys at the sites 1 and 2, low resistivity zones, which are 70 ~ 120 ohm-m and 20 ~ 50 ohm-m, respectively, were found under the subsidence zones. For the study site 1, the possibility of subsidence was confirmed by using three-dimensional (3D) inversion performed with 2D resistivity profiles. For the study site 2, the cause of the subsidence and the possibility of subsidence occurrence were confirmed by rock engineering computation with regard to measurement line 7 in which low resistivity accompanied by subsidence area was observed.
One-dimensional Modeling of Airborne Transient Electromagnetic using a Long Grounded-wire Source
Cho, In-Ky ; Kim, Rae-Yeong ; Yi, Myeong-Jong ;
Geophysics and Geophysical Exploration, volume 18, issue 4, 2015, Pages 216~222
DOI : 10.7582/GGE.2015.18.4.216
Airborne transient electromagnetic (ATEM) surveying was introduced several decades ago in the mining industry to detect shallow conductive targets. However, conventional ATEM systems have limited depth of investigation because of weak signal strength. Recently, the grounded electrical source airborne transient electromagnetic (GREATEM) system was proposed to increase the depth of investigation. The GREATEM is a semi-airborne transient electromagnetic system because a long grounded wire is used as the transmitter. Traditionally, ATEM sounding data have been interpreted with 1D earth models to save the computing time because modern ATEM systems generally collect large data sets. However, the GREATEM 1D modeling requires numerical integration along the wire, so it takes much more time than the 1D modeling of conventional ATEM. In this study, the adaptive Born forward mapping (ABFM) was applied to the ATEM 1D modeling because the ABFM is incommensurably faster than the ordinary GREATEM 1D modeling. Comparing the results from ordinary and ABFM 1D modeling, it was confirmed that the ABFM can be applied to the 1D modeling of GEATEM.
Modeling of SP responses for geothermal-fluid flow within EGS reservoir
Song, Seo Young ; Kim, Bitnarae ; Nam, Myung Jin ; Lim, Sung Keun ;
Geophysics and Geophysical Exploration, volume 18, issue 4, 2015, Pages 223~231
DOI : 10.7582/GGE.2015.18.4.223
Self-potential (SP) is sensitive to groundwater flow and there are many causes to generate SP. Among many mechanisms of SP, pore-fluid flow in porous media can generate potential without any external current source, which is referred to as electrokinetic potential or streaming potential. When calculating SP responses on the surface due to geothermal fluid within an engineered geothermal system (EGS) reservoir, SP anomaly is usually considered to be generated by fluid injection or production within the reservoir. However, SP anomaly can also result from geothermal water fluid within EGS reservoirs experiencing temperature changes between injection and production wells. For more precise simulation of SP responses, we developed an algorithm being able to take account of SP anomalies produced by not only water injection and production but also the fluid of geothermal water, based on three-dimensional finite-element-method employing tetrahedron elements; the developed algorithm can simulate electrical potential responses by both point source and volume source. After verifying the developed algorithm, we assumed a simple geothermal reservoir model and analyzed SP responses caused by geothermal water injection and production. We are going to further analyze SP responses for geothermal water in the presence of water production and injection, considering temperature distribution and geothermal water flow in the following research.
Magnetotelluric modeling considering vertical transversely isotropic electrical anisotropy
Kim, Bitnarae ; Nam, Myung Jin ;
Geophysics and Geophysical Exploration, volume 18, issue 4, 2015, Pages 232~240
DOI : 10.7582/GGE.2015.18.4.232
Magnetotelluric (MT) survey investigates electrical structure of subsurface by measuring natural electromagnetic fields on the earth surface. For the accurate interpretation of MT data, the precise three-dimensional (3-D) modeling algorithm is prerequisite. Since MT responses are affected by electrical anisotropy of medium, the modeling algorithm has to incorporate the electrical anisotropy especially when analyzing time-lapse MT data sets, for monitoring engineered geothermal system (EGS) reservoir, because changes in different-vintage MT-data sets are small. This study developed a MT modeling algorithm for the simulation MT responses in the presence of electrical anisotropy by improving a pre-existing staggered-grid finite-difference MT modeling algorithm. After verifying the developed algorithm, we analyzed the effect of vertical transversely isotropic (VTI) anisotropy on MT responses. In addition, we are planning to extend the applicability of the developed algorithm which can simulate not only the horizontal transversely isotropic (HTI) anisotropy, but also the tiled transversely isotropic (TTI) anisotropy.