• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.321-327
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• 2003

[ $CO_2$ ] sequestration in oil reservoirs can be one of the most effective strategies for long-term removal of greenhouse gas from atmosphere. This paper presents an advantage of the localized nonlinear approximation of integral equation solutions for inverting crosswell electromagnetic data, which are observed as a part of pilot project of $CO_2$ flooding at the Lost Hills oil field in central California, U.S.A. To monitor the migration of $CO_2$, we have used 2-D cylindrically symmetric and 2.5-D tomographic inversion methods. These two schemes produce nearly the same images if the borehole separation is large compared with the skin depth. However, since the borehole separation is much less than five skin depths in this $CO_2$ injection experiment, the 2.5-D model seems to be more reliable than the 2-D model. In fact, the pre-injection 2.5-D image is more successfully compared with induction logs observed in the two wells than the 2-D model. From the time-lapse crosswell imaging, we can confirm the replacement of brine with $CO_2$ makes a decrease of conductivity.

• Journal of Korean Society of Disaster and Security
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• v.10 no.1
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• pp.35-42
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• 2017

This is a comparative study on the characteristics of excavated soils, which is proceeded using soil strength parameter by literature, geotechnical investigation, standard penetration test by drilling, and downhole test by borehole at six sites in urban areas. The results of these site surveys are used as basic data for the evaluation and development of prediction of ground subsidence risk. Geotechnical properties are estimated with the result of standard penetration test-N value and literature. The dynamic geotechnical characteristics are also estimated with top-down seismic exploration at borehole.

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.209-214
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• 1999

A field experiment generating shear waves by trench method was conducted at two places in Taejun area. We were able to separate the P- and S-waves by summing and subtracting the vertical and horizontal component of the data recorded at a three component downhole geophone in the borehole. The analysis of the records revealed that the shear waves were polarized to NS and EW directions. The faster shear waves were polarized to NS direction. The NS direction generally agrees with the dominant joints direction observed from the cores collected from the borehole.

• The Journal of Engineering Geology
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• v.18 no.2
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• pp.137-144
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• 2008

The stand-off errors due to the different separations between the sonde and the borehole wall were measured and analyzed in 4 physical borehole models located in Kangwon National University having different densities with cylindrical and half cylindrical PVC and/or acrylic casings. The analysis of the stand-off error data based on the "spine and ribs" technique suggests a well defined rib line for each model irrespectively of the types and thicknesses of the casing, and that the gradients of the ribs are proportional to the densities of the models. By using these characteristics successful density correction could be made for the plastic casings in NX sized boreholes.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1708-1717
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• 2023

The grade analysis of lead-zinc ore is the basis for the optimal development and utilization of deposits. In this study, a method combining Prompt Gamma Neutron Activation Analysis (PGNAA) technology and machine learning is proposed for lead-zinc mine borehole logging, which can identify lead-zinc ores of different grades and gangue in the formation, providing real-time grade information qualitatively and semi-quantitatively. Firstly, Monte Carlo simulation is used to obtain a gamma-ray spectrum data set for training and testing machine learning classification algorithms. These spectra are broadened, normalized and separated into inelastic scattering and capture spectra, and then used to fit different classifier models. When the comprehensive grade boundary of high- and low-grade ores is set to 5%, the evaluation metrics calculated by the 5-fold cross-validation show that the SVM (Support Vector Machine), KNN (K-Nearest Neighbor), GNB (Gaussian Naive Bayes) and RF (Random Forest) models can effectively distinguish lead-zinc ore from gangue. At the same time, the GNB model has achieved the optimal accuracy of 91.45% when identifying high- and low-grade ores, and the F₁ score for both types of ores is greater than 0.9.

• Geophysics and Geophysical Exploration
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• v.25 no.4
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• pp.167-176
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• 2022

We designed a borehole deviation survey tool applicable for steel-cased holes, K-DEV, and developed a prototype for a depth of 500 m aiming to development of own equipment required to secure deep subsurface characterization technologies. K-DEV is equipped with sensors that provide digital output with verified high performance; moreover, it is also compatible with logging winch systems used in Korea. The K-DEV prototype has a nonmagnetic stainless steel housing with an outer diameter of 48.3 mm, which has been tested in the laboratory for water resistance up to 20 MPa and for durability by running into a 1-km deep borehole. We confirmed the operational stability and data repeatability of the prototype by constantly logging up and down to the depth of 600 m. A high-precision micro-electro-mechanical system (MEMS) gyroscope was used for the K-DEV prototype as the gyro sensor, which is crucial for azimuth determination in cased holes. Additionally, we devised an accurate trajectory survey algorithm by employing Unscented Kalman filtering and data fusion for optimization. The borehole test with K-DEV and a commercial logging tool produced sufficiently similar results. Furthermore, the issue of error accumulation due to drift over time of the MEMS gyro was successfully overcome by compensating with stationary measurements for the same attitude at the wellhead before and after logging, as demonstrated by the nearly identical result to the open hole. We believe that the methodology of K-DEV development and operational stability, as well as the data reliability of the prototype, were confirmed through these test applications.

• The Journal of Engineering Geology
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• v.13 no.1
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• pp.83-105
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• 2003

Geochemical studies on the alluvial aquifer system near the Nakdong River were carried out for the basic investigation of the estimation of artificial recharge for the river bank filtration. In-situ data do not show any distinct difference between the pumping well and river. Most of waters belong to $_3$ and Ca-$SO_4$ types and show high Mn concentration. In the borehole installed with Multi-Ca-HCOPacker (MP) system, Na, Ca, Mg, $HCO_3$ contents of the groundwater are increased with depth increasing. Cl and $SO_4$ contents of the groundwater show the lowest values at the bottom level (18m depth) and Mn content is very high at the middle level (13.5 m depth) of MP system. There is no distinct difference in the ${\delta}^{18}O$ and D values and tritium content between MP, borehole and surface water samples. The sulfur isotope data indicate that the possible sulfur source is dissolution of sulfate mineral from sedimentary rock. Strontium isotope ratio shows a little differences between the pumping well and observation borehole samples. Nitrogen isotope data indicate that the nitrogen of water samples is originated from fertilizer or organic materials.

• The Journal of Engineering Geology
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• v.11 no.3
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• pp.303-313
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• 2001

A cut-slope near Guam-Ri Hwado-Eup Namyangju-Si Kyunggi-Do collapsed during a heavy rainfall over 400mm at 28th of August 2000. The cut-slope collapse reportedly developed mainly by block sliding along a set of discontinuities, although slope angle of the cut-slope was 40$^{\circ}$(1:1.2) that agrees with the road construction criteria. This study aims to analyze differences and correlations among several data-collecting methods limited to discontinuity analysis related with cut-slope collapse. This study started with analysing discontinuity surface characteristics, geology of the country rock and orientations of the discontinuities directly related with the collapse. Analysis of aerial photos around the study area provided regional lineament data, and discontinuity plane description and measurements were collected from core logging and Borehole Image Processing System (BIPS). Spearmans correlation ranking coefficient method was used to get correlation of discontinuity planes according to analysis methods. The result suggests that the correlation coefficient is ${\gamma}_s$ = 0.91 Plus, stability analysis of discontinuity plane orientation data using equal-area stereonet revealed that the study area is unstable to planar failure. This study suggests that the cut-slope angles currently applied should be shallower and that significant attention is required to orientation distribution of discontinuities existed in cut-slopes studies.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.11 no.3
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• pp.229-243
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• 2013

An in situ solute migration system was designed and installed in KAERI Underground Research Tunnel (KURT) constructed in the site of Korea Atomic Energy Research Institute (KAERI) in order to investigate the migration and retardation of non-sorbing and sorbing tracers through a rock fracture. The system is composed of three main parts including injection, extraction, and data treatment. For the selection of a water-conducting fracture, boreholes were drilled. The fractures in the drilled boreholes were investigated using borehole image analysis using borehole image processing system (BIPS). The results of BIPS analysis showed that borehole YH 3-1 and YH 3-2 were connected each other. Moreover, hydraulic tests were carried out to determine the test section with connectivity for the in situ experiments. The in situ solute migration experiments were accomplished to understand the migration of solutes through fractures in KURT using non-sorbing tracers which were fluorescein sodium, eosin-B, bromide and sorbing tracers which were rubidium, nickel, zirconium, and samarium.

• Economic and Environmental Geology
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• v.51 no.1
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• pp.39-48
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• 2018

We carried out the standoff compensation data from 2007 to 2011 into four different density borehole models to find out the most effectiveness of standoff compensation charts. First, we investigated the irregular collapse characteristics of gamma ray and cut the non-ideal gamma response to improve the effectiveness of the standoff compensation error data. Effectiveness of detector combinations, density of borehole, and spine and ribs techniques from the modified standoff compensation data was analyzed. As the result of comparison, LSD-MSD combination has been suitable for standoff compensation more than LSD-SSD combination and it is possible to do standoff compensation for soil or weathered zone under groundwater level without fatal errors. Even though error scales of density transformed spine and ribs techniques were generally large compared to the conventional standoff compensation, standoff compensation for soil and weathered zone under groundwater level were sufficiently effective.