• Proceedings of the Korean Geotechical Society Conference
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• 2002.10a
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• pp.231-236
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• 2002

The understanding of underground geologic structures is of great importance for the surface and subsurface constructions, prevention of natural hazards such as land-slides and subsidence, and many other areas. To get the information on the geologic conditions, many of investigations such as geologic survey, geophysical explorations, testings on the physical properties of rocks, drilling tests and logging, and groundwater surveys are usually conducted, and tremendous data are collected accordingly. In general, however, these huge amount of data are interpreted in the individual areas only. If these data are analyzed collectively, much more information on the geologic conditions can be obtained. In this study, 3D visualization of borehole logging data is attempted. Borehole logging data are obtained at the urban subsidence area. To compare the 3D logging data with other geologic and geophysical data such as resistivity tomography data, interface module was developed. The 3D visualization of logging data and the comparison with other data can be helpful for the understanding of underground geologic structures.

• Nuclear Engineering and Technology
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• v.56 no.8
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• pp.3090-3096
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• 2024

In prompt fission neutron uranium logging, borehole environmental parameters affect the measured results and must be corrected. In order to explore the influence of borehole parameters on the interpretation of logging results, this paper builds a sandstone type uranium ore block model to simulate the field production drilling device based on the "Epithermal/Thermal neutron counting rate ratio" (E/T) theory. The effects of borehole diameter, thickness of iron tube and well fluid on the decay rate of epithermal and thermal neutrons and their uncertainty correction methods were investigated. The results show that the effect of borehole diameter on E/T is negligible. The iron tube thickness has a certain effect on the moderation and absorption of epithermal and thermal neutrons, and its E/T increases slightly with increasing thickness. The influence of iron tube thickness on E/T is corrected and the relative uncertainty is less than 5%. The well fluid thickness also affects the decay rate of epithermal and thermal neutrons, and its E/T follows the law of negative exponential attenuation. The influence of well fluid thickness on E/T is corrected and the relative uncertainty is less than 5%. This study provides technical guidance for field well survey of uranium deposit.

• Journal of the Korean earth science society
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• v.34 no.3
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• pp.195-208
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• 2013

We employed electrical resistivity and optical borehole imaging methods to identify underground cavities and determine ground subsidence rate at the study area affected by land subsidence due to abandoned underground mines. At the study site 1, the anomalous zones of low resistivity ranging between 100 ohm-meter and 150 ohm-meter were observed and confirmed as an abandoned underground mine by subsequent borehole drilling and optical borehole imaging. Although the electrical resistivity survey was unavailable due to the paved surface of the study site 2, we were able to locate another abandoned underground mine with the collapsed mine shaft based on the distribution of the ore veins and confirmed it with borehole drilling. In addition, we measured vertical displacements of underground features indicating underground subsidence by conducting optical borehole imaging 6 times over a period of 43 days at the study site 2. The displacement magnitude at the deep segment caused by subsidence appeared to be 3 times larger than those at the shallow segment. Similarly, the displacement duration at the deep segment was 4 times longer than those at the shallow segment. Therefore, the combination of electrical resistivity and optical borehole imaging methods can be effectively applicable to detect and monitor ground subsidence caused by underground cavities.

• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.204-213
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• 2008

This paper presents the analysis about the stability of the Pohang deep geothermal borehole drilled in 2006. Severe wellhole instability problems such as collapse and tight hole occurred in weak rocks while drilling. Optimal mud pressure (mud window) required to prevent instability problems during drilling is obtained from analysis on in-situ stress and rock strength. The window is bounded by vertical stress in its upper limit and by either collapse pressure or pore pressure in its lower limit. Mud window varies with different types of rocks. In the top-most semi-consolidated mudstone formation, no mud window can secure borehole stability. In some weak rock types (basic dyke and crystal tuff), the borehole pressure needs to be higher by $50{\sim}60%$ than hydrostatic pressure. That means a mud density of 1.5 g/$cm^3$ or higher should be applied during drilling in order to prevent excessive collapse around the borehole.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.147.1-147.1
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• 2011

지식경제부 가스 하이드레이트 개발사업의 일환으로 동해 울릉분지 가스 하이드레이트 2차 시추(Ulleung Basin Gas Hydrate Drilling Expedition: UBGH2)가 2010년 7월 8일부터 9월 30일까지 D/V Fugro Synergy를 이용하여 수행되었다. UBGH2 수행을 위해 선정된 13개 site에서 약 1개월 동안 Schlumberger사의 장비를 이용 Logging-While-Drilling/Measurement-While-Drilling(LWD/MWD) 자료를 취득하였다. LWD/MWD 자료는 선상에서 분석되었으며, 이 결과는 coring 및 borehole plan 수립을 위하여 활용되었다. Coring Phase 동안 10개 site의 18개 hole로부터 퇴적물 코어 시료를 채취하고 선상에서 퇴적학, 지구화학, 생지화학, 물리적 특성 등 각종 분석과 측정 작업을 수행하였다. 약 2개월에 걸쳐 수행된 coring phase 동안에 2개 site에서 FAOL(Fugro Alluvial Offshore Limited)사의 장비를 이용 Wireline Logging/Vertical Seismic Profile(WL/VSP) 자료도 취득하였다. LWD/MWD phase와 coring phase 동안 12개 site에서 무인잠수정(remotely operated vehicle: ROV)를 이용하여 퇴적물 시료 채취, 해저면 관찰, 용존메탄 측정 등의 작업을 수행하였으며, 선상에서 취득된 이들 자료를 분석하였다. Coring을 수행한 모든 site에서 가스 하이드레이트 부존을 확인하였으며, 다양한 산상의 가스 하이드레이트 실물을 회수하고 분석하였다.

• Geomechanics and Engineering
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• v.16 no.3
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• pp.331-339
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• 2018

Worldwide growth in hydrocarbon and energy demand is driving the oil and gas companies to drill more wells in complex situations such as areas with high-pressure, high-temperature conditions. As a result, in recent years the number of wells in these conditions have been increased significantly. Wellbore instability is one of the main issues during the drilling operation especially for directional and horizontal wells. Many researchers have studied the wellbore stability in complex situations and developed mathematical models to mitigate the instability problems before drilling operation. In this work, a fully coupled thermoporoelastic model is developed to study the well stability in high-pressure, high-temperature conditions. The results show that the performance of the model is highly dependent on the truly evaluated rock mechanical properties. It is noted that the rock mechanical properties should be evaluated at elevated pressures and temperatures. However, in many works, this is skipped and the mechanical properties, which are evaluated at room conditions, are entered into the model. Therefore, an accurate stability analysis of high-pressure, high-temperature wells is achieved by measuring the rock mechanical properties at elevated pressures and temperatures, as the difference between the model outputs is significant.

• The Journal of Engineering Geology
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• v.26 no.1
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• pp.15-22
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• 2016

Hydraulic falling head and slug tests were carried out in an alluvium aquifer using a borehole stability device. The hydraulic testing had proved difficult in alluvial formations of sands and gravels due to borehole collapse and unstable borehole walls within the test section. This study aims to improve the hydraulic test results by using a borehole stability device. The device can minimize the collapse of borehole walls, and the use of a filter with a constant opening ratio improves the calculations per unit area of the test section. Permeability obtained from the falling head test without a borehole stability device was 8.82 × 10⁻⁵m/sec. When the borehole stability device was installed in the same test section the measured permeability increased to 4.00 × 10⁻⁴m/sec, which is 4.5 times that obtained without the borehole device. The relatively low permeability obtained using the conventional test method is attributed to the presence of a fine-grained slime generated during drilling and a reduction of the test area in the test interval due to a gradual collapse of the borehole walls. This study considers how the use of a borehole stability device to prevent borehole collapse can influence the results of hydraulic tests in alluvial formations. It is expected that the results can be used as a basis for improving the reliability and applicability of hydraulic tests performed in alluvial aquifers.

• Journal of the Korean Geotechnical Society
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• v.26 no.9
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• pp.71-74
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• 2010

During construction of deep foundation in soft rock under varying soil properties, it is essential to locate the rock stratum, especially when drilling with slurry. When slurry is used for drilling, the bottom of the borehole cannot be seen, thereafter soil cuttings cannot be differentiated from soft rock cuttings. A new static rock penetrometer, known as Rock Penetrometer was developed during this study. It could be a simple mechanical device that is attached to the bottom of a Kelly bar which is used to attach drilling tools such as augers and core barrels while drilling. After its calibration in the laboratory, the performance of the static rock penetrometer was verified in the several field test sites.

• Journal of the Korean Geotechnical Society
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• v.25 no.4
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• pp.55-68
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• 2009

A new borehole roughness and verticality measurement system (BKS-LRPS) for rock socketed drilled shafts were developed and verified its field application. The stability of BKS-LRPS was verified for several field conditions, which included the effect of measuring unit shaking, the application of water/air calibration factors, and the resistance of high water pressure inside piles. Also, effective measurement distances for various conditions of turbidity were defined in the field by measuring borehole roughness and vertical alignment for 6 drilled shafts. Vertical alignments for all drilled shafts could be measured by BKS-LRPS. However, borehole roughness was not able to be measured due to high turbidity caused by RCD drilling processing. Based on the BKS-LRPS field verification, BKS-LRPS is the first borehole roughness and verticality measurement system applying both in the water and air.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.4
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• pp.301-312
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• 2017

The concept of deep borehole disposal (DBD) for high-level nuclear wastes has been around for about 40 years. Now, the Department of Energy (DOE) in the United States (U.S.) is re-examining this concept through recent studies at Sandia National Laboratory and a field test. With DBD, nuclear waste will be emplaced in boreholes at depths of 3 to 5 km in crystalline basement rocks. Thinking is that these settings will provide nearly intact rock and fluid density stratification, which together should act as a robust geologic barrier, requiring only minimal performance from the engineered components. The Nuclear Waste Technical Review Board (NWTRB) has raised concerns that the deep subsurface is more complicated, leading to science, engineering, and safety issues. However, given time and resources, DBD will evolve substantially in the ability to drill deep holes and make measurements there. A leap forward in technology for drilling could lead to other exciting geological applications. Possible innovations might include deep robotic mining, deep energy production, or crustal sequestration of $CO_2$, and new ideas for nuclear waste disposal. Novel technologies could be explored by Korean geologists through simple proof-of-concept experiments and technology demonstrations.