• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.150-156
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• 2002

In this study, a software for crosswell seismic tomography is developed. The software consists of first arrival picking and adjusting module, crosswell traveltime tomography module, and imaging module. This software allows saying the picked first arrival times into the header of seismic data, and using this data directly to the input of crosswell seismic tomography. With an imaging module, velocity structures and ray path can be imaged directly from the output of the tomography module. Because it is developed on the basis of the SU under the Linux and the GUI environment for user, this software can be carried out directly the first arrival picking, inversion and tomogram for crosswell tomography data in the field. Therefore, this software can be improved the applicability of site investigation by tomography method.

• The Journal of Engineering Geology
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• v.16 no.3 s.49
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• pp.255-263
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• 2006

In an electrical tomographic survey using an inclined borehole with a pole-dipole array, we must consider several factors: a singular point associated with zero potential difference, a spatial discrepancy between electrode and nodal point in a model due to a inclined borehole, and a variation of geometric factors in connection with a irregular topography. Singular points which are represented by the normal distance from current source to the ground surface can be represented by serveral regions due to a irregular topography of ground surface. The method of element division can be applied to the region in which the borehole is curved, inclined or the distance between the electrodes is shorter than that of nodal points, because the coordinate of each electrode cannot be assigned directly to the nodal point if several electrodes are in an element. Test on a three-dimensional (3-D) synthetic model produces good images of conductive target and shoves stable convergence.

• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.69-76
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• 2007

High-frequency electromagnetic (EM) wave propagation associated with borehole ground-penetrating radar (GPR) is a complicated phenomenon. To improve the understanding of the governing physical processes, we employ a finite-difference time-domain solution of Maxwell's equations in cylindrical coordinates. This approach allows us to model the full EM wavefield associated with crosshole GPR surveys. Furthermore, the use of cylindrical coordinates is computationally efficient, correctly emulates the three-dimensional geometrical spreading characteristics of the wavefield, and is an effective way to discretise explicitly small-diameter boreholes. Numerical experiments show that the existence of a water-filled borehole can give rise to a strong waveguide effect which affects the transmitted waveform, and that excitation of this waveguide effect depends on the diameter of the borehole and the length of the antenna.

• 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.

• 한국지구물리탐사학회:학술대회논문집
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• 1999.08a
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• pp.92-116
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• 1999

Tomographic approaches to image underground structure using electrical properties, can be divided into DC resistivity, electromagnetic, and radar tomography, based on the operating frequency. DC resistivity and radar tomography methods have been recently applied to site investigation for engineering purpose in Korea. This paper review these two tomography methods, through the case histories acquired in Korea. As another method of borehole radar survey, borehole radar reflection method is included, and its inherent problem and solution are discussed, how to find the azimuth angle of reflector using direction-finding-antenna. Since the velocity anisotropy of radar wave has been commonly encountered in field data, anisotropic radar tomography is discussed in this paper. In DC resistivity tomography, two subjects are focussed, electrode arrays, and borehole effect owing to the conductive fluid in borehole. Using the numerical modeling data, various kinds of electrode ways are compared, and borehole effect is illustrated. Most of the case histories presented in this paper are compared with known geology, core logging data, and/or Televiewer images.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1998.11a
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• pp.109-113
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• 1998

본 연구에서는 전기전도도, 온도, 유속 검층을 이용하여 시추공내의 유동성 단열구조를 확인하고 각 유동성 단열구조를 통한 시추공간의 수리적 연결관계를 해석하였다. 검층은 자연상태와 인근 시추공으로부터의 양수에 의한 부정류상태에서 각각 실시되었다. 자연상태에서는 지하수 유동이 매우 느려 유동성 단열구조가 쉽게 인지되지 않으나, 부정류 상태에서는 각 시추공간의 수리적 연결성을 보여준다. 각 시추공별 검층에서 나타나는 유동성 단열구조는 모두 일치하지 않으며, 특히 부정류 상태에서의 유속 검층에서는 타 검층에서 인지된 유동성 단열구조중 일부만이 시추공간에 서로 수리적으로 연결되어 있음을 보여준다.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 1996.03a
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• pp.73-82
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• 1996

지하철, 지하유류비축기지와 같은 지하구조물의 건설이나, 대형 건축물의 건설을 위한 지반조사로서 시추조사는 가장 기본적이라 할 수 있으며, 서울 일대에서는 지하철 1∼8호선, 경부고속전철 등의 대규모 사업과 관련하여 많은 시추조사가 실시되었다. 그러나 이와 같은 대형 건설사업을 위한 시추공 자료들은 건설 당시에만 사용되었을 뿐 이후 자료의 보존 및 관리가 잘 되지 않았다. (중략)

• Proceedings of the Korean Geotechical Society Conference
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• 2003.06b
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• pp.141-152
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• 2003

터널 설계를 위한 조사 있어서, 요사이 시추공 조사는 물론 탄성파 탐사, 전기 비저항 탐사 등의 물리탐사가 빈번히 행해지고 있는 실정이다. 따라서 최적의 지반평가(암반 등급 등)를 위해 조사에서 얻어지는 모든 자료를 체계적으로 최대한 활용할 수 있는 방법이 절실히 요구되고 있다. 많은 연구자들이 정량적 데이터가 부족한 경우에 대처하기 위해 정상적 데이터의 이용을 적극 제안해 왔다. 본 연구에서는 신뢰도가 다른 두 종류의 자료, 즉 시추공자료와 물리탐사 자료를 활용하여 시추가 되지 않은 구간의 암반등급을 추정하는 방법을 지구통계학적 이론에 근거하여 소개하고자 한다.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.69-72
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• 2008

EZTOMO is a crosswell seismic tomography software system. The system has capability of event picking, raytracing, inversion, error analysis, and visualization of the processing results. Waveform of the first arrival signal has been utilized to select the event of the first motion, and uncertainty measured in estimation of the first breaks has been utilized to improve the inversion process.

• The Korean Journal of Petroleum Geology
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• v.6 no.1_2 s.7
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• pp.25-36
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• 1998

Organic geochemical analyses were carried out in order to characterize organic matter (OM) in the sediments recovered from Korea/japan Joint Development Zone (JDZ V-1, V-3, VII-1 and VII-2) which is located in the northern end of the East China Sea Shelf Basin. Late Miocene sediments from the JDZ V-1 and V-3 wells generally contain less than $0.5\%$ of total organic carbon (TOC). However, early Miocene and Oligocene sediments show TOC values of $0.6-0.8\%$. Middle to late Miocene sediments are rich in TOC up to $20\%$ from JDZ VII-1 and JDZ VII-2 wells. The reason for this rich TOC might be attributed to the presence of coaly shales. Kerogens in the Tertiary sediments from the JDZ series wells are mainly composed of terrestrially derived woody organic matter. Elemental analyses indicate that OM from these wells can be compared to type III. Low hydrocarbon potential and hydrogen index reflect the type of OM. According to the biomarker analyses, the input of the terrestrial OM is prevalent. Oxidizing condition is also indicated by Pristane/Phytane ratio. Samples from the JDZ V-1 and V-3 wells obtain maturities equivalent to the oil generation zone around total depth, and organic matter below 3600 m from JDZ VII-1 and VII-2 wells reached dry gas generation stage. Oligocene sediments below 3500 m in the JDZ VII-1 and JDZ VII-2 wells may have generated limited amount of hydrocarbons, showing a progressive decrease in hydrogen index with depth, due to thermal degradation with increased burial. Gas shows and finely disseminated gilsonite may indicate the generation and migration of the hydrocarbons.