• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.643-646
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• 2005

The gas hydrate exploration using seismic reflection data, the detection of BSR(Bottom Simulating Reflector) on the seismic section is the most important work flow because the BSR have been interpreted as being formed at the base of a gas hydrate zone. Usually, BSR has some dominant qualitative characteristics on seismic section i.e. Wavelet phase reversal compare to sea bottom signal, Parallel layer with sea bottom, Strong amplitude, Masking phenomenon above the BSR, Cross bedding with other geological layer. Even though a BSR can be selected on seismic section with these guidance, it is not enough to conform as being true BSR. Some other available methods for verifying the BSR with reliable analysis quantitatively i.e. Interval velocity analysis, AVO(Amplitude Variation with Offset)analysis etc. Usually, AVO analysis can be divided by three main parts. The first part is AVO analysis, the second is AVO modeling and the last is AVO inversion. AVO analysis is unique method for detecting the free gas zone on seismic section directly. Therefore it can be a kind of useful analysis method for discriminating true BSR, which might arise from an Possion ratio contrast between high velocity layer, partially hydrated sediment and low velocity layer, water saturated gas sediment. During the AVO interpretation, as the AVO response can be changed depend upon the water saturation ratio, it is confused to discriminate the AVO response of gas layer from dry layer. In that case, the AVO modeling is necessary to generate synthetic seismogram comparing with real data. It can be available to make conclusions from correspondence or lack of correspondence between the two seismograms. AVO inversion process is the method for driving a geological model by iterative operation that the result ing synthetic seismogram matches to real data seismogram wi thin some tolerance level. AVO inversion is a topic of current research and for now there is no general consensus on how the process should be done or even whether is valid for standard seismic data. Unfortunately, there are no well log data acquired from gas hydrate exploration area in Korea. Instead of that data, well log data and seismic data acquired from gas sand area located nearby the gas hydrate exploration area is used to AVO analysis, As the results of AVO modeling, type III AVO anomaly confirmed on the gas sand layer. The Castagna's equation constant value for estimating the S-wave velocity are evaluated as A=0.86190, B=-3845.14431 respectively and water saturation ratio is $50\%$. To calculate the reflection coefficient of synthetic seismogram, the Zoeppritz equation is used. For AVO inversion process, the dataset provided by Hampson-Rushell CO. is used.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.37-43
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• 2006

In 2006, the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) plans to undertake (subject to receiving the necessary approvals) a Pilot program for $CO_2$ storage within a depleted gas reservoir. The Otway Basin Pilot Program (OBPP) aims to demonstrate that subsurface $CO_2$ storage is both economically and environmentally sustainable in Australia. This will be the first $CO_2$ storage program in the world to utilise a depleted gas reservoir and, hence, the experience gained will be a valuable addition to the range of international $CO_2$ storage programs that are underway or being planned. A key component of the OBPP is the design of an appropriate geophysical monitoring strategy that will allow the subsurface migration of the $CO_2$ plume to be tracked and to verify that containment has been successful. This paper presents the results from modelling the predicted gravity response to $CO_2$ injection into the Otway Basin reservoir, where the goal was to determine minimum volumes of $CO_2$ that may be detectable using non-seismic geophysical techniques. Modelling results indicate that gravity measurements at 10 m spacing within the existing observation well and the planned $CO_2$ injection well would provide excellent vertical resolution, even for the smallest $CO_2$ volume modelled (10000 tonnes), but resolving the lateral extent of the plume would not be possible without additional wells at closer spacing.

• Geophysics and Geophysical Exploration
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• v.19 no.3
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• pp.136-144
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• 2016

Since seismic inversion is based on the wave equation, it is important to calculate the solution of wave equation exactly. In particular, full waveform inversion would produce reliable results only when the forward modeling is accurately performed because it uses full waveform. When we use finite-difference or finite-element method to solve the wave equation, the convergence of numerical scheme should be guaranteed. Although the general proof of convergence is provided theoretically, the consistency and stability of numerical schemes should be verified for practical applications. The implementation of source function is the most crucial factor for the consistency of modeling schemes. While we have to use the sinc function normalized by grid spacing to correctly describe the Dirac delta function in the finite-difference method, we can simply use the value of basis function, regardless of grid spacing, to implement the Dirac delta function in the finite-element method. If we use frequency-domain wave equation, we need to use a conservative criterion to determine both sampling interval and maximum frequency for the source wavelet generation. In addition, the source wavelet should be attenuated before applying it for modeling in order to make it obey damped wave equation in case of using complex angular frequency. With these conditions satisfied, we can develop reliable inversion algorithms.

• Tunnel and Underground Space
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• v.23 no.3
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• pp.180-191
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• 2013

The purpose of this research was to find an optimal quarrying for marble by analyzing the applicability and the work efficiency of a chain saw machine newly introduced in the underground Baekwoon mine. From the test results of the physical properties of Baekwoon marble, which affects the efficiency of rock cutting, it was found to have similar physical characteristics as the ones which are now being produced in the other areas in Korea. And especially it shows isotropic property, which can be thought to be advantageous as a dimensional stone. To check the long-term quality of the marble as a stone material, several tests such as corrosion resistance test and abrasion test were carried out. It was found to be vulnerable to acid rain with decrease of weight and seismic wave velocity after applying artificial rain at pH 5.6 for 50 times. The percentage of wear from abrasion test was 22.67%. The working time and cutting speed of the chain saw machine were recorded and analyzed during the test-run at the quarry. The overall work cycle was assorted into 9 unit operations and the operating time per each unit was drawn. The operating times for the two cutting patterns, which could be possibly applicable to the work site, were compared. The results indicated that the pattern B, that the cutting sequence was set to minimize the movement of the machine, showed 6% less working hours than the pattern A, which first cuts the outer boundary. With cutting pattern analysis, the ore body in the Baekwoon mine was 3 dimensionally modeled and a quarrying plan considering the existing conditions of the marble was suggested.

• Journal of the Korean earth science society
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• v.40 no.1
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• pp.24-36
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• 2019

In the mid-eastern Yellow Sea, glacio-eustatic sea-level fluctuations and a regional tectonic subsidence have combined to represent an aggradational stacking pattern of sedimentary units during late Pleistocene-Holocene. The accumulated sediments are divisible into two-type units of Type-A and Type-B in high-resolution air-gun seismic profiles and the deep-drilled core of YSDP-105. Type-A unit largely comprises clast-rich coarse-grained sediments of non-marine to paralic origin, whereas Type-B unit consists mostly of tidal fine-grained sediments. Based on a bottom model of the sedimentary units, this study suggested a geoacoustic model of long-coring bottom layers at the YSDP-105 drilling site of the mid-eastern Yellow Sea. The geoacoustic model of 64-m depth below the seafloor with four-layer geoacoustic units was reconstructed in continental shelf strata at 45 m in water depth. For actual modeling, the geoacoustic property values of the models were compensated to in situ depth values below the seafloor using the Hamilton modeling method. We suggest that the geoacoustic model will be used for geoacoustic and underwater acoustic experiments of mid- and low-frequency reflecting on the deep bottom layers in the mid-eastern Yellow Sea.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.2
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• pp.95-102
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• 2014

In this paper, a coupling scheme for applying finite element analysis(FEA) programs, such as, LS-DYNA and MIDAS/Civil, to a nonlinear soil structure interaction analysis by the boundary reaction method(BRM) is presented. With the FEA programs, the structure and soil media are discretized by linear or nonlinear finite elements. To absorb the outgoing elastic waves to unbounded soil region as much as possible, the PML elements and viscous-spring elements are used at the outer FE boundary, in the LS-DYNA model and in MIDAS/Civil model, respectively. It is also assumed that all the nonlinear elements in the problem are limited to structural region. In this study, the boundary reaction forces for the use in the BRM are calculated using the KIESSI-3D program by solving soil-foundation interaction problem subjected to incident seismic waves. The effectiveness of the proposed approach is demonstrated with a linear SSI seismic analysis problem by comparing the BRM solution with the conventional SSI solution. Numerical comparison indicates that the BRM can effectively be applied to a nonlinear soil-structure analysis if motions at the foundation obtained by the BRM for a linear SSI problem excluding the nonlinear structure is conservative.

• Economic and Environmental Geology
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• v.53 no.1
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• pp.33-43
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• 2020

CO₂ geological storage is currently considered as the most stable and effective technology for greenhouse gas reduction. The saline formations for CO₂ geological storage are generally located at a depth of more than 800 m where CO₂ can be stored in a supercritical state, and an extensive impermeable cap rock that prevents CO₂ leakage to the surface should be distributed above the saline formations. Trough analysis of seismic and well data, we identified the basalt flow structure for potential CO₂ storage where saline formation is overlain by basalt cap rock around PZ-1 exploration well in the Southern Continental Shelf of Korea. To evaluate CO₂ storage capacity of the saline formation, total porosity and CO₂ density are calculated based on well logging data of PZ-1 well. We constructed a 3D geological grid model with a certain size in the x, y and z axis directions for volume estimates of the saline formation, and performed a property modeling to assign total porosity to the geological grid. The estimated average CO₂ geological storage capacity evaluated by the U.S. DOE method for the saline formation covered by the basalt cap rock is 84.17 Mt of CO₂(ranges from 42.07 to 143.79 Mt of CO₂).