• Economic and Environmental Geology
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• v.40 no.6
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• pp.739-749
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• 2007

The seismic velocity at the formation varies widely with physical properties in the layers. These features on seismic shot gathers are not capable of reproducing normally by numerical modeling of homogeneous medium, so that we need that of random inhomogeneous medium instead. In this study, we conducted Gaussian autocorrelation function (ACF), exponential autocorrelation function and von Karman autocorrelation function for getting inhomogeneous velocity model and applied a simple geological model. According to the results, von Karman autocorrelation function showed short wavelength to the inhomogeneous velocity medium. For numerical modeling for a gas hydrate, we determined a geological model based on field data set gathered in the East sea. The numerical modeling results showed that the von Karman autocorrelation function could properly describe scattering phenomena in the gas hydrate velocity model which contains an inhomogeneous layer. Besides, bottom-simulating-reflectors and scattered waves which appear at seismic shot gather of the field data showed properly in the inhomogeneous numerical modeling.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2001.09a
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• pp.176-179
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• 2001

비 수용성 유기오염물(NAPL; non-aqueous phase liquid)로 오염된 불균질 토양을 계면활 성제를 이용하여 정화할 경우 효율성을 알아보기 위해 칼럼 및 박스 실험을 실시하였다. 불 균질한 지하 내부구조는 정화효과에 커다란 영향을 끼치는 것으로 알려져 있으나 이에 대한 연구는 매우 미비한 형편이다. 2차원 불균질 분포를 잘 나타내주는 박스실험을 통하여 실제 지하매질에 가까운 조건에서 실험을 실시하였다. PCE(tetrachloroethylene)와 xylene이 NAPL로 올리에마이드(01eamide)가 비이온-계면활성제로 이용되었으며, 1%용액과 증류수를 주입하여 NAPL을 세정하였고 가스크로마토그래피를 이용하여 NAPL의 농도를 분석하였다. 계면활성제를 주입할 경우가 증류수를 주입할 때보다 최대유출농도가 약 200배 정도가 높게 나타났으며 빠른 시간 내에 대부분의 NAPL이 정화되었다. 본 실험을 통하여, 불균질 매질에서의 계면활성제를 이용한 토양세정방법의 효율성이 정량화 되었으며, 계면활성제를 이용한 채수주입법의 현장 적용가능성을 확인하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1996.10a
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• pp.8-13
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• 1996

균질 매질내에 형성되는 근거리 음장의 해석에는 종래 회절 이론에서의 Rayleigh 적분식에 근거한 Lommel 근사식이 주로 이용되어져 왔다. 그러나, 불균질한 매질에서는 그 방법의 적용이 어렵고, 유한요소법등 새로운 방법이 적용되어야 한다. 본 연구에서는 불균질 매질에서의 음장을 해석하는 한 방법으로 Angular Spectrum법을 제안하고, 경계를 가상한 등수온의 물에 대하여 Lommel 근사식에 의해 직접 산출한 음장과 Angular Spectrum법을 적용하여 산출한 음장을 서로 비교함으로써 그 유효성을 검토하였다.

• Economic and Environmental Geology
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• v.44 no.2
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• pp.161-170
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• 2011

The multiphase flow simulator, CHEMPS, was developed based on the fractional flow approach reported in the petroleum engineering literature considering fully three phase flow in physically and chemically heterogeneous media. It is a extension of MPS developed by Suk and Yeh (2008) to include the effect of wettability on the migration of NAPL. The fractional flow approach employs water, total liquid saturation and total pressure as the primary variables. Most existing models are limited to two-phase flow and specific boundary conditions when considering physically heterogeneous media. In addition, these models focused mainly on the water-wet media. However, in a real system, variations in wettability between water-wet and oil-wet media often occur. Furthermore, the wetting of porous media by oil can be heterogeneous, or fractional, rather than uniform due to the heterogeneous nature of the subsurface media and the factors that affect the wettability. Therefore, in this study, the chemically heterogeneous media considering fractional wettability as well as physically heterogeneous media were simulated using CHEMPS. In addition, the general boundary conditions were considered to be a combination of two types of boundaries of individual phases, flux-type and Dirichlet type boundaries.

• Journal of Soil and Groundwater Environment
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• v.6 no.4
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• pp.51-59
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• 2001

Column and box tests were performed to investigate the removal efficiency of NAPL using the surfactant enhanced flushing In heterogeneous medium. Homogeneous Ottawa sand and heterogeneous soil were used to verify the increase of remediation efficiency for the surfactant enhanced flushing in column test. Box tests with two different heterogeneous sub-structure were performed to quantify the capability of the surfactant enhanced flushing as a remediation method to remove NAPL from the heterogeneous medium. Two different grain size sand layers were repeated in the box to simulate the heterogeneous layer formation and the modified fault structure was built to simulate the fault system in the box. O-xylene as a LNAPL and PCE as a DNAPL were used and oleamide as a non-ionic surfactant. The maximum NAPL effluent concentration with 1% oleamide flushing in the homogeneous column test increased about 460 times compared to that with only water flushing and about 250 times increased in the real soil column test. In heterogeneous medium, the maximum effluent concentration increased about 150 times in 1% oleamide flushing and most of NAPL were removed from the box within 8 pore volume flushing, suggesting that the removal efficiency increased very much compared to in only water flushing. Results investigated the capability of the surfactant enhanced remediation method to remove NAPL even in heterogeneous medium.

• The Korean Journal of Petroleum Geology
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• v.1 no.1 s.1
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• pp.47-52
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• 1993

A method and results of computations are presented for the 2-D seismic migration process in the frequency-wavenumber domain for the laterally and vertically inhomogeneous medium. In order to take the intrinsic attenuation effect into account in the migration process the complex-valued wave velocity is used in the wavefield extrapolation operator, improving the generalized frequency-wavenumber migration technique. The imaginary part of the complex-valued wave velocity includes the seismic quality factor Q value. In derivation of the solution of the wave equation for the medium of inhomogeneous wave velocity and anelasticity, the inhomogeneous medium is mathematically converted to an equivalent system which consists of a homogeneous medium of averaged slowness and an inhomogeneous distribution of hypothetical wave source. The strength of the hypothetical wave source depends on the deviation of squared slowness from the averaged value of the medium. Results of numerical computation using the technique show more distinct geologic images than those using the convensional generalized frequency-wavenumber migration. Especially, the obscured images due to the wave attenuation by anelasticity are restored to show sharp boundaries of structures. The method will be useful in the imaging of the reflection data obtained in the regions of possible petroleum or natural gas reservoir and of fractured zone.

• The Journal of Engineering Geology
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• v.13 no.1
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• pp.51-65
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• 2003

A series of numerical simulations were carried out using STOMP( Subsurface Transport over Multiple Phase) simulator. The flow and distribution of LNAPL were analyzed in homogeneous fine and coarse sand. Vertical movement of LNAPL is faster in the coarser sand. But the total volume of LNAPL retained in the unsaturated zone is larger in the finer sand. A fine layer in the coarse sand domain is also simulated. The results showed that the retained LNAPL volume and shape are highly influenced by the Position of the fine layer. Flow and distributions of LNAPL were simulated when there were heterogeneous lenses in the sand domain. Water table fluctuation was also considered. In these cases, it was found that the heterogeneous lens was a barrier to LNAPL flow, and water table fluctuation stimulated the downward movement of retained LNAPL. The LNAPL flow and distribution observed in these numerical experiments show that in the subsurface environment, the behaviors of LNAPL highly depend on heterogeneities of unsaturated zone and the dynamic hydrogeologic condition such as water table fluctuation. These results can explain some of the complexity of LNAPL flow and distribution Patterns in LNAPL contaminated field sites.

• The Journal of Engineering Geology
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• v.28 no.1
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• pp.35-45
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• 2018

Imaging technologies are applied at various geological scales including pore scale, core scale and intermediate scale in order to characterize pore space of rocks as well as to map the fluid distribution in porous media. This technical report presents experimental results using core-flooding apparatus suited with imaging technology. Three different core samples, that are homogeneous, fractured and heterogeneous cores, were used to assess the two-phase fluid migration behavior as $CO_2$ displaces resident brine. We show that imaging technology can be effective in characterizing salt-precipitation, capillary pressure and spatio-temporal variation of trapping mechanisms.

• Geophysics and Geophysical Exploration
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• v.9 no.2
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• pp.148-154
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• 2006

The effect of small-scale near surface inhomogeneity on Rayleigh wave propagation and dispersion has been investigated in this study using two-dimensional FEM elastic modeling. Various inhomogeneity models with a variety of geometrical shape and embedment depth which exist in homogeneous half-space and two-layered media are considered. Results show that any near surface inhomogeneity greater than one wavelength in terms of minimum wavelength of Rayleigh wave shows dispersion characteristics. Such dispersion effect become stronger as the dimensions of the inhomogeneity increase. The effect of horizontal dimension is more dominant factor governing the dispersion characteristics than vertical dimension. However, the dispersion effect can not be identifiable in seismogram if the horizontal dimension is not wide enough. Nonetheless, even in this case, the existence of inhomogeneity can be inferred by the reflection or transmission event of Rayleigh wave. The results can be expected to provide insights on the behavior of Rayleigh wave which may be helpful for designating field work or new processing scheme to detect near surface inhomogeneity by surface wave method.

• Geophysics and Geophysical Exploration
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• v.8 no.1
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• pp.41-49
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• 2005

We have developed a random heterogeneous velocity model with bimodal distribution in methane hydrate-bearing Bones. The P-wave well-log data have a von Karman type autocorrelation function and non-Gaussian distribution. The velocity histogram has two peaks separated by several hundred metres per second. A random heterogeneous medium with bimodal distribution is generated by mapping of a medium with a Gaussian probability distribution, yielded by the normal spectral-based generation method. By using an ellipsoidal autocorrelation function, the random medium also incorporates anisotropy of autocorrelation lengths. A simulated P-wave velocity log reproduces well the features of the field data. This model is applied to two simulations of elastic wane propagation. Synthetic reflection sections with source signals in two different frequency bands imply that the velocity fluctuation of the random model with bimodal distribution causes the frequency dependence of the Bottom Simulating Reflector (BSR) by affecting wave field scattering. A synthetic cross-well section suggests that the strong attenuation observed in field data might be caused by the extrinsic attenuation in scattering. We conclude that random heterogeneity with bimodal distribution is a key issue in modelling hydrate-bearing Bones, and that it can explain the frequency dependence and scattering observed in seismic sections in such areas.