• Geophysics and Geophysical Exploration
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• v.6 no.3
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• pp.153-159
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• 2003

Using reciprocity theorem, one direction aperture of seismogram can be extended to full aperture seismogram. Modified seismogram is applied to reverse time migration only to acquire improved migration image. In this paper, we tested reverse time migration with the Marmousi velocity data to examine efficiency of modified seismogram. And linearly increasing velocity model is selected and examined for a case where velocity data is insufficient. When true velocity is applied, using modified seismogram enhances the reverse time migration image more than using original seismogram. In the case of using linearly increasing velocity model, migration image is distorted. So low frequency source is brought in migration process. Reverse time migration image with low frequency source and linearly increasing velocity model is improved when modified seismogram is used. From the result of study, seismogram modification by reciprocity theorem is useful and migration image can be enhanced.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.233-236
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• 2005

Polarization filtering based on the multicomponent complex trace analysis method is performed to reject Rayleigh waves and to enhance S waves. To test the polarization filter, synthetic seismic data were constructed for a simple two-layer model based on the finite difference method. Rayleigh waves with elliptic motion are eliminated effectively and P and S waves with linear motions are well separated each other.

• Geophysics and Geophysical Exploration
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• v.21 no.1
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• pp.15-25
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• 2018

Seismic inversion is a high-resolution tool to delineate the subsurface structures which may contain oil or gas. On the other hand, marine controlled-source electromagnetic (mCSEM) inversion can be a direct tool to indicate hydrocarbon. Thus, the joint inversion using both EM and seismic data together not only reduces the uncertainties but also takes advantage of both data simultaneously. In this paper, we have developed a simultaneous joint inversion approach for the direct estimation of reservoir petrophysical parameters, by linking electromagnetic and seismic data through rock physics model. A cross-gradient constraint is used to enhance the resolution of the inversion image and the maximum likelihood principle is applied to the relative weighting factor which controls the balance between two disparate data. By applying the developed algorithm to the synthetic model simulating the simplified gas field, we could confirm that the high-resolution images of petrophysical parameters can be obtained. However, from the other test using the synthetic model simulating an anticline reservoir, we noticed that the joint inversion produced different images depending on the model constraint used. Therefore, we modified the algorithm which has different model weighting matrix depending on the type of model parameters. Smoothness constraint and Marquardt-Levenberg constraint were applied to the water-saturation and porosity, respectively. When the improved algorithm is applied to the anticline model again, reliable porosity and water-saturation of reservoir were obtained. The inversion results indicate that the developed joint inversion algorithm can be contributed to the calculation of the accurate oil and gas reserves directly.

• Geophysics and Geophysical Exploration
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• v.12 no.3
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• pp.255-262
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• 2009

Conventionally, vertical-seismic-profiling (VSP) survey that provides high-resolution information has mainly performed to obtain the exact depth of the gas hydrate-bearing sediment, which is one of the key factors in the development of the gas hydrate. In this study, we extracted interval velocities and created corridor stacks from the first domestic zero-offset VSP data, which were acquired with three component receivers at UBGH09 borehole in Ulleung Basin where gas hydrate exists. Then we compared the corridor stacks with a CMP stacked section from surface seismic data. First of all, we converted the signals recorded with three component receivers to true vertical and horizontal components by phase rotation, and divided the data into direct waves and reflected waves by wavefield separation processing. The trend of the interval velocity extracted from the zero-offset VSP was similar to that of the sonic log obtained at the same borehole. Because the interval velocity of the gas hydrate-bearing sediment above the BSR was high, and it decreased suddenly through the BSR, we could infer that free gas is accumulated below the BSR. The results of comparing the corridor stacks to the CMP stacked section of the surface seismic data showed that most reflection events agreed well with those in the surface CMP stacked section and that the phase-rotated VSP data corresponded better with the surface seismic data than the VSP data without phase rotation. In addition, by comparing a corridor stack produced from the transverse component with the CMP stacked section of the surface seismic data, we could identify PS mode-converted reflections in the CMP stacked section.

• Journal of the Korean Geotechnical Society
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• v.29 no.9
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• pp.17-29
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• 2013

The geophysical methods have an advantage for investigating the wide area with low cost, and thus the application of these methods has been increased. The objective of this paper estimates the characteristics of alluvium through the geophysical methods including elastic wave, electrical resistivity and ground penetration radar. And the standard penetration test is also carried out for verifying the geophysical data with comparison. The sources of elastic wave method are divided into hammer and sissy and the electrical resistivity method is applied with different sizes, shapes and arrays of electrode for deciding the effective way. The center frequency is determined to be 270 MHz for considering the characteristics of soil. The results of ground penetration radar are also compared with those of standard penetration test. The high resolution shows when the source is a sissy in elastic wave method, however, the water level is not identified. In the electrical resistivity method, the non-polarizable electrode and schlumberger array show highly reliable data and the resolution of ground penetration radar is low. Thus, the results of this study are widely applied for determining the appropriate method when investigating the characteristics of alluvium.

• Geophysics and Geophysical Exploration
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• v.25 no.3
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• pp.109-119
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• 2022

The computational efficiency of reverse time migration (RTM) based on numerical modeling is not secured due to the high-frequency band of several hundred Hz or higher for data acquired through a three-dimensional (3D) ultra-high-resolution (UHR) seismic survey. Therefore, this study develops an RTM program to derive high-quality 3D geological structures using UHR seismic data. In the traditional 3D RTM program, an excitation amplitude technique that stores only the maximum amplitude of the source wavefield and a domain-limiting technique that minimizes the modeling area where the source and receivers are located were used to significantly reduce memory usage and calculation time. The program developed through this study successfully derived a 3D migration image with a horizontal grid size of 1 m for the 3D UHR seismic survey data obtained from the Korea Institute of Geoscience and Mineral Resources in 2019, and geological analysis was conducted.

• Geophysics and Geophysical Exploration
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• v.7 no.3
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• pp.157-163
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• 2004

In this study, a travel-time tomography software was developed under the MS Windows system and GUI environment for user. The software supports following features: (1) supporting various data input format (2) flexible treatment of shot and receiver coordinate coding (3) flexible first arrival picking and modification (4) easy modification of intermediate tomogram. It is expected that the effort of the user can be minimized in each data processing step.

• Geophysics and Geophysical Exploration
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• v.25 no.4
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• pp.227-241
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• 2022

Full waveform inversion (FWI) in the field of seismic data processing is an inversion technique that is used to estimate the velocity model of the subsurface for oil and gas exploration. Recently, deep learning (DL) technology has been increasingly used for seismic data processing, and its combination with FWI has attracted remarkable research efforts. For example, DL-based data processing techniques have been utilized for preprocessing input data for FWI, enabling the direct implementation of FWI through DL technology. DL-based FWI can be divided into the following methods: pure data-based, physics-based neural network, encoder-decoder, reparameterized FWI, and physics-informed neural network. In this review, we describe the theory and characteristics of the methods by systematizing them in the order of advancements. In the early days of DL-based FWI, the DL model predicted the velocity model by preparing a large training data set to adopt faithfully the basic principles of data science and apply a pure data-based prediction model. The current research trend is to supplement the shortcomings of the pure data-based approach using the loss function consisting of seismic data or physical information from the wave equation itself in deep neural networks. Based on these developments, DL-based FWI has evolved to not require a large amount of learning data, alleviating the cycle-skipping problem, which is an intrinsic limitation of FWI, and reducing computation times dramatically. The value of DL-based FWI is expected to increase continually in the processing of seismic data.

• Geophysics and Geophysical Exploration
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• v.6 no.1
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• pp.13-22
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• 2003

TSP (Tunnel Seismic Profiling) survey is a technique for imaging and characterizing geological structures ahead of a tunnel face. The seismic modeling algorithm and the synthetic data could be helpful for TSP surveys. However, there is few algorithm to describe the propagation of the elastic waves around the tunnel. In this study, existing 2-dimensional seismic modeling algorithm using finite element method was modified to make a suitable algorithm for TSP modeling. Using this algorithm, TSP modeling was practiced in some models. And the synthetic data was analyzed to examine the propagation characteristics of the elastic waves. First of all, the modeling for the homogeneous tunnel model was practiced to examine the propagation characteristics of the direct waves in the vicinity of the tunnel. And the algorithm was applied to some models having reflector which is perpendicular or parallel to the excavation direction. From these, the propagation characteristics of the reflected waves were examined. Furthermore, two source-receiver arrays were used in respective models to investigate the properties of the two arrays. These modeling algorithm and synthetic data could be helpful in interpreting TSP survey data, developing inversion algorithm and designing new source-receiver arrays.

• Economic and Environmental Geology
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• v.39 no.6 s.181
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• pp.711-717
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• 2006

In order to study gas hydrate, potential future energy resources, Korea Institute of Geoscience and Mineral Resources has conducted seismic reflection survey in the East Sea since 1997. one of evidence for presence of gas hydrate in seismic reflection data is a bottom simulating reflector (BSR). The BSR occurs at the interface between overlaying higher velocity, hydrate-bearing sediment and underlying lower velocity, free gas-bearing sediment. That is often characterized by large reflection coefficient and reflection polarity reverse to that of seafloor reflection. In order to apply depth migration to seismic reflection data. we need high performance computers and a parallelizing technique because of huge data volume and computation. Phase shift plus interpolation (PSPI) is a useful method for migration due to less computing time and computational efficiency. PSPI is intrinsically parallelizing characteristic in the frequency domain. We conducted conventional data processing for the gas hydrate data of the Ease Sea and then applied prestack depth migration using message-passing-interface PSPI (MPI_PSPI) that was parallelized by MPI local-area-multi-computer (MPI_LAM). Velocity model was made using the stack velocities after we had picked horizons on the stack image with in-house processing tool, Geobit. We could find the BSRs on the migrated stack section were about at SP 3555-4162 and two way travel time around 2,950 ms in time domain. In depth domain such BSRs appear at 6-17 km distance and 2.1 km depth from the seafloor. Since energy concentrated subsurface was well imaged we have to choose acquisition parameters suited for transmitting seismic energy to target area.