• Proceedings of the KSEEG Conference
• /
• 1999.04a
• /
• pp.100-102
• /
• 1999

• Proceedings of the KSEEG Conference
• /
• 2000.04b
• /
• pp.186-197
• /
• 2000

• Geophysics and Geophysical Exploration
• /
• v.1 no.3
• /
• pp.155-160
• /
• 1998

EM tomography technique has been developed. The algorithm used the extended Born approximations for forward modeling and reconstructed a conductivity image by a smoothness constraint least squares inversion method. Observed data, the vertical components of secondary magnetic fields, were simulated with the 3-D integral equation code. The results showed that the location of anomalous body could be imaged very well, but conductivity of the body was lower than real one and the vertical resolution was much higher than the horizontal resolution.

• The Korean Journal of Applied Statistics
• /
• v.12 no.2
• /
• pp.537-551
• /
• 1999

방출형 토모그래피와는 다르게, 토과형 토모그래피를 위한 통계적 알고리즘들은 매우 늦은 수렴속도와 엄청난 계산시간을 감수해야 했다. 그 주된 이유는 Lange-Carson 모형에 기초한 EM 알고리즘을 사용하고 있기 때문인데, 최근 GCA 기법의 등장으로 계산 시간을 현저히 단축할 수 있는 가능성이 제공되었다. 그러나 GCA 알고리즘은 우도의 단조중가성을 만족시키기 위해 부가적인 계산시간을 희생해야만 한다. 이에 본 연구에서는 프로그래밍이 간편하며, 처리시간이 짧고, 자체로 우도의 단조증가성을 만족하는 투과형 토모그래피를 위한 재구성 알고리즘을 제안한다.

• Geophysics and Geophysical Exploration
• /
• v.2 no.2
• /
• pp.104-111
• /
• 1999

As a practical developing step of electromagnetic (EM) tomography technique, we quantitatively analyzed the effects of borehole fluid and casing on the borehole EM responses. The EM response turns out to have nothing to do with the property of the borehole fluid except in the close vicinity of the transmitter, which shows the wide perspective of the application of borehole EM. Single-hole responses in the presence of the steel casing throughly reflect those of the casing itself since its extremely high induction number or shallow skin depth. EM responses through steel casing do show the information of the host medium. In the near field region which corresponds to low frequency or the vicinity of the borehole, however, we can not separate the signal containing the information of the host from that of casing. Otherwise, the severe attenuation of energy in the casing at high frequencies renders the signal undetectable. The optimum frequency is, therefore, to be chosen to extract the information of the host considering both the property of the casing and the skin depth of the medium and the practical technique to determine the casing property through single-hole measurements is required.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2007.06a
• /
• pp.185-190
• /
• 2007

In this study, we developed the 2.5D EM modeling and inversion algorithm for cross-hole source and receiver geometry. Considering the cross-hole environment, we use a VMD (vertical magnetic dipole) as a source and vertical magnetic fields as a measuring data. Developed inversion algorithm is tested for the isolated block model which has a conductive and a resistivity anomaly respectively. For the conductive anomaly, its size and resistivity are inverted well on the inversion results, while for the resistive anomaly, the location of anomalous block is shown on the inverted section, but its values are far from the exact value. Furthermore, artificial conductive anomalies are shown around the resistive anomalous zone. If we consider the inversion artifact shown in the test inversion of restive block, it is almost impossible to image the resistive zone. However, the main target of EM tomography in the engineering problem is conductive target such as fault zone, and contaminated zone etc., EM tomography algorithm can be used for detecting the anomalous zone.

• Geophysics and Geophysical Exploration
• /
• v.18 no.3
• /
• pp.143-153
• /
• 2015

Polymer flooding for enhancing hydrocarbon production injects into a reservoir polymer solution that is viscous. It is very important to monitor the behavior pattern of the polymer solution in order to evaluate the effectiveness of polymer flooding. To monitor the distribution of polymer solution and thus fluid substitution within the reservoir, we first construct seismic and resistivity rock physics models (RPMs), which are functions of reservoir parameters such as rocks and type of fluid, fluid saturation. For the seismic and resistivity RPMs, responses of seismic and electromagnetic (EM) tomography are numerically simulated as polymer injection, using two dimensional (2D) staggered-grid finite difference elastic modeling and 2.5D finite element EM modeling algorithms, respectively. In constructing RPM for EM tomography, three different reservoir rocks are considered: clean-sand, dispersed shale-sand, and sand-shale lamination rocks. The polymer solution is assumed to have 2 wt% of polymer as normally generated, while water is freshwater or saltwater. Further, neutron logging is also considered to check its sensitivity to polymer flooding. The techniques discussed in the paper are important in monitoring not only hydrocarbon but also geothermal reservoirs.