• Title/Summary/Keyword: 해양 CSEM

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Computation of Apparent Resistivity from Marine Controlled-source Electromagnetic Data for Identifying the Geometric Distribution of Gas Hydrate (가스 하이드레이트 부존양상 도출을 위한 해양 전자탐사 자료의 겉보기 비저항 계산)

  • Noh, Kyu-Bo;Kang, Seo-Gi;Seol, Soon-Jee;Byun, Joong-Moo
    • Geophysics and Geophysical Exploration
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    • v.15 no.2
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    • pp.75-84
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    • 2012
  • The sea layer in marine Controlled-Source Electromagnetic (mCSEM) survey changes the conventional definition of apparent resistivity which is used in the land CSEM survey. Thus, the development of a new algorithm, which computes apparent resistivity for mCSEM survey, can be an initiative of mCSEM data interpretation. First, we compared and analyzed electromagnetic responses of the 1D stratified gas hydrate model and the half-space model below the sea layer. Amplitude and phase components showed proper results for computing apparent resistivity than real and imaginary components. Next, the amplitude component is more sensitive to the subsurface resistivity than the phase component in far offset range and vice versa. We suggested the induction number as a selection criteria of amplitude or phase component to calculate apparent resistivity. Based on our study, we have developed a numerical algorithm, which computes appropriate apparent resistivity corresponding to measured mCSEM data using grid search method. In addition, we verified the validity of the developed algorithm by applying it to the stratified gas hydrate models with various model parameters. Finally, by constructing apparent resistivity pseudo-section from the mCSEM responses with 2D numerical models simulating gas hydrate deposits in the Ulleung Basin, we confirmed that the apparent resistivity can provide the information on the geometric distribution of the gas hydrate deposit.

Three-dimensional Modeling of Marine Controlled-source Electromagnetic Surveys Based on Finite Difference Method (유한차분법에 기초한 인공송신원 해양전자탐사 모델링)

  • Han, Nu-Ree;Nam, Myung-Jin;Ku, Bon-Jin;Kim, Hee-Joon
    • Geophysics and Geophysical Exploration
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    • v.15 no.2
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    • pp.66-74
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    • 2012
  • This paper presents development of a three-dimensional marine controlled-source electromagnetic (mCSEM) modeling algorithm and its application to a salt and reservoir model to examine detectability of mCSEM for a reservoir under complex subsurface structures. The algorithm is based on the finite difference method, and employs the secondary field formulation for an accurate and fast calculation of modeling responses. The algorithm is verified for a two-layer model by comparing solutions not only with analytic solutions but also with those from other 3D modeling algorithm. We calculate and analyze electric and magnetic fields and their normalized responses for a salt and reservoir model due to three sources located at boundaries between a salt, a reservoir, and background. Numbers and positions of resistive anomalies are informed by normalized responses for three sources, and types of resistive anomalies can be informed when there is a priori information about a salt by seismic exploration.

Marine Controlled-source Electromagnetic Surveys for Hydrocarbon Exploration (탄화수소 탐지를 위한 해양 인공송신원 전자탐사)

  • Kim, Hee-Joon;Han, Nu-Ree;Choi, Ji-Hyang;Nam, Myung-Jin;Song, Yoon-Ho;Suh, Jung-Hee
    • Geophysics and Geophysical Exploration
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    • v.9 no.2
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    • pp.163-170
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    • 2006
  • The shortage of proven hydrocarbon reserves has resulted in exploration progressing from the offshore into progressively deeper water of the continental shelf. Despite the success of seismic acquisition at ever greater depths, there are marine geological terrenes in which the interpretation of seismic data is difficult, such regions dominated by scattering or high reflectivity that is characteristic of carbonate reefs, volcanic cover and submarine permafrost. A marine controlled-source electromagnetic (CSEM) method has recently been applied to the oil and gas exploration thanks to its high-resistivity characteristics of the hydrocarbon. In particular, this method produces better results in terms of sensitivity under the deep water environment rather than the shallow water. Only in the last five years has the relevance of CSEM been recognized by oil companies who now use it to help them make exploration drilling decisions. Initial results are most promising and several contractors now offer magnetotelluric and CSEM services.

Fast numerical methods for marine controlled-source electromagnetic (EM) survey data based on multigrid quasi-linear approximation and iterative EM migration (다중격자 준선형 근사 및 반복적 전자탐사 구조보정법에 기초한 해양 인공송신 전자탐사 자료의 빠른 수치해석 기법)

  • Ueda, Takumi;Zhdanov, Michael S.
    • Geophysics and Geophysical Exploration
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    • v.11 no.1
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    • pp.60-67
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    • 2008
  • In this paper we consider an application of the method of electromagnetic (EM) migration to the interpretation of a typical marine controlled-source (MCSEM) survey consisting of a set of sea-bottom receivers and a moving electrical bipole transmitter. Three-dimensional interpretation of MCSEM data is a very challenging problem because of the enormous number of computations required in the case of the multi-transmitter and multi-receiver data acquisition systems used in these surveys. At the same time, we demonstrate that the MCSEM surveys with their dense system of transmitters and receivers are extremely well suited for application of the migration method. In order to speed up the computation of the migration field, we apply a fast form of integral equation (IE) solution based on the multigrid quasi-linear (MGQL) approximation which we have developed. The principles of migration imaging formulated in this paper are tested on a typical model of a sea-bottom petroleum reservoir.

A Scheme for Computing Primary Fields in Modeling of Marine Controlled-Source Electromagnetic Surveys (해양전자탐사 모델링을 위한 1차장 계산법)

  • Kim, Hee-Joon
    • Geophysics and Geophysical Exploration
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    • v.14 no.3
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    • pp.185-190
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    • 2011
  • In marine controlled-source electromagnetic (CSEM) modeling, it may be difficult to evaluate primary fields accurately using conventional linear filters because they decay very rapidly with distance. However, since there exists a closed-form solution to the Hankel transform in TM mode for a homogeneous half space, we can assess the accuracy of linear filters for evaluating the Hankel transform. As a result, only nine out of 36 source-receiver pairs show that EM fields decrease linearly in semi-log scale with an increase of source-receiver distance, while EM fields are either 0 or not reduced significantly due to an effect of the air layer. There also exist closed-form solutions for the nine pairs, and the others can be evaluated accurately with a relatively short filter. This paper proposes a method which uses closed-form solutions for TM-mode Hankel transforms and a filter with 61 coefficients for TE-mode ones.

Joint Electromagnetic Inversion with Structure Constraints Using Full-waveform Inversion Result (완전파형역산결과를 구조적 제약 조건으로 이용한 고해상도 전자탐사 복합역산 알고리듬 개발)

  • Jeong, Soocheol;Seol, Soon Jee;Byun, Joongmoo
    • Geophysics and Geophysical Exploration
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    • v.17 no.4
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    • pp.187-201
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    • 2014
  • Compared with the separated inversion of electromagnetic (EM) and seismic data, a joint inversion using both EM and seismic data reduces the uncertainty and gives the opportunity to use the advantage of each data. Seismic fullwaveform inversion allows velocity information with high resolution in complicated subsurface. However, it is an indirect survey which finds the structure containing oil and gas. On the other hand, marine controlled-source EM (mCSEM) inversion can directly indicate the oil and gas using different EM properties of hydrocarbon with marine sediments and cap rocks whereas it has poor resolution than seismic method. In this paper, we have developed a joint EM inversion algorithm using a cross-gradient technique. P-wave velocity structure obtained by full-waveform inversion using plane wave encoding is used as structure constraints to calculate the cross-gradient term in the joint inversion. When the jointinversion algorithm is applied to the synthetic data which are simulated for subsea reservoir exploration, images have been significantly improved over those obtained from separate EM inversion. The results indicate that the developed joint inversion scheme can be applied for detecting reservoir and calculating the accurate oil and gas reserves.

Petrophysical Joint Inversion of Seismic and Electromagnetic Data (탄성파 탐사자료와 전자탐사자료를 이용한 저류층 물성 동시복합역산)

  • Yu, Jeongmin;Byun, Joongmoo;Seol, Soon Jee
    • 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.