지구물리와물리탐사 (Geophysics and Geophysical Exploration)

  • 제14권2호
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  • Pages.164-175
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  • 2011
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  • 1229-1064(pISSN)
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  • 2384-051X(eISSN)
한국지구물리·물리탐사학회 (Korean Society of Earth and Exploration Geophysicists)
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유한요소법을 이용한 MT 탐사 자료의 모델링: 보조장 계산의 고찰

Modeling of Magnetotelluric Data Based on Finite Element Method: Calculation of Auxiliary Fields

  • 남명진 (세종대학교 에너지자원공학과) ;
  • 한누리 (세종대학교 에너지자원공학과) ;
  • 김희준 (부경대학교 에너지자원공학과) ;
  • 송윤호 (한국지질자원연구원 지열자원연구실)
  • Nam, Myung-Jin (Department of Energy and Mineral Resources Engineering, Sejong University) ;
  • Han, Nu-Ree (Department of Energy and Mineral Resources Engineering, Sejong University) ;
  • Kim, Hee-Joon (Department of Energy Resources Engineering, Pukyong National University) ;
  • Song, Yoon-Ho (Groundwater and Geothermal Division, Korea Institute of Geoscience and Mineral Resources)
  • 투고 : 2011.05.06
  • 심사 : 2011.05.25
  • 발행 : 2011.05.28
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초록

낮은 주파수의 자연 전자기장을 이용하는 MT 탐사는 지하 심부의 전기전도도 구조를 규명할 수 있기 때문에, 지열에너지자원 탐사, 이산화탄소의 지중저장을 위한 부지 선정, 인공저류층 지열발전 시스템 유망 지역 탐사 등에 적용되고 있다. 또한 해양 MT 자료를 활용하면 해양전자탐사 자료 해석의 정확도를 높일 수 있다. MT 자료의 해석에 있어 정확한 모델링 기법은 필수적이다. 변유한요소법을 이용한 기존의 MT 모델링 알고리듬에서는 보조장인 자기장을 차분적 방법론에 기초하여 계산하였기 때문에 수직자기장의 정확한 계산에 한계가 있었다. 이 논문에서는 변유한요소법의 기저함수들의 선형결합으로 근사된 전기장을 직접 미분하는 방법으로 수직자기장을 계산하였다. 수치 실험을 통해, 지형이 있는 경우에 수직자기장에 대한 기존의 알고리듬의 결과에 오차가 있음을 확인하였다. 최종적으로, 지형이 있는 모형에 대한 기존의 인덕션 벡터와 티퍼의 결과는 오차가 있는 수직자기장을 이용하였으므로, 이 논문에서는 개선된 알고리듬을 이용하여 올바른 결과를 제시하고자 한다.

Using natural electromagnetic (EM) fields at low frequencies, magnetotelluric (MT) surveys can investigate conductivity structures of the deep subsurface and thus are used to explore geothermal energy resources and investigate proper sites for not only geological $CO_2$ sequestration but also enhanced geothermal system (EGS). Moreover, marine MT data can be used for better interpretation of marine controlled-source EM data. In the interpretation of MT data, MT modeling schemes are important. This study improves a three dimensional (3D) MT modeling algorithm which uses edge finite elements. The algorithm computes magnetic fields by solving an integral form of Faraday's law of induction based on a finite difference (FD) strategy. However, the FD strategy limits the algorithm in computing vertical magnetic fields for a topographic model. The improved algorithm solves the differential form of Faraday's law of induction by making derivatives of electric fields, which are represented as a sum of basis functions multiplied by corresponding weightings. In numerical tests, vertical magnetic fields for topographic models using the improved algorithm overcome the limitation of the old algorithm. This study recomputes induction vectors and tippers for a 3D hill and valley model which were used for computation of the responses using the old algorithm.

키워드

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