| 講演要旨(和文) | | 人工電流源海洋電磁（CSEM）探査は，海底下の高比抵抗な炭化水素資源の探査手法の一つとして注目されているが，その解像度の向上が大きな課題となっている．本研究では，仮想波動領域を用いたCSEM探査の解像度の向上に着目する．仮想波動領域における電磁場の伝搬はマクスウェル方程式を数式変換することで得る（Mittet, 2010）．これは主に高速計算のために開発されたが，楠田・後藤（2015）による3次元順計算の結果，高比抵抗異常体により生じる二次的な電磁場は実領域よりも仮想波動領域において大きく表れており，仮想波動領域における解析が従来法よりも高い解像度を有する可能性を示唆している．そこで本研究では，地下構造の解像度について議論を行うために，仮想波動領域における勾配法を用いた3次元全波形逆解析手法を開発した．数値計算の結果，仮想波動領域において高比抵抗異常体を高解像度で検出することが確認できた． |
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| | 講演要旨(英文) | | Marine controlled-source electromagnetic (CSEM) survey is considered as a technique in practice for the exploration of resistive hydrocarbon resources. Although CSEM survey could provide additional information to seismic surveys, the improvement of its resolution is one of the great issues. In this study, we focus on the fictitious wave domain to improve the resolution of CSEM survey. Electromagnetic (EM) field in the fictitious wave domain can be derived by transforming Maxwell equations from the diffusive wave domain (Mittet, 2010), mainly with the aim of faster numerical time-domain calculations. However, the resolution to the resistive hydrocarbon in the fictitious wave domain has not been well exploited. We conduct several tests of numerical simulations using the finite-difference time-domain (FDTD) method and a 3D resistivity model of a sub-seafloor structure. The sensitivity of resistive anomalies in fictitious wave domain becomes higher compared with the raw data in the diffusive domain, since the responses of anomalies are separated from other waves. For discussion on the resolution, we develop a gradient-based 3D full waveform inversion of CSEM data in the fictitious wave domain. From our numerical results, we conclude that a high resolution can be achieved by our inversion analysis in the fictitious wave domain. |
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