| 講演要旨(和文) | | 海洋人工電流源電磁 (CSEM) 探査は，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である．本研究では，実領域データを仮想波動領域に変換し，仮想波動領域上で逆解析する手法を詳解する．全波形逆解析手法を適用することで，高比抵抗体を高解像度かつ高速に検出できた．さらにニュージーランド沖で取得されたCSEM探査データに対して本手法を適用した結果，変換後の波形には地下深部からの反射電磁波と推測される信号が含まれてい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 below seafloor. However, the improvement of its resolution is one of the great issues for hydrocarbon exploration. Electromagnetic (EM) field in the fictitious wave domain can be derived by the analytically transforming Maxwell equations from the diffusive wave domain, mainly with the aim of faster numerical calculations of time-domain EM propagation. In the present study, we hypothesize that the transformation from the diffusive to the fictitious wave domain could be utilized to improve the response of resistive anomaly and conduct several tests of numerical simulations using the finite-difference time-domain (FDTD) method and a 3D resistivity model of a sub-seafloor structure, which includes resistive anomaly. From our numerical results, the sensitivity of anomalies in fictitious wave domain becomes higher compared with the raw data in the diffusive domain. We apply a gradient-based 3D full waveform inversion of CSEM data in the fictitious wave domain and high resolution can be achieved. In addition, marine CSEM data collected in offshore New Zealand can be transformed to the fictitious wave domain. We conclude that EM signals from sub-seafloor can be estimated from the transformed data. |
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