資源開発技術・岩盤工学

[1201-10-04] 時間領域差分法を用いた海洋CSEMデータの全波形逆解析

○Amani Sajjad¹、三ケ田 均¹、武川 順一¹ (1. 京都大学)

司会：木﨑 彰久（秋田大学）

キーワード：海洋CSEM、資源探査、全波形逆解析、仮想領域法

The high contrast of the resistivity between the hydrocarbon reservoirs and their surrounding media is a key criterion that makes the marine controlled source electromagnetic method (CSEM) to be considered among the top supplementary methods for decreasing the risk of oil and gas explorations. The continuously increasing costs of seismic surveys, on the other side, even make the CSEM method more popular. However, two main problems make the marine CSEM method vulnerable for hydrocarbon explorations and monitoring. The first one is due to the strong attenuation of propagating EM waveforms in the conductive seawater layer and the earth layers. The next one is the computational cost of CSEM simulations arising from the very small time sampling rate. Inspiring by the similarity of the seismic and electromagnetic data, we deal with the first problem using the most advanced seismic inversion method; full waveform inversion (FWI). The FWI method is an iterative method that uses all the waveform information to find the best possible model parameter that fits the observed data. For CSEM data modeling, we use a fast fictitious-diffusive finite difference scheme that makes the computation cost efficient and practical. Through the numerical calculations on a synthetic marine model including a hydrocarbon reservoir, we investigate the possibility of using time domain FWI for hydrocarbon explorations using marine CSEM data. Our results confirm the high capability of CSEM method for hydrocarbon explorations and monitoring with a practical computation cost.