陆地可控源电磁法三维勘探的激电效应影响研究

Influence of induced polarization effects on 3D land CSEM sounding

可控源电磁法(CSEM)的正演模拟与反演解释中常忽略激电介质的影响.本文基于电磁三维正反演开源平台ModEM,分别开展了陆地CSEM三维正反演以及考虑激电介质的陆地CSEM三维正演研究,并与一维模型解析解对比验证了三维计算的准确性.数值模拟结果显示,模型含激电效应与不含激电效应的电场Ex频率响应差异明显,激电效应会导致电场Ex幅值减小、相位增加,且对Ex的影响程度与激电异常体的频谱特性及观测的收发距均相关.合成数据的陆地CSEM反演结果显示,数据中含激电效应会使得反演出的异常体在深度、规模和电阻率值上都与真实异常体存在较大偏差,忽略观测数据中的激电效应会明显影响观测的准确性.本文研究表明当陆地CSEM三维观测资料中包含激电效应时,有必要考虑其影响.

Induced Polarization(IP)effects are often ignored in the Controlled-Source Electromagnetic(CSEM)data inversion and interpretation.To study the influence of IP effects on 3 D land CSEM sounding,we have developed 3 D land CSEM forward modeling and inversion based on the open source EM modular inversion platform ModEM.The 3 D land CSEM forward modeling with IP effects is also developed.The accuracy of the 3 D forward modeling is verified by comparing the 3 D numerical results with the 1 D analytical solution.The numerical modeling results indicates that IP effects can decrease the amplitude and increase the phase of the electric field Ex.Such influence depends on the IP spectral characteristics of the abnormal body and the distance of between transmitter and receiver.The inversion results of the synthetic CSEM data with and without IP effects show that the IP effects can cause clear deviation in the inversion results,such as the depth,scale and resistivity of anomalous.This study indicates that it is necessary to consider the IP effects in 3 D land CSEM exploration.