对人工源频域电磁法视电阻率的探讨

A tentative discussion on apparent resistivity of the artificial source frequency domain electromagnetic method

对人工源频域电磁法的三种视电阻率计算方法进行了有关理论、一维地电模型正演、野外实验数据的对比分析,得出:广域视电阻率对于地质基底电阻率反映更真实,具有更强的抗干扰能力,但计算公式复杂;远区视电阻率对于地质基底电阻率反映没有广域视电阻率真实,但计算公式简单,且对于远区与过渡区的电阻率反映情况与广域视电阻率相同,也具备强抗干扰能力;卡尼亚视电阻率在远区与其他两种方法的结果相似,其计算视电阻率公式简单,但对于基底电阻率反映较差,且需额外测量磁场,导致抗干扰能力和工作效率不及前两者。故单纯从视电阻率反映的地质情况特别是基底地质情况看,广域视电阻率最优,远区视电阻率次之,卡尼亚视电阻率最次,但后两者计算公式简单。从勘探数据的正、反演角度而言,后两者的计算量要少于前者。

In this paper the authors proposed three methods to calculate the apparent resistivity for frequency domain controlled source electromagnetic methods. Comparison was carried out involving the analysis of their related theory, 1-D geoelectric forward modeling re-sults and field data. The results show that the wide field apparent resistivity can better interpret the geological base resistivity and has such advantages as strong anti-interference capability but has the shortcoming of complex formula. The far field apparent resistivity with simple formula and likewise strong anti-interference capability gives less information on the base resistivity.At far field and transition zone, the result from the wide field apparent resistivity is similar to that of the apparent resistivity method. The result of the Cagniard apparent resistivity in the far-zone is similar to that of the two methods mentioned above with the simple formula, in which extra magnet-ic field is required which leads to relatively weak anti-interference capability and poor efficiency. However, the method can not resolve the base resistivity. The comparison of the resolutions on the base resistivity shows that the wide field apparent resistivity is the most fa-vorable method among these methods, followed by the far-zone apparent resistivity, and the last is the Cagniard resistivity. However, the formulas of the last two methods are relatively simpler. The computation cost for the last two methods is less than that of the first one. The inconsistency of the three methods is observed at the far field, which absolutely needs further studies.