Improving Inversion Quality of IP-Affected TEM Data Using Dual Source

Abstract

The induced polarization (IP) effects in transient electromagnetic (TEM) responses pose difficulties to the TEM data interpretation and inversion. The IP effects break the monotony in TEM decay curves and can even cause sign reversals and lead to the singularity and non-monotony of inversion. The singularity problem is still urgent to be solved. In this paper, the forward modeling method of IP-affected TEM responses is developed using the Cole–Cole model and a frequency-time domain transformation. A TEM data acquisition scheme using a dual-source method without a significant increase in field work is proposed to weaken the singularity and improve the inversion quality finally. Based on the modeling and analysis, the dual-source scheme is designed to guarantee all stations be measured twice with different loops. The joint inversion of dual-source datasets is realized by using an objective combing function and the particle swarm optimization (PSO) algorithm. The synthetic data test proved the validity of the algorithm and illustrated that the joint dual-source method greatly weakened the singularity and stabilized the inversion. The field example of the Baiyun golden deposit showed well consistency with resistivity logging and TEM logging results and predicted the gold mineralization below 2000 m.

Keywords

• inversion
• TEM method
• induced polarization
• PSO algorithm
• dual source
• gold deposit