Analysis and removal of electromagnetic coupling effects in the large-depth induced polarization method
JI Zhen-Xing1(), QIN Hao-Jie2,3, CHEN Ru-Jun2,3,4,5(), WANG Quan-Gong1
1. Jiangsu Geological Bureau, Nanjing 210018, China 2. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China 3. AIoT Innovation and Entrepreneurship Education Center for Geology and Geophysics, Central South University, Changsha 410083, China 4. Hunan Key Laboratory of Non-ferrous Resources and Geological Hazard Exploration, Changsha 410083, China 5. Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Ministry of Education, Central South University, Changsha 410083, China
With the gradual depletion of shallow mineral resources, deep mineral exploration has emerged as an essential development trend in the mining industry. Increasing the distance between receiver electrodes of induced polarization (IP) devices is the most direct and effective approach to enhance the exploration depth. However, a long distance can cause strong electromagnetic (EM) coupling effects, severely interfering with IP signals. Addressing this challenge, this study calculated the EM coupling effects of various measuring devices in homogeneous half-space and layered media using analytical methods. Furthermore, this study comparatively analyzed the impacts of various factors, including measuring device type, wiring layout, distance between receiver electrodes, earth resistivity, and frequency, on the EM coupling intensity. Based on the phase differences between IP and EM coupling effects in the frequency domain, this study derived the calculation equation of the relative phase spectrum, followed by a theoretical analysis of the decoupling effects in application scenarios. The results indicate that increasing distance between receiver electrodes, decreasing earth resistivity, and raising working frequency all significantly intensified the EM coupling interference. Under consistent conditions and detection depths, the Schlumberger array suffered from higher EM coupling interference compared to the pole-dipole array. Compared to the traditional IP phase spectrum, the relative phase spectrum enhanced the maximal working frequency of the pole-dipole and Schlumberger arrays by four and 10.6 times, respectively, suggesting the decoupling capability of the relative phase method in large-depth IP exploration. Overall, this study provides significant guidance for the field implementation of large-depth IP exploration.
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