Abstract
In the field of frequency-domain electromagnetic detection, skin depth is an important parameter for electromagnetic data interpretation and imaging. The classic skin depth formula is calculated based only on conductivity; the induced-polarization effect in real earth is not considered, so the imaging results have obvious errors. To solve these problems, based on plane wave theory and the Cole–Cole conductivity model, a generalized skin depth formula of polarized media is derived in the frequency domain. The accuracy of the generalized skin depth is verified through comparison with the classical skin depth. To show the practicability of this study, the theoretical data with induced polarization (IP) effects are used to explain the generalized skin depth for polarized porous media. The generalized skin depth calculation for a typical porous polarization model is related not only to conductivity, but also to polarization parameters, such as chargeability, characteristic time constant, and frequency dependence. At low-frequency excitation, the generalized skin depth formula can be used to calculate the propagation depth of electromagnetic waves relatively accurately for porous polarized media. This method can be applied to the calculation of electromagnetic wave propagation depths in complex dispersive media. Compared with non-polarized media, in porous polarized media, under low-frequency excitation, the electromagnetic wave propagates deeper, allowing the detection of deeper objects. The data interpretation and imaging of polarized porous media by the generalized skin depth formula have higher accuracy.
Highlights
In practical work, the calculation of the detection depth of the electromagnetic (EM) method is very important for survey design and data interpretation
Many scholars have studied the detection depth of EM methods, and most studies have been based on the classical formula of skin depth; the effect of induced polarization (IP) has not been considered
There is no polarization, and the generalized skin depth of polarized medium is consistent with the calculation results of the classical skin depth expression
Summary
The calculation of the detection depth of the electromagnetic (EM) method is very important for survey design and data interpretation. Singh (2002) studied the effective skin depth of horizontal electric dipoles and large horizontal loop sources using the concept of plane wave skin depth [5]. Many scholars have studied the detection depth of EM methods, and most studies have been based on the classical formula of skin depth; the effect of induced polarization (IP) has not been considered. Based on the Cole–Cole conductivity model of underground polarized media and the principle of plane wave propagation, a generalized skin depth formula is deduced to calculate the skin depth for polarized media, and the characteristics of skin depth under the polarized media model are analyzed. The purpose of this paper is to improve the interpretation accuracy of underground polarized media and to illustrate the application of the proposed method in survey design and data interpretation
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