The author reworks his total current conductivity function introduced in a previous paper, related to electrical polarization of rocks in the frequency range of 1 MHz to 10−3 Hz. The original five parameters in this function are replaced by new ones, which from the beginning have clear petrophysical and electrochemical meanings and well‐defined ranges of variation. Some classical models are derived as particular cases of it. The main existing models proposed to describe induced polarization (IP) are analyzed, and most of them are grouped together under a common circuit analog representation and a respective generating function. A circuit analog is assigned to each model. The multi‐Cole‐Cole model circuit analog reveals intrinsic constraints involving the values of its circuit elements. Because of these constraint relations and the relaxation times ratio (τ1/τ2)—usually many orders of magnitude from unity—the model has no physical validation to represent single‐phase material systems (in the sense of the polarization). The performance and analysis of the various models to describe a few well‐selected experimental data show that only two of the models, the multi‐Cole‐Cole and Dias models, can provide a function structure capable of fitting these data. This fact, the associated petrophysical interpretation consistency, and the basic characteristics of these two models, such as the way they were derived (empirically, the former; phenomenologically, the latter) and the number of coefficients in the function (directly related to the degree of ambiguity of their determination), make the author’s model attractive and promising.

The Maxwell equations are written and discussed in the frequency domain for a medium exhibiting electrical polarization at radio and lower frequencies, in the range of linearity between current density and electric‐field intensity. A complex function of frequency is proposed for the conductivity, which is able to describe all the families of available experimental curves for rock samples in the natural state, showing the effect of polarization. Such a function is a constitutive relation for the polarizable medium in the frequency domain. The concept of ‘abnormal’ dielectric constant for rocks is discussed in the context of the physical mechanisms responsible for the effect of electrical polarization at radio frequencies and below. Such a concept, always possible theoretically, only introduces confusion in the understanding of the basic physical mechanisms involved. As an alternative the extensive use of the concept of a total current complex conductivity is suggested.

The types of physical mechanisms that generate induced electric polarization (IP) in rocks are here identified and their respective relaxation times are provided. Thus, the complex resistivity function associated with Dias’ model that describes the IP phenomenon is decomposed into partition fractions of an inverse third-degree polynomial in [Formula: see text]. Twelve rock samples’ data from the literature were used for this investigation. Using this procedure, two basic relaxations appear in the frequency range 1 mHz–1 MHz, where the phenomenon occurs. The first relaxation is associated with polarization caused by ionic diffusion proximal to the disseminated particle-electrolytic solution interfaces, which dominates in the low-frequency interval (approximately 1 mHz–100 Hz). The second process is capacitive-inductive polarization relaxation caused by an interaction between the electric double-layer capacitance and polarization-free pore resistances inside the polarization unit cell, which dominates in the high-frequency interval (approximately 10 kHz–1 MHz). At intermediate frequencies, these two processes combine to yield a transitional type of relaxation that dominates in the intermediate frequency interval (approximately 100 Hz–10 kHz). Our results, obtained using a given set of experimental data, provide a new method for determining the water salinity and clay content in the rock matrix without metallic particles. The rock permeability was also well determined by introducing Dias’ model parameter relationships and substituting the double-layer thickness for the grain size radius in a previously proposed formula.

In this work we discuss the results of an experimental study performed with a multi-frequency electromagnetic method over a mature oil field in Recôncavo basin, Bahia-Brazil. Five 1.8 km transects 200m apart and extending over a block of the oil reservoir were surveyed. The processed EM data are represented as cross-sections of apparent resistivity and induced polarization parameter, using a consistent plotting procedure developed by Dias and Sato (1981). All the sections, controlled by seismic and well log data, although showing some distortions in the IP-resistivity configurations, allow to recognize the following geological features: (i) the oil sandstone horizons and their trapping shales; (ii) the oil-water interface and some zones of steam invasion; and (iii) lateral electric contrasts representing fault zones. These results suggest the real possibility of the use of the spectral EM method in the direct detection of hydrocarbons, as well as for monitoring the efficiency of the artificial fluid injection used for secondary recovery.

A B S T R A C TThe electric and magnetic fields generated by an individual horizontal current ring induced inside a homogeneous conductive half-space, originating from an external large circular loop source of current in the presence of a flat half-space, are deduced. A check of self-consistency for these expressions led to the known general functions for these fields due to the same external source in the presence of that medium. The current rings' mutual coupling related to the magnetic field's radial component is thoroughly analysed and its specific members are presented. The existence of a relatively small zone inside the half-space responsible for the main contribution for the signal measured at the observation point, with the source and receiver on the ground surface, is made evident. For increasing values of frequency, at a given transmitterreceiver (T-R) configuration, this zone shrinks and its central point moves away from a maximum depth of about 30% and horizontal distance of nearly 85%, of the T-R separation, to a point very close to the receiver position. The coordinates of the central point of this zone of main contribution are provided as approximated functions in terms of the induction number [(μ 0 ωσ/2) 1/2 r ].