Applications derived from electromagnetic principles have been fundamental in the development and advancement of a large number of technologies, and this is due to the physical principles and mathematical models developed for decades in this area of knowledge by great scientists who have been the pillar of these achievements
Application of electromagnetic techniques in the exploration of the subsoil is one of them. These techniques based on these principles have allowed, through the measurement of electrical and magnetic parameters, the characterization of the subsoil and have turned it into essential support in the detection of oil and hydrological reserves, geological faults, layer thickness, preliminary studies in civil engineering and widely used in archaeological studies.
In oil exploration, the electromagnetic method is used with success, and given the variety of instruments it has, it is a versatile, low-cost, and rapid data acquisition method.
The characterization of the subsoil through the electromagnetic induction method, key parameters such as conductivity or its electrical resistivity are obtained, which are properties that allow inferring about the constituent materials of the subsoil. This data is used to create stratigraphic and geological maps of the study area, thus obtaining a tomography of the subsoil from the spatial distribution of the electrical conductivity of the area.
Figure 1 shows the instruments and the methodology used by the electromagnetic induction method in the conductivity analysis of the study area.
(Own elaboration)
The electromagnetic induction method is based on Faraday's Law and consists of the generation of a variable electromagnetic field originating from a transmitter coil through which an alternating current circulates. This field known as the primary field induces electrical currents in conductive materials present in the subsoil called Foucault's currents. These currents in turn produce a secondary field in the opposite direction to the primary field and which is registered by a second receiving coil placed on a surface separated from the primary coil a distance "S".
This process is carried out at different points on the analyzed terrain, in order to obtain a complete scan of the area of interest.
By obtaining the conductivity distribution and the penetration depths associated with these conductivities, an image of the subsoil is obtained whose applications have important scopes, among which the following stand out:
- Inclination of strata.
- Location of faults.
- Detection of metals or conductive materials in shallow archaeological studies.
- Detection of aquifers.
It is important to highlight that the penetration of the wave into the subsoil is diminished for high-frequency values (see figure 2), so frequency controls are used in the transmitter sources that allow greater penetration and resolution in the subsoil mapping.
(Own elaboration)
Although there are other electromagnetic modalities or techniques in the determination of electrical and magnetic parameters of the subsoil, the electromagnetic induction method has been characterized by the ease of mobility of the transmitting and receiving instruments in the field, which allows obtaining a greater Lateral coverage in the area of conductivity distributions significantly minimizing the costs and effort required by other methods.
Reference
- Tratado de Geofísica Aplicada. José Cantos Figuerola. Librería Ciencia-Industria, S.L. Pl. San Luis de la Cruz, Madrid. 520 pag.
- Applied Geophysics. W.M. Telford, L.P. Geldart, R. E. Sheriff. Second Edition. Cambridge University Press.
- Introduction To Electromagnetic Fields Third Edition / Clayton R. Paul, Keith W. Whites, Syed A. Nasar
- Teoría electromagnética. Willian H. Hayt, Jr., John A. Buck. Séptima edición. McGraw Hill.
