Electrical method of exploration

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The electrical method is another method of exploration used by the oil and mining industry. This method allows to obtain the lateral and vertical variations of the resistivity, which once obtained, are mapped through the sections of resistivity that facilitate the interpretation of the composition and the stratigraphic distribution of the different layers of the subsoil.

The method consists in the injection of an electric current "I" through two electrodes A and B nailed to the surface which generates an artificial electric field. The difference in potential generated "ΔV" is measured with the electrodes M and N. See images 1 and 2.

Figure 1 - Schematic diagram of the distribution of electrodes on the surface
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Figure 2 - Distribution of electrodes in the work area
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The Resistivity is given by the Equation:

ΔV ➡ Potential Difference (V)

I ➡ Current Intensity (A)

K ➡ Geometric Factor (m)

ρ ➡ Resistivity (Ω.m)

According to the type of configuration of the device, the geometric factor "K" will be given by the functions:

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Images 3 and 4 show two sections of resistivity obtained in the field with different distributions of emission and detection electrodes.

Figure 3 - Resistivity section
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Figure 4 - Resistivity section
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The method of electrical resistivity has allowed locating anomalies originated by complex geological structures as well as the detection of fluids of interest.

Given the high amount of conductive materials in the subsoil, the response obtained from the application of an electric current and therefore an artificial electric field, translates into a wide range of resistivities that favor the interpretation and prediction of the composition of the medium.

References

• De la Vega, Miguel O. “Ingeniería de puesta a tierra. Colección de textos politécnicos” Limusa –1998.
• Ollendorf, F. Erdstroeme , (Corrientes telúricas),“Birkhauser Verlag”, basel u Stuttgart. 1969
• ORELLANA, E. 1982,“Prospección Geoeléctrica en Corriente Continua”.2ª ed. Madrid: Paraninfo.Vol1.
• Telford, W.M., L. P. Geldart, and R. E. Sheriff, 1990. “Applied Geophysics”(2nd Edition), Cambridge.