On the historical side, Electrical methods dedicated to Geosciences began with the Schlumberger Brothers in the late 20’s (Step 1). In a century, technology started from a simple DC resistivity method and went up to complex Electromagnetism methods implying natural or controlled sources, from 1D to 4D models, from acquisition in boreholes to land, air and sea. EM is now used in, tectonic studies, Oil & Gas and Mining Industry, Geothermal and Near surface studies (civil engineering, groundwater monitoring and environmental purposes).
First known success occurred with mineral exploration on highly conductive sulfide metal ores bodies.
A behavior of an EM field is controlled by 3 main parameters:
The Electrical conductivity is the most important for low frequency methods whereas the Electric permittivity is the most important for high frequency methods.
Predominance of the electrical resistivity and the very large domains of application could be explained considering simple physical phenomena:
Understanding other milestones of EM methods such as skin depth or importance of dielectric permittivity may require to get back to some more physics exploring the so-called Maxwell’s equations.
Ohm’s law and Maxwell’s equations represent the basement for all exploration technologies used nowadays.
