Electro-Resistivity
VERTICAL ELECTRICAL SAMPLING TECHINIQUE
The Vertical Electrical Sampling is a technique used mainly in the study of horizontal interfaces, where all the array of electrodes is expanded around a central fixed point. It measures the vertical variation of the electrical resistivity in subsurface. The bigger the electrodes spacing is, the deeper is the investigation.
It is highly applied in geotechnical studies and hydrogeology.
ELECTRICAL TOMOGRAPHY TECHNIQUE (or ELECTRICAL IMAGING) 2D, 3D e 4D.
This method uses artificial electrical current, inserted in the ground through two electrodes with the objective of measuring the potential generated by other electrodes, allowing us to calculate the resistivity shown in subsurface.
It measures the lateral variation as well as the electrical resistivity depth of the ground in subsurface and it is indicated to investigate complex geological situations, such as deposits of metallic sulfide and contamination plumes in groundwater.
Through the use of data automatic acquisition systems, this technique is based in a large number of electrical resistivity measurements, using different electrode arranges. The information is processed and the results are presented as true 2D and 3D images of resistivity, because of the depth, with high resolution.
The repeated application of this technique allows us to monitor the evolution of contamination plumes generated by waste deposits through time. (Electrical tomography 4D)
Induced Polarization
The induced polarization – IP – is a very efficient method applied in the metallic sulfide prospecting, even where the mineralization is presented with lower levels (disseminated).
The method is based in the measurement of voltage variations according to the time or frequency (time and frequency domain and spectral IP).
CONVENTIONAL INDUCED POLARIZATION TECHNIQUE – DIPOLE-DIPOLE ARRAY
The acquisition is made through the interaction between dipole-dipole electrodes. The information is processed using specialized software, and the results are presented as pseudo-sections of chargeability and resistivity related to the depth.
2D ELECTRICAL IMAGING TECHNIQUE BY INDUCED POLARIZATION – IMIP2D
The IMIP technique – Electrical Imaging by Induced Polarization (resistivity and chargeability) is a way to apply the IP method, induced polarization, which has been developed and tested by the AFC Geofísica, since 2004 (Costa, 2010; Fornari, 2012). Basically, this technique is characterized for making it possible to deeply investigate of lands, comparing with what the conventional IP allows us to do, maintaining the good quality for the data and image resolution, even in these great depths, performing and huge number of readings, using automatic acquisition data systems and combination of different electrodes arrays.
The data is processed as set and the result is presented as two-dimensional figures of true resistivity and chargeability, as a function of the depth.
The amount of reading points is, normally, about ten times bigger than the conventional technique, using the dipole-dipole array.
ELECTRICAL IMAGING TECHNIQUE BY DEEP 3D INDUCED POLARIZATION – IMIP3D
The IMIP3D was developed by AFC Geofísica and it has as main feature the automatic acquisition of IP data (electrical resistivity and chargeability) in 3D mesh, using parameters which allow us to investigate great depth with high quality and resolution.
In 2012 we performed the first experimental works, with acquisition and 3D processing (IMIP3D), with defined parameters for investigation reaching depths up to 1.000m. Altogether there has been more than 10.000 reading points in the 3D mesh, for different positions of AB and with 168 electrode receivers interconnected.