MAE ET300 Georresistivímetro Multicanal 24-48 Canais

This survey method calculates ground resistivity based on voltage difference (d.d.p.) measurements. The process involves introducing an electric field into the ground using current electrodes and measuring the d.d.p. at separate measurement electrodes. Using Ohm's second law, the resistivity value is determined, reflecting the intrinsic properties of the material. Since rocks are naturally resistive, variations in resistivity are primarily due to the presence of water in varying amounts.

In 2D-3D electrical tomography, electrode grids (16, 32, 64, 128, etc.) are fixed into the ground at regular intervals. These electrodes are connected to commutation boxes that automatically select the measuring and current electrodes, performing all possible combinations. The system generates numerous measurements based on the number of electrodes and the geometric configuration used. The tomographic inversion of this data produces a 2D or 3D reconstruction of the ground, allowing the identification of anomalies such as cavities, water bodies, and their shapes, sizes, and spatial distribution.

Induced Polarization (IP) is an electrical phenomenon that occurs within material media. In the time domain, it is observed as chargeability, which happens when stress is released after the interruption of a step-type electric current. In the frequency domain, it involves the dispersion of electrical resistivity as the frequency of an alternating current changes. IP sources are primarily linked to redox processes at the interfaces between metal grains and interstitial fluids (electrode polarization). Another significant IP source is the accumulation of ions in moving electrolytes due to variations in mobility along the path (electro-kinetic polarization).

Through tomographic inversion of surface data, the resulting images reflect chargeability, enabling the identification of areas with potential hydrocarbon accumulations or other significant concentrations. Chargeability is directly proportional to the amount of charge stored by the lithotype, indicating the concentration of conductive materials in the multi-electrode area.

The Spontaneous Potential (SP) method involves measuring potential differences on the surface that are associated with natural electric fields, which are linked to the underground flow of aqueous electrolytic solutions in porous media. By analyzing SP anomalies on the surface, the intensity and position of ionic charge concentrations of both polarities can be determined.

The test involves placing two electrodes: one near the measurement station and the other moved along subsequent stations on the line. Alternatively, both electrodes can be moved while maintaining a consistent interval between them, mapping the ground based on spontaneous potential variations. This method is particularly useful in mining for locating sulfides and graphite, as well as in archaeology. Underground water flows can be influenced by archaeological structures, which may act as drains or obstacles. By identifying SP anomalies, it is possible to indirectly detect these underground structures.