Geoelectrical

Geoelectrical, also known as electrical geophysics, is a geophysical method used to characterize the subsurface by measuring its electrical properties. The principal quantity is bulk electrical resistivity (or its reciprocal, conductivity); in some methods complex conductivity or induced polarization is measured to detect chargeability differences related to mineralogy and fluid content. Geoelectrical methods are applied on the surface or in boreholes and are used to map variations in lithology, porosity, salinity, moisture, and temperature.

Common field techniques include DC resistivity and electrical resistivity tomography (ERT), along with induced polarization (IP). Current is injected into the ground through electrode pairs, and resulting ground-to-surface potential differences are recorded by potential electrodes. Various array configurations are used, such as Wenner, Schlumberger, and dipole-dipole, to balance sensitivity, depth of investigation, and resolution. Data are processed by forward modeling and inversion to produce 2D cross-sections or 3D resistivity models.

Interpretation relies on relating apparent resistivity to subsurface properties such as porosity, pore-fluid salinity, mineralization, and clay content. Inversion is non-unique and often constrained by geological information, boreholes, or petrophysical models. Time-lapse surveys can monitor changes due to pumping, recharge, contamination, or geothermal processes.

Applications include groundwater exploration and management, pollution delimitation, mineral and hydrocarbon exploration, geothermal reservoir delineation, civil engineering site investigations, and archaeology. Geoelectrical methods are relatively fast and cost-effective for covering large areas and can be used in combination with other geophysical and geological data.

Limitations and considerations: resolution decreases with depth; surface conditions (soil moisture, temperature, and contact resistance) strongly influence data quality; salinity and clay content strongly affect resistivity; results depend on inversion assumptions and require proper calibration with boreholes or other datasets.