Supported EM Methods
Natural EM Field
Self-potential (SP) is one of the easiest electroprospecting methods due to its simplicity of implementation in the field and equipment requirements. The purpose of the investigation is to register spontaneous electrical field potentials on the surface. Resulting anomalies can be associated with oxidation-reduction, filtration, diffusion-adsorption processes. SP surveys are cost effective, whereas SP data set is very informative. SP method is mainly used for solving prospecting, engineering and environmental tasks.
Audiomagnetotellurics (AMT), Magntetotellurics (MT), Low Period Magnetotellurics (LMT), Broadband Magnetotellurics (BMT), Magnetovariational Profiling (MVP), Telluric Currents (TC)
The 5-component measurements of the natural alternating EM field combine two methods – Magnetotelluric (MT) and Magnetovariational Profiling (MVP). The magnetotelluric method (MT) is effective for the investigations of horizontal-layered cross-sections, whereas, the Magnetovariational Profiling method (MVP) is sensitive to vertically inclined objects. The combination of both methods allows to construct a geoelectrical cross-section in wide depth intervals (from first few meters to several hundreds of kilometers). The present-day modern EM equipment allow to effectively and successfully solve a wide range of tasks in different climate and terrain conditions. It is also possible to substantially decrease the number of measurement sites using ability of MVP response functions to sense anomalies located away from observation profiles. The depth of investigation in MT-MVP methods is regulated by frequency. At high frequencies, the electromagnetic field penetrates in the near-surface part of the section, whereas with the decrease of frequency, the deeper part of the section are being investigated. As the result, MT-MVP technology does not require change of the transmitting and receiving dipoles size to increase the depth of investigation.
Control Source EM Field
Resistivity – Electrical Profiling (EP), Vertical Electric Soundings (VES), Dipole Electic Soundings (DES), Electrotomography (ET)
A group of electrical methods which are based on measurements of constant electric field are called resistivity methods or direct current methods. The depth of investigations in resistivity methods depends on the dipole moment (size of AB x current in AB). In other words, to increase the depth of investigations, it is necessary to increase the current dipole moment. Resistivity methods are subdivided into three groups: electrical sounding, electrical profiling and misse-a-la-masse methods. The area studies with resistivity methods and with application of 2D and 3D inversion are called electrotomography (ET) method. Various modifications of resistivity methods allow to solve a wide range of both engineering and mining exploration tasks. Resistivity methods are mostly effective (“productivity + result” / “cost”) for investigations of shallow cross-sections.
Induced Polarization (IP) – Time-Domain (TDIP), Frequency Domain (FDIP – Amplitude), Frequency Domain (FDIP – Phase), Spectral IP (SIP)
The Induced Polarization (IP) is one of the leading methods for disseminated ore exploration, since the IP is the only electroprospecting method which allows to highlight the dissemination of electron-conducting minerals. Its presence of such is an indicator of hydrothermal or metasomatic processes in the rocks which often involve mineralization of gold, uranium, polymetals, etc. This is due to the fact that the electric field causes a change in the position of the charges which is connected to various physical-chemical processes taking place. Commonly, the IP method is applied simultaneously with the resistivity methods. The depth of investigation in IP methods is also dependent on the size of the measurement layout.
Frequency Domain EM Soundings (FDEMS)
The FDEMS method is the only electroprospecting method that combines both Geometrical and Induction Soundings principles which allows FDEMS with high degree of accuracy to determine the depth to near-horizontal layers of the section even in areas with high level of industrial noise. The depth of investigation in FDEMS is regulated by both the frequency and the momentum of the measurement setup which allows to “fine-tune” field measurements to achieve required accuracy of results. At high frequencies, the electromagnetic field penetrates in the near-surface part of the section, whereas with the decrease of frequency, the deeper part of the section are being investigated. Nowadays, modern broadband multifunction EM receivers, current sources, software for data processing and interpretation allow to apply FDEMS method to solve a variety of exploration and engineering problems in wide depth intervals.
Induction Profiling (IEP)
TDEM (FasTEM / LowTEM / MulTEM)
The TDEM (TEM) methods are based on the investigation of transients processes induced in the Earth as the result of “step-like” change of the current amplitude in non-grounded loop or grounded power dipole. The depth of investigation in TDEM is regulated by the moment of the power dipole and duration of the recording. Therefore, measured field carries information about the variation of the electrical properties of the rocks depending on the depth. The method can be used with a high level of artificial noise and the maximum depth of investigation with TDEM does not exceed 5-10 km. TDEM method is mainly used for mining exploration, structural tasks, as well as oil and gas exploration.