In modern measuring registration systems used in direct current methods (VES, VES-IP, DEP, electrotomography, etc.), a sequence of pulses of different polarity is used to excite the cut . As a rule, a sequence with a current pause is used to measure induced polarization (IP), and a pauseless mode is used for apparent electrical resistivity (ρc). The entire sequence of pulses is recorded on the receiving electrodes, however, the minimum amount of information corresponding to the stationary approximation is used – the amplitude is averaged before the current pulse is turned off and, after several tens or hundreds of milliseconds, several readings are taken in time windows to calculate the apparent polarizability (ηc). The high-frequency component of the signal after turning off (or turning on) the current is simply cut out of the data, since it is dominated by induction processes that cannot be interpreted in the classical technique. However, it is in these first milliseconds of the formation of the field that contains the most valuable information about the geoelectric structure of the section, the distribution of resistivity and polarization parameters . Registration of the full form of the transient process makes it possible to switch from using apparent parameters (ρk, and ηk) to a full-fledged solution of problems of one-dimensional or three-dimensional inversion, taking into account the frequency dispersion of electrical conductivity for the formation of the field of a horizontal electric dipole.
This approach significantly increases the information content of traditional direct current methods and makes it possible to study the lithological structure of the section in more detail. In addition, high-resistance screens are transparent for induction currents : permafrost, basalts, traps, etc., which significantly limit the scope of direct current methods. As a result, the concept of a new technology of electromagnetic sounding and induced polarization (EMS-IP) was formulated, which will allow solving a wide range of problems in ore geophysics.
The EMS-IP technology is excellent for performing areal surveys , for example, in combination with 3D seismic. As a result, it will be possible to fill the seismic data cube with information on the non-conductivity of rocks (reservoirs are often conductive due to the presence of brines), but also polarization parameters, which indicate anomalous values in the upper part of the section about the presence of hydrocarbons. The information obtained from the EMS-IP data will make it possible to more accurately determine the inhomogeneities of the upper part of the section (VSL) (the presence of traps, permafrost, tectonic faults, etc.), which, due to the introduction of appropriate corrections, will significantly improve the quality of seismic data interpretation.
Tasks that can be solved with the help of EMS-IP
Construction of three-dimensional geoelectric models, including near-surface models;
Mapping the distribution of permafrost by polarization parameters;
Determining the presence of a collector as a conductive zone;
Determining the position in terms of hydrocarbon deposits by epigenetic changes (calcitization, pyritization, etc.), including on the shelf, at sea depths from 0 to 1 m;
Forecast of deep drilling conditions (determination of the presence of fault zones that complicate the drilling process);
Search and exploration of groundwater deposits, including to ensure the development of oil and gas fields;
Monitoring of the production process of hydrocarbon deposits
Search and exploration of uranium mineralization zones, deposits of ore minerals (gold, copper, polymetals, etc.);
Discovery of hidden diamondiferous kimberlite bodies;
The study of the lithological structure of the section and the identification of fault tectonics in the complex of engineering and construction surveys.
The Results of Application of Pulsed Electrical Prospecting in Search for Deposits of Ore Minerals in the Mountain Altai
Опыт применения технологии электромагнитного зондирования и вызванной поляризации в республике Казахстан