Electrical intelligence

In 1829, R.V. Fox measured the natural electric fields associated with redox processes at the copper pyrite deposits of Cornwalls ( England ).

In 1903, a Russian engineer E. I. Ragozin published a monograph “On the Use of Electricity for the Exploration of Ore Deposits”.

In 1910, the French scientist C. Schlumberger developed the resistance method, which later found wide application in geological and structural studies.

In the years 1919-1922. The Swedish scientists N. Lundberg and K. Sundberg laid the foundation for electrical prospecting with alternating fields and, in particular, methods based on the observation of equipotential electric field lines and magnetic field strengths. A little later in America, the method of induction (radiator) was proposed.

The studies of the German scientist I. Gummel and, in particular, the Romanian scientist S. Stefanescu, who developed methods for calculating the electric fields of point sources at plane-parallel interfaces, played an important role in the development of the theory of DC electrical intelligence.

In 1924, A.A. Petrovsky, the founder of domestic electrical exploration, conducted electrical exploration for the first time in the Soviet Union using natural field methods ( Ridder polymetallic deposit in Altai). In 1925, the method of equipotential lines was supplied using alternating current, and in this modification in the following years it was widely tested at sulfide deposits of the USSR. By 1925 also included the first experimental work on the application of the intensity method, carried out in the Urals (Bogomolovsky mine). Since 1926, the practice of electrical exploration includes the induction method. Since 1928, A. A. Petrovsky has been conducting systematic research in the field of radio wave reconnaissance methods.

Thus, in the twenties of the XX century, electrical exploration was used mainly in the search and exploration of ore deposits. However, the work carried out was largely experimental in nature, the volume of production work was small. In 1928-1929 electrical exploration is beginning to be used for prospecting and exploration of oil and gas structures. In subsequent years, the volume of these works increases substantially in accordance with the general increase in the volume of geophysical work in the search for oil and gas and the organization of a geophysical service in the oil industry.

In 1930, A. S. Semenov carried out the first electrical exploration work to solve hydrogeological and engineering-geological problems.

In 1932, the first electrical exploration work was carried out with the aim of prospecting and exploring deposits of fossil coal . In this area of ​​geological research, electrical exploration has been used as a method for studying the geological structure of coal basins and searching for coal seams, as well as coal-bearing formations.

In the 1960-1970s. A. I. Zaborovsky ^[2] , as well as the works of V. A. Komarov , L. M. Alpin, V. N. Dakhnov, A. N. Tikhonov, A. P. Kraev, made a great contribution to the development of DC electrical intelligence. E. N. Kalenova, A. M. Pylaeva and others. Other methods of electrical exploration were developed by E. A. Sergeev (natural field method), A. S. Semenov (charge method), A. G. Tarkhov, I. G. Mikhailov (induction method), etc.

In electrical exploration, there are now over fifty different methods and modifications intended for both in-depth studies and for studying the upper part of the section. Depending on the research principle, they can be divided into the following groups: resistance methods (direct current methods) and electromagnetic methods.

Apparent Resistance Methods

The apparent resistance methods are based on transmitting a known direct current in the ground using a pair of electrodes and measuring the voltage caused by this current using another pair of electrodes. Knowing the current and voltage, it is possible to calculate the resistance, and taking into account the configuration of the electrodes, it can be established to which part of the subsurface space this resistance relates. An increase in the spacing of current electrodes entails an increase in the depth of investigation and is a probing factor for vertical electric sounding (VES). In addition to VES, the group includes its modifications based on measuring the amplitudes (VES-VP) and phases (VES-VPF) of the field caused by polarization, unipolar combination (OKES) and dipole (DEZ) electrical sensing, as well as electrical profiling (EP), in which the spacing does not change, and the entire installation moves along the profile or site. In recent decades, the resistance method has been used in the modification of two- and three-dimensional direct current tomography (Electric Resistivity Tomography).

Resistance methods do not apply to electromagnetic methods, since although the reality is not a constant, but a low-frequency current, the magnetic field does not appear in this group of methods. According to the resistance methods, one can find out the distribution in the medium of the resistivity and the vector of induced polarization.

Electromagnetic sounding is used mainly in regional, structural-mapping and exploratory studies, when the tasks are to divide the geological section into layers and blocks, determine the sequence of occurrence of layers and map tectonic structures, in particular when searching for oil and gas deposits. Electrotomography is used for ore exploration, environmental and geotechnical tasks.

Induction Methods

The group of methods includes a huge number of different modifications, the essence of which can be described as follows. Under the influence of an alternating electric or magnetic field in the earth, an electromagnetic field arises due to the phenomenon of magnetic induction. Knowing exactly the parameters of the field source, it is possible to measure various electric and magnetic components of the induced field, restoring the medium parameters from them. In contrast to resistance methods, where the spacing parameter is the probing parameter, in induction methods, in addition to the installation dimensions, the depth also depends on the frequency of the current in the generator (subgroup of frequency soundings - BW) or on the time of recording after turning off the current in the generator (subgroup of soundings by field formation - CS) . When transferring along the profile or area of ​​an installation with constant dimensions, frequency or time, electromagnetic profiling is obtained.

The mathematical apparatus for processing data of induction electrical exploration is much more complicated than resistance methods. When working in the high-frequency region, the signal is affected not only by the electrical conductivity of the medium, but also by its dielectric and magnetic permeabilities .

Due to the special conditions, downhole electrical exploration methods are singled out as a separate group, although geophysical well survey methods (GIS) are not limited to electrical exploration methods.

Downhole Electricity

Downhole electrical exploration refers to the method of volumetric study of the interwell space, based on the excitation and study of the field both inside the wells and on the surface of the earth, as well as electromagnetic transillumination of the environment between the wells, this includes all options for electrical profiling in wells (EPS), methods of induced polarization (UPU, UPFS), natural electric field (EEPS, PEEMPS), electrical correlation (IEC), immersed electrodes (MPE), including methods of electric (MV) and magnetic (ML) ) charge, contact and non-contact methods of polarization curves (KSPK, BSPK), as well as all types of borehole electromagnetic profiling, based on the study of the field of a dipole source (DEMPS), an ungrounded loop (NPS), transients (MPPS), radio wave transmission (RVP) etc. Well modification is used to search for mineral deposits in the near-well and inter-well spaces, to study the shape, size and component composition of the reservoir, as well as to link the results of surface and borehole observations.

The Instructions for Electrical Exploration (1984) adopted the technological principle of dividing methods and modifications into groups according to working conditions. Land, sea, mine, and airborne sounding and profiling methods, as well as downhole research methods, are distinguished. All of them, in essence, come down to three distinguished groups.

• Electrical Exploration: Handbook of Geophysics / Ed. A.G. Tarkhova. - M., 1980
• Yakubovsky Yu.V., Lyakhov L.L. Electrical exploration. - Moscow, "Nedra", 1982
• Vanyan L. L. Electromagnetic sounding. - M., 1997