2. Seismoelectrics.

Seismoelectrics (SE) is the geophysical method, allowing to leave on a new level of knowledge of the real geological media – to receive the information on its energy conditions and about a structure of rocks. At subjection of geological media by elastic field (of a natural or artificial origin) in the areas of its energy instability occur irreversible changes of physical parameters, in particular, specific resistivity (SE effect of the first type). These changes can be fixed by EM methods and can give the interpreter an information about a presence such unstable zones (for example, active breaks), which are necessary for taking into account at engineering works or to consider as the most sensitive indicators at geodynamic monitoring.

The basic attention in works of Laboratory is given to  development SE method based on effect of the second type - to partial transformation of an elastic field in rocks in EМ field. The most widespread mechanism of such transformations, inherent practically to any rock, is inverse electric osmosis. Briefly, the essence of this phenomenon consists in the following. Under action of a seismic field in porous water-saturated rock it is appeared a relative movement of a liquid and a solid skeleton of rock. As water always contains ions of the dissolved salts by virtue of selective ionic adsorption on interface of solid and liquid phases the liquid and a skeleton of rock oppositely charged, and their relative movement results in occurrence of a external electric current. This external current generates EM field. Observation and interpretation of this phenomenon can give geophysists some information on porosity and permeability of rocks, about type and the contents in it of a fluid, about its mineralization. These data are especially valuable in oil-field, hydro-geological and ecological geophysics (in its field and logging variants). The work of Laboratory in this area, has complex character and combines theoretical,  experimental (field and logging) and laboratory researches.

 

Theoretical researches: To present time, basically, the mathematical theory adequately enough describing SE effect of 2 type in porous water-saturated media  is developed. It is based on works of J.Frenkel, M. Biot, S. Pride and researchers of Laboratory (together with V.Gubatenko (Saratov Technical University)). Its basis is the consecutive solving problems of elastic waves in the porous two phase medium, electro kinetics and electrodynamics. The developed theory allows to carry out calculations of a SE field (seismic and induced by it EМ fields) in models of a various configuration. Programs of calculation SE field are developed in horizontally layered (with reference to field SE) and cylindrically layered (with reference to SE logging) media. The layers differ among themselves on set of elastic (modules of elasticity of solid and liquid phases), fluid-dynamic (porosity, permeability, viscosity), electro kinetic (density of a surface charge or dzeta-potential) and electric parameters. The analysis of the received solutions and the carried out calculations allow to project and interpret experimental SE works.

 

 Field experimental works: In Laboratory it is developed and has been applied in field works  an experimental 24-channel SE equipment. The equipment is intended for not deep (up to 100 м) geophysical researches with the hydro-geological and ecological purposes. The multichannel equipment allows to register synchronously components seismic (12 channels) and electric (12 channels) fields produced by any source of an elastic field (as impacts of a sledge hammer). Registration is carried out with sampling 0.25 ms in a dynamic range of 24 bits. Synchronization is carried out on the radio channel.

 Seismoelectric logging: The Laboratory has experience of SE researches in the bore holes. They carried out in two directions:

·        Studying SE field and definition SE transfer functions of rocks (SE effect of 2 type);

·        Studying of change of physical properties of the geological media (conductivity) as a result of subjection on it by an elastic field (SE effect of 1 type).

 

·        In Laboratory the equipment for SE researches in bore holes is developed. Range of frequencies - 1-10 кHz. For registration the serial logging station is used. The equipment is tested in two bore holes at depth from 500 up to 3000 m. Bore holes experiments have shown an opportunity of measurement SE fields in real conditions and the relation of determined SE transfer functions with a petrophysical properties of geological medium.

For revealing an opportunity of forecasting on a basis of SE transfer functions  the petrophysicai parameters of rocks, are necessary specially focused experimental researches in oil-gas and hydrological bore holes.

 

 

 Laboratory researches: In Laboratory the computerized SE measuring unit is developed, allowing to carry out experimental researches on samples of rocks. In the equipment the voltage from the pulse generator is passed to a piezoelectric transducer, elastic fluctuations from the transducer enter a rock sample, in which they partially transform in electric field. Measuring acoustic (by means of piezoelectric receiver) and electric signals (by means of ring electrodes) are amplified and then enter  computer. A dynamic range of registration - 12 bits. The equipment allows to carry out measurements in low-frequency (60 - 2000 Hz), and in high-frequency (2000 - 60000 Hz) bands of frequencies. 

With laboratory equipment measurements of SE transfer functions of rocks  are carried out and on this basis may be performed:

·        Studying of dependence SE transfer functions from litho type and structures of porous space of rocks, and also character and type of a saturating fluid ;

·        Studying of correlation of SE transfer functions with the basic petrophysical parameters of rocks and their fluid saturation.

 

Results of laboratory measurements have shown:

·        Close enough correlation of  SE   transfer functions of rocks on  litho type, petrophysical parameters (porosity, permeability etc,) type and a degree of fluid saturation of porous space.

The wide frequency range allows to obtain the data which can be used at interpretation of results both of   field SE researches, and of SE logging data.

 

We invite to cooperation:

- On realization of  SE field works for the solution of hydro-geological and ecological problems;

·        On realization of measurements in hydro-geological and oil wells.

·        On realization of laboratory researches of SE effect of 2 ti]ype on samples (cores) of rocks.

·        Measurement of SE transfer functions of rocks;

·        Measurement of velocity of elastic waves.

On a contractual basis field and logging SE equipment can be developed/

 

The basic publications:

1. Svetov B.S., Gubatenko V.P. Electromagnetic field of a seismoelectric origin in porous water saturated rocks: I. Statement of a problem. Physics of the Solid Earth, 1999, N 10, p. 67-73.

2. Svetov B.S. To a theoretical substantiation of smoelectric  method of geophysical investigation // Geofisica (Russian). N 1, p. 28-39.

3. Ageeva O.A., Svetov B.S., Sherman G.H., Shipulin S.V., 1999, Seismoelectric  effect of the second type in rocks: Geology and geophysics, 40, 8, 12-51-12-57.

4. Svetov B.S., Ageev V.V., Aleksandrov P.N. etc. Some results of experimental field seismoelectric  researches. Geofisica (Russian), 2001, N 6, p. 15-23.

5. Svetov B.S., Ageeva O.A., Lisicin V.S. Bore hole research of seismoelectric   phenomena // Geofisica (Russian), 2001, N 3,p. 44-48

6. Ozerkov E.L., Ageeva O.A., Osipov V.G., Svetov B.S., Tikshaev V.V. About influence vibration on electric properties of the geological medium. Geofisica (Russian). 1998. N 3. p. 30-34.